Hello everyone,
We are planning to build a single-family house in spring 2012 (KfW 70; underfloor heating with district heating) with about 140 m² (1507 sq ft) of living space. External dimensions: 9 m x 11.20 m (30 ft x 37 ft).
Currently, we are wondering whether we should insulate the concrete slab. What do you think? Is it advisable? How much does such insulation typically cost?
Do you have any tips regarding this?
Thanks and best regards from the Rhineland,
Katinka
We are planning to build a single-family house in spring 2012 (KfW 70; underfloor heating with district heating) with about 140 m² (1507 sq ft) of living space. External dimensions: 9 m x 11.20 m (30 ft x 37 ft).
Currently, we are wondering whether we should insulate the concrete slab. What do you think? Is it advisable? How much does such insulation typically cost?
Do you have any tips regarding this?
Thanks and best regards from the Rhineland,
Katinka
B
Bauexperte17 Oct 2011 12:39Hello Katinka,
this question is like a "Jehovah topic." To give you an idea of the savings from additional insulation:
The concrete slab we installed (insulated from the inside) typically has a U-value of 0.26. The heat loss through transmission downward is approximately:
[U-value] * 5 [liters of heating oil per m² (square meter) per year] = 1.3 liters of heating oil per m² (square meter) per year (or an equivalent). 1 liter of heating oil delivers about 10 kWh of heat.
With 10 cm (5 inches) of insulation under the slab, the U-value improves to 0.18. This corresponds to a saving of:
(0.26–0.18) * 5 = 0.4 liters of heating oil per m² (square meter) per year.
For an assumed 140 m² (square meter) area, this would be around 0.4 * 0.60 cent * 140 = €34.00 per year.
With 20 cm (8 inches) of insulation under the slab, the U-value improves to 0.12. This corresponds to a saving of:
(0.26–0.12) * 5 = 0.7 liters of heating oil per m² (square meter) per year.
For an assumed 140 m² (square meter) area, this would be around 0.7 * 0.60 cent * 140 = €59.00 per year.
So much for the theory. Depending on the insulation material, the extra 10 cm (5 inches) of insulation quickly adds costs of around €3,500 and more. Personally, I consider additional insulation under the slab economically unjustifiable (I have never received verifiable information about what happens to insulation placed beneath the slab over the years), especially if renewable energy systems are used. However, there is also an ideological aspect: environmental, climate, and resource protection, sharply rising energy prices (gas and oil; ultimately it will rely on electricity as the energy carrier) in the future, which always depend on each individual’s personal attitude towards these topics—more or less strongly.
Kind regards
this question is like a "Jehovah topic." To give you an idea of the savings from additional insulation:
The concrete slab we installed (insulated from the inside) typically has a U-value of 0.26. The heat loss through transmission downward is approximately:
[U-value] * 5 [liters of heating oil per m² (square meter) per year] = 1.3 liters of heating oil per m² (square meter) per year (or an equivalent). 1 liter of heating oil delivers about 10 kWh of heat.
With 10 cm (5 inches) of insulation under the slab, the U-value improves to 0.18. This corresponds to a saving of:
(0.26–0.18) * 5 = 0.4 liters of heating oil per m² (square meter) per year.
For an assumed 140 m² (square meter) area, this would be around 0.4 * 0.60 cent * 140 = €34.00 per year.
With 20 cm (8 inches) of insulation under the slab, the U-value improves to 0.12. This corresponds to a saving of:
(0.26–0.12) * 5 = 0.7 liters of heating oil per m² (square meter) per year.
For an assumed 140 m² (square meter) area, this would be around 0.7 * 0.60 cent * 140 = €59.00 per year.
So much for the theory. Depending on the insulation material, the extra 10 cm (5 inches) of insulation quickly adds costs of around €3,500 and more. Personally, I consider additional insulation under the slab economically unjustifiable (I have never received verifiable information about what happens to insulation placed beneath the slab over the years), especially if renewable energy systems are used. However, there is also an ideological aspect: environmental, climate, and resource protection, sharply rising energy prices (gas and oil; ultimately it will rely on electricity as the energy carrier) in the future, which always depend on each individual’s personal attitude towards these topics—more or less strongly.
Kind regards
B
Bauexperte18 Oct 2011 11:15Hello Katinka,
Hmm, I was hoping other users/moderators would answer here.
The foundation of the concrete slab (25 - 30 cm (10 - 12 inches)) depends on the structural engineering results in combination with the soil survey. Usually, strip footings are constructed. Under the concrete slab, if necessary, a capillary-breaking gravel layer with a plastic membrane is installed; a foundation earth conductor is standard anyway.
Above the concrete slab—if it is a living floor—a floating screed is installed along with the required thermal insulation and impact sound insulation. Basement rooms—except for the basement hallway—usually receive only a smooth concrete finish without thermal insulation.
Kind regards
katinka schrieb:
How is it generally? Is any kind of insulation applied under or on top of the concrete slab? If so, what does it look like?
Hmm, I was hoping other users/moderators would answer here.
The foundation of the concrete slab (25 - 30 cm (10 - 12 inches)) depends on the structural engineering results in combination with the soil survey. Usually, strip footings are constructed. Under the concrete slab, if necessary, a capillary-breaking gravel layer with a plastic membrane is installed; a foundation earth conductor is standard anyway.
Above the concrete slab—if it is a living floor—a floating screed is installed along with the required thermal insulation and impact sound insulation. Basement rooms—except for the basement hallway—usually receive only a smooth concrete finish without thermal insulation.
Kind regards
P
perlenmann18 Oct 2011 11:33Bauexperte schrieb:
Mmh, I was hoping that other users/mods would respond here Alright,to put it in numbers from my side:
The concrete slab is 25-30cm (10-12 inches) thick (I don’t know the exact figure by heart),
then there is 8cm (3 inches) of insulation,
the underfloor heating is covered with 8cm (3 inches) of screed.
On the upper floor, the insulation is only 6cm (2.5 inches).
Thank you for the responses.
Unfortunately, I’m still not sure whether insulation is necessary or not. After all, you can’t access the slab foundation once the house is completed. I’ve also read about mold growth caused by thermal bridges when there is no insulation under the slab. Now I’m concerned that if the slab foundation isn’t insulated, the house might develop mold.
So, if I understand correctly, the investment may not pay off in terms of energy savings. What are the benefits of insulating the slab foundation?
Thank you and best regards,
Katinka
Unfortunately, I’m still not sure whether insulation is necessary or not. After all, you can’t access the slab foundation once the house is completed. I’ve also read about mold growth caused by thermal bridges when there is no insulation under the slab. Now I’m concerned that if the slab foundation isn’t insulated, the house might develop mold.
So, if I understand correctly, the investment may not pay off in terms of energy savings. What are the benefits of insulating the slab foundation?
Thank you and best regards,
Katinka
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