Building with PIR insulation without air gap

[Liljeros]

Hello

I am planning to construct an attefallshus/shed on my property that will be heated year-round. In such small houses, the wall thickness is quite crucial, so I've been thinking about how to make them as thin as possible. If I build with conventional insulation (mineral wool), the walls will end up being at least about 190mm thick.

I would prefer to get sandwich panels, but it's not simple or cheap for such a small project, which led me to the idea of making my own wall following the sandwich principle. What do you think about the following construction?
Cembrit fiber cement/45mm Kingspan PIR+metal studs/Kingspan 45mm PIR/Gyproc Habito. The idea is to adhere each layer completely to the others and cross-lay the PIR insulation. This should provide the following advantages:
-Strong
-Maintenance-free
-No thermal bridges
-Thin wall, only 110mm with reasonable insulation values.

Now, the question is, will this work in practice? With these materials, I shouldn't have any mold problems, and it should be strong enough to support the roof without issues... or? I am aware that this might not be the most economical solution, but it yields about 1.4m2 more space in a shed.

What do you think, forum? Could this be an idea, or should it just be scrapped?

 

[BSOD]

Whether it holds depends on which metal studs you have, right? Metal studs are usually used as non-load-bearing interior walls, aren't they?

The most important thing is to ensure proper ventilation in any case.

I would rather build with a proven construction method and either get slightly worse insulation properties or a slightly thicker wall.

Have you calculated how many kWh per year you gain by building like this compared to building in a more traditional way?

 

[Rabbithole]

Sandwich panels and elements sheet-insulation-sheet from, for example, Lindab or Kingspan probably provide the thinnest wall.

They are available both as roof elements and wall or the same for both. They are designed to be mounted on a framework, perhaps a few poles might suffice for a small cabin, or you might build a thin type 70mm regular load-bearing frame and then panels on the outside.

 

[krillan]

If you are going to build an attefallshus with 100mm sandwich panels with a core of pir insulation and sheet metal as the exterior covering on both the inside and outside, the panels do not need to be mounted on a steel frame if the panels are mounted vertically and you do not have large glass sections in the wall.

 

[Liljeros]

Whether it holds depends on which metal studs you have. Metal studs are usually used for non-load-bearing interior walls, right?

The most important thing, in any case, is to get the ventilation right.

I would rather build with a proven construction method and either get slightly worse insulation properties or slightly thicker walls.

Have you calculated how many kWh per year you save by building this way compared to building a bit more traditionally?

I haven't calculated the difference in kWh; it ends up with a U-value of around 0.25 with PIR, and if I want approximately the same thickness with mineral wool, the U-value is 0.54. I've searched but haven't found a calculator where you can input square footage, geographic area, and U-value. Most are for windows.

Even if the annual cost difference isn't astronomical, I still think there's quite a significant comfort difference.

I also think that regular metal studs should be sufficient for a 15m2 roof, and when the wall is fully assembled, the load-bearing capacity should be quite good.

 

[Liljeros]

Is there any place where an individual can get hold of smaller quantities of sandwich panels in various standard dimensions? I understand how to build but haven't really found anywhere to buy them?

 

[Ironcastle]

Hello Liljeros.

Don't scrap... yet.
But first of all, don't buy from Kingspan... they are the most expensive.
Unfortunately, they have bought Finnish SPU, which was previously the largest producer in the Nordics, so now they have almost no competition.
Maybe you can buy smaller quantities through a reseller of Balex products.
https://balex.eu/en/
I myself have bought two trucks of 160mm PIR boards from them and replaced all the insulation in my own house. Good.
You could absolutely make your own sandwich construction with fiber cement (preferably on both the inside and outside). There are ready-made solutions, such as ZIP elements. https://zenergy.se/zip-element/

However, I don't quite understand your idea with the studs… can you draw it out?

And how are you going to anchor it? Foundation?

There won't be moisture anywhere, anyway!

 

[Ironcastle]

That's right, also check with Finnfoam (finnfoam.se)

 

[BSOD]

I haven't calculated the amount of kWh difference, but it results in a U-value around 0.25 with PIR and if I want roughly the same thickness with mineral wool, I end up with 0.54 in U-value. I’ve searched but haven’t found any calculator where you can enter square meters, geographical area, and U-value. Most are for windows.

Even if it doesn't make a huge difference in cost per year, I still think it becomes a significant comfort difference.

I also think that regular metal studs should be sufficient for a 15m2 ceiling, when the wall is finally mounted, the load-bearing capacity should be quite good.

If you want to fine-tune, you should use energy indexes. But SMHI charges for delivering that, so many use degree days to get a sense of energy consumption.

Stockholm has about 3000 degree days per year. If your U-value is about 0.54, I think the energy consumption will be about 0.54 x 3000 x 24 /1000 = 43 kWh/sqm wall area. If you have about 60m2 of wall area, then it will be about 2500 kWh/year, and around half the energy consumption with the more energy-efficient wall. If you heat with an air-to-air heat pump, it should be about 500 SEK per year in difference in operating cost.

It’s been a while since I calculated degree days, I might’ve missed a unit in the calculation.

I’m not so sure you’ll notice it in comfort. But I could be wrong. A bad window gives noticeable draughts, but then the U-value is certainly well over 2.5. We have 3-pane windows with a U-value of 0.9, and I usually don’t think about draughts (I don’t have any radiators under the window). But maybe I’m insensitive? I remember the old 2-pane windows that were there before caused terrible draughts in winter.

 

[Liljeros]

Here is a conceptual sketch of how I envisioned it.

 

[Liljeros]

If you're going to do detailed calculations, you should use an energy index. But SMHI charges for providing that, so many use degree days to get a sense of energy consumption.

Stockholm has about 3000 degree days per year. If your U-value is about 0.54, I think the energy consumption will be about 0.54 x 3000 x 24 /1000 = 43 kWh/sqm wall area. If you have about 60m2 wall area, it'll be about 2500 kWh/year, and around half that energy consumption with the more energy-efficient wall. If you heat with an air-to-air heat pump, it should be about 500 SEK per year in difference in operating costs.

It's been a while since I calculated degree days, maybe I forgot a unit in the calculation.

I'm not so sure you'll notice it in terms of comfort. But I could be wrong. A poor window does give noticeable drafts, but then the U-value is probably well over 2.5. We have triple-glazed windows with a U-value of 0.9, and I usually don't think about drafts (I don't have any radiators under the window). But maybe I'm insensitive? I remember that the old double-glazed windows that were there before caused horrible drafts in winter.

Thank you, our gable wall is made of 20cm lightweight concrete with a PIR+Gypsum combo board mounted on the inside. This wall makes the rooms feel colder than they are even though they are at a normal temperature, despite a U-value of just under 0.6. The walls, for example, become very cold even when it's just over 5 degrees outdoors.

 

[jurkeller]

Hi

I'm planning to build an outbuilding/small house on the plot that will be heated year-round. For such small houses, wall thickness is very crucial and I've been thinking about how to make these as thin as possible. If I build with conventional insulation (mineral wool), the walls will end up at least around 190mm thick.

I would prefer to use sandwich panels, but it's not very straightforward and cheap for such a small project, which led me to the idea of creating my own wall based on the sandwich principle. What do you think about the following construction?
Cembrit fiber cement/45mm kingspan PIR+metal studs/kingspan 45mm PIR/Gyproc Habito, The idea is to fully glue each layer to the others and cross-lay the PIR insulation. This should provide the following benefits:
-Strong
-Maintenance-free
-No thermal bridges
-Thin wall, only 110mm with reasonable insulation values.

Now the question is, will this work in practice? I shouldn't have any mold problems with these materials, and it should be strong enough to support the roof without any issues...right? I'm aware that this may not be the most economical solution, but it still gives about 1.4m2 on a small house.

What do you think on the forum? Could this be an idea or should it just be scrapped?

Hwj, I have exactly the same considerations. Did you do this and were you satisfied!?

 

[Cuzzoss]

Sandwich panels and elements sheet-insulation-sheet from e.g. Lindab or Kingspan probably provide the thinnest wall.

They are available both as roof elements and wall or the same for both. They are designed to be mounted on a framework, maybe a few posts would suffice for a small cabin, or you could build a thin type 70mm regular load-bearing frame and then panels on the outside

Do they sell these to lilja projects or just for large industrial halls?

I also think this is an interesting solution.

 

[Liljeros]

Hello

I chose not to proceed with this solution, it became a bit too cumbersome for small-scale building.

I would still like to try, but it makes it easier to purchase these products if you are going to buy in larger volumes.

 

[Rabbithole]

Do they sell them to lilja projects or just for large industrial halls?

I also think this is an interesting solution.

Do they sell them to lilja projects or just for large industrial halls?

I also think this is an interesting solution.

Kingspan I believe sells directly to private individuals, unsure about Lindab but there are several suppliers so it's just a matter of calling around. Otherwise, you have to go through a construction company, local independent building stores usually can get hold of just about anything.

Pir panels or with mineral wool