Interlocking Stabilised Soil Block
Draft Construction Manual
Double Interlocking Rectangular Blocks for House Construction
Part I: Planning, Setting-out and Construction
[Part II: Building Services, Finishes and Maintenance]
CONTENTS A. PREFACE ... ii B. DISCLAIMER ...iii C. ACKNOWLEDGEMENTS ...iv D. INTRODUCTION ... 1 D.1 Building Plan... 1
D.2 Good Quality ISSBs ... 1
E. SUB-STRUCTURE... 3
E.1 Introduction ... 3
E.2 Site Clearance ... 3
E.3 Setting Out ... 4
E.4 Excavations... 5 F. FOUNDATION STRIP ... 6 G. FOUNDATION PLINTH... 7 G.1 Introduction... 7 G.2 Mortars ... 7 G.3 ISSB Parts ... 8 G.4 Single Wall ... 8 G.5 Double Wall ... 9
G.6 Plinth Wall Construction... 10
G.7 Ground Slab ... 11 H. WALLING... 13 H.1 Introduction... 13 H.2 Corners/Wall Intersections... 13 H.2.1 the “L” Junction... 14 H.2.2 the “T” Junction... 15 H.2.3 the “+” Junction ... 16
H.2.4 the “Y” Junction... 17
H.2.5 Stopped Ends, Door and Window Openings ... 17
H.3 Super-structure Wall Construction ... 18
H.3.1 Layout, Door Openings and First Course... 18
H.3.2 Raising the Walls ... 19
H.4 Ring Beam / Bond Beam and Formwork ... 19
H.5 Finishing the Wall... 21
H.6 Scaffolding/Platforms ... 21
I. ROOFING ... 24
I.1 Introduction... 24
I.2 Roof Structure ... 24
I.3 Connecting the Wall Plate and Trusses... 25
I.4 Roof Cover and Rainwater Harvesting ... 26
J. APPENDIX ... 27
J.1 Some Design Considerations... 27
J.2 Typical Low-Cost Home Plans... 28
A. PREFACE
ISSB (interlocking stabilized soil block) is an alternative and appropriate building material for East Africa with proven success for a wide range of housing types from simple buildings such as latrines to more involved and sophisticated single-rise and storied residential, institutional and commercial structures. The technology has been in use in East Africa for over twenty years but scanty specialized technical information is available for potential users of the technology. It is against this background that this Draft ISSB Construction Manual has been prepared by Good Earth Trust (GET) primarily targeting the informal and small-scale formal building associations and companies in the region. Nevertheless, fully-fledged establishments may also find it useful.
The main objective of the Manual is to provide trainees and potential users of the ISSB technology with simple but sufficiently detailed and well illustrated ISSB construction guidelines for easy assimilation and effectual adoption and use of the technology on any construction site without the need for further information. Detailed sketches and lists of relevant tools/equipment which may be manufactured or available locally are provided. In the few instances where the available information is not sufficient, the reader may obtain additional technical details from any credible source available or contact the nearest Good Earth Trust office for assistance.
B. DISCLAIMER
The construction techniques presented here are derived from the best practices in East Africa where the initial target audience is based. However, it is assumed that the potential users of this Manual are trained persons who already are familiar with the conventional building practices. Therefore, Good Earth Trust reserves the right not to be responsible for the topicality, correctness, completeness or quality of the information provided in this Manual. Liability claims regarding damage caused by the use of any information provided, including any kind of information which is incomplete or incorrect, will thus be rejected. Information in this document might be extended, changed or partly or completely deleted without prior notice. [To be edited]
C. ACKNOWLEDGEMENTS
The Good Earth Trust teams in Uganda, Kenya and the UK for every support and facilitation, Technology for Tomorrow (T4T) (Uganda) for the invaluable training expertise, Makiga Engineering Services Ltd. (Kenya) – the manufacturer of the block press.
D. INTRODUCTION D.1 Building Plan
All building projects must have relevant drawings (of sorts) usually produced by competent person(s) or group(s) thereof. As this manual is based on building construction using the straight double interlocking stabilized soil block, a simple 2 bed-roomed ISSB building plan is provided below, Fig. D.1, which will therefore be used throughout the manual for illustrations (detailed architectural models of low-cost homes are included in the Appendix to this Manual). Other related features such as cross-sections and elevations will be derived and used as and where necessary. Note that the building dimensions are ISSB-specific (see Section D.2 below for the block dimensions).
D.2 Good Quality ISSBs
For best results, good quality interlocking stabilized soil blocks (ISSBs) (see Fig D.2 for dimensions) should have been produced while carefully considering the following points: (1) adoption of optimum proportions of soil, stabiliser (usually cement (OPC)), and water, taking into consideration the characteristics of local soil; (2) careful mixing of the various components of stabilised soil blocks; (3) application of an adequate compaction pressure to the moist soil/cement mixture in order to obtain dense and strong building blocks with well-shaped surfaces and edges – by the correct use of the block press as detailed in its operational manual; and (4) allowing blocks to cure sufficiently before usage to minimise the risk of damages to the blocks and cracks in the finished structure as well as give an excellent finish to
Fig D.1 Ground Plan
REAR SID E ( 2 ) FRONT SID E ( 1 ) STORE BEDROOM PORCH BEDROOM LIVING ROOM 7.82 m 6. 75 m
a wall surface. Obtaining a smooth block surface can further permit their use without rendering or with a minimum use of rendering materials if required.
The Kenya Standard Specification (KS 02-1070: 1993) and Draft Uganda Standard (DUS 849: 2009) provide the following (minimum) physical characteristics of stabilized soil blocks necessary for good building construction:
• Dry Compressive Strength of blocks at 28 days 2.5 N/mm2; • Wet Compressive Strength of blocks at 28 days 1.5 N/mm2; • Rapture Strength of blocks at 28 days 0.5 N/mm2;
• Water Absorption of blocks 15 per cent of the original mass; • [Dry] Density of blocks 1600 Kg/m3;
• Weathering loss of mass 15 per cent of the original mass;
• Shrinkage cracks 0.5 mm wide and 50 percent of the parallel block dimension; and • Visibly free of broken edges, honeycombing, and other defects that would impair quality.
Please note that determinations of the above parameters are beyond the scope of this Manual therefore the reader is advised to refer to relevant local authority for detailed procedures.
