How To Achieve U-Values For Code For Sustainable Homes Level 5/6
 The Energy Saving Trust has developed a range of guidance to help housing
professionals meet the energy performance requirements of the Code for Sustainable
Homes. This is aimed at reducing the UK’s carbon dioxide emissions. The document
CE292 referenced here may be downloaded from the EST website.
Isothane Ltd has a range of products for insulating the building envelope based on
modern rigid polyurethane foam technology, (being CFC and HCFC free and therefore
having Zero Ozone Depletion Potential), of which two are illustrated here. Isothane
has a well established approved contractor network serving the UK, and Ireland.
The target of 100% less CO2 emissions than the current maximum allowed calls for
stringent U-values and air tightness - that we believe are best met by using the most
efficient insulation commonly available. On-site sprayed or injected polyurethane foam
characteristically seeks and seals all gaps. Therefore no costly correction for air gaps
is necessary in the calculations. Unwanted air leakage is restricted very efficiently and
we have achieved Air Permeability test results of 3 m³/h/m².
Aspect |
National Building Regulations |
Energy Savings Trust 100% & Zero Carbon Solutions |
Opaque Elements
W/m².K (Area weighted average) |
roof |
0.25 |
0.13 |
| walls |
0.35 |
0.15 |
| exposed floors |
0.25 |
Aspect |
National Building Regulations |
Energy Savings Trust 44% |
Maximum Permissible Air Permeability m³/(hr.m²)@50Pa
Confirmed after construction (but prior to completion) by a pressure test carried out in the ATTMA publication "measuring air permeability of building envelopes"
For more guidelines see "Improving airtightness in dwellings" (CE137/GPG224) and "Achieving airtightness in new dwellings: case studies" (CE248) |
10² |
3 |
Construction Type
| Element |
: Pitched roof - Zero Carbon, u=0.13 |
| Roof Pitch |
: 30° |
| Internal Surface Emissivity |
: High |
| External Surface Emissivity |
: High |
Construction
| |
Thickness (mm) |
Thermal Conductivity (W/mK) |
Thermal Resistance (m²K/W) |
Pitch (°) |
Bridge Details |
| Outside Surface Resistance |
- |
- |
0.040 |
30.0° |
|
| Clay Tiles (BS5250) |
15.0 |
0.840 |
0.018 |
30.0° |
|
| Airspace Between Tiles and Roofing Felt (inc. Restistance) |
- |
- |
0.120 |
30.0° |
|
| Breather Membrane (BS5250) |
- |
- |
- |
30.0° |
|
| Duratherm > 120mm |
210.0 |
0.024 |
8.750 |
30.0° |
6.3% Timber (210.0mm) |
| Cavity >= 25mm, roof(CBIS) |
- |
- |
0.340 |
30.0° |
6.3% Timber (25.0mm) |
| Vapourcheck Wallboard |
12.5 |
0.180 |
0.069 |
30.0° |
|
| Loft Space |
- |
- |
0.180 |
|
|
| Plasterboard (BS5250) |
12.5 |
0.170 |
0.074 |
|
|
| Plaster, Lightweight (BS5250) |
2.0 |
0.220 |
0.009 |
|
|
| Inside Surface Resistance |
- |
- |
0.100 |
|
|
U-value - 0.13W/m²K
U-value, Combined Method : 0.13 W/m²K (upper/lower limit 8.107 / 6.784 m²K/W. dUf 0.0000, dUg 0.0000, dUp 0.0000, dUr 0.0000, dUrc 0.0000)
(Correction for mechanical fasteners, Delta Uf = 0.000 W/m²K)
(Correction for air gaps, Delta Ug = 0.000 W/m²K)
(Based on the combined method for determining U-values of structures containing repeating thermal bridges.)
In this scenario, 210mm of Duratherm® has achieved 0.13.
Construction Type
| Element |
: Wall - Zero Carbon, U=0.15 |
| Internal Surface Emissivity |
: High |
| External Surface Emissivity |
: High |
Construction
| |
Thickness (mm) |
Thermal Conductivity (W/mK) |
Thermal Resistance (m²K/W) |
Pitch (°) |
Bridge Details |
| Outside Surface Resistance |
- |
- |
0.040 |
|
|
| Brick - Outer Leaf (BRE) |
103.0 |
0.770 |
0.134 |
|
17.3% Mortar (103.0mm) |
| Cavity >= 25mm, Wall (CIBS) |
- |
- |
0.180 |
|
|
| Breather Membrane (BS5250) |
- |
- |
- |
|
|
| Plywood |
9.0 |
0.170 |
0.053 |
|
|
| Duratherm > 120mm |
185.0 |
0.024 |
7.700 |
|
8% Timber (185.0mm) |
| Vapourcheck Wallboard |
12.5 |
0.180 |
0.069 |
|
|
| Plaster, Lightweight (BS5250) |
2.0 |
0.220 |
0.009 |
|
|
| Inside Surface Resistance |
- |
- |
0.130 |
|
|
U-value - 0.15W/m²K
U-value, Combined Method : 0.15 W/m²K (upper/lower limit 6.665 / 6.302 m²K/W, dUf 0.0000, dUg 0.0000, dUp 0.0000, dUr 0.0000, dUrc 0.0000)
(Correction for mechanical fasteners, Delta Uf = 0.000W/m²K)
(Correction for air gaps, Delta Ug = 0.000W/m²K)
In this scenario, 185mm of Duratherm® has achieved 0.15. In block & brick, 0.15 is possible with a full fill of Technitherm® into a 100mm cavity, using eg; Thermalite Turbo 100mm block, and 50mm of foam backed plasterboard
Construction Type
| Element |
: Solid Ground Floor - Zero Carbon, U=0.15 |
| Internal Surface Emissivity |
: High |
| External Surface Emissivity |
: High |
Construction
| |
Thickness (mm) |
Thermal Conductivity (W/mK) |
Thermal Resistance (m²K/W) |
Pitch (°) |
Bridge Details |
| Inside Surface |
- |
- |
0.040 |
|
|
| Screed - aerated (BS5250) |
75.0 |
0.400 |
0.188 |
|
|
| Duratherm > 120mm |
125.0 |
0.024 |
5.200 |
|
|
| Ground |
- |
- |
0.170 |
|
|
Ground Floor Details
Calculation method : EN ISO 13370
| P/A |
: 0.570m |
| Floor Type |
: Solid Floor |
| Edge Insulation |
: None |
U-value - 0.15W/m²K
U-value, Combined Method : 0.15 W/m²K (upper/lower limit 5.598 / 5.598 m²K/W, dUf 0.0000, dUg 0.0000, dUp 0.0000, dUr 0.0000, dUrc 0.0000)
(Correction for mechanical fasteners, Delta Uf = 0.000W/m²K)
(Correction for air gaps, Delta Ug = 0.000W/m²K)
In this scenario 125mm of Duratherm® has achieved 0.15. (Concrete base disregarded; neither edge insulation nor flooring included, 7m x 7m floor).
Isothane provides a U-value and Condensation Risk analysis free of charge. Each project must be assessed individually and therefore all examples shown here can only be illustrative.
Please see the partner document ‘Level 4 U-values’.
Please also see our ‘SAP Pass Rescue’ case study that gives more detail of an Air Permeability result of 3m³/h/m² for Block & Brick and Timber Frame detached houses, again using Duratherm® and Technitherm®.
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| |
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SAP Pass Rescue - Air Tightness |
How to achieve Level 4 U-Values |
How to achieve Zero Carbon U-values |
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