ᐅ Unheated and Uninsulated Basement

Dear forum,

We are currently planning our single-family house with an uninsulated basement without heating, due to cost reasons. The basement will be used solely for storage and is completely underground. The house is intended to meet the KFW 55 standard.

Is the omission of insulation problematic, or will it affect the ground floor?

Then you need to insulate the ground floor ceiling. Otherwise, there is a risk that the basement will be too cold and develop mold.

Hendrik1980 schrieb:

The house is supposed to meet the KFW 55 standard.
Is omitting insulation problematic, or would the ground floor be affected by this?

For KfW55, the ceiling between the basement and the ground floor is likely required to be insulated, so I would say "no."

Hendrik1980 schrieb:

For cost reasons, we are currently planning our single-family house with an uninsulated basement without heating. The basement will be used purely as a utility cellar and is located entirely below ground level.

If the exterior wall remains completely below ground level, I don’t see a need to insulate it for an unheated basement. On the other hand, your description suggests a flat site, which according to my basement formula means the basement would be a “luxury.” Therefore, I find the cost reasons contradictory to building a basement.

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11ant schrieb:

For KfW55, the basement to ground floor ceiling will likely need to be insulated, so I would say "no."

If the exterior wall remains completely below ground level, I don’t see a need to insulate it in an unheated basement. On the other hand, the description suggests a zero-slope site, so according to my basement formula, the basement would be "luxury," which makes the "cost reasons" contradictory to building a basement.

That sounds interesting. We thought for a long time about building without a basement but ultimately decided to include one since we’re building in a rural area and need the extra storage space. The basement also gives us an office and a guest room on the ground floor/upper floor because those areas had previously been planned as storage rooms.

Our basement is part of the thermal envelope; for KfW55 standard, practically every section of the basement in contact with the ground must be insulated.

Keeping this in mind, simply insulating the basement ceiling is not enough. The insulation missing along the walls upward must be considered, and the basement door also needs to be a special type, especially when I think of my attic ladder.

Furthermore, even if you do not plan to heat the basement, which is fine, the insulation for the basement should not cost more than approximately 5,000 euros in materials. To spend about 5,000 euros and end up with a permanently damp basement that will always be cold is, sorry to say, quite unwise considering the basic costs of having a basement.

If you have an unheated basement, in addition to insulating the basement ceiling, you will also need an insulated basement stairwell.