ᐅ Attic insulation upgrade from KfW 55 to KfW 40 standard applied to the attic floor
Created on: 5 Feb 2020 12:18
A
annab377
Hello everyone,
We are planning to build a single-family house in Baden-Württemberg with the following current key specifications:
- approximately 12x12 m (39x39 ft) external dimensions
- basement with about 16 cm (6 inches) perimeter insulation and a good layer (exact height unknown) of glass foam gravel underneath (within the thermal envelope)
- 49 cm (19 inches) Poroton exterior wall filled with perlite (U-value around 0.16)
- windows/doors adapted to the exterior wall (U-value currently unknown, but roughly at the same level as the facade)
- gable roof (attic outside the thermal envelope)
- domestic hot water heat pump or geothermal heat pump with an appropriate annual performance factor to qualify for BAFA incentives
- photovoltaic system on the roof
- controlled ventilation system with heat recovery
Now, regarding the gable roof, I have the following question. For a KfW-certified house, besides the exterior walls, basement, and openings in the facade (windows, doors), the roof also needs to be properly insulated. Is it sufficient to insulate the attic floor itself (about 30-40 cm (12-16 inches) of insulation material, then covered with wood to allow access to the attic—the technical term escapes me), or is it necessary to insulate directly under the roof (between or below the rafters) to meet KfW 55 or, ideally, KfW 40 standards?
I believe that insulating the attic floor would be much easier as a DIY project and thus more cost-effective than insulation between or below the rafters. Or are the costs for both methods comparable?
Which material would you recommend for roof insulation in a KfW 40 house?
Are we mistaken in thinking that with the materials mentioned above, achieving a KfW 40 standard is fairly straightforward? Or is the effort of upgrading from KfW 55 to KfW 40 economically unjustified?
So far, we have not yet had a conversation with an energy consultant from the list.
Thanks in advance,
Best regards
Ann.
We are planning to build a single-family house in Baden-Württemberg with the following current key specifications:
- approximately 12x12 m (39x39 ft) external dimensions
- basement with about 16 cm (6 inches) perimeter insulation and a good layer (exact height unknown) of glass foam gravel underneath (within the thermal envelope)
- 49 cm (19 inches) Poroton exterior wall filled with perlite (U-value around 0.16)
- windows/doors adapted to the exterior wall (U-value currently unknown, but roughly at the same level as the facade)
- gable roof (attic outside the thermal envelope)
- domestic hot water heat pump or geothermal heat pump with an appropriate annual performance factor to qualify for BAFA incentives
- photovoltaic system on the roof
- controlled ventilation system with heat recovery
Now, regarding the gable roof, I have the following question. For a KfW-certified house, besides the exterior walls, basement, and openings in the facade (windows, doors), the roof also needs to be properly insulated. Is it sufficient to insulate the attic floor itself (about 30-40 cm (12-16 inches) of insulation material, then covered with wood to allow access to the attic—the technical term escapes me), or is it necessary to insulate directly under the roof (between or below the rafters) to meet KfW 55 or, ideally, KfW 40 standards?
I believe that insulating the attic floor would be much easier as a DIY project and thus more cost-effective than insulation between or below the rafters. Or are the costs for both methods comparable?
Which material would you recommend for roof insulation in a KfW 40 house?
Are we mistaken in thinking that with the materials mentioned above, achieving a KfW 40 standard is fairly straightforward? Or is the effort of upgrading from KfW 55 to KfW 40 economically unjustified?
So far, we have not yet had a conversation with an energy consultant from the list.
Thanks in advance,
Best regards
Ann.
@nordanney @face26 do you happen to have any pictures of those narrow slit windows?
I only know them from the house I’m currently living in. Two years ago, the exterior facade was retrofitted with a 36cm (14 inch) brick wall and an external thermal insulation composite system (ETICS), so now the wall thickness is quite substantial. Actually, apart from the initial adjustment to such deep exterior window sills, I don’t find it that bad.
However, from what I see, a KfW40 standard is generally no longer economically justifiable—it’s usually unprofitable as a rough rule of thumb. Thanks.
I only know them from the house I’m currently living in. Two years ago, the exterior facade was retrofitted with a 36cm (14 inch) brick wall and an external thermal insulation composite system (ETICS), so now the wall thickness is quite substantial. Actually, apart from the initial adjustment to such deep exterior window sills, I don’t find it that bad.
However, from what I see, a KfW40 standard is generally no longer economically justifiable—it’s usually unprofitable as a rough rule of thumb. Thanks.