ᐅ Sealing off heating recesses – what is the correct way to do it?

Hello everyone,

I have already looked around online and found everything from aerated concrete blocks to gypsum wallboards with insulation.

The fact is, new screed will be installed, along with new windows. Exterior insulation will also be added.

Should these be done first? Which materials are the right ones?

Thanks to all!

Two questions – two answers: with the question "Which materials should I use to properly close off the heating niche?", you will inevitably end up with aerated concrete, drywall, or similar DIY-friendly options.

With the question "What is the correct way to do it?", the answer is different. In that case, I would recommend using the same material as the surrounding wall. Using any other material will result in a finished wall surface that does not have a matching thermal conductivity; consequently, it will create a (relative) heating or cooling surface with better or worse values, leading to various effects on the indoor climate.

However, this approach requires a skilled mason, and you must first be clear about which type of brick or block was used in the rest of the wall.

Whether it is Reichs- or DIN-format, NF or 2DF, it does not matter. But filling a solid brick wall niche with porous bricks would be just as inappropriate as using aerated concrete or drywall.

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icefly2k schrieb:
External insulation will also be installed new.

Should this be done first? Which materials are the right ones?

Depending on the current wall structure, you can simply leave the recesses as they are. For example, if you currently have only 24 cm (9.5 inches) of brick and in the recess just 11.5 cm (4.5 inches), and you add 12 cm (5 inches) of insulation on the outside, the overall U-value across the whole surface will be quite uniform. It is then important not to choose radiators that are too tall, to ensure proper air circulation, and definitely to thermally decouple or replace the windowsill on the exterior.

To do it properly: if the external insulation is sufficiently thick, it is optimal to continue the outer wall structure, meaning you should build up with bricks and plaster flush.

More important than having homogeneous material is that the vapor permeability increases from the interior to the exterior. If external insulation is applied, I would avoid experimenting with highly insulating materials and instead use sand-lime brick or clay brick. Additionally, fill the recess WITHOUT an air gap. Ideally, remove the old plaster and build the new bricks flush.

dertill schrieb:
If you currently have, for example, only 24cm (9.5 inches) brickwork and the niche is only 11.5cm (4.5 inches), and you add 12cm (5 inches) of insulation on the outside, the U-value across the entire surface is fairly uniform.

Well, the wall thickness isn't exactly U-value-neutral after all.

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I don’t think it makes a significant or noticeable difference if you simply fill the area with standard bricks and then apply appropriate insulation on the outside. Using the same bricks is obviously better, but saying it directly affects the indoor climate seems a bit exaggerated.