ᐅ Perimeter insulation beneath the foundation slab and additional XPS insulation under the screed?
Created on: 27 Sep 2016 20:44
G
GottesJunky
Hello,
Our house construction is getting closer, but today I noticed something that I don’t quite understand. Maybe someone can clarify it for me.
Under the concrete slab (according to the structural engineer 180mm (7 inches), but probably going to be 220mm (9 inches)) there is supposed to be an 80mm (3 inches) perimeter insulation (125m² (1,345 ft²)) installed. The floor build-up according to the architect looks like this:
...
5mm (0.2 inches) carrier board
120mm (5 inches) wood fiberboard insulation, thermal conductivity class 035
20mm (0.8 inches) wood chipboard insulation, thermal conductivity class 035
10mm (0.4 inches) waterproof membrane
Now my question is:
Isn’t this a bit redundant? Wouldn’t just the 120mm (5 inches) XPS insulation board above the slab be sufficient?
It will be a standard house built according to the 2014 energy saving ordinance.
Best regards,
Rico
Our house construction is getting closer, but today I noticed something that I don’t quite understand. Maybe someone can clarify it for me.
Under the concrete slab (according to the structural engineer 180mm (7 inches), but probably going to be 220mm (9 inches)) there is supposed to be an 80mm (3 inches) perimeter insulation (125m² (1,345 ft²)) installed. The floor build-up according to the architect looks like this:
...
5mm (0.2 inches) carrier board
120mm (5 inches) wood fiberboard insulation, thermal conductivity class 035
20mm (0.8 inches) wood chipboard insulation, thermal conductivity class 035
10mm (0.4 inches) waterproof membrane
Now my question is:
Isn’t this a bit redundant? Wouldn’t just the 120mm (5 inches) XPS insulation board above the slab be sufficient?
It will be a standard house built according to the 2014 energy saving ordinance.
Best regards,
Rico
Hello,
we decided on 10 cm (4 inches) of insulation above and 10 cm (4 inches) below the base slab. The payback period for the slab insulation alone is 30 years. However, since this helps us achieve KfW 40 (+) energy efficiency, the overall investment pays off in 10 to 15 years with the subsidy and low-interest loan.
Best regards,
Judyyy
we decided on 10 cm (4 inches) of insulation above and 10 cm (4 inches) below the base slab. The payback period for the slab insulation alone is 30 years. However, since this helps us achieve KfW 40 (+) energy efficiency, the overall investment pays off in 10 to 15 years with the subsidy and low-interest loan.
Best regards,
Judyyy
For KfW reasons, we do not need the extra insulation. Funding is not planned and therefore not factored in.
From what I have read so far, it’s hardly possible to make this look financially attractive.
The energy cost savings would be between 60 and 120 € per year. At that rate, it would take about 25 years to recoup the initial costs.
This is a rough calculation. Changes in energy prices, interest rates, and so on are not taken into account.
From what I have read so far, it’s hardly possible to make this look financially attractive.
The energy cost savings would be between 60 and 120 € per year. At that rate, it would take about 25 years to recoup the initial costs.
This is a rough calculation. Changes in energy prices, interest rates, and so on are not taken into account.
Personally, I don’t think €2300 is a lot when considered in isolation. Also, 25 years is not long for a house, in my opinion.
Of course, you can’t just spend an extra €2000 on every trade.
Couldn’t you, for example, install the insulation under the screed yourself and save some money?
As you said: you won’t get access to it again.
Of course, you can’t just spend an extra €2000 on every trade.
Couldn’t you, for example, install the insulation under the screed yourself and save some money?
As you said: you won’t get access to it again.
The general contractor would roughly pass this on at material cost if we insist on it – hence the price.
Including DIY work at these points is not an option for us. We have no experience in this area and don’t want to take anything away from the well-coordinated team.
They just need to know whether they should perform this additional work or not.
Including DIY work at these points is not an option for us. We have no experience in this area and don’t want to take anything away from the well-coordinated team.
They just need to know whether they should perform this additional work or not.
I would like to revisit this topic.
We are planning a construction project using timber frame construction, and the whole building is intended to meet KFW 55 standards.
Two out of three contractors offer a slab-on-grade insulated with XPS.
A third contractor says that the insulation for KFW 55 is not necessary and that he would omit the insulation beneath the slab and instead increase the screed insulation. This would save costs.
Is this approach acceptable, up-to-date, and reasonable?
Should we invest in the additional insulation if we can still achieve KFW 55 without it?
Or could we encounter issues with the slab, such as moisture problems, if we do not insulate?
Thank you very much.
Best regards
Sky
We are planning a construction project using timber frame construction, and the whole building is intended to meet KFW 55 standards.
Two out of three contractors offer a slab-on-grade insulated with XPS.
A third contractor says that the insulation for KFW 55 is not necessary and that he would omit the insulation beneath the slab and instead increase the screed insulation. This would save costs.
Is this approach acceptable, up-to-date, and reasonable?
Should we invest in the additional insulation if we can still achieve KFW 55 without it?
Or could we encounter issues with the slab, such as moisture problems, if we do not insulate?
Thank you very much.
Best regards
Sky
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