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Iso-Spray Foam Insulation, Roof Insulation and Building Regulations
Installed Isothane Duratherm OS Roof System
Spray Foam Insulation and Building Regulations, this web page provides specifiers, architects and inspectors with the technical specifications and good installation practice that IsoSpray adopts to meet all Building Regulations when installing polyurethane foam insulation.
The new Building Regulations from April 2006 require that the sloping part of roofs exposed within loft conversions require a “U” value of 0.2 W/m2.K, previously it was 0.3 W/m2.K. This is achieved with a 130 mm depth of foam, previously it was 75 mm. See also foam insulation depths and U value tables.
Thermal Performance
Thermal Insulation requirements are defined in Approval Document L which is currently the subject of revision in the light of the Government's commitment to reduce carbon dioxide gas emission levels. Thermal Insulation standards, air leakage, gaps and cold bridges in installed systems are particularly under review. Iso-Spray's installed spray foam insulation products meet all requirements and indeed exceed them.
Typical Iso-Spray Foam depth and 'U' values are listed below.
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Flat Roof: |
0.25W/m2K |
65mm | |
Pitched Roof, Horizontal Ceiling: |
0.25W/m2K |
70mm | |
Pitched Roof, Ceiling at Rafter Line: |
0.25W/m2K |
75mm |
For full technical specification (Adobe pdf file format) on Duratherm OS right click here and select "save target as" or alternatively just click to view in your browser (broadband connection preferable). Essentially, by varying the thickness of Duratherm OS the required Building Regulations 'U' value can be met or exceeded. By Iso-Spray's installation method requirements for condensation and cold bridging via a warm deck method are also met.
Pitched Roof Analysis, ceiling at rafter line U value Element 1
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Construction |
Thickness (mm) |
Thermal conductivity (W/mK) |
Thermal resistance
(m2K/W) |
Vapour resistivity (MNs/gm) |
Vapour resistance (MNs/g) | | |
Outside surface resistance |
- |
- |
0.040 |
- |
- | |
Tiling including batten space |
15.0 |
0.120 |
0.180 |
- |
2.50 | |
Duratherm |
70.0 |
0.022 |
3.182 |
200.00 |
14.00 | |
Cavity >24mm, roof |
- |
- |
0.170 |
- |
0.00 | |
Aluminium foil |
- |
- |
- |
- |
1000.00 | |
Plasterboard |
12.0 |
0.167 |
0.072 |
45.00 |
0.54 | | Inside surface resistance | - | - | 0.100 | - | - |
U-value - 0.27W/M2K
U-Value combined method: 0.27 W/m2K (lower limit 3.744M2K/W, upper limit 3.744M2K/W, dUf 0.000, dUg 0.000 (correction for mechanical fasteners |Delta Uf= 0.000W/m2K, correction for air gaps, Delta Ug = 0.000W/m2K)
Cold Bridging
The method of installation ensures that the rafters do not form a cold bridge. The foam insulation is sprayed between the rafters and the roof surface, tile or slate. The space between the tile/slate and the rafter is foam filled thus ensuring that the rafter is insulated and no cold bridge is formed. This method of installation meets the requirement for a warm deck as defined in the building regulations.
Condensation
Ventilation requirements are defined in Approval Document F under the categories of 'Cold Roofs', 'Warm Roofs', and 'Alternative Approach'. The 'Alternative Approach' is a free design method which has to comply with the requirements of BS 5250:'Control of Condensation in Buildings'. Isotech Spray Foam Duratherm OS meets the Building Regulations in respect of condensation control by compliance with the Approved Document F 'Alternative Approach' for non-ventilated roofs. Control calculations are made in accordance with BS 5250 clauses 9.1 and 9.3.
Condensation Risk Analysis
Internal/external conditions: 20.0C @ 60.0%RH /5.7C @ 83.5%RH Buildup period 28 days
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Interface temp C |
Dewpoint temp C |
Vapour Pressure kPa |
Saturated V.P. kPa |
Condensation | |
Outside surface resistance |
5.9 |
3.1 |
0.76 |
0.93 |
No | |
Tiling including batten space |
6.5 |
3.2 |
0.77 |
0.97 |
No | |
Duratherm |
18.7 |
3.3 |
0.77 |
2.15 |
No | |
Cavity >24mm, roof |
19.3 |
3.3 |
0.77 |
2.24 |
No | |
Aluminium foil |
19.3 |
12.0 |
1.40 |
2.24 |
No | |
Plasterboard |
19.6 |
12.0 |
1.40 |
2.28 |
No |
Materials & Workmanship (Regulation 7)
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Isotech Spray Foam Insulation Duratherm OS meets the requirements on the basis of: | |
a) past experience in the usage of roofs in the UK | |
b) The relevant physical properties of Isotech Spray Foam Duratherm OS with regard to: | |
- vapour resistance | |
- water resistance | |
- durability | |
- thermal resistance | |
- behaviour in fire | |
as assessed in Isothane technical calculations and specifications and tested by BBA. |
To calculate a composite 'U' value further information is typically required. However, for thin skin structures (i.e. aluminium sheet, asbestos, steel sheet, etc.) the effect of the substrate can be ignored and the composite 'U' value taken as simply that of the foam, in the knowledge that the composite will be better.
'U' value of a structure if a certain thickness of foam is used
For any further technical information and specific project calculations to demonstrate compliance with Building Regulations please contact our technical consultant directly:
Martin Gill
Gill Jenkins & Co. Surveying Technical Services Tel: 0798 513 7429
Email:
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Building Regulations 
