Thinnest outer wall?

[Bor i trähus från 1920]

How thin can exterior walls be built, and how?

(We will maximize the building area on our plot by building an extension of 25 square meters on 2 floors, with thinner walls we get a larger living space... especially important in a bedroom where every centimeter makes a difference)

 

[Jonatan79]

At least 145mm but there may be requirements from the building permit department in the municipality for something thicker due to the energy value. Also due to load-bearing capacity considering the 2-story structure.

 

[Bor i trähus från 1920]

It is a total energy value that counts for our building permit, meaning that if we choose windows with a U-value of 0.9 and add extra insulation to the floor, we can have somewhat thinner exterior walls. But of course, they still need to be insulated for our sake! Right now, we have log walls with the facade directly on them, they are 16 cm (including inner wall covering) and retain heat fantastically. Our existing walls would have a U-value around 0.85, and a poorly performing modern wall is 0.2.

If a maximum of 20 cm would be okay, how do you reduce the thickness to that? It sounds very reasonable, but as soon as we calculate it, we end up higher!

 

[Jonatan79]

OK, 145mm regel + 45mm regel internally e.g.

 

[Bor i trähus från 1920]

Still calculating on thin outer walls! Drew this today, does it seem reasonable?
(thin and toxin-free walls)

 

[Jonatan79]

Maybe use the 170 rule instead? We built our new cabin with 195+45. It becomes stable.

 

[surris]

What requirements has the municipality set? Only the U-average value or also the calculated energy usage?
Your wall is approximately 0.2 W/m2,K. Whether that is sufficient depends on how the other parts of the enclosing building envelope are constructed and their size.

 

[Bor i trähus från 1920]

What requirements has the municipality set? Only the U-value or also the calculated energy usage?
Your wall is about 0.2 W/m2,K. If that's sufficient depends on how the other parts of the enclosing building envelope are constructed and their sizes.

Thanks! Exciting, how did you calculate it?
In our invitation to the technical consultation, it just states “U-value calculation,” but on the municipality's website, it mentions “energy balance calculation” as an example of necessary documents.

 

[surris]

Thank you! Exciting, how did you calculate?
In our call for technical consultation, it only says "U-value calculation," on the municipality's website it says "energy balance calculation" as an example of documents needed.

I just quickly calculated that you have 170mm insulation with lambda 0.04, then it becomes 0.235=1/(0.17/0.04). With the remaining parts of the construction, it ends up around 0.2.

U-value calculation is easy, energy balance calculation takes a little longer. Ensure exactly what is needed.