ᐅ Insulation Under Reinforced Concrete Slab for KfW 55 Standard
Created on: 20 Feb 2018 22:07
T
turbotopo
Hello everyone,
We are going to build a prefabricated house on a concrete slab foundation. Our builder told us that with KFW55 standard, insulation beneath the slab is not required.
Now we are wondering whether we should add it anyway and if it is a worthwhile investment.
The concrete slab:
Reinforced concrete slab as a load-bearing element made of in-situ concrete (c20/25, approx. 15-20cm (6-8 inches) thick, edge reinforced) with reinforcement according to structural requirements.
Costs for the insulation:
120 mm (5 inches) insulation with thermal conductivity class 040 under the slab of the residential building: 3115€
160 mm (6.3 inches) insulation with thermal conductivity class 040 under the slab of the residential building: 4930€
Will these costs ever be recovered through energy savings?
Best regards
We are going to build a prefabricated house on a concrete slab foundation. Our builder told us that with KFW55 standard, insulation beneath the slab is not required.
Now we are wondering whether we should add it anyway and if it is a worthwhile investment.
The concrete slab:
Reinforced concrete slab as a load-bearing element made of in-situ concrete (c20/25, approx. 15-20cm (6-8 inches) thick, edge reinforced) with reinforcement according to structural requirements.
Costs for the insulation:
120 mm (5 inches) insulation with thermal conductivity class 040 under the slab of the residential building: 3115€
160 mm (6.3 inches) insulation with thermal conductivity class 040 under the slab of the residential building: 4930€
Will these costs ever be recovered through energy savings?
Best regards
T
turbotopo24 Feb 2018 15:28Do I understand correctly that you then insulate only under the foundation slab and no longer under the screed at all?
T
Trasher1926 Feb 2018 17:10We are currently building a 55 standard house as well; the shell is already up, and our heat loss calculation showed the following:
14 cm XPS insulation under the slab
25 cm concrete slab
6 cm polystyrene insulation
6 cm screed
If, like us, you plan to use the basement rooms not only for storage but also as an office or guest room, I would recommend insulating the slab. It should improve comfort alone. Whether it is cost-effective, however, is another question. You can certainly still achieve the 55 standard by improving other components, but then you would need to, for example, insulate the roof better or install a ventilation system. There are many ways to reach your goal—err, KfW standard.
14 cm XPS insulation under the slab
25 cm concrete slab
6 cm polystyrene insulation
6 cm screed
If, like us, you plan to use the basement rooms not only for storage but also as an office or guest room, I would recommend insulating the slab. It should improve comfort alone. Whether it is cost-effective, however, is another question. You can certainly still achieve the 55 standard by improving other components, but then you would need to, for example, insulate the roof better or install a ventilation system. There are many ways to reach your goal—err, KfW standard.
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