ᐅ Same Price: KfW 55 with Poroton solid masonry OR KfW 40 with Poroton insulated exterior wall system (ETICS)?
Created on: 5 May 2023 13:33
A
Ari_tau
Hello everyone,
The recent shock with one house provider has settled, and we have started over again. We have made good progress, and one provider has now drawn our house and created several offers with different masonry options based on our request. We compared the financing and calculated it down (KfW 40 with 100,000 euros for 1.54% interest rate target).
Assumptions: The houses vary in price, but the more expensive one qualifies for KfW financing, so the costs balance out. The question now is:
Exactly the same house,
a) KfW 55 with Poroton (brick - 36.5 cm (14 inches) thickness / Thermo Plan S-8 or T-8), 36.5 cm (14 inches) monolithic construction
OR
b) KfW 40 with Poroton (brick - 24.0 cm (9.5 inches) thickness / Thermoplan T-14) plus 18 cm (7 inches) Styrodur insulation
For the KfW 40 house, the remaining debt after 10 years is 4,000 euros higher; however, assuming an annual heating cost saving of 200 euros compared to the KfW 55, this difference would be recovered within 20 years. Therefore, I would say the overall cost or remaining debt after 10 years is basically the same.
What would you choose and why? Can it be said that a KfW 40 house has a higher resale value?
Thanks and best regards!
The recent shock with one house provider has settled, and we have started over again. We have made good progress, and one provider has now drawn our house and created several offers with different masonry options based on our request. We compared the financing and calculated it down (KfW 40 with 100,000 euros for 1.54% interest rate target).
Assumptions: The houses vary in price, but the more expensive one qualifies for KfW financing, so the costs balance out. The question now is:
Exactly the same house,
a) KfW 55 with Poroton (brick - 36.5 cm (14 inches) thickness / Thermo Plan S-8 or T-8), 36.5 cm (14 inches) monolithic construction
OR
b) KfW 40 with Poroton (brick - 24.0 cm (9.5 inches) thickness / Thermoplan T-14) plus 18 cm (7 inches) Styrodur insulation
For the KfW 40 house, the remaining debt after 10 years is 4,000 euros higher; however, assuming an annual heating cost saving of 200 euros compared to the KfW 55, this difference would be recovered within 20 years. Therefore, I would say the overall cost or remaining debt after 10 years is basically the same.
What would you choose and why? Can it be said that a KfW 40 house has a higher resale value?
Thanks and best regards!
This is how it was done in my case. You need to ensure that this row has higher compressive strength and that the overlap dimensions for the second row are strictly followed everywhere, because the masons tend to get confused by the shorter bricks (at least mine did)...
Also, it’s important to make sure the waterproofing is installed behind the insulation.
In my case, this was not done because the first layer of insulation was used as lost formwork for the foundation slab.
Technically, this is still not entirely correct. It was heavily criticized by most people at the shopping center around the corner. My building inspector considered it unsightly but not seriously problematic, so I decided to leave it as it was.
Also, it’s important to make sure the waterproofing is installed behind the insulation.
In my case, this was not done because the first layer of insulation was used as lost formwork for the foundation slab.
Technically, this is still not entirely correct. It was heavily criticized by most people at the shopping center around the corner. My building inspector considered it unsightly but not seriously problematic, so I decided to leave it as it was.
WilderSueden schrieb:
There is the option to lay the first row of blocks using narrower blocks, with insulation placed in front of this row and the concrete slab. From the second row onward, the standard blocks are used. I am mostly in favor of keeping a distance from this method, which unfortunately seems to be popular. A common "side effect" is that a misaligned stretcher bond often originates here:
Tolentino schrieb:
That’s how it was done for me. You have to make sure this row has higher compressive strength, and that the stretcher bond dimensions are strictly maintained in the second row, because the masons tend to get confused by the shorter blocks (at least mine did)... .
Tolentino schrieb:
Also, it’s important to ensure that the waterproofing is applied behind the insulation.
This wasn’t done in my case, because the first insulation layer was used as lost formwork for the concrete slab.
However, this is not entirely correct from a technical perspective. It was heavily criticized by most people at the shopping center around the corner. My expert deemed it unpleasant but not particularly critical, so I let it rest. One reason for this construction method might be to run the insulation over the edge of the concrete slab or basement ceiling. The bed joint of the second block layer is also a popular reference point for the base plaster finish. In particular, this has become a common approach when using 6cm / 2x 6cm / 12cm (2.4 inches / 2x 2.4 inches / 4.7 inches) thickness of insulation. This won’t cause a house to collapse, but I still consider it a shortcut solution.
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W
WilderSueden8 May 2023 08:25My expert had no objections to the basic construction. In your opinion, what would be a better solution for the base insulation in monolithic walls?
WilderSueden schrieb:
My expert had no objections to the basic construction. I actually state this more out of principle, that I don’t consider such solutions to be the perfect answer. In every real-world project, the pure theory has to be compromised about eight and a half times. Keeping Pareto’s principle in mind, I always aim to reduce this to a quarter or three-quarters if possible. But completely eliminating this phenomenon is probably impossible. Still, I see no reason to give up and just switch to a laissez-faire approach, so I at least point it out (with the note that no house will collapse on that basis alone).
WilderSueden schrieb:
What, in your opinion, would be a better solution for base insulation with monolithic walls? That’s a tricky issue, varying in each individual case. I generally recommend a detailed drawing rather than a one-size-fits-all solution. The problem mainly occurs with slab-on-grade foundations (less so with basement ceilings, as long as the basement is included within the thermal envelope). Concrete is thermally challenging—that’s why the slab is insulated. It’s correct not to forget the slab edge insulation. The most elegant solution would probably be to use thermal insulation connectors (Isokörbe®), but that is likely the most expensive option. I would probably choose the most efficient insulation material here to minimize its thickness and thus the reduction of the load-bearing masonry thickness. For this purpose, I would exceptionally cut through an entire masonry course if needed. For a wall thickness in the standard layers of caliber 365, I would probably use stones with a caliber 300 here—this way the base would have a 6cm (2.4 inches) insulation thickness in front of the first masonry course and be set back by half a centimeter (0.2 inches). Rotating the stones to work with a wall thickness of caliber 248 would strike me as borderline, even with higher density.
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In their schematic, Wienerberger simply extends the perimeter insulation underground. As a result, the entire slab and the first row of blocks are also below ground level. This is interesting because the waterproofing then becomes even more crucial. However, since it falls outside their scope of work, they don’t take responsibility for it.
I’m not sure if this approach works under hydrological load conditions.
Even with my groundwater level at 7m (23 feet) and medium infiltration capacity of the subsoil, the foundation recommendation was a slab 20cm (8 inches) above ground level.
I’m not sure if this approach works under hydrological load conditions.
Even with my groundwater level at 7m (23 feet) and medium infiltration capacity of the subsoil, the foundation recommendation was a slab 20cm (8 inches) above ground level.
Tolentino schrieb:
In their basic diagram, Wienerberger simply shows the perimeter insulation extending underground. Then please send that to me (or the link to it).
Tolentino schrieb:
The entire slab and the first row of blocks are also underground. [...] Even with my groundwater level at 7m (23 feet) and average ground infiltration capacity, the foundation recommendation was a slab 20cm (8 inches) above the ground surface. If the top of the slab equals the top of the raw floor level, I could (grudgingly) accept that. But the ground level above the top of the first block course—oh wow, that calls for a moat around the building ;-)
Even with modern thick floor constructions usually between 16 and 18cm (6 to 7 inches), a block course with the usual 3DF height ends up relatively higher—i.e., above ground level—or do they only mean a half-height block course?
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