INSULATED PITCHED ROOFING

DOW CONSTRUCTION PRODUCTS

(a division of the Dow Chemical Company Ltd)

“INSULATED PITCHED ROOFING”

Welcome to this RIBA approved CPD self tutorial.

First some information about the Dow Chemical Company itself:

US origin, 100 years old.

2nd largest chemical company in the world Produces: chemicals, plastics, agrochemicals. Annual sales: £18 billion.

Employs: 45,000 globally (Europe 8,000)

Dow in the UK

STYROFOAM* production since 1969 : polystyrene produced at Barry, Wales; extruded foam insulation produced in Kings Lynn.

Dow Construction Products offers the STYROFOAM range of blue extruded polystyrene foam insulation:

Floors - Floormate* 200,350,500 and 700 Cavity Walls - Wallmate* CW

Walls internally - Styrofoam* IB Structures below ground - Perimate* DI Pitched Roofs - Roofmate* PR, RL Inverted Flat Roofs - Roofmate* SL, LG Conventional Flat Roofs - Deckmate* CM, FF

Dow Construction Products

Insulated Pitched Roofing

This self-tutorial seminar covers all aspects of the so called “ Warm Roof Concept” at rafter level pitched roof insulation.

You will discover

• The insulation options

• The advantages of the “warm” versus the “cold” roof

• How a “warm” roof is constructed

• The general design considerations, relevant codes of practice and applicable standards to adhere to

• The role and selection of the various components with particular emphasis on the insulation, the underlay, fasteners and methods of securement

• The relevance and importance of the building physics issues, thermal insulation, condensation and ventilation

• The “ins and outs” of detail design: eaves, ridge, valley, hip and roof penetrations

• How the warm roof concept has been put to the test in the field

INSULATED PITCHED ROOFING

INTRODUCTION:

It is estimated that today around 10% of new pitched

roofs are insulated at rafter level and that this

figure is increasing.

Various insulation solutions are available which are

dependent on the type of insulation used and its

location ( ie above, between or below the rafters or a

combination of these ), and the type of underlay

used. Although the insulation of pitched roofs cannot

be considered a new application it is now the subject

of much debate both in the technical press and within

the industry itself - indeed the BRE, NFRC and BSI

are all actively involved.

The aim of this seminar is to review the application

from an insulant manufacturer’s point of view.

•

Insulation options

• Advantages of an insulated

roof structure

• The Warm roof concept

• Design considerations

• Roof build-up: the components

• Building Regulations: requirements

• Case study

• Detailing

• Conclusions

Roof structure: uninsulated

attic/loft

space

insulation at

ceiling level

• insulation at ceiling / joist level - mineral / glass fibre normally used

• attic / loft space ventilated (vents provided at eaves and at ridge)

Note: Could adequate ventilation be provided by a water vapour permeable (breather) underlay and thus do away with providing vents at eaves’ and ridge level ?

Roof structure: insulated

room in

the roof

insulation at

rafter level

c) below the rafters or a combination of these • ‘Warm’ roof

insulation above rafters

sometimes referred to as sarking insulation

(see BRE Thermal insulation: avoiding risks BR262 • Hybrid roof : insulation between and/or under rafters.

Note: Focus of this seminar will be on the ‘warm’ pitched roof as this is the

ADVANTAGES : INSULATED VS

UNINSULATED ROOF STRUCTURE

• Increased living /working space for same

“footprint”

• Additional space at lower cost

• Added value

• Allows room to grow

Cost of providing additional space in the attic can be less than

50% of the standard floor cost.

plus

with a ‘warm’ roof:

- reduced risk of condensation on structural membranes. - thermal movement of roof structure reduced.

- roof structure kept dry - no need for timber preservative treatment.

THE WARM PITCHED ROOF

Rafter

Tiling batten

Tiles

Counterbatten

Insulation

Vapour permeable

underlay

-

roof build up

• Insulation shown above and between rafters

• Vapour permeable underlay (breather type) can be laid either in direct

contact with the insulation ( as shown ) or over the counterbattens

• Suitable for new build or where the roof covering is to be replaced ( note increase in roof height ! ) and where it would be difficult to provide

eaves ventilation

Note: Need for a vapour control layer (VCL) ? YES for areas exposed to high humidity levels e.g swimming pools, kitchens, changing

rooms.

