Post on 13-Apr-2018
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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
* Trademarks of the Dow Chemical Company
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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
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INSULATED PITCHED ROOFING
INTRODUCTION:
It is estimated that today around 10% of new pitched
roofs are insulated atrafter leveland that this
figure is increasing.
Various insulation solutions are available which aredependent 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 manufacturers point of view.
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Insulation options Advantages of an insulated
roof structure
TheWarm roof concept
Design considerations
Roof build-up: the components
Building Regulations: requirements
Case study
Detailing
Conclusions
CONTENT
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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 prov ided by a
water vapour permeable (breather) underlay and
thus do away wi th providing vents at eaves and
ridge level ?
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Roof structure: insulated
room in
the roof
insulation at
rafter level
Insulation can be a) above,
b) between
c) below the rafters
or a combination of these Warmroof
insulation above rafters
sometimes referred to as sarking insulation (see BRE Thermal insulation: avoiding risks BR262
Hybridroof : insulation between and/or under rafters.
Note: Focus of this seminar will be on the warmpitched roof as this is the
optimum( and perhaps the most challenging ) of the insulation options.
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ADVANTAGES : INSULATED VS
UNINSULATEDROOF 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 warmroof:
- reduced risk of condensationon structural membranes.
- thermal movementof roof structure reduced.
- roof structure kept dry- no need for timber
preservative treatment.
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THEWARM PITCHED ROOF
Rafter
Tiling batten TilesCounterbatten
InsulationVapour permeable
underlay
- roof build up
Insulation shown above and betweenrafters
Vapour permeable underlay(breather type) can be laideither in direct
contactwith the insulation( as shown ) or over the counterbattens
Suitable for new bui ld 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.
Use plasterboard (13 mm) to cover exposed XPS insulation.
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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.
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THE WARM PITCHED ROOF
First thatched roofing !
Developed from Scottish sarking - early 80s
Agrment certification - mid 80s
Thousands roofs, millions sq metres installed
Includes all insulation types
Minimal condensation problems
No securement problems
Note: Thatched roof- really is a breathing warm roof
Sarking - originated in Germany / Scandinavia refers to a sheet or
underskirt of boarding.
- traditionally in Scotland 25mm thick close timber boarding at
underslating level.
- helps reduce effect of wind uplift on slates.
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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 &
snow loading
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ROOF BUILD-UP - THE COMPONENTS
Rafters
Vapour Control Layer
Insulation
Underlay
Battens
Fasteners
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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.
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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 useof 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.
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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
Location:
(a) over the rafters
(b) between the rafters(c) under the raftersor any combination of these
Note : Option (a) is sometimes referred to as a warm roof construction or assarking 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 ->
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Thickness:
The thickness of the insulation will be determined by the required thermal
performance as well as by the roof construction (see Approved DocumentL). 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 andaround 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 rafterspacing 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.
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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/m 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 immediatelyafter production ie before equilibrium
reached - short term value.
Water vapour resistanceDetermined relative to MF(air) for equivalent U-value thicknesses (XPS=50mm)
Water absorption
Be sure to take into account likely effect on thermal conductivity !
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ROOFMATE* RL, PR
- physical characteristics
PR RL
Density kg/m3 34 34
Thermal conductivity W/mK 0.025 0.025
Compressive strength kN/m2
300 300Water 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).
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UNDERLAYS-REQUIREMENTS
- TRADITIONAL
Keep water (snow, dust) out
Air tight
Adequate strength
- WATER VAPOUR PERMEABLE (Breather)
As Traditional
plus water vapour permeabil ity
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 : 1995Flexible building membranes (breather type)
- max. water vapour resistance 0.6MNs/g BRE Thermal Insulation : Avoiding risks- specifies 0.1 - 2.0 MNs/g.
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UNDERLAYS
WATER VAPOUR RESISTANCE
Traditional MNs/g
BS 747 Type IF felt 50 - 270
Monarfil* 250 420
Breather
Permo* 0.20
Tyvek* HD - Soft 0.24Tyvek* 2001 - Pro 0.16
Roofshield* 0.08
Monarperm* 450 0.11
Insulation
XPS - 90mm 85
PUR - 80mm 46
MF - 115 mm 0.6 * Tradenames
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)
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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 +800C, 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!
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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
(insulation, battens, underlay,tiles)
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SECUREMENT
- need to secure tiles/slates, underlay and
insulation against dead wind and imposed
loads
Insulation
consider:-thickness (over rafters), physical properties
Fasteners
egBS 1202 nails, Helifix Inskew, Proctor PR nails
consider:- penetration, pull-out strength, deflection under load - ease and accuracy of installation
Refer to manufacturers for advice
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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: pull-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 isrecommended 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
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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 m2
)
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.
Refer to manufacturers l iterature for the specialist fasteners.
