It has been estimated that up to 30% of the heatloss in a well insulated house is through these 'Non Repeating Thermal Bridges' at wall/floor junctions, corners, reveals, ceiling junctions heads and sills etc, building regulations ask that this heatloss is measured and minimized.
As with every element/component within the energy strategy of a building design, U-values, air tightness, boiler efficiency etc, this 'Continuity' of insulation at the junctions has a numerical value within the SAP calculation tool - it's called the 'Y' value. From 2010 the Y value must now be actually calculated by the building designer, with a target of around 0.04 achieving the Fabric Energy Efficiency Stand for Zero Carbon and the higher levels of the Code for Sustainable Homes; let's look at how it is calculated.
Example Calculation
Appropriate detailing to ensure the 'Continuity of insulation' can be satisfied by following details printed in the publication Accredited Construction Details, published by the DCLG. Using these details will allow the assessor to ascribe a PSI (?) value to the particular junction being measured; for example the wall/floor junction has a default value of 0.16 taken from Table K of the
SAP workbook.
The designer should measure the length of each of the junctions in the designed building and multiply the length by the default ? value from Table K - or from manufacturers own figures calculated by a qualified thermal bridging assessor working to BR497 and ISO 10211/2007. The total of all heatloss from all the junctions are then divided by the total heatloss area of the building to determine the Y-value for input into SAP. It has been estimated that every 0.01 reduction in the Y-value will result in a 1% energy reduction in the design.
Semi Detached House - TER 18.24
Total Envelope Area = 190.580
Which details to use?
|
|
Accredited |
Xtrathem |
| Junction Detail |
Length (m) |
Ψ (W/m2K) |
Ψ (W/m2K) |
| Lintels |
13.970 |
0.30 |
0.03 |
| Sills |
12.170 |
0.04 |
0.04 |
| Jamb |
29.550 |
0.05 |
0.02 |
| Ground Floor |
19.600 |
0.16 |
0.05 |
| Intermediate Floor |
19.600 |
0.07 |
0.00 |
| Corner (normal) |
20.400 |
0.09 |
0.04 |
| Corner (inverted) |
10.200 |
-0.09 |
-0.06 |
| Ceiling (insulation at eases) |
11.000 |
0.06 |
0.05 |
| Ceiling (insulation at gables) |
8.900 |
0.24 |
0.05 |
| Party Ground Floor |
8.900 |
0.04 |
0.04 |
| Party Wall (imtermediate floor) |
8.900 |
0.00 |
0.00 |
| Party Ceiling (insulation at ceiling) |
8.900 |
0.06 |
0.05 |
Total L x Y |
|
15.27 |
4.48 |
Y-Value (L x Y / total area) |
|
0.08 |
*0.02 |
| * Ψ Based on Lightweight block |
|
|
|
Guidance can be found in the paper IP1/06
'Assessing the effects of thermal bridges
at junctions and around openings'.
The following table shows the PSI value results that are achieved when using 100 - 150mm CavityTherm in a traditional wall.
There is a separate column showing results for both Aerated Block construction with a thermal conductivity of 0.15W/mK
Xtratherm Accredited Details
Click on the links below to download a PDF of PSI Value Analysis Certificate:
Table K1 Ref |
Ref |
Description |
| MCI-WD-02 |
E2 |
Other lintels including steel lintels (Seperated)
|
| XT-WDC-02* |
E2 |
Other lintels including steel lintels (Checked) (Seperated)
|
| XT-WDC-03 |
E2 |
Other lintels including steel lintels (Box lintel)
|
| XT-WDC-03* |
E2 |
Other lintels including steel lintels (Checked) (Box lintel)
|
| MCI-WD-04 |
E3 |
Sill
|
| XT-WDC-04* |
E3 |
Sill (Checked)
|
| MCI-WD-05 |
E4 |
Jamb
|
| MCI-WD-06 |
E4 |
Jamb (Checked)
|
| MCI-GF-01 |
E5 |
Ground floor (Insulation above slab)
|
| MCI-GF-02 |
E5 |
Ground floor (Insulation below slab)
|
| XT-GFB&B-01* |
E5 |
Ground floor (Beam & block floor with beams perpendicular)
|
| XT-GFB&B-02* |
E5 |
Ground floor (Beam & block floor with beams parallel)
XT- E5-XT-GFB&B-01-0001 |
|
 |
 |
|
| MCI-IF-01 |
E6 |
Intermediate floor within a dwelling (Concrete)
|
| MCI-IF-02 |
E6 |
Intermediate floor within a dwelling (Timber)
|
| MCI-IF-01 |
E7 |
Intermediate floor between dwellings (Concrete)
XT-E7-MCI-IF-01-0001 |
 |
|
|
|
| MCI-IF-02 |
E7 |
Intermediate floor between dwellings (Timber)
XT-E7-MCI-IF-02-0001 |
|
|
|
|
| MCI-RE-01 |
E10 |
Eaves (Insulation at ceiling level)
|
| MCI-RE-04 |
E11 |
Eaves (Insulation at rafter level)
|
| MCI-RG-01 |
E12 |
Gable (Insulation at ceiling level)
|
| MCI-RF-01 |
E14 |
Flat roof
|
| MCI-RF-02 |
E15 |
Flat roof with Parapet
|
| XT-CRN-01* |
E16 |
Corner (Normal)
|
| XT-CRN-02* |
E17 |
Corner (Inverted)
|
| MCI-IW-01 |
E18 |
Party wall between dwellings
|
| MCI-IW-01 |
E18 |
Party wall between dwellings (With Cavity barrier)
|
| XT-PGF-01* |
P1 |
Ground floor
|
| XT-PRC-01* |
P4 |
Roof (Insulation at ceiling level)
XT-P4-XT-PRC-01-0001 |
|
|
|
|
| |
|
|
* No official accredited detail available
All of the above details are based on the accredited details for construction published bt DCLG. |
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