ᐅ Installations should not compromise the building envelope.

Hello and good day,

we are currently looking for a suitable builder who focuses on ecological construction.

It is also important to us that the building envelope is not pierced or damaged by the installations, so that it does not have to be sealed again afterwards. We cannot imagine that it would be as airtight as the original.

Is this only achievable with an installation layer, or are there other options?
One provider responded to the question about an installation layer that they work with pre-installed electrical conduits.

What does that mean exactly, and would you recommend it?

I assume you prefer or have already considered timber frame construction or something similar? Usually, in standard setups, a vapor barrier or vapor retarder is installed directly behind the drywall, which is then naturally penetrated by every cable and electrical box.

That’s why airtight electrical boxes are used in that area, and the cables are routed through conduit pipes that are sealed as well. This is probably what the mentioned provider meant; they likely do not offer an installation cavity.

An installation cavity usually comes at an additional cost with most providers. Here, an extra layer is added in front of the standard wall, which can be filled with mineral wool, for example. This means you have an additional 6-8cm (2.5-3 inches) before the actual vapor barrier or vapor retarder, so airtightness there is less critical. With our provider, this was already included in the standard exterior wall. Optionally, we could have had the cavity insulated with cellulose for a more “eco-friendly” approach.

I would definitely recommend an installation cavity, especially since it makes it much easier to add extra electrical boxes during interior finishing if you forget to install them initially.

Regarding ecological building: Please take a close look at the materials used. Wood fiber insulation and cellulose, for example, sound very eco-friendly, but the problem is fire protection. These materials often have to be treated with boric acid and similar substances, which means they are not necessarily more environmentally friendly than fired bricks.

Hello Uwe82,
yes, that’s correct. These are prefabricated house suppliers.

What advantages are there besides the easier installation of the electrical boxes during construction, or what disadvantages arise if you do without them?

Are the seals at the points where they are penetrated really airtight?

If you install decentralized ventilation units, you have to penetrate the wall in any case, whether there is an installation cavity or not, or am I mistaken?

Kind regards

bauherrin1 schrieb:
Are the seals around the penetrations really watertight?

That’s exactly the question. Since sometimes hundreds of boxes are installed, the risk of leaks is relatively high. In individual cases, this might not be a big issue, but it could turn into a problem over time if something loosens, for example due to movements caused by plugging and unplugging connectors. That’s what I wanted to avoid.

Also, nails or screws penetrating the wall can potentially break the barrier. Usually, this isn’t a big problem. If they remain in place, the seal generally stays intact. But the holes would need to be properly sealed again if the screws are removed.

bauherrin1 schrieb:
When installing decentralized fans, you necessarily penetrate the wall, whether or not there is an installation cavity, right? Or am I mistaken?

Absolutely correct, but the number of those penetrations is usually much smaller. There are plenty of other elements that will penetrate the barrier as well (conduits for electric shutters/blinds, exterior lighting, intercom systems, etc.). The fewer penetrations there are, the lower the risk and the more effort people are generally willing to put into sealing them properly. With 100 conduit boxes, that willingness usually decreases. Especially since the conduits have to come out somewhere on the interior side as well...

Here, people are counting far too many minor details.

What is truly important is a proper vapor barrier installation. This work is tedious and can be done well or poorly. I would find it much more important to then inspect it thoroughly. A nail in the wall certainly does not compromise the overall building envelope. In theory, the vapor barrier is damaged, but in practice, this is hardly noticeable, since there are many areas that cannot be sealed 100%, and these have a much greater impact.

Decentralized ventilation systems can indeed become a problem, even when trying to meet KfW standards. The cross-sections are relatively large. Calculate the total perimeter of the ventilation holes and think about how many small nails you might be driving through the vapor barrier for that.

86bibo schrieb:
Here, a lot of peas are being counted.

A large number of peas also makes soup for many people—that’s the point. If you insert empty conduits into airtight hollow wall boxes, you will never achieve a 100% seal. The same applies when the conduit has to pass through the barrier again at the floor. This can lead to up to four leaks per box, especially since there are usually two conduits per box.

With a service cavity, I experience fewer issues both during the construction phase and afterward, even if I sometimes need to drill holes for hollow wall anchors to hang heavy items. After careful consideration, I would not build without a service cavity, as the risk of having to account for the barrier at every single point would be too high for me altogether.