Hello,
even though similar questions have been asked here before, I am starting a new thread.
We are planning a new build and are currently comparing insulation options for the exterior walls, basement, roof, etc.
We want to build a solid structure with a double-shell masonry made of aerated concrete.
The construction companies all insulate the exterior walls with mineral wool at a thickness between 8 to 14 cm (3 to 6 inches), thermal conductivity value (WLG) 035.
For roof insulation, there is always a 20-24 cm (8 to 10 inches) insulation layer between the rafters with WLG 035. The attic space is insulated only if a finish is planned. If financially feasible, we would like to have this insulated as well.
Now the first question: can you recommend mineral wool insulation? And if yes, what thickness should be used and should one demand WLG 032 instead? Of course, better insulation is better, but what really makes sense when comparing initial investment costs to possible heating savings?
We also consulted a structural engineer who individually plans and supervises house constructions. He became quite concerned when looking at the specifications from the building companies. He recommends insulation with polyurethane boards having a thermal conductivity value (WLS) of 024 and a thickness of 20-24 cm (8 to 10 inches). For the roof, he recommends a full inboard insulation (above-rafter insulation) using the same material.
With this, our exterior wall would achieve a U-value of around 0.10-0.12 instead of possibly 0.16-0.18 with good mineral wool insulation (according to the information brochure).
Of course, this would be better, but his cost estimate showed that such a house would cost at least 50,000 € more and thus would no longer be financially feasible for us.
We really want to think this through carefully and do everything as properly and sensibly as possible and would be very grateful for professional answers!
Maya
even though similar questions have been asked here before, I am starting a new thread.
We are planning a new build and are currently comparing insulation options for the exterior walls, basement, roof, etc.
We want to build a solid structure with a double-shell masonry made of aerated concrete.
The construction companies all insulate the exterior walls with mineral wool at a thickness between 8 to 14 cm (3 to 6 inches), thermal conductivity value (WLG) 035.
For roof insulation, there is always a 20-24 cm (8 to 10 inches) insulation layer between the rafters with WLG 035. The attic space is insulated only if a finish is planned. If financially feasible, we would like to have this insulated as well.
Now the first question: can you recommend mineral wool insulation? And if yes, what thickness should be used and should one demand WLG 032 instead? Of course, better insulation is better, but what really makes sense when comparing initial investment costs to possible heating savings?
We also consulted a structural engineer who individually plans and supervises house constructions. He became quite concerned when looking at the specifications from the building companies. He recommends insulation with polyurethane boards having a thermal conductivity value (WLS) of 024 and a thickness of 20-24 cm (8 to 10 inches). For the roof, he recommends a full inboard insulation (above-rafter insulation) using the same material.
With this, our exterior wall would achieve a U-value of around 0.10-0.12 instead of possibly 0.16-0.18 with good mineral wool insulation (according to the information brochure).
Of course, this would be better, but his cost estimate showed that such a house would cost at least 50,000 € more and thus would no longer be financially feasible for us.
We really want to think this through carefully and do everything as properly and sensibly as possible and would be very grateful for professional answers!
Maya
Maya2011 schrieb:
He recommends insulation with polyurethane boards of WLS 024 and 20-24 cm (8-9.5 inches) thickness.Is the goal to build a passive house?
Also, I’m curious how the 20 cm (8 inches) cavity gap is supposed to be bridged. There are approvals for cavity wall ties longer than 150 mm (6 inches), but that also comes with additional costs. Everything has to be in proportion, and for a solid house, this seems a bit exaggerated.
Maya2011 schrieb:
Yes, the polyurethane boards are apparently meant to be installed on the exterior wall, where the mineral wool and cladding would otherwise go.Polyurethane (PUR) can be used as core insulation, but I’m not really a fan. Mainly due to cost and building physics. PUR doesn’t seem vapor-permeable enough to me.
Maya2011 schrieb:
So you find the polyurethane insulation on the roof not very sensible? But isn’t an exterior (above-rafter) insulation better than insulation between the rafters? What are the possible advantages and disadvantages?...and again, the costs. For a renovation, this might make sense in very few cases—the emphasis is on very few—but for new builds? I can avoid the thermal bridge at the rafters in other ways.
Regards
Hello E.Curb,
No, actually a KfW 70 house, since we want a gas heating system, but with SENSIBLE, possibly better insulation – without going overboard.
-- I don’t know that either. He just presented his ideas and was really “shocked” by the conventional double-skin masonry construction used by the local builders, basically saying... that’s how I insulated 10 years ago.
What do you think about that?