Fig D.2 ISSB Dimensions
STRAIGHT DOUBLE INTERLOCKING BLOCK Format Size: 290 x 140 x 115 mm
Coordinating Dimensions: 266 x 140 x 95 mm (Order: Length x Breadth x Height)
Courtesy of Makiga Engineering Services-2009
115 mm 95 mm 266 mm 140 mm 290 mm SIDE PLAN END
E. SUB-STRUCTURE E.1 Introduction
Sub-structure generally includes all the components of a building that bear directly onto the ground (see Fig E.1 below). The usual order of the activity sequence in its construction is: (1) Site Clearance, (2) Setting Out, and (3) Excavations – as preliminary operations; (4) Foundation Strip (plain concrete), (5)
Foundation Plinth (double ISSB wall), and (6) Ground Slab (usually a composite structure consisting
of 25 mm cement/sand screed on 100 mm mass over-site concrete (plain or reinforced) on rubbles or “hard core” on well compacted formation). Each operation is described in more detail hereafter.
E.2 Site Clearance
Vital Tools/equipment: Hoe, Spade, Pick axe, Wheelbarrow. Others: Axe, Rake, Machete, and
Bow-saw. These can readily be obtained from the local hardware shops and the specific types and numbers will depend on the nature of the proposed building site and the number of operatives to be deployed on the job – depending on the availability and cost of labour at the project site.
Start by clearing the site of any obstacles such as trees, rocks, vegetative cover etc. using the building plan in Fig D.1 above and providing 0.5 m as width of the foundation trenches and 0.6 m clearance around the walls, a minimum area of about 9 m long by 8 m wide (72 m2) should be stripped of the top
vegetative soil to an average depth of 150 mm from the existing ground level. Vegetative soil is not good for use in construction, so remove and deposit the spoil away from the building area but in a place where it can eventually be used for gardening purposes.
Fig E.1 Typical Sub-structure Detail
Stripped ground level
Foundation strip Backfill
Plinth wall
Ground slab Finished floor level
E.3 Setting Out
Vital Tools/equipment: Pegs & profiles (4x2 timber or 60 mm poles cut to 1 m), Nylon strings, Claw
hammer, Hoe, Long tape (30 m), Steel tape ( 5m), Water level, Spirit level, Bow saw, Wire nails (assorted). Others: Plumb bob, Machete, Sledge hammer, Crow bar, white (pit) sand or ash for marking, Mortar pan. These can readily be obtained from the local hardware shops. Note that “vital tools” are necessary for a proper setting-out operation to be conducted while “others” are optional tools that may be improvised. The building is set-out for excavation by use of profiles fixed clear of the trenches by at least 1 m so as not to disturb the lines by excavation activities or bury the profiles in the heap of excavated soil (Fig E.3a). All profiles should be established to a fair level (using a water level) and set off the ground by at least 0.5 m (Fig E.3b).
Fig E.2 Site Clearance Plan
9 m 8 m FRONT REAR SI D E ( 1 ) SI D E ( 2 )
Fig E.3a Setting Out Plan
7 m 6 m FRONT REAR SI D E ( 1 ) SI D E ( 2 ) Profiles Lines/Strings Keep profiles clear
of excavation (1m) 0. 5 m 0. 5 m 0.5 m 0.5 m 2.7 m 0.7 m 2 m 2.5 m
E.4 Excavations
Tools/equipment: Hoe, Spade, Pick axe, Machete, Wooden rammer. Others: Wheelbarrow, Watering
jar.
Excavate strip foundation trenches 500 mm wide (Fig. E.4) using the simple hand tools listed above, to a depth usually determined on site where uniform and stable soil is encountered, but 0.5 m. Heap the excavated soil within the building area – clear of the trenches – to be eventually used for backfilling. Ensure that the sides of the trenches are fairly vertical if in stable soil by trimming with machete; otherwise if the soil is seen to be unstable then the sides should be cut to a suitable slope outwards to avoid the ground caving-in and causing accidents to the operatives. Depending on the general nature of the local terrain, the foundation trenches may be stepped for safety and economic reasons. Level the trench bottom and compact with a wooden rammer (see Section E.5 below) and if required, apply anti-termite treatment to the bottom and sides of the trenches by sprinkling the solution with a watering jar.
Note that a strip foundation may not be suitable for use in unconsolidated landfills, marshes and other unstable ground conditions in which case specialist advice must be sought.
Fig E.4 Strip Excavation
500 mm
Stripped ground level
100mm vertical to receive concrete 500 mm A: Stable soil (vertical sides) B: Unstable soil (reposed sides)
Fig E.3b Profile Set-up Peg: 4"x2" timber or
60mm pole sharpened on one end
350 mm 350 mm
Profile: 4"x2" timber or
60mm pole 1m long nailed to fair level on pegs
500 m
m
F. FOUNDATION STRIP
Tools/equipment: Hoe, Spade, Jerry-can, Bucket, Wheelbarrow, Wooden rammer, Wire nails, Claw
hammer, Water level, Nylon string. Others: Porker vibrator, Water reservoir, Gauge box (Fig. F.3), Timber (12”x1”), 100mm Diameter eucalyptus poles – platforms for pushing the wheel barrow in case of soft ground (rain & loose soil).
Materials: Cement, Sand (both coarse and fine if available), ” Aggregate (ballast), Water (clean).
The footing is usually plain concrete of class C10 – C15 commonly associated with a volume mix ratio of 1:3:6 (cement: fine aggregate (or sand): ” coarse aggregate (or ballast)). Note that sand for concrete is not normally sieved. Use the same gauge box or bucket to measure all the ingredients including cement and mix concrete on clean platform using clean water; pour 50-100 mm thick in trenches. Compact concrete with a porker vibrator or manually using a wooden rammer (Fig F.1) to a fairly level finish and cure by wetting the strip twice daily for at least 2 days to allow concrete to harden reasonably well before setting and constructing the plinth wall.
Fig F.1 Placing Foundation Concrete (trench in stable soil)
500 mm Stripped ground level
Foundation concrete
100 mm Wooden rammer
300 mm 6"x2" or 4"x2"
timber firmly nailed on end of pole
1200 mm 60 mm pole
G. FOUNDATION PLINTH G.1 Introduction
Tools/equipment: Builders tools (trowel, square, plumb bob, spirit level, water level, building lines),
Machete, Hoe, Spade, Jerry-can, Wheelbarrow, Mortar pan. Others: Gauge rod (Fig G.4c below), Water reservoir, Gauge box (Fig. F.2 above), Metal saw, Timber (12”x1”), 100 mm Diameter eucalyptus poles – platforms for pushing the wheel barrow in case of soft ground (rain & loose soil). Personal Safety Gear: Overall, Boots, Helmet, Gloves, Goggles.
Materials: Good quality ISSBs (see Section D.2 above), Mortar (see Section G.2 below): Cement, Sand
(both coarse and fine if available), Water (clean). Others: 1.2 mm Flat bars (mild steel), Weld mesh (8'x4').
