Vapor barrier against plank wall circa 1920?

[Job Andersson]

I have torn down old loose masonite and now have a wall in bare wood that I plan to put drywall on. Should you have plastic/vapor barrier inside the drywall?

The house is from 1920 and from what I can see it is from the outside: new outer siding, new wind protection sheet, some insulation, tar paper, standing solid planks, wind protection paper and finally the horizontal planks you see in the picture.

 

[sinuslinus]

No. You only risk moisture problems with plastic in that construction.

 

[slacker]

No, in a house from 1920 where the ventilation is mainly based on natural draft, there should not be any form of vapor barrier.

 

[Job Andersson]

Doesn't it reduce moisture in the construction if you place plastic on the inside? Then only heat would travel out into the wall while the moisture remains in the indoor air?

 

[jel]

The trick is to have sufficiently good ventilation so that the indoor moisture is not allowed to penetrate into the wall. A small part will always do so, but in your case, a vapor barrier is probably recommended. Something that slows the moisture so it can be ventilated out. An insulation that can "breathe" is also recommended, such as flax.

It's difficult to add plastic afterward and you'll never get everything airtight, so I would invest in something else...

If there is already insulation in the wall, as I understand, it would be good to know what you use to heat the house? If the chimney is cold, it's always a good idea to assist with mechanical ventilation. Either something like a PAX fan in the bathroom, laundry room, etc., or something more central, for example, mounted on the chimney...

 

[sinuslinus]

It does not become completely airtight to install a vapor barrier afterwards.

At least read the summary in this report:
https://uu.diva-portal.org/smash/get/diva2:697670/FULLTEXT01.pdf