THE WARM PITCHED ROOF CONCEPT

• rigid insulation over (and between) rafters

plus

• a water vapour permeable (breather) underlay

Note: Where proprietary products are to be specified,

manufacturers’ recommendations should be followed.

Designers should satisfy themselves that the performance of

these products and the given recommendations have been

proven by relevant experience in use or by test data based

on the conditions and methods of application in equivalent

and appropriate internal and external climatic conditions.

THE WARM PITCHED ROOF

• First …… thatched roofing !

• Developed from Scottish sarking - early 80’s

• Agrément certification - mid 80’s

• Thousands roofs, millions sq metres installed

• Includes all insulation types

• Minimal condensation problems

• No securement problems

Note:

Sarking

- originated in Germany / Scandinavia refers to a sheet or underskirt of boarding.

- traditionally in Scotland 25mm thick close timber boarding at underslating level.

Design considerations

! BS 5268 : Part 7 : 1990 Roof

construction - rafters & purlins

(Approved Document A : 1994 )

! BS 5534 : Part 1 : 1997 Slating & tiling

! BS 6399 : Part 1 : 1984 Dead loading

! BS 6399 : Part 2 : 1995 Wind loading

! BS 6399 : Part 3 : 1988 Imposed &

ROOF BUILD-UP - THE COMPONENTS

Rafters

Vapour Control Layer

Insulation

Underlay

Battens

RAFTERS

Consider:

• Roof slope

• Cut vs trussed

• Dimensions (and tolerances)

• Spacing

• Bracing

Note:

Must assume that insulation does not contribute to

the racking strength of roof structure.

VAPOUR CONTROL LAYER (VCL)

• Usually a membrane (eg 500 gauge polyethylene

sheet)

• Substantially reduces transfer of water vapour

• Installed on warm side of insulation

A VCL reduces water vapour transfer through any building component in which it is incorporated.

(BRE document BR 262: ‘Thermal insulation - avoiding risks’ specifies a

minimum water vapour resistance of 200 MNs/g. BS 5250 refers to the use of 500 gauge polyethylene with a range of 200 to 350 MNs/g, typically 250 MNs/g.)

The VCL should be installed on the warm side of the insulation. ( Note that a VCL at ceiling level will require increased ventilation below it during the wet trade phases of construction.)

Performance of a VCL also is dependant on workmanship and build ability -see Clause 9.2 of BS 5250.

It is essential that it is adequately lapped and sealed so as to maintain its integrity.

Particular care should be given to detail design and installation around penetrations through the VCL (e.g services, compartment walls) and to the sealing of punctures caused by fasteners.

INSULATION

• Location

- above / between / below

(or any combination)

• Selection

- thermal performance

- water vapour permeability

- water resistance (absorption)

- user friendliness

• Thickness

• Installation

- thermal integrity

- convection tight

(a) over the rafters (b) between the rafters (c) under the rafters

or any combination of these

Note : Option (a) is sometimes referred to as a “warm” roof construction or as

“sarking” insulation.

All options can be used for new roof constructions or where the roof is to be replaced from rafter level up.

Only options (b) and (c) can be used in situations where the roof covering cannot be removed or replaced.

Selection:

Rigid, semi-rigid and flexible insulants can be used. Each has its own specific physical characteristics as regards performance and installation requirements -the manufacturers’ recommendations should be followed. cont ->

Thickness:

The thickness of the insulation will be determined by the required thermal performance as well as by the roof construction (see Approved Document L). It is important to ensure the continuity of the thermal insulation. If this is broken eg by the rafters and /or penetrations through the roof, the resulting thermal bridges can increase the risk of localised condensation and pattern staining of ceilings at rafter line.

Note: Building Regulations require the effect of thermal bridging to be

taken into account when calculating the thermal performance (U-value) of the roof. Refer to BS 5250 Section 9.6 and BRE Document 262: Thermal insulation - avoiding risks.

Installation:

Thermal integrity is essential.