Which insulation: thickness and thermal conductivity value (WLG) would be good and reasonable for a 150 m2 (1,615 sq ft) single-family house? How thick should the perimeter insulation around the basement be?
How can thermal bridges be avoided with insulation between rafters, or what should we look out for when dealing with suppliers?
My parents want to modernize a house from the 1970s, about 110 m2 (1,184 sq ft). The roof needs to be redone (tiles), and it should be insulated at the same time, which hasn’t been done so far. Also, wall insulation with foam, new windows and front door, new heating system (switching from oil to gas plus solar). However, this is estimated to cost around €100,000, and they are already quite discouraged.
Is it supposed to be a passive house?
No, actually a KfW 70 house, since we want a gas heating system, but with SENSIBLE, possibly better insulation – without going overboard.
I’m also curious how the cavity distance of 20cm (8 inches) is supposed to be bridged. There are approvals for cavity wall ties longer than 150mm (6 inches), but that also costs money. Everything has to be proportional, and for a solid house that seems a bit exaggerated.
-- I don’t know that either. He just presented his ideas and was really “shocked” by the conventional double-skin masonry construction used by the local builders, basically saying... that’s how I insulated 10 years ago.
What do you think about that?
Which insulation: thickness and thermal conductivity value (WLG) would be good and reasonable for a 150 m2 (1,615 sq ft) single-family house? How thick should the perimeter insulation around the basement be?
...and again the costs. For a renovation, it might make sense in a few cases—the emphasis is on few—but for new construction? Thermal bridging at the rafters can also be avoided in other ways.
How can thermal bridges be avoided with insulation between rafters, or what should we look out for when dealing with suppliers?
My parents want to modernize a house from the 1970s, about 110 m2 (1,184 sq ft). The roof needs to be redone (tiles), and it should be insulated at the same time, which hasn’t been done so far. Also, wall insulation with foam, new windows and front door, new heating system (switching from oil to gas plus solar). However, this is estimated to cost around €100,000, and they are already quite discouraged.
Hello,
For a KfW 70 house, an insulation thickness of 200mm (8 inches) with a thermal conductivity rating (WLG) of 024 is excessive. I estimate you would achieve a U-value around 0.1 W/m²K, which corresponds to a passive house standard!
If you have a certain budget and the requirement for a KfW 70 house, your architect or planner can best answer that question for you.
Use insulation below the rafters or an underlay board (e.g., Gutex).
Best regards
Maya2011 schrieb:
No, actually a KfW 70 house, since we want a gas heating system, but with a SENSIBLE, possibly better insulation – without overdoing it.
For a KfW 70 house, an insulation thickness of 200mm (8 inches) with a thermal conductivity rating (WLG) of 024 is excessive. I estimate you would achieve a U-value around 0.1 W/m²K, which corresponds to a passive house standard!
Maya2011 schrieb:
What do you think about that?
Which insulation: thickness and WLG is good and practical for a 150 m² (1,615 ft²) single-family house? How thick should the perimeter insulation around the basement be?
If you have a certain budget and the requirement for a KfW 70 house, your architect or planner can best answer that question for you.
Maya2011 schrieb:
How can thermal bridges be avoided with insulation between the rafters?
Use insulation below the rafters or an underlay board (e.g., Gutex).
Best regards
Hello,
Yes, I’ve realized that by now as well. But would that really be such a problem? It would definitely be somewhat more expensive.
We actually wanted to work with a developer. However, they usually start with their standard insulation levels and don’t really explain how much additional insulation makes sense, or I don’t fully trust their claims.
That’s why it would be helpful to know how much insulation for walls, basement, and roof really makes sense and how the investment costs relate realistically to the energy savings.
Best regards, Maya
For a KFW 70 house, an insulation thickness of 200mm with a thermal conductivity of 0.024 W/mK is over the top. I estimate that you will achieve a U-value around 0.1 W/m²K. That’s Passive House level!
Yes, I’ve realized that by now as well. But would that really be such a problem? It would definitely be somewhat more expensive.
If you have a certain budget and the requirement of a KFW 70 house, your designer is the best person to answer that question for you
We actually wanted to work with a developer. However, they usually start with their standard insulation levels and don’t really explain how much additional insulation makes sense, or I don’t fully trust their claims.
That’s why it would be helpful to know how much insulation for walls, basement, and roof really makes sense and how the investment costs relate realistically to the energy savings.
Best regards, Maya
Hello,
No, that wouldn’t be a problem, of course. But you yourself said you don’t want to overdo it.
So why don’t you build a passive house? (This question is genuinely serious.)
