ᐅ Basement for Utility Use: Insulation, Heating, Raising the Ceiling?
Created on: 18 Nov 2021 10:43
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blubbernase
Hello,
We’re a bit overwhelmed and I’d like to organize my thoughts here and also hear other opinions. Unfortunately, our architect and basement builder haven’t been much help so far— all we get is “You need to know what you want.” Our building inspector won’t be back for another two weeks.
Let me start from the beginning:
Since our space requirements would exceed the allowable floor area ratio, we planned a partial basement outside the thermal envelope of our KfW55 house, intended for technical equipment, storage, and a small workout room. The basement is completely underground.
This was the initial plan (room layout is not final yet, please ignore):
It then became clear that we would switch directly to the full basement, with the same specifications as the partial basement.
Well—suddenly we have much more space, and the workshop we had planned attached to the garage could fit inside the basement. This also makes an external basement entrance useful, as well as a possible living area where multimedia equipment could be set up or where kids could be noisy without disturbing others.
This brings up the question: Should we still leave everything uninsulated and unheated? We originally planned to install perimeter insulation ourselves, but the basement builder said doing it ourselves would affect the warranty. Now we have an offer for an insulated basement here, though the room layout is also not finalized...
If we choose insulation below the basement slab, a separation within the thermal envelope is no longer necessary, and the interior basement stairs would not need to be closed off and insulated for the KfW standard.
The remaining question concerns heating. The basement builder insists on underfloor heating, but that seems oversized to me because the basement will be used too infrequently: the technical room doesn’t need heating, and for the few hours per month spent in the workshop or workout room, an infrared heater might be sufficient? In my current workout room, which is uninsulated and has two exterior walls, temperatures range between 16 and 19°C (61 and 66°F), which is completely fine. However, that room adjoins heated and insulated interior rooms.
I just don’t know what the best solution is for KfW standards and what actually makes sense. Off the top of my head, I’d say:
- Choose insulated walls with core insulation but without insulation under the basement slab
- Keep the interior basement stairs insulated
- In rooms that will be used more often, plan for infrared heaters (or similar) — right now, our workshop is in the garage, and my wife, the main user, just wears a thick sweater
Bonus question: External basement entrance— is the investment worth it? I haven’t yet received a formal offer but have heard a ballpark figure of €7,000 to €10,000.
That’s where we stand now. Any opinions?
We’re a bit overwhelmed and I’d like to organize my thoughts here and also hear other opinions. Unfortunately, our architect and basement builder haven’t been much help so far— all we get is “You need to know what you want.” Our building inspector won’t be back for another two weeks.
Let me start from the beginning:
Since our space requirements would exceed the allowable floor area ratio, we planned a partial basement outside the thermal envelope of our KfW55 house, intended for technical equipment, storage, and a small workout room. The basement is completely underground.
This was the initial plan (room layout is not final yet, please ignore):
- Room height 2.25m (7 ft 5 in)
- Technical room downstairs
- Basement exterior walls: The exterior walls are prefabricated double-shell concrete elements, C25/30, wall thickness 36.5 cm (14 in), including built-in reinforcement. The cavity between the elements is filled with ready-mixed concrete on site.
- Uninsulated
- Unheated
- Water exposure class W 1.1-E (groundwater is at 30 meters (100 ft) depth here)
- Interior insulated basement stairs
- Price: approximately €66,500
It then became clear that we would switch directly to the full basement, with the same specifications as the partial basement.
Well—suddenly we have much more space, and the workshop we had planned attached to the garage could fit inside the basement. This also makes an external basement entrance useful, as well as a possible living area where multimedia equipment could be set up or where kids could be noisy without disturbing others.
This brings up the question: Should we still leave everything uninsulated and unheated? We originally planned to install perimeter insulation ourselves, but the basement builder said doing it ourselves would affect the warranty. Now we have an offer for an insulated basement here, though the room layout is also not finalized...
- Room height 2.40m (7 ft 10 in)
- Technical room downstairs
- Insulation under basement slab (€5,605)
- 120 mm (5 inches) load-bearing perimeter insulation (XPS) below the basement slab
- 120 mm (5 inches) perimeter insulation (XPS) single-layer on the front edge in the base area
- Basement exterior walls with core insulation, 120 mm (5 inches) thick. U-value: 0.25 W/m²K. The exterior walls are made of C25/30 concrete, wall thickness about 36.5 cm (14 in), including built-in reinforcement; wall construction as shown
- Water exposure class W 1.1-E
- Price: €96,800
If we choose insulation below the basement slab, a separation within the thermal envelope is no longer necessary, and the interior basement stairs would not need to be closed off and insulated for the KfW standard.