The roof void should be completely insulated. For example gable end walls will need to be insulated to their full height.

The designer should take care to ensure that there are no gaps or breaks in the insulation envelope.

The insulation should be installed to fit tightly at ridges, at eaves and around penetrations. Seal if necessary with flexible (polyethylene) or PU foam.

Insulation boards should fit tightly together with no gaps around them. Rigid board joints should be correctly positioned so as to shed any likely incoming external water. Some types of board will require their joints to be sealed with tape - refer to the manufacturers’ instructions.

Special care needs to be taken with rebated boards designed for over and between rafter installation e.g Roofmate PR to ensure that the rafter

spacing is accurately set out so as to avoid gaps or unnecessary cutting of boards.

Convection tight/airtight:

A roof system in which the free movement of air through any section of the construction is prevented by use of airtight joints and seals is said to be “convection tight” or “airtight”.

INSULATION

- typical physical properties

XPS

EPS

PUR

MF

Thermal conductivity

W/mK

0.025 0.036 0.024 0.036

Water vapour resistance

(relative to MF)

-

140

60

80

1

Water vapour resistivity

MNs/gm 1000

300

600

5

Water absorption

% vol

0.3

6

3

?

Compressive strength

kPa

300+

190

max

175

max

120

max

Density

kg/m3

30

15-30

30

180

• XPS - extruded foamed polystyrene

EPS - expanded foamed polystyrene (bead board) PUR - polyurethane/polyisocyanurate

MF - mineral fibre • Thermal conductivity

XPS, EPS measured at 90 days (after equilibrium reached) - long term value. PUR measured immediately after production ie before equilibrium

reached - short term value. • Water vapour resistance

Determined relative to MF(air) for equivalent U-value thicknesses (XPS=50mm) • Water absorption

ROOFMATE* RL, PR

- physical characteristics

Water absorption % vol 0.3 0.3

Water vapour resistivity MNs/gm 940 940 Board size mm 2500 x 600 2500 x 600 Thickness mm 80, 90, 120 35, 50

Edge profile - rebated tongue &

groove

• Roofmate RL

Tongue and groove on all sides.

Board should be laid so the tongues in horizontal joints face up the slope. • Roofmate PR

Available with edge flanged to suit 38 and 50mm rafters - type 38 and 50 respectively.

Boards should be laid so that horizontal lap joints (i.e top and bottom of boards) point down the slope so that boards higher up the roof overlap those further down (boards are marked so as to facilitate this e.g with an arrow pointing up the slope of the roof).

UNDERLAYS-REQUIREMENTS

- TRADITIONAL

• Keep water (snow, dust) out

• Air tight

• Adequate strength

- WATER VAPOUR PERMEABLE (Breather)

• As Traditional

plus water vapour permeability

• Keep water etc. out - secondary defense against wind driven rain, snow and dust.

• Air tight - to reduce wind load on primary roof covering. • Adequate strength - tensile, tear strength (for nails), extensibility (reduce movement under wind pressure). Working temp. range - 20 to + 80 deg C. • Water vapour permeability

- Traditional underlay e.g BS747 Type IF felt

These are defined (BS5250) as having a water vapour resistance in

excess of 50MNs/g

- Water vapour permeable (breather) underlay

BS 4016 : 1995 Flexible building membranes (breather type)

- max. water vapour resistance 0.6MNs/g

UNDERLAYS

WATER VAPOUR RESISTANCE

Traditional MNs/g

BS 747 Type IF felt

50 - 270

Monarfil* 250

420

Breather

Permo* 0.20

Tyvek* HD - Soft 0.24

Tyvek* 2001 - Pro 0.16

Roofshield*

0.08

Monarperm* 450 0.11

Insulation

XPS - 90mm 85

PUR - 80mm 46

MF - 115 mm 0.6 *

• Monarfil 250 - reinforced polyethylene (0.25mm) • Permo - laminated spunbond polypropylene • Tyvek Soft - spunbond polyethylene (0.19mm)

• Tyvek Pro - spunbond polyethylene / polypropylene laminate (0.42mm)

• Roofshield - spunbond polypropylene laminate (0.60mm) • Monarperm 450 - spunbond polypropylene (0.45mm)

BREATHER UNDERLAYS

Performance criteria should reflect “real life” roof

conditions

• Water vapour permeability + water resistance

• - working conditions

• - compatibility

• - “tenting”

• - “blinding”

• Installation

• Roof conditions : - 20 to +80

_{C, 0 to 100% RH, seasonal, daily,}

hourly changes

• Compatibility - specifically with timber preservatives - water

( surfactants ) vs solvent based ( swelling )

cause loss of performance.

