ᐅ Is the additional cost for 36.5 cm aerated concrete versus 24 cm calcium silicate brick justified?

Hello everyone,

Our architect indicated in the construction drawings that the masonry (from ground floor to top floor) would be 24cm (10 inches) thick plus external thermal insulation composite system (ETICS). Based on this, we received a quote from a structural shell contractor. There, the 24cm (10 inches) calcium silicate masonry is priced at €325.20 net per cubic meter. In addition, there would be the costs for the ETICS as part of the plastering work. Approximately how much should we expect for that? The exterior wall area according to the energy performance certificate is 117 m² (1260 ft²).

I have now requested an alternative offer for a monolithic construction and was quoted the following surcharges for 36.5cm (14 inches) aerated concrete PP2:
With a thermal conductivity (lambda) of 0.1: €80.75 per m² (10 sq ft)
Lambda 0.09: €83.85 per m² (10 sq ft)
Lambda 0.08: €88.75 per m² (10 sq ft)

Is this realistic?
Basically, I find monolithic construction more appealing. However, I know this is a matter of opinion both here and in other forums. If going monolithic, I would probably choose the block with lambda 0.08 since the total cost difference compared to lambda 0.1 is "only" about €1,000, but the U-value is about 19% better.

I would appreciate your assessment and opinions.

Thanks and best regards

The comparison is off. Using 24cm (9.5 inches) sand-lime bricks overshoots the mark; 17.5cm (7 inches) should be sufficient. Use that as your basis.

jolt schrieb:

Our architect specified the masonry (from ground floor to top floor) as 24cm (9.5 inches) plus external thermal insulation in the construction drawings.

If that's what your architect says rather than the construction manager’s draftsman, it would be worth asking him why. Note my "Like" on post #2.

jolt schrieb:

On this basis, we received an offer from a shell construction contractor.

If it’s the architect, then why not also have the architect handle the tendering? You mention "architect" and "construction drawings," which really come into their own if the architect also manages construction supervision—so I wouldn’t exclude him from the tendering process.

jolt schrieb:

Basically, I find monolithic construction more attractive. I also know this is a matter of belief both here and in other forums.

If you belong to the monolithic camp, your architect should know that. I tend to agree, but even more so, I would not separate the proven team of "construction manager plus their usual wall build." The same essentially applies to the overall team of "architect/construction supervisor + tendering + construction manager + wall construction."

jolt schrieb:

We have now received a good offer for the shell construction. This builder has proposed lightweight clay blocks (KLB) for the walls. Based on the specifications, he initially quoted 24cm (9.5 inches) blocks but would also be willing to build monolithically with 36.5cm (14.4 inches) blocks.

I would definitely pursue that further.

Ceterum censeo, you should seek comprehensive advice here, even if you want to avoid changing the floor plan. But the patchwork approach of asking separately about blocks, windows, and then other items later will not result in a coherent, well-managed project.

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guckuck2 schrieb:

The comparison is flawed. With 24cm (9.5 inches) sand-lime brick, the planner is overshooting; 17.5cm (7 inches) should be sufficient. Use that as a basis.

The problem here is probably that the structural calculations have already been made and would likely need to be recalculated for 17.5cm (7 inches) sand-lime brick masonry, right?

11ant schrieb:

If you subscribe to the monolithic approach, your architect should be aware of that. I lean in that direction too – but even more so, I think it’s best not to separate the proven team "general contractor + their usual wall construction". The same basically applies to the whole team "architect/construction manager + procurement + general contractor + wall construction".

The shell builder is open to both options and said something along the lines of “WDVS (external thermal insulation composite system) used to be standard with him, nowadays he would prefer more monolithic construction.”

The shell builder mentioned in my other thread who uses climate-lightweight blocks is out of the picture for us, as the company seemed very unreliable.

@11ant Could you give an estimate of the costs for a pure ETICS (external thermal insulation composite system) solution so I have some idea? I find it hard to assess the price difference compared to the monolithic offer.

jolt schrieb:

Can you give an estimate of the costs for just the external thermal insulation composite system (ETICS) that one should roughly expect?

I never deal with that. And personally, I don’t think you should either – that would only make sense if you truly didn’t care how you build. But since you’ve committed to a monolithic construction, you should first clarify why your architect isn’t on the same page about that.

jolt schrieb:

The problem here would probably be that the structural calculations have already been done, and using 17.5 cm (7 inches) calcium silicate masonry would presumably require recalculating?

Yes, it would have to be. But I think that wasn’t the point – rather, the point was that comparing 24 + ETICS is like comparing apples and oranges, and that properly comparing on equal terms, 36.5 should be compared to 17.5 + ETICS.

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