Foundation plinth or plinth wall is the block-work that is usually buried in the ground and on which the ground slab or the superstructure rests. It is therefore the means of permanently fixing a building to the Earth's surface; as such it should be made sufficiently stable to be effective. For this reason, it is recommended that the outermost plinth walls and those underlying load-bearing walls of low-rise buildings be made of double ISSB block-work as explained in Section F.5 below. Where necessary, other internal plinth walls can be made of single ISSB block-work provided that they are mortared at every course and adequately secured with hoop iron at wall intersections or corners.
G.2 Mortars
The tools/equipment and materials are listed under Section G.1 above.
Mortars are used primarily to accommodate slight irregularities in size, shape and surface finish of blocks thus providing uniformity and stability to a wall. In doing so any gaps between blocks are also closed, preventing wind and rain from passing through the wall. Mortar has a further purpose in that it improves both the shear and compressive strengths of the wall. Mortars have some binding characteristics which improve the shear resistance but do not add significantly to the tensile strength of a wall.
For ISSB construction, cement/sand mortars of different mixes are normally used for different strength requirements. For instance, a 1:3 (cement: sand) mortar is expected to be stronger than a 1:4 mix – the former often used in foundations whereas the latter in superstructure walling. Two types of sand are normally used to achieve good results; these are pit/plaster sand with very fine grains or particles and washed (lake/river) sand having coarse grains. More of pit sand to washed sand is used (say 2:1 in a 3-part mortar sand, and 2.5:1.5 in a 4-3-part mortar sand) for improved workability and bonding characteristics of mortar.
The oversize material in the sand for mortar must always be removed by sieving as a separate operation. This is because course particles in mortar will distort the alignment of blocks both horizontally and vertically – giving a poor finish to the walls as well as weakening the interconnection between the blocks and the wall at large. Just enough mortar to last for a maximum of 1 hour at a time should be mixed on a clean platform using clean water.
The simplest sieving device is a wire mesh screen, nailed to a supporting wooden frame and inclined at approximately 45° to the ground (Fig. G.2). Sand is thrown against the screen, the fine material passing through and the coarse, oversize material running down the front. Alternatively, the screen can be suspended horizontally from a tree or over a pit. This latter method is suitable in cases where most material can pass through in windy conditions; otherwise too much coarse material is collected, and the
G.3 ISSB Parts
The ISSB parts shown in Fig G.2 below are not standard names but used herein this document for descriptive purposes. The orientation of the block is as it comes out of the block press and the various parts are: (1) “head” – the depressed cross-sectional end; (2) “tail” – the protruded cross-sectional end; (3) “top” – the depressed longitudinal bed; and (4) “bottom” - the protruded longitudinal bed. For dimensions of the ISSB block, refer to Section D.2 above.
G.4 Single Wall
The tools/equipment and materials are listed under Section G.1 above.
ISSBs are self interlocking and therefore can either be dry-stacked (e.g. in a small family latrine of say 2–3 m2), mortared in say every 3rd or 4th course (e.g. in a 2-roomed residential house) or mortared in
every other course (e.g. in foundations and large walls) depending on the size, structural and environmental requirements of the walls in question. It is recommended that foundation walls be mortared in every other course for greater strength and efficient supporting system.
However, for economic reasons and to achieve greater benefits of the interlocks, the mortar should be limited to just about 5 mm – which can practically be controlled by using a gauge rod (Fig G.4c below).
Fig F.2 Simple site screen to remove coarse particles from mortar sand
Fig G.3 ISSB Parts (side elevation)
"Top" (depressed) "Bottom" (protruded) "Head" (depressed) "Tail" (protruded)
Note that ISSB vertical joints are not normally mortared and the blocks should always be stacked in such a way to avoid the vertical joints in adjacent courses coinciding or being too close to each other (Fig G.4d below).
The blocks are usually laid on their bottom face and running tail-wise from a corner outwards (see Fig G.3 above for the block parts). For the first course (often sitting directly on the foundation strip or the ground slab), the protrusion is ripped off using a machete (panga knife) so the blocks can stably bed in mortar. Ripping of the protrusion also helps to control the amount of mortar used at that level (Fig G.4d below). The first course must be carefully set to good level using water and spirit levels and building line as subsequent courses will generally assume this level. The overlying courses can be controlled using a gauge rod, building line and plumb bob and levelling tools to ensure uniform levels and verticality of the wall. A builder’s square must always be used to check right angles as shown in Fig G.4a below.
G.5 Double Wall
The tools/equipment and materials are listed under Section G.1 above.
An ISSB double wall is achieved by laying two single walls adjacent to each other (Fig G.5 below) using the same tools, materials and procedures described earlier under Single Walls. However, the interface between the two walls must be mortared and metal strips used to secure the wall leaflets as detailed in Section H.2 (Corners/Wall Intersections) below. Fig G.5 is the layout of the plinth wall for the building plan shown in Fig D.1 above. Note that no internal plinth walls are used because of the relatively small size of the building and that a great deal of the slab is directly sitting on the ground, as detailed in Fig E.1 above.
Fig G.4 Typical ISSB Corner Detail
1st (d) Elevated Wall 2nd Mortar on DPC Trim dotted portions 3rd 5th 4th 6th Spirit level
(a) 1st, 3rd, 5th, 7th … Course Plan
95mm 95mm 95mm 95mm 95mm 95mm 95mm 95mm 95mm 95mm 105mm
(c) ISSB Gauge Rod
7th 8th
Builder’s square
G.6 Plinth Wall Construction
The tools/equipment and materials are listed under Section G.1 above.
Raise the plinth wall to a minimum height of 200 mm above the stripped ground level – the idea is to have the finished floor level at least one foot (300 mm) above the stripped ground so that storm water cannot run into the house. Backfill the excavated subsoil around the plinth wall in layers not exceeding 200 mm ensuring that both sides of the walls at any point are filled to the same level every time. This ensures balanced earth pressures on either side of the wall thereby eliminating the risk of buckling or cracks in the plinth during compaction of the backfill and thereafter (see Fig G.6 below).
If the backfilled soil is not moist (especially during very dry weather), sprinkle some water onto the soil using a watering can – the amount of water used should just be enough to make a lamp of soil squeezed in the palm stick together the same way water content is tested in the soil-cement mixture for making the stabilized soil blocks. Compact both layers of soil on either side of the wall at just about the same time (it is better to have at least two people compacting at the same time, one on each side of the wall). Repeat the backfilling and compacting operations, each time in layers not exceeding 200 mm, up to the level of the stripped ground. Once done, your foundation is then ready to receive the ground slab.
