ᐅ Questions about flat roof insulation (035 vs. 029 // U-value 0.15 vs. 0.17)
Created on: 27 Feb 2020 19:36
M
M. GerdHello everyone,
we have a recessed top floor with a correspondingly smaller flat roof. It was initially assumed that the insulation would be 16cm (6.3 inches) thick with a thermal conductivity value (WLG) of 025. With the rest of the construction, this results in a U-value of 0.15. Now, the insulation thickness has been increased to 20cm (7.9 inches) (the slope changed from 23cm to 18cm (9 inches to 7 inches)), but with slightly lower insulation quality. Instead of WLG 030, WLG 035 was used, so the U-value is now 0.17.
1. How significant is this difference? I find it difficult to grasp. Is it a lot, and what kind of impact does it have roughly?
2. For a KfW55 house, does the U-value have to be 0.14, or would 0.17 be acceptable if we compensate elsewhere?
Assuming the U-value is not acceptable and we need to improve it, I currently see two options:
a) Remove the roofing membrane, replace the insulation, and close the roof again. Expensive.
b) Add an additional 4cm (1.6 inches) of insulation with WLG 029 on top of the current waterproofing.
Thanks in advance for your help—I hope someone can provide clarity here.
we have a recessed top floor with a correspondingly smaller flat roof. It was initially assumed that the insulation would be 16cm (6.3 inches) thick with a thermal conductivity value (WLG) of 025. With the rest of the construction, this results in a U-value of 0.15. Now, the insulation thickness has been increased to 20cm (7.9 inches) (the slope changed from 23cm to 18cm (9 inches to 7 inches)), but with slightly lower insulation quality. Instead of WLG 030, WLG 035 was used, so the U-value is now 0.17.
1. How significant is this difference? I find it difficult to grasp. Is it a lot, and what kind of impact does it have roughly?
2. For a KfW55 house, does the U-value have to be 0.14, or would 0.17 be acceptable if we compensate elsewhere?
Assuming the U-value is not acceptable and we need to improve it, I currently see two options:
a) Remove the roofing membrane, replace the insulation, and close the roof again. Expensive.
b) Add an additional 4cm (1.6 inches) of insulation with WLG 029 on top of the current waterproofing.
Thanks in advance for your help—I hope someone can provide clarity here.
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