• “Tenting” - a problem with the early materials. Underlay

leaks when touching surface below.

• “Blinding” - by dust, ice (?)

• Installation - laid direct on insulation (common practice in

North)

- can cause noise (ie wind flutter ) ?

or

- supported on counterbattens(common

practice in South)

- userfriendliness => slipperiness underfoot

for roofer !

BATTENS

●

Tiling, counter

●

Dimensions

●

Location of underlay

●

Securement

• When the insulation is installed over the rafters, counter-battens will

be required to secure the insulation to the rafters and to provide

drainage under the tile battens - refer to BS 5534 Part 1 Section

3.6.3.2.

• Care should be taken to ensure that the construction techniques

employed provide for adequate and accurate location of the fixings

used to secure the battens and counterbattens to the rafters.

• Width determined by diameter of fasteners (10 - 11 x diameter)

• Thickness determined by method of securement

• Underlay can be in direct contact with surface of insulation or

located above the counter battens

• Who installs what ?

Carpenter - up to and including counterbattens

(rafters, insulation)

Roofer - above counterbattens

(underlay, tile battens, tiles)

or from the rafters up

SECUREMENT

- need to secure tiles/slates, underlay and

insulation against dead wind and imposed

loads

• Insulation

consider: - thickness (over rafters),

physical properties

• Fasteners

eg BS 1202 nails, Helifix Inskew, Proctor PR nails

consider: - penetration, pull-out strength,

deflection under load

- ease and accuracy of installation

When the insulation is installed over the rafters the fasteners securing the counter battens or battens through to the rafters must be of sufficient strength and length and correctly spaced so as to resist dead, wind and imposed

loads.

The following should be considered:

• Site locality - the assessment and determination of wind and imposed loads • Roof Construction - roof pitch, rafter spacing, depth and width, insulation thickness; batten/counter batten length, width and depth; fastener diameter, length and spacing.

• Materials and related properties - slate/tile weight; rafter and

battens/.counter battens: timber specification; fasteners: out and pull-through strengths, shear strength and deformation under load characteristics. • Consideration should also be given to the deflection and possible

overloading of the fasteners under load down the slope of the roof. It is recommended that the deflection should not exceed 3mm. A fastener must be capable of withstanding the dead and imposed loads vectored down the slope of the roof i.e its maximum allowable bending stress must not be exceeded - refer to the fastener and insulation manufacturers for advice. It may be necessary to provide stronger and larger diameter fasteners (with a corresponding increase in batten and rafter dimensions) or a reduced

spacing and/or stop battens (i.e parallel to the eaves/ridge)

Note : The trend towards increased thickness of insulation with reduced

U values (June 2000 proposals to change Approved Document L).

Securement cont

! BS 6399 : Part 1 : 1996 Deadloads

! BS 6399 : Part 2 : 1995 Wind uplift

! BS 6399 : Part 3 : 1988 Imposed Loads

! BS 5268 : Part 2 : 1996

! BS 5534 : Part 1 : 1997

! BS 1202 : Part 1 : 1994

use above to determine fastener size

and density ( per m

2

₎

Note:

Designers must take into account the two loading conditions for

the fasteners:

• Wind uplift on the roof.

• Resistance to slip (deflection of the fastener) down the slope

dependant on the pitch of the roof and the dead and imposed

loading. Insulation should not be considered to be a structural

material.

Fasteners

- method of securement

Tile battens

nailed to counter battens

Counter battens nailed to

rafters through insulation

Rafter thickness

• Figure above shows a method of securement for insulation laid over and between the rafters, in this case Roofmate PR.