The remaining question concerns heating. The basement builder insists on underfloor heating, but that seems oversized to me because the basement will be used too infrequently: the technical room doesn’t need heating, and for the few hours per month spent in the workshop or workout room, an infrared heater might be sufficient? In my current workout room, which is uninsulated and has two exterior walls, temperatures range between 16 and 19°C (61 and 66°F), which is completely fine. However, that room adjoins heated and insulated interior rooms.
I just don’t know what the best solution is for KfW standards and what actually makes sense. Off the top of my head, I’d say:
- Choose insulated walls with core insulation but without insulation under the basement slab
- Keep the interior basement stairs insulated
- In rooms that will be used more often, plan for infrared heaters (or similar) — right now, our workshop is in the garage, and my wife, the main user, just wears a thick sweater
Bonus question: External basement entrance— is the investment worth it? I haven’t yet received a formal offer but have heard a ballpark figure of €7,000 to €10,000.
That’s where we stand now. Any opinions?
Hangman schrieb:
Yes, you could certainly do it that way. From my perspective, though, it’s like using a sledgehammer to crack a nut. For ventilation with moisture protection, the mentioned Maico AKE units are probably the more practical option.Oh, please don’t, I don’t like being thrown around—and certainly not on my friend, the sparrow from Wallrafplatz! The AKE units are definitely sufficient—I didn’t mean to suggest that the basement would require an elaborate mechanical ventilation system with heat recovery. In my opinion, that would be excessive there. What I meant was: 1. Mechanical ventilation with heat recovery and a cold basement don’t necessarily exclude each other, but 2. if used together, the systems would need to be kept separate—ideally with completely independent setups. Of course, a suitable, less complex solution is perfectly acceptable instead of a high-end system.https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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blubbernase25 Nov 2021 12:57Yes, that’s correct, KNX and Gussek houses are not compatible. In that case, all electrical installations must be completely removed.
Me too! That’s why I asked in the first place!
Hangman schrieb:
For example, I would be concerned about condensation moisture on cold basement walls during the summer.
Me too! That’s why I asked in the first place!
Hangman schrieb:I noted that and will discuss it again with the basement builder.
For ventilation with moisture protection, the mentioned Maico AKE units are probably the more practical option.
blubbernase schrieb:
Yes, that's right, KNX and Gussek house are not compatible. Then you have to remove all the electrical system, Oh no, you want to "retrofit" electrical in a prefabricated house?
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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blubbernase25 Nov 2021 15:1411ant schrieb:
Oh no, you want to retrofit electrical systems in a prefabricated house? It would then be handled through Luxone, their preferred partner. We are sticking to the standard; otherwise, Gussek Haus probably wouldn’t have been an option.H
HoisleBauer2226 Nov 2021 00:29I would like to expand the topic a bit here:
Our turnkey solid construction house provider has supposedly included the basement within the thermal envelope due to the KFW 55 standard and thermal bridge considerations (insulation under the foundation slab and perimeter insulation around the basement—we wanted a home office in the basement). They planned underfloor heating throughout the basement everywhere except in the utility room (HAR), which is located below, and are now running 40°C (104°F) supply temperature through the pipes throughout the entire house.
And here’s the kicker: In a conversation with an independent energy consultant, who is also an architect, I learned that this approach (underfloor heating everywhere in the basement) is complete nonsense and not understandable.
What are your thoughts on this?
Our turnkey solid construction house provider has supposedly included the basement within the thermal envelope due to the KFW 55 standard and thermal bridge considerations (insulation under the foundation slab and perimeter insulation around the basement—we wanted a home office in the basement). They planned underfloor heating throughout the basement everywhere except in the utility room (HAR), which is located below, and are now running 40°C (104°F) supply temperature through the pipes throughout the entire house.
And here’s the kicker: In a conversation with an independent energy consultant, who is also an architect, I learned that this approach (underfloor heating everywhere in the basement) is complete nonsense and not understandable.
What are your thoughts on this?
It depends on how it is used. In my opinion, pure storage space definitely does not need underfloor heating. But you definitely need surface heating or low-temperature radiators.
In any case, a flow temperature of 40°C (104°F) is no longer state of the art nowadays. Depending on the design outdoor temperature (DOT), the aim is usually to get down to around 30°C (86°F) or even lower. My calculation is based on 33°C (91°F) at a DOT of -12°C (10°F), and I am not really satisfied with that...
In any case, a flow temperature of 40°C (104°F) is no longer state of the art nowadays. Depending on the design outdoor temperature (DOT), the aim is usually to get down to around 30°C (86°F) or even lower. My calculation is based on 33°C (91°F) at a DOT of -12°C (10°F), and I am not really satisfied with that...
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