Hello dear forum members,
We are currently planning our single-family house. We are in the preliminary planning phase and have already had the first discussions with an architect and potential builders. The house will be a single-family home with two living units (a granny flat), a pitched roof, 1.75 stories (knee wall at 185 cm (6 ft 1 in)), and a double-layer wall construction built to KfW 40 standards.
Our architect is kind and nice, but somehow I have a strange gut feeling... (a different topic).
Here is an example of the exterior wall construction. Our architect has planned a 525 mm (21 inch) wall assembly as follows:
- 11.5 cm (4.5 inch) facing brick layer (clinker brick)
- 10 cm (4 inch) core insulation (lambda 0.032)
- T9-30 clay brick
- Lime interior plaster
U-value: 0.149 (0.154 required for KfW)
Two builders have offered/suggested the following wall assembly:
- 11.5 cm (4.5 inch) facing brick layer (clinker brick)
- 16 cm (6.3 inch) core insulation (lambda 0.032 or 0.035)
- T14-24 clay brick
- Lime interior plaster
-> U-value: 0.145 / 0.151
-> Better sound insulation
Same wall thickness. The material costs are 40% lower than the architect’s proposal.
This made me a bit suspicious. I have not won the lottery and as a client, I also have to watch the costs. Is there a flaw in the wall construction concept either from my side or from the builders? The builder also advised against using bricks filled with perlite or mineral wool, saying they are far too expensive, even though I could save on core insulation between the bricks and the outer wall this way.
Incidentally, this was also an alternative suggestion from the architect...
I would appreciate some feedback!
We are currently planning our single-family house. We are in the preliminary planning phase and have already had the first discussions with an architect and potential builders. The house will be a single-family home with two living units (a granny flat), a pitched roof, 1.75 stories (knee wall at 185 cm (6 ft 1 in)), and a double-layer wall construction built to KfW 40 standards.
Our architect is kind and nice, but somehow I have a strange gut feeling... (a different topic).
Here is an example of the exterior wall construction. Our architect has planned a 525 mm (21 inch) wall assembly as follows:
- 11.5 cm (4.5 inch) facing brick layer (clinker brick)
- 10 cm (4 inch) core insulation (lambda 0.032)
- T9-30 clay brick
- Lime interior plaster
U-value: 0.149 (0.154 required for KfW)
Two builders have offered/suggested the following wall assembly:
- 11.5 cm (4.5 inch) facing brick layer (clinker brick)
- 16 cm (6.3 inch) core insulation (lambda 0.032 or 0.035)
- T14-24 clay brick
- Lime interior plaster
-> U-value: 0.145 / 0.151
-> Better sound insulation
Same wall thickness. The material costs are 40% lower than the architect’s proposal.
This made me a bit suspicious. I have not won the lottery and as a client, I also have to watch the costs. Is there a flaw in the wall construction concept either from my side or from the builders? The builder also advised against using bricks filled with perlite or mineral wool, saying they are far too expensive, even though I could save on core insulation between the bricks and the outer wall this way.
Incidentally, this was also an alternative suggestion from the architect...
I would appreciate some feedback!
Thanks for the information. That already helps me understand a lot better. No, we are in phase 2, still in the preliminary planning stage.
If I understood correctly, the wall construction with the corresponding insulation will not fit the modular dimensions, or I will end up with arrow slit-like gaps.
In this case, a random bond pattern will probably be the preferred option. I also don’t want to do the brickwork myself...
Right now, my concern is whether an alternative wall construction (two-layer) is generally possible if it alone reduces material costs by 40%.
I understand that the architect’s fee is based on the total construction cost. So I can somewhat “follow” his reasoning. I don’t want to push my budget to the limit and want to have a buffer for myself, not for the architect.
I think that is understandable.
If I understood correctly, the wall construction with the corresponding insulation will not fit the modular dimensions, or I will end up with arrow slit-like gaps.
In this case, a random bond pattern will probably be the preferred option. I also don’t want to do the brickwork myself...
Right now, my concern is whether an alternative wall construction (two-layer) is generally possible if it alone reduces material costs by 40%.
I understand that the architect’s fee is based on the total construction cost. So I can somewhat “follow” his reasoning. I don’t want to push my budget to the limit and want to have a buffer for myself, not for the architect.