• Counterbattens 32 mm thick secured with galvanised slab nails 100mm long x 3.35 mm dia spaced at 200 and 150 mm centres for duo and mono pitched roofs respectively - refer to BS 5268 : Part 2 : 1996.

• Tiling battens are secured with galvanised slab nails at the required gauge - refer to BS 5534 : Part 1: 1997.

BUILDING

REGULATIONS

“

Reasonable provision shall be made

for the conservation of fuel and power

in buildings by limiting the heat loss

through the fabric of the building”

• Building Regulations 1991, amended 1994

BUILDING REGULATIONS

Approved Document L : 1995

U-values

Approved Document L

Maximum U-values

DWELLINGS

SAP </= 60

>60

Cold roof

0.20

0.25

Warm roof

0.20

0.35

OTHER BUILDINGS

Cold roof 0.25

Warm roof - residential 0.35

- others 0.45

• If roof slope is greater than 70

_{then max U = 0.45 W/m}

_K

• For building classification see Approved Document B

• Building Regulations specify maximum allowable Uvalues

the optimum cost effective U-values are in fact lower eg:

W/m

_K

Floors 0.35

Roofs 0.20 - 0.25

Walls 0.30 - 0.35

BUILDING REGULATIONS

CONDENSATION

Approved Document F:1995

“Adequate provision shall be made to prevent excessive

condensation in a roof”

but …. Is based on traditional underlay experience

therefore …..

refer to:

BRE Thermal insulation : avoiding risks 1994

- see Section 2.7 - 2.10 ‘Sarking insulation’

BS 5250 1989

CONDENSATION - it’s prevention

•

Short, long term concerns

• Insulation

- continuity, convection tight, performance

• Underlay

- choice, performance

• Roof covering (tiles/slates)

- air permeability (?)

• Ventilation

YES - between underlay/roof covering

YES - between insulation/traditional underlay

NO - between insulation/breather underlay

Control of condensation is of particular concern for those roof

systems where a breather underlay is used without a ventilated

airspace between it and the insulation. It is recommended that a

condensation risk analysis is undertaken - refer to to BS 5250.

Use of the criteria for condensation build-up within the roof system

as detailed in BS 6229 : 1982 (Section A.2.5.5.) is recommended.

The roof system below a breather underlay should be designed

and installed so as to be convection tight as is possible throughout

its design life.

Consideration should be given to installing a VCL on the warm

side of insulation if the insulation has a low water vapour

resistance - refer to the insulation manufacturer for advice.

For buildings with high internal temperatures and humidities it is

recommended that a VCL be installed and for exceptional conditions,

as may be experienced in say swimming pools, laundries, that the

advice of a design specialist be sought.

Ventilation

- defined as “ the controlled movement of air”

There are two air spaces to be considered:

Between the underlay and the insulation

For traditional underlays ventilation should be provided in

accordance with the recommendations given in BS 5250 and

Approved Document F2 (1990). For breather underlays ventilation is

not normally required.

Between the roof covering and underlay

Where a traditional underlay is used it is not normally necessary to

provide ventilation.

Where a breather underlay is used without ventilation between the

underlay and insulation it will be necessary to ensure that there is

adequate ventilation. This may be provided through the slate/tile

assembly. Apertures for ventilation can be provided at the eaves,

ridge or incorporated into the slate/tile assembly - refer to BS 5250 for

ventilation aperture sizes.

NOTE: Ventilation through the slate/tile joints may not be sufficient

due to the close fitting of the slates/tiles. There may also be a risk

that the joints become blocked by vegetation or dust over the lifespan

of the roof. Additional ventilation inlets or outlets may, therefore, be

required. Particular attention should be given to long span roofs to

ensure that adequate ventilation is provided.

BUILDING REGULATIONS

FIRE

APPROVED DOCUMENT B : 1992

EXTERNAL FIRE SPREAD - B4

BS 476 : Part 3 : 1958

AA (best) rating - tile/slate roofs

- unaffected by insulation

INTERNAL FIRE SPREAD - B2

BS476 : Part 7 : 1971

Class O rating - 13mm plasterboard

• BS476 : Part 7 External fire exposure roof tests

• BS476 : Part 1 Surface spread of flame test

- lists Classes 1 (highest) to 4; XPS is unclassifiable

Class O is not identified in BS476. However, it can be

achieved by materials of limited combustibility

e.g plasterboard or a Class 1 material which has a fire

propagation index (I) < 12 and a sub-index (I,) < 6.

