ᐅ Basement for Utility Use: Insulation, Heating, Raising the Ceiling?
Created on: 18 Nov 2021 10:43
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blubbernaseB
blubbernase18 Nov 2021 10:43Hello,
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?
Either insulate everything and include it within the thermal envelope, or don’t insulate at all and close off the stairwell. Intermediate solutions with wall insulation but no floor insulation don’t make sense.
For the intended use, the non-insulated option is sufficient. In that case, you can also skip underfloor heating and use, for example, infrared heating for the workshop / gym / playroom.
If you’re not really planning rooms with usable windows and for longer stays (office / guest room), I would probably spend the $30k upgrade elsewhere. For instance, on the exterior stairs. That’s quite useful if they lead, for example, to the laundry room with a sink. Then the kids can come in dirty, or if you’ve been working outside in the garden or on the car, you can go straight there to wash your hands.
However, this also depends heavily on the plot situation. Such a staircase takes up a lot of space directly at the house, so you need to have that space available and not need it for something else.
For the intended use, the non-insulated option is sufficient. In that case, you can also skip underfloor heating and use, for example, infrared heating for the workshop / gym / playroom.
If you’re not really planning rooms with usable windows and for longer stays (office / guest room), I would probably spend the $30k upgrade elsewhere. For instance, on the exterior stairs. That’s quite useful if they lead, for example, to the laundry room with a sink. Then the kids can come in dirty, or if you’ve been working outside in the garden or on the car, you can go straight there to wash your hands.
However, this also depends heavily on the plot situation. Such a staircase takes up a lot of space directly at the house, so you need to have that space available and not need it for something else.
I have a different opinion: if budget allows, insulate everything and do not include an external staircase. This way, you can use the basement much more flexibly and it will increase the property value.
I would also install underfloor heating throughout. I wouldn’t rely solely on infrared heating since it heats wall surfaces or areas close to the head, which is less ideal for low ceilings.
However, I would skip the 2.40 meters (7 ft 10 in) ceiling height; 2.25 meters (7 ft 5 in) should be sufficient in the basement. Isn't 2.40 meters (7 ft 10 in) possibly even considered living space?
I would also install underfloor heating throughout. I wouldn’t rely solely on infrared heating since it heats wall surfaces or areas close to the head, which is less ideal for low ceilings.
However, I would skip the 2.40 meters (7 ft 10 in) ceiling height; 2.25 meters (7 ft 5 in) should be sufficient in the basement. Isn't 2.40 meters (7 ft 10 in) possibly even considered living space?
Well, it is clear that with an unrestricted budget, an insulated basement is the better choice.
The question is whether the additional costs are justified by the added value.
In my opinion, they are not in this planned usage. I don’t think the insulation will increase the resale value by $30,000.
Living space is not only created by ceiling height; appropriate window areas are also a requirement. However, as far as I understand, this is not an issue here anyway. Of course, an infrared heater requires some space, but there seems to be more than enough available. I mean, there is a 30m² (320 sq ft) hallway and still 4 reasonably sized rooms for the intended use.
The question is whether the additional costs are justified by the added value.
In my opinion, they are not in this planned usage. I don’t think the insulation will increase the resale value by $30,000.
Living space is not only created by ceiling height; appropriate window areas are also a requirement. However, as far as I understand, this is not an issue here anyway. Of course, an infrared heater requires some space, but there seems to be more than enough available. I mean, there is a 30m² (320 sq ft) hallway and still 4 reasonably sized rooms for the intended use.
Planned use today!
At 14°C (57°F) in the home theater, watching Batman vs Pumuckl 3 is not very comfortable, or the children don’t really like playing there with their train set, so it has to be placed upstairs after all.
But yes, for 30,000 EUR, you can also operate direct heating for a long time.
At 14°C (57°F) in the home theater, watching Batman vs Pumuckl 3 is not very comfortable, or the children don’t really like playing there with their train set, so it has to be placed upstairs after all.
But yes, for 30,000 EUR, you can also operate direct heating for a long time.
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pagoni202018 Nov 2021 11:41We use infrared heating as the main heating system alongside the wood-burning stove, and so far, based on my experience over the past few weeks, I’m quite satisfied with it.
Our manufacturer offers glass panels that can be recessed into the concrete ceiling, so from below, you only see a stylish smoked glass surface. In the open-plan kitchen and living area, we only have panels rated at 240 or 242, and my initial concern that the lack of a smooth surface might cause burns has turned out to be completely unnecessary. Additionally, the panels are positioned so that no one stands or lies directly underneath them.
Having a separate basement entrance is definitely a nice feature, as I had in my previous house. I am not very knowledgeable about insulation and building envelopes, but considering your planned use, I would probably recommend maximizing the insulation under the concrete ceiling while definitely avoiding underfloor heating in the basement. Underfloor heating tends to overheat, is slow to adjust, and you would only need heating there occasionally or spontaneously. These are situations that underfloor heating does not handle well.
Our former house from 1990 also had a basement with likely no excessive insulation of the base slab at the time. We used the rooms for different purposes, including as bedrooms, and eventually, there was a granny flat there. The tenant is apparently still living there... heating costs are "normal," and the new owner would have told me otherwise if there were issues.
Back then, carpet flooring was common, which may have contributed to me never feeling that the rooms were too cold, as we often walked barefoot there.
Calculations are definitely useful, but I wouldn’t disregard my personal experience; that’s what I’ve shared with you now.
Our manufacturer offers glass panels that can be recessed into the concrete ceiling, so from below, you only see a stylish smoked glass surface. In the open-plan kitchen and living area, we only have panels rated at 240 or 242, and my initial concern that the lack of a smooth surface might cause burns has turned out to be completely unnecessary. Additionally, the panels are positioned so that no one stands or lies directly underneath them.
Having a separate basement entrance is definitely a nice feature, as I had in my previous house. I am not very knowledgeable about insulation and building envelopes, but considering your planned use, I would probably recommend maximizing the insulation under the concrete ceiling while definitely avoiding underfloor heating in the basement. Underfloor heating tends to overheat, is slow to adjust, and you would only need heating there occasionally or spontaneously. These are situations that underfloor heating does not handle well.
Our former house from 1990 also had a basement with likely no excessive insulation of the base slab at the time. We used the rooms for different purposes, including as bedrooms, and eventually, there was a granny flat there. The tenant is apparently still living there... heating costs are "normal," and the new owner would have told me otherwise if there were issues.
Back then, carpet flooring was common, which may have contributed to me never feeling that the rooms were too cold, as we often walked barefoot there.
Calculations are definitely useful, but I wouldn’t disregard my personal experience; that’s what I’ve shared with you now.
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