Fig G.5 Foundation Plan
3000mm 1640mm 2000mm 7250mm 7850mm 6150m m 6750m m SID E ( 1 ) SID E ( 2 ) 300mm 300mm 300m m 300m m FRONT REAR 1000mm
G.7 Ground Slab
The ground slab is usually a composite load-bearing structure comprising two or more layers of different materials. The most common detail includes 1 inch (25 mm) cement/sand screed; on 2, 3, or 4 inches (50, 75, or 100 mm) plain or reinforced concrete; on 4, 6, or 8 inches (100, 150, or 200 mm) stone base (commonly referred to as ‘hardcore’); on well compacted backfill or formation (Fig G.7 below).
Fig G.6 Backfilling around the Plinth Wall
Backfill in layers not exceeding 200mm & compact up to this level
200 mm 200 mm
Stripped ground level
300 mm
Part of plinth wall above stripped ground level
500 mm Foundation concrete
Backfill
100 mm
Fig G.7 Typical Low-Cost Ground Slab and Weathering Detail
Stripped ground level (Or Formation level)
Foundation strip Backfill
No “splash apron” but part of plinth wall to be rendered to serve the same purpose
Gro
und
s
lab
Finished floor level Super-structure wall to be
rendered externally to at least 900 mm above formation level
300 mm
1ft “ring” of hardcore along the plinth walls
150mm Backfill 75mm Ballast
50mm Concrete 25mm Screed
300mm Seal the top of the
backfill and the vicinity with big stones to prevent run-off water from entering the foundation
In constructing the slab, it is always important to bear in mind the final or finished floor level and the design or construction detail (that is, the materials and thicknesses to be used and therefore the sequence of placing them into the slab). It is good practice to always mark the various depths of the flooring materials on all sides of the slab against the corresponding plinth walls before commencing with the slab construction. These levels should be coordinated with a water level and always referred to when laying the floor materials.
In the case of a low-cost slab (Fig G.7 above) and after backfilling around the plinth walls as described earlier, start by compacting the stripped ground within the plinth walls using stamping rods and sprinkling water where necessary. Pack a “ring” of hardcore at least 1' (300 mm) wide and up to 8" (200 mm) high along the plinth walls, on the inside part of the house. This hardcore “ring” acts to reduce soil pressure against the plinth walls during compaction and thereafter. Backfill the “basin” so created with plain excavated soil (sprinkle water onto the soil if necessary) to a depth of about 7" (175 mm) and compact with stamping rods – the soil will hopefully settle at 150 mm above the formation level. Spread a thin layer of 3" (75 mm) crushed stone and level with strings and sledge hammers if necessary. Prepare concrete (1:3:6) with 1" (25 mm) aggregates or ballast and cast, compact and level to an average depth of 2" (50 mm) above the stone base. Note that this level should also be approximately 11" (275 mm) above the formation level.
Cure the concrete adequately by soaking it in a pool of water or by pouring water onto the slab at least three times a day (morning, noon, and evening) for a minimum of seven consecutive days before proceeding to set and raise the walls (Section H below). After walling, the house is then roofed, plastered internally if required and eventually the floor finished off with a thin layer of about 1" (25mm) cement/sand screed, which must also be cured for at least 7 days before painting and applying any other internal finishes.
Note also that Fig G.7 above does not have the traditional independent “splash apron” but the exposed part of the plinth wall external to the house is rendered with 1:3 mortar to serve as splash guard or “boot” of the house in rainy conditions. Top of the backfilled portion of the foundation trench is then adequately sealed with closely packed boulders to prevent run-off water from entering the foundation. Depending on the local terrain, suitable storm water drains must be provided to ensure water does not pool around the house after a heavy downpour.
H. WALLING H.1 Introduction
Tools/equipment: Builders tools (trowel, square, plumb bob, spirit level, water level, building lines),
Machete, Hoe, Spade, Jerry-can, Wheelbarrow, Mortar pan. Others: Gauge rod (Fig G.4c above), Water reservoir, Gauge box (Fig. F.2 above), Metal saw, Timber (12”x1”), 100 mm Diameter eucalyptus poles – for scaffolding and platforms for pushing the wheel barrow in case of soft ground (rain & loose soil). Personal Safety Gear: Overall, Boots, Helmet, Gloves, Goggles.
Materials: Good quality ISSBs (see Section D.2 above), Damp proofing material (bituminous felt or
G1000 polythene sheet) Mortar (see Section G.2 above): Cement, Sand (both coarse and fine if available), Water (clean). Others: 12 mm steel bars, 5 or 6 mm round bars, 1.2 mm flat bars (mild steel), 60 mm Diameter hollow steel pipes, Door/Window frames.
The superstructure wall is set directly onto the ground slab, and for a small residential house such as the one shown in Fig D.1 above single walling with the 140 mm wide ISSB mortared in every course is sufficient. The wall will ultimately be plastered internally and skirted externally up to the window level and around the corners to improve its structural and environmental performance (see Appendix Section for drawings). Mortar for this purpose is of mix 1:4 (cement: sand). Both pit and washed sands must be used at the ratio 2.5:1.5, and remember that sand for mortaring ISSBs must always be sieved.
H.2 Corners/Wall Intersections
The tools/equipment and materials are listed under Section H.1 above.
Room Room Lobby
1
3
2
4
5
Corners or wall intersections are critical sections of walls as they help to increase the lateral stability and load carrying capacity of the walls. In ISSB construction, special corner details are involved which are not often met with ordinary bricks or blocks. However, the cardinal principle in assembling all sorts of building units is to avoid straight joints or locating vertical joints above or very close to each other to eliminate potential lines of weakness where cracks can develop in the wall. In severe cases of loading and differential settlements, the wall can even open-up or collapse.
Five (5) different scenarios of wall intersections or junctions often encountered in ISSB construction will be considered: (1) the “L” junction, (2) the “T” junction, (3) the “
+
” junction, (4) the “Y” junction, and (5) the stopped end (see Fig H.2 above). If dry-stacking the narrow (140 mm) blocks or not mortaring every course, remember always to use mortar in the vertical joints at the corners because there are no vertical interlocks there.H.2.1 the “L” Junction
These are usually found at the extreme ends of a rectangular shaped house. Note that an ISSB crossed on top of another will not key-in or sit in good alignment with the rest of the blocks at that level because of the bottom protrusion, which should therefore be carefully trimmed with a machete prior to laying the block (Fig H.2.1c). A double “L” corner is derived by laying two single “L” corners adjacent to each other and adequately securing them with mortar at the interface and metal strips (flat bars) on every third or fourth course as illustrated in Fig H.2.1d and Fig H.2.1e below.