• For useful information on aspects of XPS in building

applications see BS 6203 : 1989

INSULATED PITCHED ROOFING

In summary:

• Warm roof concept

15 + years proven track record

minimal condensation problems

secure

• Design for the total system

• Pay attention to the design of details*

• Take care in installation

The issues:

• Insulation - location, selection, installation

• Underlay - selection, performance, installation

• Condensation - its prevention

• Securement

Case

Case study

- Hospital

- Hospital

Extension - 2600m

2

_{insulated pitched roof}

• Architects:

Watkins, Gray International

• Main contractor:

J Longley & Co.

• Insulation installer: NH Etheridge Ltd

• Roofer:

Cobsen, Davies

• Location: Conquest Hospital, Hastings,

East Sussex

Case study - Hospital

! Insulation: Roofmate* PR Type 50 (90mm)

! Roof space for services - heating,

Case study - Hospital

! Underlayer

:

:

Tyvek

Tyvek

2001-B Pro

2001-B Pro

(over

(over

counterbattens

counterbattens

)

)

!

!

Securement

Securement

:

:

Helifix Inscrew

Helifix Inscrew

600

600

fasteners - 110mm long

fasteners - 110mm long

!

Case study - Hospital

U-value calculations

Tiles

Tyvek 2001-B Pro

Roofmate PR

U-value = 0.25 W/m

_K

Vented airspace

Unvented airspace

Plasterboard

Outside surface resistance - 0.020 Concrete tiles 8.00 0.007 Vented airspace - 0.120 (between tiles and sarking)

Tyvek 2001-BPro -Unvented airspace - 0.180 Roofmate PR 90.00 3.600 Unvented airspace - 0.180 Plasterboard 13.00 0.081 Inside surface resistance - 0.100

•Notes:

•Element: Pitched roof, ceiling at rafter line, warm pitched roof •Exposure: exposed

•Internal surface emissivity: high •External surface emissivity: high •Building use: hospital

•Environmental conditions Summer Winter •Internal temp ºC 25 25 •External temp ºC 18 5 •Internal humidity % 60 60 •External humidity % 65 95

•Construction Thickness (mm) Vapour Resistance (MNs/g) •Outside surface resistance -

-•Concrete tiles 8.00 0.91 •Vented airspace -•(between tiles and sarking)

•Tyvek 2001-BPro - 0.16 •Unvented airspace -•Roofmate PR 30.00 28.08 •Roofmate PR 60.00 56.16 •Umvented airspace -•Plasterboard 13.00 0.68 •Inside surface resistance -

