Vapor tightness in inner vapor barrier with wood fiber insulation?
There are two common misconceptions regarding vapor barriers/brakes:
- Due to today's extreme requirements for airtightness in low-energy houses, people think it's a disaster if you accidentally drive a screw through the vapor barrier in your new house.
- (Old) houses with organic insulation don't need a vapor barrier or brake at all.
You should always strive to have the inside of the construction slightly more airtight than the outside and protected against air migration, so some form of air and diffusion-resistant layer is always needed. Even in old houses.
It is quite possible that airtight paper, paint, etc., is sufficient in an old house with little insulation, but that is not the same as saying no protection against air migration is needed.
- Due to today's extreme requirements for airtightness in low-energy houses, people think it's a disaster if you accidentally drive a screw through the vapor barrier in your new house.
- (Old) houses with organic insulation don't need a vapor barrier or brake at all.
You should always strive to have the inside of the construction slightly more airtight than the outside and protected against air migration, so some form of air and diffusion-resistant layer is always needed. Even in old houses.
It is quite possible that airtight paper, paint, etc., is sufficient in an old house with little insulation, but that is not the same as saying no protection against air migration is needed.
You can add a third misconception:
- If it's not possible to make a completely airtight seal when renovating/expanding, it's better not to have any vapor barrier at all. Otherwise, all moisture will concentrate at the places where there is no barrier, and the house will rot away.
- If it's not possible to make a completely airtight seal when renovating/expanding, it's better not to have any vapor barrier at all. Otherwise, all moisture will concentrate at the places where there is no barrier, and the house will rot away.
Member
· Västernorrland
· 12 030 posts
Yes, but here we are again, you say there's a lot of moisture and the house is rotting away..........How much is there in a normal house then? Can we really talk about such levels that houses rot away because of this? It sounds like we are talking about large amounts of moisture, but what is it really like?
Read the first line of the post too.....
No, it's not large amounts, but people have read on the Internet that it is a big problem. However, even small amounts can cause problems over a long period. The house we moved into 4 years ago had some rot in the sawdust in the cold attic directly above the bathroom. I replaced it with new sawdust in those 4 square meters, installed a fan that runs constantly on low speed in the bathroom, and painted the ceiling with bathroom paint. So far, the sawdust is dry and looks completely unaffected...
Member
· Västernorrland
· 12 030 posts
Yes, I understood that he meant it was a misunderstanding, but I was mostly thinking about what I wrote earlier regarding whether anyone knows what levels we're talking about at all? Is it over a day 2ml of water that gets through the walls, or is it several liters? Does anyone know? Some people reason almost as if you should have drip channels inside the walls..........
I recommend reading the chapter on moisture diffusion in the Moisture Handbook. Everything is explained in detail there, and it states how everything is calculated as well as the criteria that apply for a construction to be approved.
All the horror scenarios mentioned here. Can't these be avoided by simply using cellulose insulation that buffers and releases moisture? Combined with not using a vapor barrier that traps it, but instead a vapor retarder on the inside.
A common construction for cellulose-insulated houses is from the inside out:
This construction should be safe regardless of whether someone happens to nail a hole in the vapor retarder, right? At the same time, the vapor retarder is 45 mm into the wall, so it doesn't risk being punctured as much/often, but even if it does, it shouldn't be a problem?
In other words, isn't it the non-moisture-buffering mineral wool insulation that's causing the issue?
A common construction for cellulose-insulated houses is from the inside out:
- drywall
- plywood/OSB
- 45 mm installation layer with cellulose insulation
- vapor retarder
- cellulose insulation between load-bearing studs, 120, 145, 170, 195 or whatever
- 45 mm insulation crosswise to break thermal bridges
- asphalt board
- air gap
- siding
This construction should be safe regardless of whether someone happens to nail a hole in the vapor retarder, right? At the same time, the vapor retarder is 45 mm into the wall, so it doesn't risk being punctured as much/often, but even if it does, it shouldn't be a problem?
In other words, isn't it the non-moisture-buffering mineral wool insulation that's causing the issue?
There are formulas for how to calculate even with moisture-absorbing materials in the Moisture Handbook, and the principle is that moisture should not accumulate year after year by ensuring that the evaporation capacity during the drying period is preferably 2 times greater than the condensed moisture during the condensation period.
Even mineral wool can bind moisture, which is obvious if you have left such a slab outdoors for a long time. Villa walls also usually consist of moisture-sensitive wooden studs that need to be protected against condensation moisture.
There might be a bit too much concern about punctures in the vapor barrier/vapor retarder, as it is a diffusion barrier and not primarily a convection barrier.
Even mineral wool can bind moisture, which is obvious if you have left such a slab outdoors for a long time. Villa walls also usually consist of moisture-sensitive wooden studs that need to be protected against condensation moisture.
There might be a bit too much concern about punctures in the vapor barrier/vapor retarder, as it is a diffusion barrier and not primarily a convection barrier.
Approved according to what?
It is almost a direct quote from the Moisture Handbook, so one can interpret it as the calculation/construction being considered approved on the criterion that it is moisture-proof. There is value in leaning on a respected handbook that states what are acceptable criteria if one, for example, prescribes a construction and thereby takes responsibility for it. For instance, as a designer or architect. But it should not be interpreted as, for example, an approved fluorescent fixture.D Daniel 109 said:
What makes over 100-year-old wooden houses with 3-inch planks or logs more "moisture-proof" (protected against moisture damage in the walls) than today's cellulose-insulated houses?
Is it that the dew point shifts due to better insulation?
These old houses stand even today, and most of them have completely healthy timber, provided they have not been wrapped in plastic and have been maintained correctly over the years.
Is it that the dew point shifts due to better insulation?
These old houses stand even today, and most of them have completely healthy timber, provided they have not been wrapped in plastic and have been maintained correctly over the years.
There is a large temperature difference across the wall.
Wood can handle a lot of moisture before it becomes moist enough for mold to thrive.
Fireplaces draw out a lot of air, creating a negative pressure in the house and ventilating out the moisture.
It is not because they lack a moisture barrier.
Wood can handle a lot of moisture before it becomes moist enough for mold to thrive.
Fireplaces draw out a lot of air, creating a negative pressure in the house and ventilating out the moisture.
It is not because they lack a moisture barrier.
Do you have any more information that supports the idea that the houses would become worse just because they are wrapped in plastic? In most cases, the plastic is added during renovation, additional insulation, change of use, and change of heating source. Then the plastic is blamed when something goes wrong...tompax said: