Facade board, thickness and lambda value

[Jimmy_gbg]

I'm trying to learn the basics of cladding and insulation. We are going to take over a family farm with a log house from the 1700s/1800s (unknown). It is currently uninsulated and has a fancy asbestos panel facade from the 60s that we plan to remove and add additional insulation as well as replace all the windows.

I started looking at cladding panels to understand how they work and what thickness to choose. Isover seems to be a major manufacturer as far as I can tell and they have panels in various thicknesses. What is most confusing is the lambda values; it seems that several of the panels in different thicknesses have the same lambda value (32), and at the same time, I understand that the lambda value indicates the losses in the insulation regardless of thickness. So if you have 32, it insulates just as well as another that has 32, even if one is twice as thick. So why choose the thicker one then, is it a cost issue?

Which manufacturers should one look at, is Isover a good choice?

 

[justusandersson]

The lambda value is a material constant that expresses the material's thermal conductivity without regard to thickness. One can use the lambda value when wanting to compare the thermal conductivity of different materials. If one wants to look at the insulation effect, the u-value for different wall constructions must be compared.

 

[Jimmy_gbg]

The lambda value is a material constant that expresses the material's thermal conductivity without regard to thickness. You can use the lambda value when you want to compare the thermal conductivity of different materials. If you want to look at the insulation effect, you need to compare the U-value of different wall constructions.

Ok, so should you be able to get a U-value for each panel then? Or do you only get that for a complete construction? I'm curious about how 50mm vs 100mm affects my insulation level for such a panel, so I'm thinking about how to approach that.

 

[justusandersson]

The unit for lambda value is W/m x degree, for U-value W/m2 x degree. If you want to know the U-value for different constructions, you can visit the insulation manufacturers' websites, as they usually contain many examples. With the help of the U-value, you can calculate energy consumption under given temperature conditions.

In your case, if you plan to add insulation to an old log frame, you can use the lambda value to compare the insulation capability of the timber with that of mineral wool. If the siding board has a value of 0.032, solid wood has 0.14, a difference by a factor of just over 4. This means that if your timber is 5 inches thick, it has the same insulation capability as a 28 mm thick siding board. I don't think you will benefit much from U-value calculations because it is not realistic to achieve modern insulation standards on an old log house. Moreover, insulation is not the only thing that is important. The timber has weight which allows it to store heat better and thereby delay cold/heat from outside. In the perfect condition, the day's heat comes in at night and the night's cold comes in during the day. Insulation on the outside of the timber increases the time delay.

 

[Jimmy_gbg]

The unit for lambda value is W/m x degree, for U-value W/m2 x degree. If you want to know the U-value for different constructions, you can visit the insulation manufacturers' websites, they usually contain many examples. Using the U-value, you can calculate energy consumption under given temperature conditions.

In your case, planning to add insulation to an old timber frame, you can use the lambda value to compare the timber's insulation capacity with that of mineral wool. If the facade board has a value of 0.032, then solid wood has 0.14, a difference of just over a factor of 4. This means that if your timber is 5 inches thick, it has the same insulation capacity as a 28 mm thick facade board. I don't think U-value calculations will be very useful for you since it's not realistic to achieve modern insulation standards on an old timber house. Also, insulation is not the only important factor. Timber has a weight which allows it to store heat better and thereby provide a delay of cold/heat from outside. In the perfect state, the day's heat comes in at night and the night's cold comes in during the day. Insulation on the outside of the timber increases the time delay.

Thanks for the great info!

I understand it's a difficult calculation then, but how would you recommend thinking about it? It feels like even 50mm should have quite a significant effect on heating costs, if the existing frame only corresponds to 28mm. Then we're also considering spraying up 30cm loose fill in the attic since it's not insulated upwards, which maybe contributes more to the total than the walls.

In terms of cost, you might as well go for 100mm on the walls, I think, since you're doing it anyway, but the only reason 50mm would be nice is to reduce the impact on eaves and windows. The windows are going to be replaced anyway, but the eaves seem tricky and I'd preferably not touch them if possible. There’s quite a big difference between 50mm and 100mm then

 

[justusandersson]

With 30 cm of loose-fill insulation in the attic, the effect of thick panels on the outside of the timber becomes negligible. I would stop at 50 mm, mainly for the delay effect. It's also important that the wall is airtight. Old timber walls are usually caulked with moss and similar materials. A windproof barrier on the outside is suitable. Under no circumstances use plastic foil on the inside. Another common source of drafts in old houses is insufficiently caulked window frames, but if you're going to replace the windows, that issue will be resolved anyway.

 

[Jimmy_gbg]

With 30 cm of loose-fill insulation in the attic, the effect of thick boards on the outside of the timber becomes negligible. I would stick to 50 mm, mostly for the delay effect. It is also important that the wall is sealed. Old timber walls are usually caulked with moss and similar materials. A wind proofing on the outside is suitable. Under no circumstances use plastic sheeting on the inside. Another common source of draughts in old houses is insufficiently caulked window frames, but if you are replacing windows that will solve itself anyway.

Great, thanks for the tip!

I thought wind proofing was built into the facade board generally, do you mean there should be additional wind proofing?

 

[justusandersson]

The density varies slightly between different manufacturers, and they therefore recommend different handling of the wind barrier (as I see after a quick Google search). Old log walls can be significantly drafty, so it is never wrong to first apply a wind membrane directly to the timber regardless of the choice of facade board. Note what the manufacturer writes.

 

[Jimmy_gbg]

The density varies slightly between different manufacturers, which is why they recommend different handling of the wind barrier (I see after a quick google). Old timber walls can be quite drafty, so it's never wrong to first place a wind barrier directly on the timber regardless of the choice of facade board. Note what the manufacturer writes.

Ok, I will do that, thanks for the tips!