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Fasteners
- method of securement
Tile battens
nailed to counter battens
Counter battens nailed torafters 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.
Tiles
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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
- Requirement LI : Conservation of Fuel and Power
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BUILDING REGULATIONS
Approved Document L : 1995 U-
values
Approved Document L
Maximum U-values(W/m2K)
DWELLINGS
SAP 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 70o then max U = 0.45 W/m2K
For building classification see Approved Document B
Building Regulations specifymaximum allowable U-values -
the optimum cost effective U-values are in fact lower eg:
W/m2K
Floors 0.35
Roofs 0.20 - 0.25
Walls 0.30 - 0.35
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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
-see Clauses 9.1, 9.2 and 9.3
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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.
cont ->
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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
Fortraditional
underlays ventilation should be provided in
accordance with the recommendations given in BS 5250 and
Approved Document F2 (1990). For breatherunderlays 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.
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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
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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
* see end of tutorial for typical details
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CaseCase study- Hospital- Hospital
Extension - 2600m2insulated 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
Project: BUPA extension - completed 1998
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Case study - Hospital
! Insulation: Roofmate* PR Type 50 (90mm)
! Roof space for services - heating,
ventilation
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Case study - Hospital
! Underlayer:: TyvekTyvek 2001-B Pro2001-B Pro
(over(over counterbattenscounterbattens))
!! SecurementSecurement:: Helifix InscrewHelifix Inscrew600600
fasteners - 110mm longfasteners - 110mm long
!! Tiles:Tiles: MarleyMarleyModernModern
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Case study - Hospital
U-value calculations
Tiles
Tyvek 2001-B Pro
Roofmate PR
U-value = 0.25 W/m2K
Vented airspace
Unvented airspace
Plasterboard
Thickness Thermal Resistance (mm) (m2K/W)
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
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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 C 25 25
External temp C 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 30Red : Actual temperature profile
Blue : dew point temperature
Condensation occurs where red and blue lines touchor cross
Case study - Hospital
Condensation risk
analysis
U-value: 0.25 W/m2K
Condensation build up
winter 0 g/m2
summer 0 g/m2
annual 0 g/m2
Temperature C
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Warmpitched roof construction
- detailing
7
6
5
4
3
2
1
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Warm pitched roof construction
Rafter
Tiling battens TilesCounter battens
Vapour permeable
membrane
Type A - insulation over and between
rafters - Roofmate PR
Roofmate PR Insulation
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A1- Eaves detail
Ensure continuity
of insulation
Set rebated edges of insulation
over rafters
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A2 - Hip detail
Cut insulation
to line of hip and set over
support battens
Hip rafter
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A3 - Roof window detail
Cut insulation to fit tight against roof
window trimmers and seal with gap fillerRoof window
Counter batten
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A4 - Valley detail
Cut insulation boards to
line of valley. Form rebate
to set over valley boards
Discontinuous edge batten to
allow drainage and ventilationGutter lining on
separating layer
Set valley boards
between rafters
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A5 - Ridge detail
Cut insulation to fit
tight at ridge and seal
with gap filler
Nail counter
battens to rafters
Nail tiles to
battens
Nailtiling battensto counterbattens
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A6 - Abutment detail
Fix batten in
gap between insulation
and wall
UnderlayInsulationoverand
between rafters
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A7 - Verge detail
Insulation set over and
between rafters BargeboardFlying rafter
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Warm pitched roof construction
Type B - insulation over rafters Roofmate RL
Tiling battensCounterbattens
Vapour
permeable
membrane
Tiles
RafterRoofmate RL
Insulation
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B1 - Eaves detail
Ensure continuity
of insulation
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B2 - Hip detail
Cut insulation
to line of hip and set onto
support battensHip rafter
Support
battens
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B3 - Roof window detail
Cut insulation to fit tight against
roof window trimmers and seal
with gap fillerRoof window
Counter batten
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B4 - Valley detail
Cut insulationboards to line of
valley and set over
valley boards
Discontinuous edgebatten to allow
drainage and
ventilation
Gutter lining onseparating layer
Set valley boards
between rafters
Valley rafter
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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
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B6 - Abutment detail
Plasterboard
ceiling
Nail battens to counter
battens
Lay insulationboards
over rafters
Nail counter
battens to rafters
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B7 - Verge detail
Plasterboard ceiling Bargeboard
Make up piece of insulationset
over gable wall
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INSULATED PITCHED ROOFING
Summarising:
WarmRoof: 15 years proven
experience ! minimal condensation,
securement problemsDesign for total system
Attention to detaildesign
Care in installation
Issues :
Insulation selection, performance,
installation
Underlay selection, performance,
installation
Condensation: its prevention
Securement
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If the following questionnaire is successfully completed and sent to Dow ConstructionProducts, 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
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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
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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/reducethe 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
Width of battens, rafters
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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 _______________________________________
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