Mortar
Fig H.2.1d 1st & 3rd Course Plan
Mortar Mortar Mortar Metal Strips (Flat Bars) Mortar
Fig H.2.1e 2nd Course Plan
Mortar
Mortar Mortar
Use mortar here
Fig H.2.1a 1st Course Plan
Use mortar here
Fig H.2.1b 2nd Course Plan
1st
Fig H.2.1c Joining Corner Blocks
2nd Mortar on DPC Trim dotted portions 3rd 5th 4th 6th
H.2.2 the “T” Junction
The “T” is an extension of the “L” corner and must always be made to coincide with a vertical joint of the running (main) wall. In order to avoid straight joints, the adjoining blocks (i.e. the blocks forming the cross on the “T” in the main wall must be cut to reduce their lengths in such a way that the established block pattern in this wall is not interrupted. Note that the narrow ISSB length (266 mm) is not an exact multiple of its width (140 mm) therefore never cut the block in two equal halves. When laying corner blocks, always remember to trim portions of the bottom protrusion as described earlier so the blocks can sit neatly on those underlying them. A double “T” corner is constructed as detailed in Fig H.2.2c and Fig H.2.2d below, adequately secured with mortar at every interface and tied with metal strips (flat bars) on every third or fourth course.
3rd 5th
1st
Use mortar here
2nd 3rd 6th 5th 4th 1st
Fig H.2.2b 2nd Course Plan & Wall Elevation
Full blocks Main wall
2nd 4th Mortar
Fig H.2.2a 1st Course Plan & Wall Elevation
Mortar 75mm Cut tail 75mm Cut head Cut
Fig H.2.2c 1st Course Plan
Cut Mortar Metal Strips (Flat Bars) Mortar Cut
A further extension of the “T” junction is a pier, which is a buttress-like reinforcing section of a very long wall – usually of more than 3 m – commonly found in perimeter walls and large institutional buildings such as classrooms blocks, halls, dormitories, etc. As there are usually no close junctions in such walls, piers are introduced at intervals not exceeding 3 m so as to stiffen the walls and enhance their structural integrity.
H.2.3 the “
+
” JunctionThe “
+
” or cross Junction is similar to the “T” junction where blocks in the main wall have to be cut to reduce their lengths to create room for the intersecting wall, without altering the established block pattern in this wall and avoiding vertical joints. Note that the blocks should always tie at the centre of the cross. However, one has to decide which one of the two walls is the “main wall” as it will always have the “tie block” (see Fig H.2.3a and Fig H.2.3b below for illustration).Fig H.2.2f 1st Course Plan
Mortar
Maximum 3 meters
Fig H.2.2e Plan of Long Wall with Piers
Pier Wall
Fig H.2.2g 2nd Course Plan
Mortar
Use mortar here
Fig H.2.3b 2nd (& even Nos.) Course Plan
Tie block Main wall
Mortar
Fig H.2.3a 1st (& odd Nos.) Course Plan
Mortar
75mm
Cut head
H.2.4 the “Y” Junction
The “Y” junction is ideally an “L” junction where the interior angle is greater than 90o. However, the
corner blocks have to be cut to the required angle with a hack (metal) saw prior to laying the blocks.
H.2.5 Stopped Ends, Door and Window Openings
Walls are usually stopped to create openings such as doors and windows. Given that vertical joints are always staggered for succeeding courses in a wall, cutting of the blocks to create a regular vertical edge is inevitable. It is recommended that an opening or a stopped end be introduced just after full blocks in alternate courses (see Fig H.2.5b below). This implies that doors or window frames to be used in ISSB construction should have breadths in multiples of a unit ISSB length (i.e. 266 mm) so the frames can fit nicely in place and the blocks can connect perfectly well above the frames. Note also that for good stability of the walls, maximum recommended breadth for any opening into ISSB walls without extra reinforcements at the stopped ends is 1.2 m. Furthermore, if cut neatly using a metal saw, the two block pieces should always fit properly in the gaps adjacent to the opening – this ensures non-wastage of the blocks and cost saving.
In ISSB construction, it is recommended that any door or window frames be installed during construction of the walls because some difficulty may be encountered when installing them later. Installing the frames in the traditional way (after the wall has been constructed) often requires nails or anchors of some sorts on the sides that normally involves cutting out the wall in those locations whereby the walls may be damaged if the operator is not very careful or does not have the right tools for the job. Subsequently, large amounts of cement mortar or concrete will be required to secure the frames onto the walls.
Use mortar here
Fig H.2.4a 1st Course Plan Fig H.2.4b 2nd Course Plan
Use mortar here
Cut off
Cut off
Fig H.2.5a ISSB Window Frame with Wall Anchors
Flat bars attached to a window frame at strategic positions to coincide with horizontal ISSB wall joints
Properly cured and treated wooden frames are safe to use in ISSB construction and they are preferred for low-cost housing for ease of adaptability and relatively low material and fabrication costs (as compared to steel frames). For better anchorage, the frames must be made with grooves to accommodate the ISSB keys (protrusions) and metal strips such as flat bars nailed onto the frame at strategic positions to coincide with horizontal ISSB wall joints (Fig H.2.5a above).
During construction, a frame is raised to its final position in the wall and supported with long poles fixed to the ground. As the wall is raised, the metal strips on the frame are slotted into the ISSB channels and secured with small-sized nails before applying mortar and laying the succeeding courses. Provisions should be made for ultimately screwing the shutters onto the frames; avoid nailing the shutters into place as the hammering impacts may damage the wall.
H.3 Super-structure Wall Construction
The tools/equipment and materials are listed under Section H.1 above.
H.3.1 Layout, Door Openings and First Course
Once the ground floor is done and set, arrange strips of plastic sheet or bituminous-felt membrane (commonly referred to as DPC) on the slab following the proposed layout of the superstructure walls. The entire house should be laid out on the first course including the door openings to ensure that the blocks tie up above the door lintels.
Fig H.2.5b Stopped End / Opening in ISSB Wall
10th Cut Cut Mortar Mortar PLAN VIEW 1st Trim dotted portions 1st 7th 8th 10th 9th 11th Cut block Cut block
Window Opening in ISSB Wall
Mortar on DPC
9th Mortar
Before continuing with the second course, check that the base or first course is level and that all corners are square. Once this is completed the blocks of the door areas should then be removed and door frames inserted and supported as described earlier. Note that the first course is always laid in mortar (even where the blocks are to be dry-stacked) with the ISSB top upwards and the bottom protrusion trimmed as described before.
H.3.2 Raising the Walls
With the base course established and all door frames in place (and for whatever reason, one may as well raise the walls without first installing the door frames), the next courses can then be continued. The corners are first raised to about five courses high at a time and every corner level must be coordinated using a water level (Fig H.3.2 below). A string is then fixed along a given course and blocks are laid from the corners towards the middle of the wall. Depending on the orientation of blocks from either corner, the tying blocks are likely to meet head-on-head or tail-on-tail and in this case mortar will be required in the vertical joint and for the latter scenario the tail protrusions will need to be removed (Fig H.3.2). This joint should be staggered for subsequent courses as the wall grows in height and the corners should be checked regularly for square and vertical alignment. Note that if the layout on the first course was correct, the blocks should fit into the wall without trimming.
