Total renovation - Install vapor barrier or not??

[Daniel 109]

Any type of source for that? I'm skeptical.

 

[eddiw]

One should not enclose organic material between two diffusion-tight layers (vapor barrier and roofing felt). All 1.5 and 2.5 story houses built before about 1950 have slanted roofs with sawdust insulation or something similar, without an air gap. It is not an ideal construction, but providing it with a vapor barrier on the underside makes it catastrophic.

Thanks, then I'll continue without a vapor barrier. If it has worked for 70+ years, there won't likely be any difference now either. The attic hasn't in any way sealed the roof from indoor air as there have been both holes and a door (not sealed at all).
We haven't added additional insulation to the roof or the attic, as our inspector advised against it when we bought the house. He suggested that you could take some waste energy and keep the attic in fine condition (it is in very good condition for being over 70 years old) rather than start adding insulation and basically invite problems.

 

[justusandersson]

To eddiw: I agree with your inspector.

To Daniel 109: The easiest way is to refer to all the building codes that have existed over the years. In BABS 1960 in chapter 21, Protection against moisture, it states: "If building materials are placed between dense layers, e.g., in exterior wall construction or solid roof, the building part is executed so that the built-in material can dry out to the necessary extent."

 

[Daniel 109]

Do you mean that it gets better if it is open for moisture to enter the material?

 

[justusandersson]

No, it's better not to install any vapor barrier under the sloped roof. The best option is to have a vapor barrier combined with a vapor-open membrane on the top side of the roof.

 

[Andreas12345]

This topic has come up many times before and the same argument always arises: old houses must breathe. I disagree with that argument, as I believe it is wrong.

When you add insulation, you no longer have the same construction and the conditions change. I would say that you should not insulate too much and use a vapor retarder, not a vapor barrier. Also, ensure that there is negative pressure in the house.

And cellulose is not better if you do not use a vapor barrier.

http://www.diva-portal.se/smash/get/diva2:435031/FULLTEXT01.pdf

 

[Cancerman_777]

One thing that ALL opponents of interior vapor barriers miss is that today we live RADICALLY different than when the leaky houses were built and were relevant. Today we shower at least once a day per person; that's a lot more moisture for the house to handle than a bath a week per person. Today we want negative pressure in the houses so that we get as little heat waste as possible. Previously, we heated the outdoors and in doing so, dried out the moisture that migrated into the structure from the indoor climate. There are enormous differences.
I absolutely(!) say vapor barrier on the inside. No doubt about it. I base my statement on two older houses that I have renovated, and both are in excellent condition after 10 years. There is NO reason whatsoever to allow moisture from indoor air to migrate into the structure. Anyone who claims it's "good," I want them to justify why moisture in the structure would be good. Otherwise, it's nonsense.
Furthermore; absolutely no organic material BETWEEN two membranes. Not even if there is also an air gap between the membranes. Zero organic material. Period.

That's my $.25

 

[ricebridge]

Well, @Andreas12345 and @Cancerman_777, the arguments apply on the condition that you completely rebuild the house and thereby use non-hygroscopic insulation. With hygroscopic insulation and for that matter, vapor barrier, you align more with the house's basic construction.

Sure, we shower more. But we usually do that in a wet area. And there it should of course be sealed and insulated according to all the proper standards. But in the rest of the house, we're not really wetter than before.

We used to waste more heat. But that's something you have to take into account with an old house. It's not a newly built house with today's energy requirements, and you have to live with that a little, I think.

 

[Cancerman_777]

Well, @Andreas12345 and @Cancerman_777, the arguments apply on the condition that you completely rebuild the house and in doing so use non-hygroscopic insulation. With hygroscopic insulation and indeed vapor brake, you are more in sync with the house's basic construction.

Sure, we shower more. But we usually do that in the wet area. And there it should definitely be plasticized and sealed according to all the rules. But in the rest of the house, we're not more wet than before.

We used to heat for the crows more. But that's a bit you have to take into consideration also with an old house. It is not a new house with today's energy requirements, and a little you have to live with it, I think.