--10 0 10 20 30

Red : Actual temperature profile

Blue : dew point temperature

Condensation occurs where red and blue lines touch or cross

Case study - Hospital

Condensation risk

analysis

Warm pitched roof construction

- detailing

7

6

5

4

3

2

1

Warm pitched roof construction

Rafter

Tiling battens

Tiles

Counter battens

Vapour permeable

membrane

Type A - insulation over and between

rafters - Roofmate PR

A1- Eaves detail

Ensure continuity

of insulation

Set rebated edges of insulation

over rafters

A2 - Hip detail

Cut insulation

to line of hip and set over

support battens

A3 - Roof window detail

Cut insulation to fit tight against roof

window trimmers and seal with gap filler

Roof window

A4 - Valley detail

Cut insulation boards to

line of valley. Form rebate

to set over valley boards

Discontinuous edge batten to

allow drainage and ventilation

Gutter lining on

_{separating layer}

Set valley boards

between rafters

A5 - Ridge detail

Cut insulation to fit

tight at ridge and seal

with gap filler

Nail counter

battens to rafters

Nail tiles to

battens

Nail

tiling battens

to counterbattens

A6 - Abutment detail

Fix batten in

gap between insulation

and wall

Underlay

Insulation over and

A7 - Verge detail

Insulation set over and

Warm pitched roof construction

Type B - insulation over rafters Roofmate RL

Tiling battens

Counterbattens

Vapour

permeable

membrane

Tiles

Rafter

Roofmate RL

Insulation

B1 - Eaves detail

Ensure continuity

of insulation

B2 - Hip detail

Cut insulation

to line of hip and set onto

support battens

Hip rafter

Support

battens

B3 - Roof window detail

Cut insulation to fit tight against

roof window trimmers and seal

with gap filler

Roof window

B4 - Valley detail

Cut insulation

boards to line of

valley and set over

valley boards

Discontinuous edge

batten to allow

drainage and

ventilation

Gutter lining on

separating layer

Set valley boards

between rafters

Valley rafter

B5 - Ridge detail

Cut insulation to fit tight at ridge

and seal with gap filler

Nail counterbattens to rafters

Nail tiles to battens

Nail tiling battens to

counterbattens

B6 - Abutment detail

Plasterboard

ceiling

Nail battens to counter

battens

Lay insulation boards

over rafters

Nail counter

B7 - Verge detail

Plasterboard ceiling

Bargeboard

Make up piece of insulation set

over gable wall

INSULATED PITCHED ROOFING

Summarising :

• Warm Roof: 15 years proven

experience ! minimal condensation,

securement problems

• Design for total system

• Attention to detail design

• Care in installation

Issues :

• Insulation selection, performance,

installation

• Underlay selection, performance,

installation

• Condensation: it’s prevention

• Securement

If the following questionnaire is successfully completed and sent to Dow Construction

Products, 2 Heathrow Boulevard, 284 Bath Road, West Drayton, Middx UB7 0DQ Fax Number 0208 917 5413 a CPD certificate will be forwarded to you.

1. In the “warm roof concept” the insulation is placed above the rafters

between the rafters

above and between the rafters between the rafters

2. If a pitched roof is insulated at rafter level (and the loft space is to be utilised) What are the maximum allowable U-values

0.25 0.35 0.45 Domestic Buildings (SAP>60)

Non-Domestic

- Old Peoples Home - Office

3. What is the difference between a “traditional” and “breather” underlay Water tight

Air tight

Tear Strength (nails) Tensile properties

Water Vapour permeable

4. Where would you provide ventilation in a pitched roof construction insulated at rafter level if a) a traditional or b) a breather underlay is used ?

(a) (b) Below rafters

Below insulation

Between insulation and underlay Between underlay and tiles/slates

5. Which properties are of particular importance for breather underlays ?

Water resistance

Water vapour resistance

Compatibility with timber preservatives Tear strength Tearing resistance Slipperiness Blinding resistance Colour Air tightness

6. In designing a pitched roof which standards should you refer to for

1 2 3 4 5

General design - slating/tiling Wind loads

Design - timber structure Dead loads Imposed loads 1 = BS 6399 : Part 1 2 = BS 6399 : Part 2 3 = BS 6399 : Part 3 4 = BS 5534 : Part 1 5 = BS 5268 : Part 2

7. Where would you go for advice on how to avoid condensation in a pitched roof ? BS 5250

Approved Document L Approved Document F

BRE 262 Thermal Insulation : avoiding risks BS 5534

Insulation manufacturers

8. In a “warm roof construction” what issues did you need to consider to avoid/reduce the risk of condensation. ?

Use of a vapour control layer

Water vapour permeability of insulation Convection tightness of insulation layer Type of underlay

Location of underlay Where to ventilate

Air permeability of primary roof covering Drying our of building structure

Attention to details e.g. at eaves Securement of underlay

9. What factors must be considered when selecting and specifying fasteners ? Length

Diameter

Pull-out strength (from timber) Bending stress

Ease and accuracy of installation Deflection under load

10. Which of these should be considered when selection of insulation for installation or rafter level ?

Location

Compressive strength Rigidity

Water vapour permeability Water resistance Thermal conductivity Ease of installation Fire resistance Nail ability Name _______________________________________ Company Name ______________________________________________________ Address ______________________________________________________ ______________________________________________________ ______________________________________________________ Telephone Number ______________________________________________________