ᐅ Insulating a house with 30 cm thick walls?

Created on: 24 Jul 2017 23:53
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DerZert
D
DerZert
24 Jul 2017 23:53
Hello,

the question of whether to insulate or not is increasingly being discussed, and of course, there are many related issues.
I am interested in the current knowledge of those who are more experienced with the topic than I am...

The property we purchased was built in 1965 and unfortunately has only 30cm (12 inches) exterior walls.
During the gut renovation, we didn’t notice any significant issues except at 1-2 spots in the basement.
Now, the basement and attic are going to be insulated, and new windows (probably double-glazed) will be installed.
Would you generally recommend an external thermal insulation composite system (ETICS / EIFS) for walls of this thickness?

Thanks for your effort!
11ant25 Jul 2017 15:16
30 what? - Solid clay brick, lightweight calcium silicate brick, pumice or ...?
DerZert schrieb:
The single-story new building is planned to be made of aerated concrete blocks and will feature a wide window front.
That’s definitely not a masonry stone for exposed brickwork. Will it be plastered or clad? – In my opinion, that depends on the answers regarding the existing part of the house. Even if the extension is meant to look completely separate, I wouldn’t recommend using different construction approaches for the wall structure.
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D
DerZert
25 Jul 2017 17:58
A look at the structural calculations from that time shows that the masonry consists of "cement-rendered bricks 'V50' in mortar group II."

The planning concerning the extension was only loosely requested here and will, of course, be designed by a structural engineer/architect.
11ant25 Jul 2017 18:52
DerZert schrieb:
A look at the original structural calculations shows that the masonry consists of "cement-lime concrete blocks 'V50' in mortar class II."

Cement-lime concrete block refers to a type of lightweight concrete block, and V50 is a compressive strength class. If you search for these terms along with "thermal conductivity," this will give your energy consultant the data needed for further calculations. The mortar class only indicates the structural role of the mortar used to bond the blocks together—block and mortar work as a team here. Thermally, this is a negligible factor.

When extending a building, you often create spaces bounded partly by old walls and partly by new ones. Therefore, for the new construction (possibly with varying wall or insulation thickness), I would try to achieve an overall wall assembly with properties coordinated to the existing structure. That is why I suggest considering them together.
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D
DerZert
27 Jul 2017 11:19
Regardless of a possible extension, I would be interested to know if, based on experience, it makes sense to add insulation to a 30cm (12 inches) lightweight concrete wall or not.
11ant27 Jul 2017 17:08
DerZert schrieb:
whether it is generally advisable to apply insulation on a 30 cm (12 inch) pumice block wall or not.

Advisable for what purpose exactly?

Insulation always improves the thermal transmittance value—regardless of my personal stance on insulation trends.

A 30 cm (12 inch) pumice block wall, at least without cavity filling, is no longer up to current standards. Whether it meets the requirements of energy-saving regulations, I am not sure—probably not for KfW55 standard anymore.

If you have a different approach to insulation than I do and would apply an external insulation system (ETICS / EIFS) on porous brickwork, you can do the same on pumice blocks; I see no fundamental difference in principle. Thirty centimeters (12 inches) is considerably thicker than 17.5 cm (7 inches) walls, so to achieve similar overall thermal values, you would need roughly 8 cm (3 inches) or perhaps 12 cm (5 inches) of insulation, rather than 16 cm (6 inches).

You won’t freeze or waste all your money on heating with a 30 cm (12 inch) pumice wall even without insulation. I live in such a house myself (30 cm (12 inch) pumice block monolithic, probably unfilled, without external insulation or brick cladding). How much you need to upgrade older buildings to meet current standards depends on the share of new construction involved—I don’t know.

The frequently mentioned warnings about mold damage depend on ventilation and correct workmanship; this applies to pumice just as it does to any other building material.
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