No, ricebridge. That's romantic talk; "more in sync with the house's basic construction". Yes, if you want to live like people did when the house was built, otherwise not. Most of us don't want that. So you apply plastic.

I think you're completely wrong there. We're not talking about the waterproofing layer regarding what's under the tiles, but the construction of the house, not specific space requirements. Previously, you should NOT plastic the outer walls in a bathroom as people didn't understand that a regular gypsum board is covered with paper, which means that you lock organic material between the waterproofing of the wet room and the waterproofing of the outer wall. I don't know how it is today, but I remember that ordinary gypsum boards were discouraged in wet rooms for a period. I make it simpler; I use mineral boards.

No. No one who buys a house expects that you have to "take" that heating costs 7,000 SEK per month to "keep the house in sync with the basic construction". Houses should absolutely be modernized and follow the times' development in terms of energy efficiency, material choice, and more, when renovation is to be done and great opportunities present themselves. That's precisely what renovation means; to renew.

Or you add insulation, vapor tightly on the inside, and enjoy almost the same energy efficiency as a newly built house. I know what I choose, and apparently have chosen. It's cheaper, healthier for the house, and simply just better.

 

[Cancerman_777]

Mja, @Andreas12345 and @Cancerman_777, the arguments apply on the condition that you completely rebuild the house using non-hygroscopic insulation. With hygroscopic insulation and indeed vapor brakes you are more in tune with the house's basic construction.

Sure, we shower more. But usually in wet areas. And there it should obviously be sealed with plastic according to all the rules. But in the rest of the house, we are not wetter than before.

We used to burn more for the crows. But it's something to take into account with an old house. It's not a new house with today's energy requirements, and you have to live with that a bit, I think.

And yes, I want you to show WHY indoor moisture in the construction is good, other than "in tune with basic construction".

 

[JohanLun]

Currently working on a sloped roof without an air gap, originally filled with torv. Redone with partial mineral wool without plastic. Now I've replaced mineral wool with isolina, keeping torv where I could reach. Installed isolina's paper on the inside. http://www.isolina.com/se/isolering-byggpapper.cfm

Does this feel like a reasonable solution? Or is it better without paper???

 

[ricebridge]

Tone it down @Cancerman_777 and don't get hung up on a wording.
As I wrote, I agree that we shower more, so we have vapor-barriered wet rooms. But how big of a difference is it, do you mean, in the moisture load in the rest of the house? Do we sweat more? Do we breathe more?
Rather, that moisture load has decreased because we are not as crowded as before. Fewer people per square meter of living space means less moisture load.

 

[Cancerman_777]

Calm down @Cancerman_777 and don't get hung up on a phrasing.
As I wrote, I agree that we shower more, so we have moisture-proofed wet areas. But how big is the difference, do you mean, in the moisture load in the rest of the house? Do we sweat more? Do we breathe more?
Rather, that moisture load has decreased since we are not as crowded as before. Fewer people per square meter of living space means less moisture load.

I am totally calm and have been so all day and evening.

Before I respond to your statement, I want an answer from you on WHY humid indoor air would be "good" for the construction. What are your actual (not emotional) arguments?

 

[mattiasp]

I have now cleaned up the thread. If you want to discuss moisture migration in different types of constructions, please use factual arguments. In this case, according to some people, it's a physicalist problem. According to others, albeit not entirely expressed, it's an emotional discussion. Remember that the laws of physics apply everywhere, even in older houses. At the same time, those who argue with emotional arguments are rarely receptive to arguments based on scientific principles. It's futile to fight against windmills regardless of how right you are.

 

[Mikael_L]

How did you think now? If there is inadequate ventilation, it is even more important that the indoor moisture does not enter the construction

No, I don't think that was the meaning of what justus wrote.
I think he writes that you should not have two airtight layers surrounding a construction part (in this case enclosing insulation and the surrounding wood in the attic between diffusion-tight plastic and diffusion-tight roofing felt).

And I agree with that, I think you do too.