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Grantlhaua25 Apr 2019 13:18Snowy36 schrieb:
What do you think could happen?
The insulation under the slab isn’t that thick... even if it gets compressed, the house isn’t going to collapse, right (-:I don’t think so, but I feel better knowing my house is on solid ground.
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pffreestyler25 Apr 2019 13:47Just use better insulation on the floor slab.
Our offer included 10 cm WLG 035 insulation both below and above the floor slab. The heat demand calculation showed that this was not necessary to meet our Energy Saving Ordinance 16 requirements, so the plan included 14 cm WLG 035 insulation on the floor slab only — resulting in a U-value of 0.24. This saved us almost €3,500 since we used 6 cm less insulation overall and didn’t need any basement wall blocks. The downside was that we ended up with a 22 cm floor build-up and a ceiling height of only 2.53 m (8 ft 4 in) — which is still within standard range anyway.
In the end, the front doors were installed 1 cm too low, the screed company was cautious and added another 0.5 cm, and the heating installers insisted on their Rolljet system with only WLG 045 insulation. We then lacked 2 cm of insulation, which raised the U-value, and I didn’t want to argue with the heating company about deviating from their usual process. So we faced the problem: What to do? We talked again with the screed company, who reduced the screed height from 7.0 cm to 6.5 cm, and we used a 10 cm alukaschiert (foil-faced) insulation with WLG 023. This cost us about €800 more than standard WLG 035 insulation but now gave us a U-value between 0.18 and 0.19 instead of the calculated 0.24, and we still saved €3,500 - €800 = €2,700 compared to the option with insulation below the floor slab.
This only works if you’re flexible with the build-up height and probably not building a turnkey house. If you do the insulation yourself (anyone can do it, but it does require some time), the result will be much better, because in my opinion, no company has the time and care to do it as thoroughly as you would yourself. Doing it yourself can save you a significant amount of money overall.
Our offer included 10 cm WLG 035 insulation both below and above the floor slab. The heat demand calculation showed that this was not necessary to meet our Energy Saving Ordinance 16 requirements, so the plan included 14 cm WLG 035 insulation on the floor slab only — resulting in a U-value of 0.24. This saved us almost €3,500 since we used 6 cm less insulation overall and didn’t need any basement wall blocks. The downside was that we ended up with a 22 cm floor build-up and a ceiling height of only 2.53 m (8 ft 4 in) — which is still within standard range anyway.
In the end, the front doors were installed 1 cm too low, the screed company was cautious and added another 0.5 cm, and the heating installers insisted on their Rolljet system with only WLG 045 insulation. We then lacked 2 cm of insulation, which raised the U-value, and I didn’t want to argue with the heating company about deviating from their usual process. So we faced the problem: What to do? We talked again with the screed company, who reduced the screed height from 7.0 cm to 6.5 cm, and we used a 10 cm alukaschiert (foil-faced) insulation with WLG 023. This cost us about €800 more than standard WLG 035 insulation but now gave us a U-value between 0.18 and 0.19 instead of the calculated 0.24, and we still saved €3,500 - €800 = €2,700 compared to the option with insulation below the floor slab.
This only works if you’re flexible with the build-up height and probably not building a turnkey house. If you do the insulation yourself (anyone can do it, but it does require some time), the result will be much better, because in my opinion, no company has the time and care to do it as thoroughly as you would yourself. Doing it yourself can save you a significant amount of money overall.
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Grantlhaua25 Apr 2019 13:52@pffreestyler
We also ran a test calculation using WLG023 insulation, and it made a negligible difference for us (I think about 0.5 kWh/m² per year). Did it really make such a big difference for you? Did you build without a basement?
Which company supplied your insulation? With an €800 price difference, you seem to have gotten a very good deal...
We also ran a test calculation using WLG023 insulation, and it made a negligible difference for us (I think about 0.5 kWh/m² per year). Did it really make such a big difference for you? Did you build without a basement?
Which company supplied your insulation? With an €800 price difference, you seem to have gotten a very good deal...
