Add insulation to brick structure with Leca (lightweight aggregate blocks)?

[jaso]

My outer walls currently consist of a brick structure (one brick thick) with thick plaster on the outside. On the inside, there are 7 cm lightweight clinker blocks. It feels somewhat weak.

Since I'm doing a complete renovation of the house, I have a chance to improve this. Therefore, I am considering building an additional layer of lightweight clinker on the inside of the wall, either 7 cm thick or 15 cm. Then plaster on the inside. What do you think of this solution? Could I get condensation between the blocks I install and the old blocks? Could I also have mortar on the backside of the blocks to "glue together" these with the existing wall, thereby avoiding condensation?

I would rather not start experimenting with different barriers and insulations. When I bought the house, there was interior additional insulation with fiberglass in some places and rock wool in others. On all the walls, black mold had formed between the insulation and the lightweight clinker blocks. I've also heard that it's difficult to add insulation to heavy structures in old houses. Another layer of the existing material feels more appropriate.

 

[miry]

you haven't thought about adding insulation externally and what do you have outside the blocks?

I assume you want to keep the climate of a heavy house or maybe you didn't have that before?

because what I can imagine would fit is 7cm leca and 10cm cell foam and it's about 10 times better addition than just 7cm leca, so with such an addition and if you don't have more in the wall than the existing 7cm (and estimate it equivalent to today) then you will improve the insulation in your walls by about 5 times
a good window today lets through igeon 1W/K/sqm and that's as much as 20cm leca or 3.5cm cell foam or 15cm solid timber, so it's worth considering that you can either build up with timber or use cell foam and leca but as you saw, wool in various forms against a damp wall is not something that works, so that type of insulation shouldn't be used in my opinion

 

[Mikael_L]

15 cm LECA corresponds to about 3 cm of mineral wool or foam plastic. You should keep that in mind, i.e., the walls will be thick but still cannot be called well-insulated. You can benefit from the heat storage effect, especially during a few months in spring, so 15 cm LECA can probably be considered equivalent to 4 cm of conventional insulation.

I don't dare to advise purely on construction techniques. Personally, I would consider, for example, 5-10 cm of foam plastic and then as thin LECA as possible, but many questions need to be answered beforehand, such as whether the combination works well, where the dew point falls in the wall, how the inner wall becomes sufficiently stable, and so on.

 

[jaso]

Thanks for the answers! You seem to be on the same track - lightweight expanded clay aggregate is a weak insulation.

I've considered foam plastic but I'm very afraid that the dew point will end up behind the foam board just as it did with the previous insulation, glass wool/mineral wool. It would mean that the frame will fetch cold from outside, the foam holds back heat, and between the foam and the frame you get the dew point. The only solution to that is probably to try to put a vapor barrier against the wall, but I think it's difficult to get it tight in an old house. And some form of wall ventilation is probably too advanced for me to build.

It's for these reasons I might dare to put another layer of lightweight expanded clay blocks. There will be no "new" materials in the wall; the frame will just be a bit thicker from the same material. But on the other hand, if 7 cm of lightweight expanded clay would correspond to about 2 cm of conventional insulation, I wonder if it’s worth all the effort. I think almost the same about 15 cm corresponding to 3-4 cm conventional. It's a big consideration... at least the cost is manageable.

miry,

haven't you considered adding insulation externally and what do you have outside the blocks?

I assume you want to keep the climate of a heavy house, or didn't you have that before?

Outside the lightweight expanded clay blocks is the house's brick frame (one brick thick). The brick frame has thick plaster on the outside. Inside the blocks, I was only thinking of having a thin plaster. I don't really have a preference when it comes to the climate of a heavy frame or not. The house is newly purchased, so I haven't had the chance to experience the climate before I started tearing down the additional insulation (I could already see from the viewing that the construction was poor).

I haven't thought about insulating externally due to the cost, which I don't believe I'll recoup in energy savings since I have geothermal heating and the area above ground is about 150 sqm. It's quite a nice functionalist house from the 30s and if I want to keep it as nice with white plaster, adapted eaves (hipped) and moved-out windows so that they almost sit flush with the facade, it becomes very costly (many hundreds of thousands of kroner).

 

[jaso]

Still standing and hesitating... anyone have more thoughts on this?

Perhaps I could get help from the moderator to move the thread to the insulation section? Realize I created the thread in the wrong place.

 

[Skånelängan]

Today, I have something similar. Two layers of bricks from 1910 with an air gap between them, and then a layer of lightweight clinker inside. The lightweight clinker is 15 cm and has an air gap against the brick. Plaster both inside and outside. This works very well for us and creates a good living environment.

 

[jaso]

Today, I have something similar. Two layers of brick from 1910 with an air gap between them and then a layer of lightweight expanded clay aggregate inside this. The lightweight clay is 15 cm and has an air gap against the brick. Plaster both inside and outside. This works very well for us and creates a good environment to live in.

That was interesting! Have I understood you correctly that there are two air gaps: one between the two layers of brick and one between the lightweight clay layer and the brick? Do you know if the air gap provides any benefits? Have you had the opportunity to investigate if you've had any condensation in these? Are they perhaps ventilated in some way?

My idea is to add a new layer of lightweight clay directly against the previous layer so that no condensation can form in the wall.

 

[miry]

The air gap has a certain insulating effect, and brick and leca transport moisture quite well in both directions both absorbing and releasing it.

Then I should have written that it's one thing to give theoretical opinions on how one might think, and it doesn't necessarily mean it suits your specific case without an assessment by a knowledgeable person on-site.

Then, XPS is waterproof, so you won't get moisture through it into the wall, whereas EPS allows vapor through and can cause condensation in the wall as it's easy for the vapor barrier to come out too far in the wall, leading to condensation in the wrong place.
But with brick and leca, it doesn’t matter so much with moisture if it's not for long periods and it's too humid since the amount of water that would penetrate an EPS board is quite limited, as I understand it, but I don't have exact figures on that either

 

[Skånelängan]

That was interesting! Have I understood you correctly that there are two air gaps, one between the two layers of bricks, and another between the lightweight clinker layer and the brick? Do you know if the air gap adds any benefits? Have you had the opportunity to check if you've had any condensation in these? Are they perhaps ventilated in any way?

My thought is to add a new layer of lightweight clinker directly against the previous layer so that no condensation can form in the wall.

Exactly, 3 walls and two air gaps. The air gaps are perhaps about 50 mm and they are bone dry. Vents on the outer side ventilate the gap between the brick walls. The air gaps have an insulating effect.