Generally for the entire building, wall construction should proceed in an organized fashion with all walls raised at fairly the same rate in order to maintain the overall stability of the structure. On reaching the windows level, install the window frames and support adequately to the ground using long poles and continue raising the walls around the frame as described earlier. Once again, for whatever reason, one may raise the walls without first installing the window frames although this procedure is not recommended. Note that checking the vertical alignment using a plumb bob as illustrated in Fig H.3.2 is very important as the walls gain height and the window openings create breaks in the structure.
H.4 Ring Beam / Bond Beam and Formwork
The bond beam (commonly referred to as “ring beam”) is an important part of the structure as it ties the walls together at the weak openings. Traditionally, 150 – 200 mm in-situ (cast-in-place) reinforced concrete of mix 1:2:4 (cement: sand: ballast or stone aggregates) is used for this purpose. This normally requires formwork to be fixed all over the walls just above the openings for moulding the concrete.
Fig G.3.2 Raising the Walls
1st 1st 2nd 3rd 5th 4th
Blocks meet here, so mortar this joint
Mortar on DPC
Use a string to fill-in blocks Use a water level to
set opposite corners Check verticality of wall using plumb bob
Blocks are laid towards middle of wall
Use a water level to set opposite corners
However, nailing into ISSB walls is not recommended where the walls will not eventually be plastered or rendered. The nails usually damage the surface of the blocks with the risk of cracking them and rendering the blocks vulnerable to moisture attacks especially in rainy weather. Therefore, the best way to do formwork in ISSB construction is to use pre-fabricated moulds normally assembled on the ground and lifted into place. Reinforcement wire is then installed (often 4 mild steel bars of 10 or 12 mm in the beam section). Concrete is cast and carefully compacted using tamping rods (Fig H.4a). Separate strips of tying wire (say 5 or 6 mm round mild steel bars (or 1.2 mm mild steel flat bar)) should be secured to the reinforcement cages and allowed to stick out of the bond beams with sufficient lengths to hoop around the top of the wall at strategic locations to ultimately tie the wall plates or the roof structure firmly onto the walls.
ALTERNATIVELY, for a properly designed small low-cost house (say up to 45 m2) using the narrow (140
mm ISSBs) having a light roof structure, NOT IN AN EARTHQUAKE PRONE AREA, and in which the door and window frames have been installed during construction of the walls, the walls can adequately be tied just above the openings with 12 mm diameter mild steel bars placed in the ISSB channels and running all over the walls in pairs secured in 1:2 (Cement: sand) mortar. In this case, the overlying block should have the bottom protrusion removed to create room for the reinforcement/mortar matrix (Fig H.4b below). Note that this method avoids the time and cost of moulding concrete thereby speeding up construction; and ultimately, the “ring” of concrete usually visible around the house is not there even when the house is not rendered externally.
Fig H.4a ISSB Ring Beam Formwork in Cross-section
200 mm 100 mm
140 mm
50x25x140 mm timber struts, 600 mm apart ISSB Wall
Use 3" nail here
300x25 mm (12"x1") timber board Reinforcement wire (Y10 & R5) 50x25 mm timber ties, 600 mm apart Tying wire/bar protruding out of beam Use 3" nail here
Fig H.4b Alternative ISSB Wall Tie in Cross-section
140 mm
Pair of reinforcement wire (Y12) in mortar & sitting on the R5 bars as spacers
Tying wire/bar protruding out of joint for tying the wall plates (900 mm on either side) Note that the bottom protrusion of this block has been removed
Maintain a regular joint & key-in neatly if wall is not plastered
H.5 Finishing the Wall
Where specialised trusses are to be used as the main load-bearing roof components, it is recommended that the house is roofed when all the walls are at the level of the wall plate for easy installation of the roof trusses. Once the roof cladding (or cover e.g. iron sheets) is installed, the walls should then be extended up to the cladding especially where there is no ceiling to be fixed – to provide privacy and security in each room of the house. However, appropriate vents must be provided in these walls to allow for proper air circulation across the house.
Otherwise where a simple roof structure that sits directly on the walls is to be used, the walls should be fully raised before roofing the house. In this case, it is important to follow the correct slope of the roof when finishing off the walls and all walls at the same level must be coordinated using a water level.
H.6 Scaffolding/Platforms
When constructing walls at levels above the chest (normally between 1.0 – 1.5 m from a standing position), it becomes increasingly strenuous to lay the blocks and difficult to level and plumb the wall. Therefore, the block layers should always keep elevating their working positions by using appropriate scaffolding systems or platforms. Simple, low-cost and safe scaffolds can be constructed at the site using lower-grade timber and poles. For elevations up to 300 mm and where the ground is stable and fairly level around the walls, two 12"x1" timber boards sitting directly on dry-stacked ISSB blocks at intervals not exceeding 1 m is a safe and inexpensive accessibility means (Fig H.6a below).
Fig H.6a ISSB-stack Platform
1000 mm Ground level
1000 mm 1000 mm
200 mm 200 mm
300 mm ISSB stacks 2 Pieces of 12"x1" timber Stick this block firmly
into the ground
Fig H.5 Finishing the Wall
Wall finished following the roof
slope
Roof truss
Wall plate (4"x3" timber) Wall plate level
For elevations between 300 mm and 1 m, another inexpensive platform similar to the one above uses 60 mm poles (eucalyptus or bush type) instead of the ISSB stacks. Two poles are buried in the ground adjacent to each other about 0.4 m apart and a cross-pole nailed onto them; bracing poles may be required across the supports when the elevation is above 600 mm from the ground. The platform should be clear of the wall (Fig H.6b below).
There is also an option of a mobile platform that uses pole-framed tripods instead of the fixed supporting poles (Fig H.6c below). A tripod has two long legs that are supported on the ground and a short leg that is supported against the wall. Note that this system is only suitable to use on double walls or where single walls are adequately mortared at every course. Allow the supporting portion of the wall to set adequately before using the tripod system.
Fig H.6b Pole-framed Platform
1000 mm Ground level 1000 mm 1000 mm 200 mm 200 mm 1000 mm 60 mm poles 2 Pieces of 12"x1" timber Plant poles firmly
into the ground
END VIEW SIDE VIEW Use 4" nails here Bracing 400 mm Wall Platform clear of wall
Fig H.6c the Tripod System
2000 mm Ground level 2000 mm 200 mm 200 mm 1000 mm END VIEW SIDE VIEW Tripods made of 60mm poles 600 mm Wall Tripod supported on wall 600 mm Temporary bracing poles nailed on tripods Tripods supported on the ground Timber planks
For higher elevations (1 m), the usual eucalyptus pole framed scaffold can be used. It is similar to the pole-framed platform described above but has the vertical members extending to greater heights and multiple braces at intervals of about 1 m (Fig H.6d below).