I think that is understandable.
stjonas schrieb:
No, we are in phase 2. Everything is still in preliminary planning. This is a good time to "change horses" (if necessary). But does this fit with the contract you have with your current architect? - it would be best if you now explained where else the issues lie.
stjonas schrieb:
If I understand correctly, the wall construction with the corresponding insulation will not fit the modular dimension, or I will end up with loopholes. I have no idea what you mean by loopholes *completely lost*
stjonas schrieb:
What I am wondering now is whether an alternative wall construction (two-shell) is basically possible if it alone reduces material costs by 40%. I consider the two options essentially equivalent, but I would put a question mark behind the 40%.
stjonas schrieb:
I understand that the architect’s fee is based on the construction cost. So I can somehow "relate" to his explanations. Which explanations exactly are you referring to here? - fee linkage to the construction cost is not strictly binding, meaning it is not proportional to the actual construction expenses. This small cost item "alternative wall construction" should not affect the fee scale classification at all.
stjonas schrieb:
So, laying the masonry in a random bond will probably be the preferred option. I also don’t want to do the masonry work myself... I wasn’t thinking of doing it myself either, but rather of subcontractors working independently – see: https://www.hausbau-forum.de/threads/mauern-mit-fbr-roboter-hadrian-x.39688/page-7#post-508099
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- He recommended a partial basement/storage cellar and a fixed garage, which is supposed to save costs. Since we need the space (3 children), we prefer a full basement and a carport.
- The initial proposal included a hip roof!? The plot is oriented north-south. We can install a larger photovoltaic system on a gable roof, and it is significantly cheaper in terms of construction.
Somehow, I feel like they are trying to sell us an existing design with minor changes. We have another meeting next week. I’ll report back then.
I can’t follow you at all regarding the loopholes *completely lost*
It was just an idea. If you use bigger bricks and adjust the insulation, you could create a 60cm (24 inches) exterior wall. But who would want that anyway?
I consider the two options essentially equivalent, although I would put a question mark behind the 40%.
The builder only roughly sketched the example for the exterior wall. For a T9 30cm (12 inches) Poroton brick, the costs are about €65 per sqm (square meter). For a T14 24cm (9.5 inches) brick, costs are around €35 per sqm (material costs only). The insulation on the 24cm version is thicker, but the price difference is only about €4-5 per sqm. I think that’s quite significant. Whether the mason installs a 30cm or 24cm brick probably doesn’t make much difference.
- The initial proposal included a hip roof!? The plot is oriented north-south. We can install a larger photovoltaic system on a gable roof, and it is significantly cheaper in terms of construction.
Somehow, I feel like they are trying to sell us an existing design with minor changes. We have another meeting next week. I’ll report back then.
I can’t follow you at all regarding the loopholes *completely lost*
It was just an idea. If you use bigger bricks and adjust the insulation, you could create a 60cm (24 inches) exterior wall. But who would want that anyway?
I consider the two options essentially equivalent, although I would put a question mark behind the 40%.
The builder only roughly sketched the example for the exterior wall. For a T9 30cm (12 inches) Poroton brick, the costs are about €65 per sqm (square meter). For a T14 24cm (9.5 inches) brick, costs are around €35 per sqm (material costs only). The insulation on the 24cm version is thicker, but the price difference is only about €4-5 per sqm. I think that’s quite significant. Whether the mason installs a 30cm or 24cm brick probably doesn’t make much difference.
stjonas schrieb:
- He recommended a partial basement/storage cellar and a fixed garage to us. This was supposed to save costs. Since we need the space (3 children), we want a full basement and a carport.
- The first proposal included a hip roof!? The plot is oriented north-south. With a gable roof, we can install a larger photovoltaic system, and it is significantly cheaper in terms of construction. Partial basements are generally more expensive in proportion. We don’t know if your plot even supports having a basement—you haven’t shown your plot or the preliminary design so far. A garage is one of the least essential features overall (except as a basement replacement space). Hip roofs tend to be more costly. However, a hip roof can obviously be more cost-effective for photovoltaic installation than a gable roof with an unfavorable orientation. Considering the combination with KfW40 standards and a granny flat, I suspect you might be caught up in a funding incentive fantasy.
Cost additions for bricks and insulation often lead to simplistic calculations of varying quality but rarely provide truly insightful conclusions. Exterior walls are often overvalued because of their strong impact on the building’s appearance, but in terms of construction costs, they mainly fall into the category of minor expenses.
I still don’t understand where the idea of loophole windows came from. I take that to mean narrow windows, but what do those have to do with wall thickness or specifically with an octameter grid?
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