I am a happy amateur in the construction area. I am working on a small extension that will be heated occasionally throughout the year. The walls are as follows (from outside to inside): Outer panel-Air gap-Asfaboard-Cellulose insulation-Vapor barrier-Batten strips-Inner panel. I have tried to read up on a reasonable construction. Previously, when I knew even less, I used regular insulation, like Rockwool, without any moisture barriers at all in the older section. For the extension, I also tore down an approximately 6-year-old exterior wall, and it looked completely healthy inside, just insulated with Rockwool and then wind paper under the outer panel. I obviously understand the point of a vapor barrier when using regular insulation, but the strange thing is that I have never seen any pictures of moisture damage when the moisture barrier is omitted. Does anyone here have any pictures that can clear up the mystery?
Self-builder
· Stockholm
· 8 227 posts
That is a bit of a jungle.Jan Fahleson said:
If you're using cellulose, you should not have a vapor barrier, but rather a vapor brake.
But if you plan to decommission, maybe not even that is needed/good.
I've also built with glass wool without any vapor barrier, as preparation for decommissioning, which worked just fine for 10 years. However, it was only 95mm of insulation in the wall, it can get worse if it's thicker, or more moisture load from inside periodically.
In my extension now, there will be a vapor brake (instead of a barrier) to reduce the moisture pressure, but give the moisture a greater chance to dry out if it does get in (which according to my experience is difficult to totally prevent unless you are very meticulous and building completely new).
Your construction looks sensible to me.
Self-builder
· Stockholm
· 8 227 posts
I understand that, but then there's hardly any point in having cellulose insulation?W witten said:
And if you want to have it heated "now and then," you probably want a vapor brake precisely to allow moisture to migrate in the other direction occasionally.
But that’s not the pointW witten said:
Why use cellulose insulation + moisture barrier
So because you have insulation that doesn't directly mold if a little moisture comes in, you should let moisture into the wall? I don't understand that logic. You will have the highest vapor pressure from the inside, so there should be a barrier there. Even though it will work excellently even with a more expensive vapor brake.
I don't quite understand the question. When I insulated my attic, I chose cellulose because it was a recycled product (circular building) and vapor barrier where possible to minimize moisture in the attic space to reduce the risk of mold on the roof sheathing.Tomture61 said:
But that's not the point
Why use cellulose insulation + moisture barrier
Living in a house with Isover + vapor barrier + mechanical ventilation, I have to live with 20% RH in the winter.D Daniel 109 said:
Not good for health with either too low/high RH.
A house insulated with cellulose insulation can both give and take moisture from the dwelling
I think you haven't understood the product cellulose insulationW witten said:
You cannot store moisture in the walls for a significant increase in humidity indoors during the winter. It is completely unreasonable.
Why is it unreasonableD Daniel 109 said:
How do hot/cold work, are they impossible to balance.
Water vapor has similar phenomena as the above.
Warmer air can carry more water vapor.
There are those who build houses with clay/straw.
Solely for a better indoor climate.
Solely for a better indoor climate.
Do the math and you'll see. It's not reasonable.Why is it unreasonable
How does warm/cold work, are they impossible to even out.
Water vapor has similar phenomena as above.
Warmer air can carry more water vapor.
You never want moisture in the insulation regardless of what it's made of. It can be advantageous to have a vapor retarder in some cases when renovating and it's not possible to achieve a complete vapor barrier, but it's definitely not the same as it being beneficial or purposeful to allow moisture migration into the insulation.