It is recommended that all scaffolds used in ISSB construction should be independent systems and not involve opening up sections of the wall for support. This implies that high level scaffolds should stride walls and have lateral members passing through window or door openings. Use 4" nails to secure the poles in place.
Fig H.6d Eucalyptus-framed Scaffold
2000 mm 1500 mm END VIEW SIDE VIEW 1000 mm Ground Scaffold a-stride wall Wall Scaffold
I. ROOFING I.1 Introduction
Tools/equipment: Carpenter’s tools (hand saw, bow saw, Claw hammer, wood chisel, square, nylon
strings, and spirit level). Others: Water level, Plumb bob, Pencil, Knife, Metal saw, Machete. Personal Safety Gear: Overall, Boots, Helmet, Gloves, Goggles.
Materials: Timber (various sizes and quantities as described in the BoQ), Roof cladding (e.g. iron sheets
and matching ridges/valleys), Wire nails (assorted sizes), Roofing nails, Rubber washers. Others: Hoop iron, Rain gutters and accessories.
Roof design and construction details are normally influenced by the local weather and available materials, and ISSB roofs are constructed following the traditional systems. The roof of a house primarily serves both functional and aesthetic requirements i.e. protecting the interior of the house from the elements (rain/cold and sunshine) and adds "beauty" to the house. In ISSB construction where external walls are not to be rendered fully (for aesthetics and economic reasons), the roof has an additional function of protecting the exterior wall surfaces from severe rain impacts – often achieved by providing a sufficient roof over-hang (usually 2' or 600 mm in plan view) in addition to at-least 600 mm high above the ground external rendering to the wall (Fig I.1 below). Where rainwater is to be harvested, then most claddings are suitable except grass thatch. The adopted roof design must therefore be able to fulfil these requirements using locally available materials.
I.2 Roof Structure
Roof designs are often a component of the approved building plans required for every project. Given that every project is unique, there are several designs and techniques of constructing roof structures ranging from simple rack-forms in small buildings where girders directly bearing on the walls carry the purlins and roof cover – to sophisticated roof trusses bearing on specialist beams or structural walls in large buildings.
Fig I.1 ISSB Roof Requirements
Sufficient roof over-hang
600 mm
Window
Plastered wall section
Roof
Open ISSB wall
Incident rain
600 mm
I.3 Connecting the Wall Plate and Trusses
The tools/equipment and materials are listed under Section I.1 above.
Often 4"x3" timber profiles, the wall plate is usually the first roof element to be installed, it serves as a load transmission or distribution facility between the roof trusses or rafters and the bearing walls; the wall plate also provides easy connection between the roof and walls of a house. It is normally a continuous system thus timbers must be joined to the required lengths using suitable connection details (see example in Fig I.3a below). Metallic roof anchors must have been connected to the wall ties or ring beam (see Section --- above) at convenient locations where the roof trusses or rafters are to sit on the wall. The wall plate is then fastened to the wall using these anchors as shown in Fig I.3b below. Note that the channel in the last ISSB course is filled with mortar to flush with the top of the blocks.
Fig I.3a Wall Plate Connection X
Wall plate (side elevation)
DETAIL AT X 100 mm
75 mm 3" Nails
100 mm
Fig I.3b Roof Construction and Wall Connection Detail
ROOF TRUSS Rafter
Tie Beam
Tying wire wound around wall plate & truss / rafter Wall plate ISSB wall Tying wire flat on wall Mortar here Roofing nail
Roof cover (Iron sheet)
Rain gutter
Fascia board Purlin
The length of construction wood in the market (Uganda) is anywhere between 10' (3 m) to 14' (4.2 m). For large buildings therefore, there will be need to join timber for roof elements, and in this case try to join the pieces accurately and tightly. Steel bands (commonly referred to as hoop iron) can be used to splice together timber members. These bands should be well secured with 2" wire nails. The usual sequence in constructing the roof detailed in Fig I.3b above is as follows: wall plates, roof trusses, purlins, fascias, covering, and rain gutters.
I.4 Roof Cover and Rainwater Harvesting
The tools/equipment and materials are listed under Section I.1 above.
One of the main uses of ISSB is to construct rainwater harvesting tanks. Water tanks made from ISSB prove to be low-cost, more durable, and safely store water without contamination. ISSB water tanks can be built both above and below ground: above ground ranging from 2,000L to 30,000L and below ground ranging from 10,000L to 200,000L. Compared to plastic tanks, ISSB tanks can generate significant cost savings (more than 50 percent) for larger tanks. Please refer to the Rainwater Harvesting Water Tank
Manual for guidelines.
The main rainwater harvesting elements of a roof are the roof cover and gutters. Most roof covering materials in East Africa are suitable for rainwater harvesting with the exception of thatch and asbestos. The gutter should be installed with a slight slope towards the collection point. Other than using strings to establish the profile, the gutter slope can be achieved by fabricating the brackets with an ascending hanger-length. The collection piece of gutter should have an outlet for connection to rainwater descend to the tank. In use, the water can either be drawn directly from the tank, which is cheaper, or by plumbing to serve the kitchen, toilet, and washroom. Please refer to ISSB Construction Manual - Part II for
J. APPENDIX
J.1 Some Design Considerations
While making design choices, keep in mind that “more”, “bigger” or “stronger” mean “more cost” but not necessarily “better!”
The following are some of the architectural design aspects to be considered when developing ISSB building plans:
1. How many rooms required? Therefore, how big should the house be? Note that room layouts should maximize the functional use of the house with minimum redundant spaces.
2. Do you want to construct a separated kitchen? (And washroom / toilets?) Or would you like these in the main house? The concept of having an open kitchen within the main house (as presented in both home plans in this Section) is relatively cheaper than a closed-in (within the main house) or separated kitchen.
3. Do you want to include in-built fuel efficient cooking devices in the kitchen? Options are for “rocket” and equivalent stoves, bio-gas systems, etc.
4. Do you need a rainwater harvesting tank? If so, then suitable roof cover should be used to collect the rainwater. We recommend a 5,000 litres tank for a typical (Ugandan) home.
5. What roof shape do you prefer: gable-ended or heaped roof? The former is usually relatively cheaper to construct whereas the latter is prettier!
6. What door/window materials to use? The choice is usually between metal and timber, the latter being relatively cheaper and more adaptive for use with ISSB construction.
