3.1 General
3.1.1 Scope of work
Supply and installation of roof screed, protected waterproof membrane, insulation and protection for flat roofs.
3.1.2 Relevant Standards
Conform to the recommendations of the following British Standards where applicable:
BS 1470 : 1987 Specification for wrought aluminium and aluminium alloys for general engineering purposes.
BS 6229 : 1982 Code of practice for flat roofs with continuously supported coverings.
BS 8000 : 1989, Part 4 Code of Practice for waterproofing.
3.1.3 Submittals
Submit to the Engineer for his approval at least 60 days prior to use, proposals for the complete roofing systems together with full specifications, technical literature and samples.
Evidence must be provided of three successful installations of a similar nature which are at least ten years old.
The roofing system is to be approved in writing by the Engineer before commencement of the work, and the work is to comply in all respects with the approved specification.
3.1.4 Co-ordination
Check and verify the positioning and fixing of all conduits and other items which are to be concealed or laid within the screed thickness. Ensure that such items requiring testing have been satisfactorily tested and approved by the
3.1.5 Workforce
All roofing works are to be carried out by competent operatives skilled in this particular work.
Roof membrane shall be applied by an approved specialist subcontractor.
3.1.6 Guarantee
Completed waterproof membranes shall be guaranteed for a period of not less than ten years from the date of contract completion. Should any damage occur to the building or its contents as a result of faulty materials or workmanship, the Contractor shall make good such defects to the satisfaction of the Engineer.
3.2 Materials
3.2.1 Cement
Ordinary Portland Cement complying with BS 12:1978, or Omani Standard No.
OS 07.
3.2.2 Fine Aggregates
Sand for use in roof screed shall comply with the requirements for sand for concrete as specified elsewhere herein.
3.2.3 Coarse Aggregates
Aggregates for use in roof screeds is to be 10mm and shall comply with the requirements for aggregate for concrete as specified elsewhere herein.
3.2.4 Water
Clean potable water, to conform to Concrete Works specification.
3.2.5 Roofing Membrane
The roof membrane shall be “Bituthene 8000 HC” manufactured by GRACE or equal and approved.
Proprietary high performance 1.5mm thick solar reflective roof cold applied, flexible pre-formed waterproofing membrane comprising a four layer cross laminated high density HDPE carrier film with a solar reflective surface and a self-adhesive rubber/bitumen compound which conforms to the following requirements:
Property Test Method Typical Value
Tape Strength ASTM D638 Long 5.2 N/mm
Trans 5.8 N/mm
Tensile Strength ASTM D638 Long 40 N/mm2
Trans 36 N/mm2
Elongation Film ASTM D638 Long 200%
Trans 170%
Elongation Compound ASTM D638 125%
Tear Resistance ASTM D 1004 Long 270 N/mm
Trans 270 N/mm
Adhesion to Primed Concrete ASTM D 1004 1.8 N/mm
Adhesion to Self ASTM D 1000 1.8 N/mm
Puncture Resistance ASTM E 154 290N 65mm
Water Resistance ASTM D570
after 24 hrs after 35 days
0.14%
0.94%
Environmental Resistance ASTN D543 Conform Moisture Vapour
Transmission Rate
ASTM E96 0.2 g/m2 / 24 hrs
3.2.6 Membrane related Products and Appurtenances
All products and appurtenances associated with the roofing membrane are to be proprietary items as supplied or recommended by the membrane manufacturer.
Examples include solar reflective membranes and paint, surface primers, fillets, mastic sealants and flashings.
3.2.7 Insulation
600 x 1200 x 50mm thick proprietary extruded closed cell polystyrene rigid foam, with skin, and rebated edges.
The material shall have the following properties:
1. Five year aged average thermal conductivity of 0.032 W/mk when tested at 24oC in accordance with DIN 52612 or ASTM C-518.
2. Compressive strength of 280kPa average, when tested according to DIN 53421 or ASTM D-1621.
3. Water absorption of 1% in volume average when tested in accordance with ASTM D-2842.
4. Water vapour permeability of 0.6 perm inch average when tested in accordance with ASTM C-355.
A minimum density of 33 kg/m3. 3.2.8 Flashings
1 mm thick super purity aluminium sheet to BS 1474.
3.2.9 Separation Layer
Polyester based synthetic fibre mesh.
3.2.10 Gravel
15 to 30mm diameter smooth edged wadi gravel.
3.2.11 Paving Slabs
400 x 400 x 50mm thick proprietary white precast concrete paving slabs.
3.3 Execution
3.3.1 Preparation for Screeds
Concrete surfaces which are to receive screeds are to be thoroughly “scrabbled”
preferably by mechanical means to form a regular rough texture. A tamped finish will not be accepted. Thoroughly clean the concrete surface and ensure that it is free from all loose particles and other extraneous matter which would adversely affect the adherence of the screed material.
