What exactly is "well insulated"?

Hello

We are currently considering selling our house built in 2000 and building a new one.

You read everywhere that it should be insulated as well as possible, etc. But what is really good and a reasonable compromise in terms of cost/benefit? We have pretty fixed ideas about how the house should look, yet every construction company comes up with different proposals. Only Poroton wants to be used by all.

Some key data

3-gable house
12x9.5 timber frame on 1/3 of the garden side, projecting 1 m, so then 10.5

1 m knee wall

Controlled residential ventilation with heat recovery

Underfloor heating in all rooms

Min. KfW 70 through insulation, not technology

Provider 1 offers 24 cm walls + 16 cm exterior insulation system 0.40 roof 20 cm 0.35

Provider 2 offers 17.5 cm walls + 16 cm exterior insulation system and 20 cm roof 0.35

Provider 3 suddenly wants to manage it with 17.5 and 10 cm exterior insulation system.

We currently favor provider 1 even though he is significantly more expensive (+-15,000 euros). I would just like to know whether the insulation is really good or rather lower standard and would then need to be improved. I would be grateful for tips.

Olli

Hello Olli,

my favorite for stone on stone construction would be a monolithic structure - that is 36.5 cm Poroton brick WITHOUT [WDVS]...

Is that not an option for you?

Regards,

Dirk

And we build Kfw 70 WITHOUT insulation. Namely with 36cm T9 Poroton bricks. In terms of technology, we only have a heat pump - no ventilation, no solar, no photovoltaics. This way, the thicker masonry also protects against heat in the summer. ;-)

How the heat is retained in the envelope is not important to me at first, so monolithic would also be an option. What is important to us is a minimal energy demand without the additional costs for insulation, whether it is a thicker stone or more [Wdvs], becoming uneconomical. Another no-go is heating with electricity. Geothermal energy on the property will be difficult; for surface or trench collectors, space will be quite tight, and I would prefer not to use probes due to former mining activities (not to mention the approvals). What is normal nowadays for roof insulation and what is better than standard? I actually don’t care what the [KfW] says; what matters is a low energy demand, and really not sugar-coated through any formulas just because wood is currently trendy or whatever is being especially subsidized at the moment.

Hello Olli,

We have quite fixed ideas about how the house should look, and yet every construction company comes up with different proposals.

That is normal. Even if you, for example, go to a kitchen studio, every sales person has a different offer for you ;)

Only Poroton wants to be used by everyone.

Hardly. There are not a few who build with aerated concrete, expanded clay, KS, pumice, or concrete.

3 gable house
12x9.5 beam on 1/3 of the garden side, projecting 1 m, so then 10.5

For a classic 3-gable house, the 3rd gable turns out quite small... all our comparable houses have a depth of 3.00 m in the 3rd gable. What you describe I would rather call a dormer.

Min. KfW 70 via insulation, not technology

Then in my opinion, the thickness of the roof insulation is not right with all 3 providers...

We currently also favor provider 1 even though he is significantly more expensive (+-15k euros); I would just like to know whether the insulation is really good or rather lower standard; then it would have to be improved there.

I would currently consider 16 cm ETICS as "normal," if you decide on a house with ETICS; depending on the location and situation of the plot, this can fit both with 17.5 cm external masonry and 24 cm brick.

These days there is a lot of talk about insulation, less about how certain KfW requirements can be met; this is not only achievable by additional insulation. Much still happens "only" on paper; from my point of view, for example, the heat recovery in ventilation systems. That means for me, you first have to decide what you want. Do you want to build a single-family house with ETICS or maybe a monolithic house, as the "Doc" or "Manu" described? A statement like "I don't care how the heat is kept in the envelope" is, in my opinion, not very helpful. Houses built with ETICS are usually cheaper... although I don't always understand that; actually, it should be the other way around.

You also write that you do not want to heat with electricity – what do you understand by that? Do you want to build classically with a gas condensing boiler and solar heating support? Because "no matter what the KfW says" can only be true for you if you forego KfW funds; then only the currently valid energy saving ordinance must be observed.

Rhenish greetings

Min. KfW 70 on insulation not technology

Provider1 offers 24 cm walls + 16 cm ETICS 0.40 roof 20 cm 0.35

Provider 2 offers 17.5 cm walls + 16 cm ETICS and 20 cm roof 0.35

Provider 3 suddenly wants to manage it with 17.5 cm and 10 cm ETICS.

Providers 1 and 2 don't sound so bad. Regarding the roof insulation, I agree with the construction expert. It's not that bad, but also not exactly generous. What kind of ETICS does Provider 1 want to use with a U-value of 0.4? Common EPS has 0.35 and is actually quite cheap.

And we are building KFW 70 WITHOUT insulation. Namely with 36 cm T9 Poroton bricks. In terms of technology, we only have an air-water heat pump – no ventilation, no solar, no photovoltaics. This way, the thicker masonry also protects against heat in summer. ;-)

Walls with 36 cm T9 are not exactly rosy either. Results in a U-value of about 0.235. That is rather on the lower end nowadays.