7. Do you require roof ceiling? This is greatly influenced by cost and the type of roof cover – a tin (iron sheet) roofed house without a ceiling can be uncomfortable to stay in during a heavy downpour.
8. What finishes (both internal including floor and external) to deploy? Refer to ISSB Construction
Manual - Part II for guidelines.
9. Do you need to install building services (plumbing, sewerage, electricity, etc)? Refer to ISSB
Construction Manual - Part II for guidelines.
The following are some of the structural aspects to be considered when developing adequate and durable ISSB buildings:
1. Interlocking stabilized soil blocks are recommended permanent building material, although they may take proper training and experience to use properly.
2. Structurally sound blocks must be produced in accordance with the Block Making Manual and training guidelines – where appropriate soils are chosen and recommended quality measures maintained throughout the block production process.
3. No vertical joint should be positioned above another vertical joint.
4. Appropriate and strong ties or ring beams around the entire perimeter of the house at the top of the major wall openings (windows and doors) which will prevent collapse at these locations. 5. A light-weight roof relative to the entire structure and adequately secured to the tie or ring beams. 6. Relatively small and uniform openings such as windows and doors that are no more than 30 percent the
wall length, and these openings should not be too close to or at corners if not necessary.
7. Good quality materials and workmanship, including plumb walls for guaranteed structural integrity. 8. Uniform thickness of mortar between joints – 5 mm is sufficient and use a suitable gauging device. 9. In large buildings, interior walls in both directions which are load bearing and similar in construction
detail as exterior walls.
10. Properly constructed foundation – double walled plinths are recommended for the narrow ISSBs. 11. Good external protection of the wall: sufficient roof overhang, splash protection on the base of the
J.2 Typical Low-Cost Home Plans
J.3 Sample Building of Costs
PROJECT : PROPOSED 57SQM LOW-COST ISSB MODEL HOME [2 beds + kitchen] ISSB DEMAND : 6,360 BLOCKS [foundation - 1,320; super wall - 5,040]
CLIENT : FOUNDATION FOR RURAL HOUSING - UGANDA SUBJECT : ITEMISED COSTING
DATE : MAR. '09
COMPILED BY : DAN A.; CHECKED BY : LISA B.
Item Description Unit Quantity Rate Amount Comments
A Preliminaries 281,500
1 Tools and equipment required Item 1 150,000 150,000 provisional sum
2 Site clearance m2 75 500 37,500 do
3 Setting-out facilitation Item 1 50,000 50,000 do
4 Trench excavations m3 11 4,000 44,000 do
B Cement 2,599,000
1 Cement for concrete (foundation strip) Bag 5 23,000 115,000 100mm thick, mix 1:3:6
2 Cement for concrete (ground slab) Bag 10 23,000 230,000 50mm thick, mix 1:3:6
3 Cement for mortar Bag 15 23,000 345,000 approx. 5mm, mix 1:3
4 Cement for internal plastering Bag 10 23,000 230,000 approx. 10mm, mix 1:4
5 Cement for rendering (external plastering) Bag 8 23,000 184,000 approx. 10mm, mix 1:5
6 Cement for screed & other finishes Bag 12 23,000 276,000 approx. 20mm, mix 1:4
7 Cement for block making (6,360 blocks) Bag 53 23,000 1,219,000 120 blocks per 50kg bag
C Stones and Aggregates 1,060,000
1 1/4" Agg. for concrete (foundation strip & floor top) Trip 2 120,000 240,000 50mm blinding on hardcore 2 3" (75mm) crushed stones for slab conc. base Trip 2 100,000 200,000 placed on compacted fill
3 Hardcore Trip 2 100,000 200,000 300mm wide around plinth
4 Coarse sand (concrete, mortar, plaster) Trip 2 120,000 240,000
5 Pit sand (concrete, mortar, plaster) Trip 2 90,000 180,000
D Reinforcements 365,000
1 Y12mm m/s (for tying wall) Bar 9 20,000 180,000 (no ring beam in the wall)
2 R5mm m/s for tying roof to wall Bar 0 6,000 0
3 1.2mm Flat bar (for tying roof to wall) No. 5 15,000 75,000 1 ring halfway in the wall
4 1.2mm Flat bar (in plinth wall) No. 0 15,001 0 2 ring halfway in the wall
5 Binding wire Kg 5 5,000 25,000
6 8'x4' Weld mesh (on top of plinth wall) No. 5 17,000 85,000
E Roofings 2,307,000
1 Wall plates (4"x3"x14' timber) No. 10 10,000 100,000 (hardwood timber)
2 Ridge Rafters (4"x3"x14' timber) No. 10 10,000 100,000 do
3 Under-purlin (4"x3"x14' timber) No. 6 10,000 60,000 do
4 Valley Rafters (4"x2"x14' timber) No. 2 6,000 12,000 do
5 Girders / Secondary Rafters (4"x2"x14' timber) No. 15 6,000 90,000 do
6 Purlins (3"x2"x14' timber) No. 36 4,500 162,000 do
7 Fascia boards (8"x1"x14' timber) No. 10 10,000 100,000 do
8 10 Ft long G30 iron sheets No. 54 21,000 1,134,000
9 6 Ft long G30 ridges No. 13 8,000 104,000
10 Valley Gutters No. 2 8,000 16,000
11 Wire nails (assorted) Kg 10 4,000 40,000
12 Roofing nails Kg 25 6,000 150,000
13 Rubber washers Pkt 3 8,000 24,000
14 Rain gutters (complete with accessories) m 15 10,000 150,000
15 Hoop iron for connecting timber Roll 1 65,000 65,000
F Scaffolding 60,000
1 12"x1" timber ("kirundu" ) for platforms
2 2"-3" Eucalyptus poles Item 1 60,000 60,000
3 Assorted wire nails
G Doors & Windows 1,335,000
1 Standard solid timber door No. 4 150,000 600,000
2 Standard solid timber window No. 5 120,000 600,000
3 Vents No. 3 45,000 135,000
H Miscellaneous Items 550,000
1 DPC (bituminous felt) Roll 2 10,000 20,000
2 Lime for plastering Bag 5 20,000 100,000
3 Hollow steel pipes (60x2mm) No. 2 40,000 80,000
4 Painting m2 140 2,500 350,000
I TOTAL 8,557,500
1 Labour (20% of Total less preliminaries) Item 0.2 8,276,000 1,655,200 2 General Contigency (5% of Total less prelim.) Item 0.05 8,276,000 413,800
J GRAND TOTAL 10,626,500
5,000Lts ISSB Water Tank Item 1 750,000 750,000 750,000
1-Stance VIP Latrine Item 1 1,770,000 1,770,000 1,770,000