If you don’t trust them, why not work with an architect?
See above.
Best regards
Maya2011 schrieb:
But would that really be such a problem? It would certainly be a lot more expensive.
No, that wouldn’t be a problem, of course. But you yourself said you don’t want to overdo it.
So why don’t you build a passive house? (This question is genuinely serious.)
Maya2011 schrieb:
We actually wanted to work with a developer. But they first propose their standard insulation and don’t really explain how much extra would actually make sense, plus I don’t necessarily trust their statements.
If you don’t trust them, why not work with an architect?
Maya2011 schrieb:
That’s why it would be helpful to know how much wall, basement, and roof insulation really makes sense and corresponds realistically, in terms of investment costs, to the energy savings.
See above.
Best regards
B
Bauexperte10 Jun 2011 14:03Hello Maya,
No offense – but some of your statements read like the "who’s who" of internet knowledge. Invest some time and maybe some money to find a seller or an architect who really knows what they’re talking about. The advantage is that internet claims won’t scare you anymore because you’ll learn to separate truth from falsehood.
It is correct that for a KfW 70 standard – if you want to use a gas condensing boiler – you need a controlled ventilation system with heat recovery. I would advise against the water-bearing stove because, firstly, it is quite expensive, secondly, it involves an additional water circuit passing through your new walls, and thirdly, its efficiency is more based on belief than solid evidence. Also, it is not that easy to coordinate the controlled ventilation system with this setup.
Regarding controlled ventilation – as far as I know, you cannot simply put this system in the basement, where most builders would prefer it, because it takes up a lot of space. Also, opposing outlets – for supply and exhaust air – must be created, which is not feasible in a basement. Therefore, sufficient space must be planned on the ground floor. Why don’t you consider including an air-to-water heat pump in your plans? It works well even in northern climates.
Mold does not occur because of thermal bridges but where houses are built very airtight – unfortunately, both the current and upcoming energy saving regulations make this more difficult – and for example, regular ventilation alone is not sufficient.
Regarding the roof/insulation, E.Curb has already given you the right answers, and the same goes for €uro in his area of expertise.
The structural engineer you described seems to want to extend his field of work to new builds as well; according to the motto “nothing is too difficult for the engineer.” You wrote “Overall, a solid house with a good balance of insulation and heating, etc.” To make things a bit clearer: how much money are you planning to invest in the house? It will probably be in the range of around 230,000 euros and up, _without_ the extras the engineer suggested.
Kind regards
No offense – but some of your statements read like the "who’s who" of internet knowledge. Invest some time and maybe some money to find a seller or an architect who really knows what they’re talking about. The advantage is that internet claims won’t scare you anymore because you’ll learn to separate truth from falsehood.
Maya2011 schrieb:
We are planning a house with about 150 m² (1,615 sq ft) and a basement. Heating system: gas condensing boiler plus solar for water and heating, water-bearing stove, underfloor heating, controlled ventilation system with heat recovery
It is correct that for a KfW 70 standard – if you want to use a gas condensing boiler – you need a controlled ventilation system with heat recovery. I would advise against the water-bearing stove because, firstly, it is quite expensive, secondly, it involves an additional water circuit passing through your new walls, and thirdly, its efficiency is more based on belief than solid evidence. Also, it is not that easy to coordinate the controlled ventilation system with this setup.
Regarding controlled ventilation – as far as I know, you cannot simply put this system in the basement, where most builders would prefer it, because it takes up a lot of space. Also, opposing outlets – for supply and exhaust air – must be created, which is not feasible in a basement. Therefore, sufficient space must be planned on the ground floor. Why don’t you consider including an air-to-water heat pump in your plans? It works well even in northern climates.
Maya2011 schrieb:
Our insulation goal: to keep energy consumption low without risking mold formation due to thermal bridges, etc. Overall, a solid house with a good balance of insulation and heating, etc.
Mold does not occur because of thermal bridges but where houses are built very airtight – unfortunately, both the current and upcoming energy saving regulations make this more difficult – and for example, regular ventilation alone is not sufficient.
Regarding the roof/insulation, E.Curb has already given you the right answers, and the same goes for €uro in his area of expertise.
The structural engineer you described seems to want to extend his field of work to new builds as well; according to the motto “nothing is too difficult for the engineer.” You wrote “Overall, a solid house with a good balance of insulation and heating, etc.” To make things a bit clearer: how much money are you planning to invest in the house? It will probably be in the range of around 230,000 euros and up, _without_ the extras the engineer suggested.
Kind regards
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