Spray concrete surface with water to thoroughly wet the surface to be screeded.
Allow free water to drain before screed application.
3.3.2 Lightweight Roof Screeds
Flat roofs shall be covered with a lightweight concrete roof screed which shall have a maximum density of 500 kg/m³ consisting of cement and sand with a foaming agent. Light weight aggregate may also be used. The work shall be carried out by a specialist agency approved by the Engineer strictly in accordance with the manufacturer’s recommendations.
The roof screed shall be laid to falls to ensure adequate run-off or rainwater and to prevent ‘ponding’. The minimum thickness shall be 50mm and the screed shall be laid in alternate bays of exceeding 3000mm in any direction.
The screed roof shall be thoroughly brushed clean of all dirt, loose stones etc.
Any small cracks shall be filled with an approved tropical grade thixotropic cold bitumen emulsion with added rubber latex.
The screed surface to be waterproofed shall be even and smooth with any high spots knocked back and local depressions and sudden changes filled with epoxy mortar or similar high strength mortar to present a true surface. All sharp projections and arises caused by formwork etc. shall be ‘scrabbled back’ to give rounded corners. Primer shall be touch dry prior to the application of one layer of the membrane. The primer must not be poured onto the surface and care must be taken to avoid ponding in depressions.
All internal angle fillets shall be preformed triangular black PVC 50mm x 50mm extrusions with a wall thickness of 5mm, and shall be coated on two faces adjacent to the corner, protected by silicone coated release paper. The material shall be of a grade suitable for use in hot climates.
External corners shall be trowelled to provide a 25mm x 25mm splay.
Where the membrane is to be terminated at an up stand, a 25 x 20mm deep splayed chase shall be provided. The chases shall be thoroughly clean and dry, and all dust, dirt, laitance etc removed from the faces by wire brushing and compressed airline.
All inside and outside angles shall be provided with an additional 300mm wide reinforcing strip of the membrane centred along the axis of the corner, prior to laying of the main membrane.
3.3.3 Roofing Membrane
Installation of roofing membrane shall be carried out in strict accordance with the manufacturer’s written instructions.
Ensure substrate is laid to the correct falls as shown on the drawings.
Thoroughly clean the surface which is to receive roofing membrane. Ensure surface is dry and clear of loose particles and grease.
All roof up stands, parapets, service penetrations and expansion joints are to be constructed in accordance with the standard details as instructed on the
drawings, or as recommended by the membrane manufacturer.
Reinforce all inside and outside angles, and other vulnerable areas with an additional 300mm wide membrane strip prior to laying of the main membrane.
Dress the roofing membrane into the roof rainwater outlets, which are to be of a design to allow draining both at membrane level and at the top of the roof tiles.
Prior to covering the completed membrane request the Engineer to make an inspection. Clean and patch any damaged areas to the approval of the Engineer.
3.3.4 Roof Insulation Boards
Lay boards in accordance with the manufacturer’s instructions, in a brick bond pattern. Where the tiles are laid over a change or roof slope they shall be neatly cut with a saw along the line of the change in roof plane. The joint shall leave a small gap.
Cut the tiles carefully around up stands, pipe work and roof mounted plant.
Alternatively in order to avoid small cut pieces the tiles may be set out to create a space round the up stand or pipe work which may then be filled with gravel or ballast.
3.3.5 Separation Layer
Lay a separation layer loose over the entire area to be insulated, carefully trimming and allowing a 50mm up stand at parapets, pipe penetrations, rainwater outlets, etc. Lap joints at least 300mm.
3.3.6 Gravel
Spread gravel over the areas indicated on the roof plans to a thickness of about
3.3.7 Paving Slabs
Where indicated on the roof plans lay paving slabs with tight but open joints, secured in place with 1:6 cement: sand mortar dabs.
3.3.8 Pipes and Services through Roof Slabs
All waste stacks, ducts and pipes penetrating the roof slab are to be
weatherproofed in accordance with the Architects details, consisting of a block work up stand and concrete slab with the pipe turned through 90 degree.
Plinths for equipment shall be built off the roof slab prior to commencing roof waterproofing. Plinths supporting pipe runs and cable trays may be built off the roof slab or precast plinths may be located on top of the insulation prior to laying paving slabs.
3.3.9 Testing
All horizontal roofing areas shall be water flood tested prior to the installation of the protection course.
No areas shall be water tested less than 72 hours after application of waterproofing membrane.
Water testing shall include flooding of the entire area either by section or in its entirety to a depth to be agreed with the Engineer for a minimum period of 72 hours.
3.4 Protection
The Contractor shall employ whatever methods are required to protect the roof at all times, up to the building handover, from damage from any cause
whatsoever, and make good any such damage at his own cost.