Basement insulation both externally and internally.

[Bengtt]

I have isodrän on the outside below ground but want to add 50mm cellplast on the inside to also get insulation on the part that is above ground. The wall can therefore breathe outward and I don't see any problem with preventing warm humid indoor air from penetrating the wall, but maybe someone else has a different experience?

 

[Fjonken]

I have isodrän on the outside below ground but want to add 50mm of foam plastic on the inside to also get insulation on the part that is above ground. The wall can thus breathe outwards and I see no problem with preventing warm, humid indoor air from penetrating the wall, but perhaps someone else has a different experience?

What is your question? If you insulate interior walls with 50mm of foam plastic, or are we talking about floors? I find it hard to see how you can insulate the walls with foam plastic and at the same time have a diffusion-open solution, unfortunately.
I don't have any U values in my head, but if I am not completely wrong, 200mm of foam plastic above a capillary-breaking layer is the minimum in Sweden to be classified as insulated. Garages probably have 200mm. In the living area, it's probably 300mm that's required, unless you choose a different insulation class, of course.

 

[Bengtt]

What is your question? Are you isolating interior walls with 50mm cell foam, or are we talking about floors? I find it hard to see how you can insulate the walls with cell foam and at the same time have a diffusion-open solution unfortunately.
I don't know any U-values by heart but if I'm not completely wrong, 200mm cell foam above a capillary-breaking layer is the minimum in Sweden to be classified as insulated. Garages are generally 200mm. In living areas, 300mm is standard, unless you choose a different class of insulation, of course.

Not floors, walls. The basement has 1.5m below ground and 0.5m above ground. The part that is below ground will be insulated with 200mm isodrän which insulates, drains, and ventilates on the outside. But I can't put external insulation above ground. That's why I thought of placing it on the inside. The wall ventilates outward and inside one usually has diffusion-tight plastic. Surely it should work with cell foam, meaning diffusion-tight insulation on the inside?

 

[Fjonken]

Not floors, walls. The basement has 1.5m below ground and 0.5m above ground. The part that is below ground is insulated with 200mm isodrän, which both insulates, drains, and ventilates on the outside. But I can't put external insulation above ground. Therefore, I thought of placing it on the inside. The wall ventilates outward and inward, you usually have vapor-proof plastic. Surely it should work with foam plastic, that is, vapor-proof insulation on the inside?

You will always have moisture in the basement regardless of how well drained it is, so personally, I would never involve plastic in such environments. Build air gaps or use insulation that can handle the environment. I glued lightweight concrete blocks on all the walls in my basement instead of trying air gaps or insulating internally. I think they were 70mm thick, then plastered over it. If it provided better insulation properties, I do not know since I sold the house before winter came. But a guideline is to insulate on the cold side. And never involve plastic or organic materials in a basement. Hope this has given you some answers at least.

 

[Jochi]

I have isodrän on the outside below ground but want to add 50mm cellplast on the inside to also get insulation on the part that is above ground. The wall can breathe outward and I see no problem with preventing warm humid indoor air from entering the wall but maybe someone else has a different experience?

Should be fine. I have a sandwich wall of two sides of concrete with intermediate insulation and porodrän externally for 20 years.