ᐅ KfW40+ with a basement inside or outside the thermal envelope?
Created on: 30 Dec 2020 11:05
K
KalterKaffee
I want to build a KfW40+ prefabricated house with a basement, two full stories, measuring 12m by 8m (39ft by 26ft). The basement will house the technical equipment as well as a music room, both featuring underfloor heating and connected to a controlled ventilation system. The plot is flat.
Provider 1 suggested calculating the basement outside the thermal envelope as "better and more cost-effective," so additional insulation would be applied between the basement ceiling and the ground floor, as well as insulation under the music room.
Provider 2 recommended calculating the basement within the thermal envelope.
I am leaning towards provider 2 because including the basement within the thermal envelope makes more sense to me. This also saves the extra insulation between the basement and the ground floor.
What do you think?
Thanks in advance.
Provider 1 suggested calculating the basement outside the thermal envelope as "better and more cost-effective," so additional insulation would be applied between the basement ceiling and the ground floor, as well as insulation under the music room.
Provider 2 recommended calculating the basement within the thermal envelope.
I am leaning towards provider 2 because including the basement within the thermal envelope makes more sense to me. This also saves the extra insulation between the basement and the ground floor.
What do you think?
Thanks in advance.
K
knalltüte30 Dec 2020 22:23And: The larger the enclosed space (volume), the easier it is (in principle/calculated) to meet KfW requirements regarding primary energy consumption in kWh per m² (square meter).
How does Anbieter1 plan to handle the staircase and the resulting edge insulation? Just leave it out?
You can meet the Building Energy Act requirements with a heat pump and a thermal bridge factor of 1.0, at least according to the old, soon-to-be-replaced DIN standard. But that won’t work with the KfW.
You can meet the Building Energy Act requirements with a heat pump and a thermal bridge factor of 1.0, at least according to the old, soon-to-be-replaced DIN standard. But that won’t work with the KfW.
K
KalterKaffee31 Dec 2020 15:38parcus schrieb:
How does Anbieter 1 plan to handle the insulation edges created by the staircase and similar details? Anbieter 1 informed me as follows:
** Anbieter 1 ** schrieb:
Sill/frame elevation for raised floor construction
a thermally insulated interior door
an interior staircase with risers
reinforced and thermally insulated interior wall under and beside the stairs
insulation increased to 180 mm (7 inches) below the underfloor heating instead of the 140 mm (5.5 inches) load-bearing insulation under the basement slab.
The basement does have living spaces but is still counted as outside the thermal envelope – this is the better and more cost-effective solution. They also offer a KfW55 basement within the thermal envelope, but believe it makes less sense for KfW40.
An independent basement builder told me:
** Basement builder ** schrieb:
We very rarely encounter a basement as KfW40 that is not part of the building envelope.
Also, if you have technical installations in the basement, they must be within the thermal envelope!
I cannot confirm 120-140 mm (5-5.5 inches) insulation for KfW40 from either homebuilder!
But your consultant knows exactly what insulation you need with your technical setup for KfW40.
We have no influence on the insulation; this is always specified by the homebuilder! The basement builder says the basement must be within the thermal envelope because I have technical installations there. This contradicts Anbieter 1.
I believe the 120-140 mm (5-5.5 inches) perimeter insulation is sufficient for KfW55, which is also offered by Anbieter 1 for KfW55 basements. Unfortunately, there is no information regarding KfW40...
It depends on many factors, but in my opinion, you can practically forget about 140 mm. The target for KfW 40 standard is (very roughly simplified) a U-value below approximately 0.19 for basement walls and the floor slab. This is achievable with waterproof concrete (WU concrete) at 28 cm (11 inches) thickness combined with XPS insulation only when using 180 mm (7 inches) or 200 mm (8 inches) of perimeter insulation.
What is also possible is cavity insulation made of PUR/PIR between the wall elements plus XPS on the outside, which allows for a somewhat thinner overall construction.
What is also possible is cavity insulation made of PUR/PIR between the wall elements plus XPS on the outside, which allows for a somewhat thinner overall construction.
Okay, then provider1 has clearly put some thought into their offer.
The critical factor here is thermal bridging rather than the thickness of the insulation. The KfW also points out the costs in this regard.
Over-insulating the surfaces is often more expensive and does not help prevent potential construction damage.
Ultimately, both providers must provide proof.
What matters here is how the thermal bridge surcharge is demonstrated.
The KfW provides three methods for this.
Only after that can the concepts/specifications and costs be properly compared.
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Oh, and it’s important to know which standard was used for the calculations—ideally according to DIN 18599 with the new supplement 2, and not the outdated DIN 4108 with DIN 4701-10, which can allow for easy “improvement” of results.
The critical factor here is thermal bridging rather than the thickness of the insulation. The KfW also points out the costs in this regard.
Over-insulating the surfaces is often more expensive and does not help prevent potential construction damage.
Ultimately, both providers must provide proof.
What matters here is how the thermal bridge surcharge is demonstrated.
The KfW provides three methods for this.
Only after that can the concepts/specifications and costs be properly compared.
---
Oh, and it’s important to know which standard was used for the calculations—ideally according to DIN 18599 with the new supplement 2, and not the outdated DIN 4108 with DIN 4701-10, which can allow for easy “improvement” of results.
N
nordanney31 Dec 2020 16:56KalterKaffee schrieb:
The basement builder says that the basement must be within the thermal envelope because I have technical equipment in the basement.Correct, the heat pump MUST be located within the thermal envelope. So you will also need a technical room above ground.Similar topics