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Mottenhausen25 Apr 2019 13:58We have 12cm (5 inches) of Styrodur / XPS insulation below the slab. The advantage is that there are no thermal bridges, since the insulation on the slab doesn’t extend under the walls (both exterior and interior), but only between them. Additionally, you end up with a dry slab (Styrodur is waterproof) because the waterproofing layer is essentially under the slab instead of on top of it (bitumen membrane). The slab is therefore inside the heated envelope, and you don’t need to be an expert to imagine that a dry, warm slab under the house is better than a cold, damp one. Yes, up to the bitumen membrane the slab is still damp despite the waterproof concrete, otherwise this waterproofing wouldn’t be necessary.
But ultimately, it’s also a matter of personal preference.
But ultimately, it’s also a matter of personal preference.
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Grantlhaua25 Apr 2019 14:57Concrete doesn’t really care whether it is cold and wet or warm and dry. With polystyrene insulation, I wouldn’t be so sure after 50 or more years. But you’re right, in the end, these are two different approaches. However, this only applies to houses with basements. For houses without basements, perimeter insulation under the slab is unavoidable. Since our entrance area is located between the house and the garage, perimeter insulation was installed there, but not in the basement, as mentioned.
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pffreestyler25 Apr 2019 15:080.05 is about right. I ran the numbers again. The improvement is 0.044 since 14 cm (5.5 inches) compared to 13 cm (5 inches) is relative (3 cm (1.2 inches) but with the lower-performance Rolljet insulation WLG 045). With 14 cm (5.5 inches) vs. 14 cm (5.5 inches) it would be 0.058. I calculated this using ubakus with the 3-week trial version. We don’t have a basement.
It is the Iko Enertherm PIR Aluminum insulation with WLS 023.
We installed the insulation ourselves. The cost was 220 m² (2,368 sq ft) x 5 cm (2 inches) thickness at a total of €8.16/m² (€8.16 per 10.8 sq ft). Using a company probably wouldn’t have been much more expensive (the company’s material price for WLG 035 was only slightly higher than the material price when I requested quotes).
The additional cost of €800.00 should pay off in about 18 to 24 years.
0.044 W/m²K x 84 heating degree days x 100 m² (1,076 sq ft) = 369.6 kWh x €0.065/kWh = €24.00 savings per year (difference from the energy demand calculation in the building permit) = 33 years payback.
0.072 W/m²K x 84 heating degree days x 100 m² (1,076 sq ft) = 604.8 kWh x €0.065/kWh = €39.31 savings per year (difference to the actual situation) = 20 years payback.
If gas prices rise, the payback period will naturally shorten.
Since I am not even 30 years old and plan to live there for more than 20 years, it was worth it for me—especially as the additional cost is offset by my self-performed work that wasn’t accounted for in the financing.
We still installed 10 cm (4 inches) insulation on the base—so the slab is insulated on the sides and from above…
It is the Iko Enertherm PIR Aluminum insulation with WLS 023.
We installed the insulation ourselves. The cost was 220 m² (2,368 sq ft) x 5 cm (2 inches) thickness at a total of €8.16/m² (€8.16 per 10.8 sq ft). Using a company probably wouldn’t have been much more expensive (the company’s material price for WLG 035 was only slightly higher than the material price when I requested quotes).
The additional cost of €800.00 should pay off in about 18 to 24 years.
0.044 W/m²K x 84 heating degree days x 100 m² (1,076 sq ft) = 369.6 kWh x €0.065/kWh = €24.00 savings per year (difference from the energy demand calculation in the building permit) = 33 years payback.
0.072 W/m²K x 84 heating degree days x 100 m² (1,076 sq ft) = 604.8 kWh x €0.065/kWh = €39.31 savings per year (difference to the actual situation) = 20 years payback.
If gas prices rise, the payback period will naturally shorten.
Since I am not even 30 years old and plan to live there for more than 20 years, it was worth it for me—especially as the additional cost is offset by my self-performed work that wasn’t accounted for in the financing.
We still installed 10 cm (4 inches) insulation on the base—so the slab is insulated on the sides and from above…
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