ᐅ KfW 40 (plus) standard for a multi-family house cannot be achieved

curverbox schrieb:

double-layer masonry wall with a thickness of 49cm (19 inches), consisting of 17.5cm (7 inches) Ytong blocks, 12cm (5 inches) PUR insulation, 0.24cm (0.1 inches) air gap, and 11.5cm (4.5 inches) facing brickwork

8cm (3 inches) air gap? Please check again.

You get 49cm (19 inches) thickness with 24cm (9.5 inches) blocks, 12cm (5 inches) core insulation, 1.5cm (0.6 inches) mortar joint, and facing bricks. If you have 17.5cm (7 inches) blocks, then the wall thickness would be around 42–43cm (16.5–17 inches) with 12cm (5 inches) insulation. With better insulation maybe 2 to 4cm (1 to 1.5 inches) more. The expensive PUR insulation seems unnecessary for KfW 40 standard. PUR behind facing bricks? Are you sure?

You seem to be trying to compensate for weaknesses of your energy consultants through the forum. Based on your information, it’s only possible to guess where the calculation problems lie.

Where is this leading? It certainly won’t be the only issue. What else are the energy consultants doing for you?

My suggestion: This is a major project. Find someone who fits your plans. Now is exactly the right time for that. Poor planning might end up costing more than corrective measures later.

I see a lot of inconsistencies here. The house is supposed to have a footprint of seven by twenty meters. That itself is an unfavorable ratio regarding exterior wall area to building volume – in such cases, meeting energy efficiency regulations economically is already challenging, and exceeding those standards is rarely the goal. Especially for a multi-family building, considering 74 sqm (about 795 sq ft) in the attic and two times two 50 sqm (approximately 538 sq ft) units that seem to be self-used zero-energy apartments. I wouldn’t even call this a five-family house but rather a building with one family apartment and four separate units. This alone sounds, to put it mildly, like a novice investor. Also, a plot that is supposedly so inefficient to use still allows for five residential units (which usually means about eight parking spaces), really?

My spontaneous impression, with all due respect, is that someone has fallen for the “easy money multiplication with borrowed capital” pitches from real estate agents, thinking along the lines of “it pays for itself with grants.” I imagine a plot awkwardly shaped with too much area to be appealing for a single-family home buyer: such a property gets sold to someone who is told that, with the right consultants, they can fully develop it up to the eaves line with profitable units.

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These are the calculated values.
Annual primary energy demand QP / QP,Anf 2.7 kWh/(m²a) (2.7 kWh/(m²yr))
Transmission heat loss H'T 0.192 W/(m²K) (0.192 W/(m²·K))

11ant schrieb:

I see a lot of inconsistencies here. The house is supposed to have a ground area of seven by twenty meters. This ratio is already unfavorable regarding the ratio of external wall area to building volume – under these circumstances, meeting energy efficiency standards economically is a challenge, and aiming to exceed the standards is unlikely. This is especially true for a multi-family house, particularly since 74 sqm (797 sq ft) in the attic and 2x 2x 50 sqm (2x 2x 538 sq ft) sound like zero self-used residential units. I wouldn’t call this a five-family house but rather a building with one family apartment and four separate apartments. That alone suggests, to put it mildly, a novice investor. At the same time, a plot that is so difficult to utilize is supposed to allow five residential units (which usually means eight parking spaces) ?

My immediate impression, with all due respect, is that someone has fallen for the “easy multiplication of borrowed money” pitches from real estate promoters, assuming that “with subsidies, this will pay for itself.” I imagine a plot that is awkwardly shaped with too much space to be interesting for a single-family home builder; such a lot is then sold to someone who is told that with the right consultants, they can fill it up to the eaves height with profitable units.

You are unfortunately mistaken; the property is a double plot and already has a house from the 1950s built on it and is already in my possession. Next to it, there is space of the indicated size. Since there is no zoning plan, the new buildings must be adapted in size according to the existing buildings, as determined by the building authority.

boxandroof schrieb:

8cm (3 inches) air gap? Please check again.

You have a total thickness of 49cm (19 inches) with 24cm (9.5 inches) masonry units, 12cm (5 inches) core insulation, 1.5cm (0.6 inches) cavity, and the facing bricks. If you have 17.5cm (7 inches) masonry units, then the wall is around 42-43cm (16.5-17 inches) with 12cm (5 inches) insulation. With better insulation, maybe 2-4cm (1-1.5 inches) more. The expensive PUR (polyurethane) insulation seems unnecessary for KfW 40 standards. PUR behind facing bricks? Are you sure?

You are trying to compensate for weaknesses in your energy consultants through the forum. Based on your information, it’s only possible to guess where the calculation issue might be.

What is your ultimate goal? This will almost certainly not be the only problem. What else are the energy consultants doing for you?

My suggestion: This is a large project. Find someone who matches your plans. Now is exactly the right time to do that. Incorrect planning can potentially cost more than having to stop and fix issues later.

The energy consultants are only doing the calculations for the KfW funding.
Using PUR insulation behind facing bricks was suggested solely to improve thermal values—does that seem like a bad idea?

curverbox schrieb:

The energy consultant doesn’t do anything else for me except the calculations for the KfW.
Using PUR insulation behind the brick veneer was only considered to improve the thermal values—was that not a good idea?

That’s what I thought. Still, this attempt apparently didn’t help. With a wall thickness of 49cm (19 inches), it’s completely unnecessary, uncommon, and expensive.

I doubt the wall thickness or your measurements—see my post above—please double-check the calculations yourself, something seems off. But the wall doesn’t seem to be your main issue. Information on where the consultant can get advice was posted by @dertill.