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?
If the basement is located outside the thermal envelope, integrating the controlled mechanical ventilation system into the basement is definitely not a good idea (and probably not even permitted). If you still want to ensure ventilation in the basement (possibly even without windows), there are specific fans available from Maico (e.g., Maico AKE 150). These devices continuously measure the temperature and humidity both inside and outside, determine the dew point, and ventilate the moisture out as needed. Similar to a decentralized ventilation system, at least two fans are always connected, alternating between pushing air in and out to ensure air exchange throughout the entire space.
Hangman schrieb:
If the basement is outside the thermal envelope, including it in the controlled ventilation system is definitely not a good idea (and probably not even allowed). From my point of view, this only means that the controlled ventilation systems for the basement and the living area should be separated, i.e., two central controlled ventilation systems need to be installed in the house.
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blubbernase24 Nov 2021 22:37I’ve also found out that a controlled residential ventilation system isn’t an option.
We are currently exploring how to handle the ventilation.
We are currently exploring how to handle the ventilation.
Hangman schrieb:
If the basement is outside the thermal envelope, integrating the controlled mechanical ventilation system into the basement is certainly not a good idea (and probably not even permitted). We have done this in both our previous and current house. So far, we have never had any problems, and personally, I believe the benefits outweigh the drawbacks.
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blubbernase25 Nov 2021 00:10Fuchur schrieb:
We have had this setup both in our previous and current house. So far, there have never been any problems, and personally, I believe the benefits outweigh the drawbacks. The technical expert from Gussek Haus said that because of the heat recovery in the mechanical ventilation with heat recovery system, we cannot include the unheated and uninsulated basement in the ventilation circuit.
Oh dear, with Gussek Haus I recently had my own experience with the building services and ended up terminating our construction contract after six months. I hope you have better luck.
I just checked the data: outside temperature 1.1°C (34°F), supply air 16.1°C (61°F), basement 18.4°C (65°F). Yes, there is some heat loss, but at least regarding humidity there is no issue. On the contrary, I’m removing moisture—and also making use of the waste heat from the technical room in the basement.
I just checked the data: outside temperature 1.1°C (34°F), supply air 16.1°C (61°F), basement 18.4°C (65°F). Yes, there is some heat loss, but at least regarding humidity there is no issue. On the contrary, I’m removing moisture—and also making use of the waste heat from the technical room in the basement.
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