The value is used to measure how much heatloss occurs at the junctions between insulated areas. To comply with the 2008 Building Regs (40% less heat-loss than Building Regs) a value of 0.08 is necessary and for the 2010 Building Regs (60% less heat-loss than Building Regs) a value of 0.04 is necessary. The more you increase the U-values of the wall and floor the bigger the value gets, so when you increase the U-value of the wall or floor you also need to increase the value of the junction just to comply.
I will show now the effect different amounts of insulating build material has on the floor-wall value and how our foundation systems deliver a zero Cold Bridge which is where we are heading for in the 2012 (80% less) Building Regs. Both of our foundation systems have been certified by the PassivHaus institute as Cold Bridge free construction.
We full filled the cavity with 200mm EPS beads as part of our improvements to avoid Thermal Looping which reduces the effect of the insulation in the cavity by 200%.
At 20° 70% RH, Condensation will occur on a 14.1°C Cold Bridge, but when the temperature falls from 20° to 18° in the evening, Condensation will occur on a 17° surface because the Relative Humidity will have risen to 85% due to the drop in temperature. The general rule is that for every 1° drop in air temperature the moisture level rises by 7%. Here is some information on the temperatures that Condensation will occur on a Cold Bridge surface.
We improved the insulation levels of the traditional build with 200mm EPS bead in the wall and 300 EPS in the floor to reduce the Heat Loss by 40% specified in the 2008 Building Regs but the value increased from 0.11 to 0.16. Then we started to put in different amounts of QuinnLite blocks and EPS at the junction to reduce the Cold Bridge effect to comply with the 2008/2010 Building Regulations and improve the temperature at the junctions reducing Condensation and fungus/mould growth.
In the image below without Cold Bridge protection the value goes up to 0.16 as the levels of insulation is increased and interestingly the temperature just above the skirting drops from 15° to 14.1° increasing the risk of condensation. This seems to support the theory that as you improve the insulation of your walls, floor and roof the heatloss through the Cold Bridges increases in intensity.
One Quinnlite 0.12 Lambda block reduces the value back down to 0.11 and increases the temperature at the coldest point on the wall, just above the skirting to 15° but QuinnLite are not suppose to be used below the dpc because they lose their insulating properties when they get wet, so this should only be viewed as an exercise. We used the QuinnLite blocks with the best Lambda value 0.12 for this exercise but the QL blocks that are recommended for foundations have a worse 0.17 Lambda value.
Two Quinnlite 0.12 Lambda blocks reduces the value to 0.08 and increases the temperature of the coldest point on the wall, just above the skirting to 16° which would be meeting the 2008 Building Regulations but not the 2010 Building Regulations which are just around the corner. There is still a good risk of condensation as the temperature drops when you go to bed and turn off the heating. One layer of Foamglas 0.055 Lambda blocks @ €25/m has a similar effect to two QuinnLite 0.12 blocks. But 3 Foamglas blocks would be required for Cold Bridge free construction requested by the PassivHaus institute.
All the QuinnLite details below using up to 6 QuinnLite blocks in the foundations have a wall temperature above the skirting of between 17° and 18.5° so the condensation risk is greatly reduced and the heatloss is minimised. The 2 Viking House details show wall temperatures of 19.2° and 19.5° which is Excellent. QuinnLite are not suppose to be used below the dpc because they lose their insulating properties when they get wet so this should only be viewed as an exercise.
As you can see below, we had to line both sides of the rising walls with EPS in order to get the value down close to the 0.04 level required for the 2010 Building Regulations.