Hello,
I didn’t find anything in the search. My architect initially planned to use cellular glass gravel under the slab-on-grade (without a basement) on strip foundations. However, he now suggests that, for cost reasons, this could be omitted and instead the insulation installed below the screed, since the clay soil beneath shouldn’t freeze in winter.
This would save me about 5,000 euros (approximately $5,000). From his perspective, this is acceptable, but he asked me if I think it’s okay. I’ve been researching for two days now but haven’t found any useful information.
What do you think?
I didn’t find anything in the search. My architect initially planned to use cellular glass gravel under the slab-on-grade (without a basement) on strip foundations. However, he now suggests that, for cost reasons, this could be omitted and instead the insulation installed below the screed, since the clay soil beneath shouldn’t freeze in winter.
This would save me about 5,000 euros (approximately $5,000). From his perspective, this is acceptable, but he asked me if I think it’s okay. I’ve been researching for two days now but haven’t found any useful information.
What do you think?
S
Sebastian7930 Mar 2016 20:44In practice, vapor barriers like that don’t really exist... only vapor retarders, if you are referring to sheets.
And under tiles, for example, this is generally not done at all.
A waterproofing layer against rising damp is usually applied using bitumen membranes, which is also not difficult to install. Or did you mean that as a barrier?
Therefore, I still don’t see any problem here where you think there is one.
By the way, installing perimeter insulation under the slab is not as straightforward as on the walls. There is also additional work involved regarding the ring grounding...
And under tiles, for example, this is generally not done at all.
A waterproofing layer against rising damp is usually applied using bitumen membranes, which is also not difficult to install. Or did you mean that as a barrier?
Therefore, I still don’t see any problem here where you think there is one.
By the way, installing perimeter insulation under the slab is not as straightforward as on the walls. There is also additional work involved regarding the ring grounding...
B
Bieber081530 Mar 2016 21:56elVincent schrieb:
a vapor barrier above the insulation is necessary to keep indoor humidity away from the surface of the floor slab. In the image you posted, it explicitly says "vapor barrier." Personally, as a layperson, I don't believe that indoor air diffuses through the prefabricated floor and the screed. That said, I find the "sheet" on top of the insulation board, where the underfloor heating pipes are laid, to be reasonable, if only to prevent the freshly poured screed from soaking the insulation underneath. Once the screed is dry, I don’t see any more issues. Experts might correct this...
There remains the scenario of a leaking heating pipe, but in that case, you would probably have to tear everything up anyway, so the insulation hardly matters.
In practice, of course, a sheet is laid and sealed, but then at each of these blue clips, there’s again a hole in the sheet. Well, practice versus theory. It’s close enough.
E
elVincent30 Mar 2016 23:15To sum it up, I’ll simply give a conclusion: there are different pros and cons, as well as various challenges in proper installation, for both interior and exterior insulation.
My preference is exterior insulation (that’s what we will do), while homeowners who chose otherwise believe their solution is better and find sufficient arguments to support it.
My arguments in favor of exterior insulation:
- thermal bridge-free construction without extra effort
- with the same shell height and insulation thickness, more usable ceiling height in the basement
- fewer building physics issues
Whether it ultimately costs more than interior insulation under the same conditions, I cannot judge, but I believe the difference is not that significant.
My preference is exterior insulation (that’s what we will do), while homeowners who chose otherwise believe their solution is better and find sufficient arguments to support it.
My arguments in favor of exterior insulation:
- thermal bridge-free construction without extra effort
- with the same shell height and insulation thickness, more usable ceiling height in the basement
- fewer building physics issues
Whether it ultimately costs more than interior insulation under the same conditions, I cannot judge, but I believe the difference is not that significant.
S
Sebastian7931 Mar 2016 04:30So, a basement after all – then your U-value calculation is incorrect anyway, because ground temperatures like that don’t apply.
And no extra effort? Sorry, just build it first, then you’ll realize that it is indeed extra work and therefore more expensive. For example, the foundation earth ring, which often isn’t installed – but is a must.
And you simply claim it’s easier from a building physics perspective – precisely because you are so convinced of your own argument.
I’m not denying the advantages (fewer thermal bridges, more build-up height—although we’re talking just a few centimeters (a couple of inches)) but please stick to the facts.
But you don’t want to hear anything else, otherwise you wouldn’t be showing such a “take-it-or-leave-it” attitude.
And no extra effort? Sorry, just build it first, then you’ll realize that it is indeed extra work and therefore more expensive. For example, the foundation earth ring, which often isn’t installed – but is a must.
And you simply claim it’s easier from a building physics perspective – precisely because you are so convinced of your own argument.
I’m not denying the advantages (fewer thermal bridges, more build-up height—although we’re talking just a few centimeters (a couple of inches)) but please stick to the facts.
But you don’t want to hear anything else, otherwise you wouldn’t be showing such a “take-it-or-leave-it” attitude.
E
elVincent31 Mar 2016 08:50Sebastian79 schrieb:
But you don’t really want to hear anything else; otherwise, you wouldn’t have such a take-it-or-leave-it attitude.People accuse me of a lot of things, but not that! I just had the impression that no matter what I write, in your follow-up post you will keep twisting my words to confirm your opinion (q.e.d. ). Besides, I haven’t contradicted anyone or spoken negatively about anything, so portraying me as resistant to advice isn’t fair.
There are certainly different opinions on building physics, but I think it’s generally fair to say that exterior insulation is better than interior insulation from that perspective. Any insulation layer in contact with interior surfaces must be protected against moisture intrusion by a vapor barrier or similar—which, in my opinion, applies not only to walls and ceilings but also to floors. With exterior insulation, this is not necessary because the problem that the vapor barrier is meant to prevent simply cannot occur.
Regarding the grounding efforts mentioned, I’m mainly concerned about the financial aspect, which, according to offers we have received, is about twice as high (around €300). I don’t know how much extra work that involves, but I don’t have to do it myself.
The additional effort required to maintain the same interior height is significantly greater, because the 14cm (5.5 inches) we put below the floor slab would mean that all basement walls and their insulation would also need to be thicker. The same applies, of course, if building without a basement.
From your point of view, what are the advantages of interior insulation?
S
Sebastian7931 Mar 2016 08:55Oops, double post.
But you are certainly right: you lose a few centimeters (centimeters), but don’t overestimate that. We have a total construction height of 14cm (5.5 inches) in the basement – that’s not excessively much. The screed requires 6-7cm (2.4-2.8 inches), and despite insulation under the slab, you still need insulation below that (if you want good quality). Then, something might still need to be installed – in our case, drainage pipes and some electrical wiring.
So, there you already have your 14cm (5.5 inches), and external insulation won’t help you gain any additional height.
But you are certainly right: you lose a few centimeters (centimeters), but don’t overestimate that. We have a total construction height of 14cm (5.5 inches) in the basement – that’s not excessively much. The screed requires 6-7cm (2.4-2.8 inches), and despite insulation under the slab, you still need insulation below that (if you want good quality). Then, something might still need to be installed – in our case, drainage pipes and some electrical wiring.
So, there you already have your 14cm (5.5 inches), and external insulation won’t help you gain any additional height.
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