vapor barriers, vapor retarders, and air barriers for timber frame houses

[davemellor]

Even for conventional stick frame houses, the terms vapor barrier, vapor retarder, and air barrier are often confused and "best practice" in the construction industry and in building codes changes from time to time.  Add the fact that different climate zones require different methods and the confusion increases.  Wondering if anyone has any good sources of information and/or experience specifically related to these issues in timber frame houses.  Personally I like what Jack Sobon wrote in regard to wall assemblies and roof assemblies in his 1993 book Build A Classic Timber-Framed House.  I'm guessing that many building inspectors would not have agreed with him at that time.

[samandothers]

I can't comment much on the building practices.  I did want to say welcome to the forum!

[kderby]

I think this a is a good question.  I see opportunity in using the new technology for insulation and vapor control.  Then I hear stories about houses rotting from the inside out, they were sealed up too tight.  What to do?   

[Ozarker]

Perhaps the links posted in the thread below will help.
https://forestryforum.com/board/index.php/topic,84364.msg1289484.html#msg1289484

[Magicman]

You have been mighty quiet for 10 months, but anyway Welcome to the Forestry Forum, davemellor.   :P

[timberwrestler]

What did Jack write in 1993?

[davemellor]

Jack Sobon indicated that vapor barriers were necessary in walls mainly due to code issues, and he felt that there were reasons and situations the vapor barrier could be omitted even in the walls.  Between a second story ceiling and an attic floor, he seemed to prefer no vapor barrier if the code official allowed it.  The  book still included insulation in walls and attic floor (for the project house in the book - classic 2-story hall and parlor house).  He indicated that houses had been built for centuries without vapor barriers and that these buildings performed well.  Because it is not explicitly stated in the book, I don't know if his ideas were meant only for houses in cold weather climate zones (i.e. northern US) or if they could be applied to mixed/humid and hot/humid locations.  Also, I'm not sure, but I'm guessing that he may not have intended that these ideas be applied to air-conditioned houses.

[jueston]

this isn't specifically related to TF homes, but just buildings in general. i work in construction and have to deal with code issues daily as well as contractors and homeowners who say they have personal experiences which contradict code. and my only experiance is in northern climates, so maybe it isn't applicable at all to southern climates.

i professionally removed stucco from homes that were rotting away from the inside due to moisture, people love to tout "old stucco is great, new stucco causes houses to rot away" but i opened up old stucco and new stucco alike and the results were mostly the same. when you have a place that moisture gets to, and can not escape, it sits on wood and it rots.

in old houses without vapor barriers when moisture leaks in, it can generally move through the interior walls and dry before the rot sets in, but that only works if evaporation is happening faster then the leak. in newer houses with vapor barriers on the inside, the water evaporates very slowly, so rot happens faster.

but the common denominator wasn't stucco, its water. there shouldn't be water inside of a wall, and if there is, then something is wrong.

so this is what i believe about vapor barriers: if you plan on water leaking into your walls, then don't put any insulation or vapor barrier, your house will be cold and drafty in the winter, impossible to cool in the summer, and expensive all year round. BUT its unlikely your walls will rot due to moisture because it can evaporate. if you  plan on doing a great job with flashing, self adhesive flashing, and siding so no water will get inside of your walls, then install insulation and ONE vapor barrier on the inside of the walls, and tyvek or tar paper on the outside of the sheathing and your home will be efficient and run well.

there is a huge amount of research that goes into the "right" amount of breath ability for homes. one PhD researcher i heard was building experimental homes with OSB with taped seems covered in 1/2inch drywall on the inside of the walls and chip board on the outside covered in siding. she said she thought this was the best way to do it and had all kinds of sensors in the walls to verify different things. i believe she did create intentional leaks in one house to see how the walls responded, and it allowed the moisture to escape before rot started.

[timberwrestler]

Dave,

The whole vapor barrier craze of the 80s and 90s has fortunately disappeared (from the code too).  They now talk a little bit about vapor retarders, and they're divided up into classes.  But the main realization is that controlling air movement through your wall is significantly more important than vapor (so I'd agree with Jack as well).  See the attachment below.



Old houses worked because they were so leaky (to air) that if anything failed, the wind blowing through the walls would dry it out.  So, like Jueston wrote, it worked, but your effectively heating (or cooling) the outside of your house.

Vapor barriers or retarders can be omitted, necessary, or on different faces depending on where you're located.  There's some good stuff on here:
http://buildingscience.com/document-search?term=&field_doc_topic_tid=60

[davemellor]

Thanks to all who have replied.  timberwrestler: I have read a lot in the past at Building Science Corp and  Joe L there seems to really be on top of all issues related to moisture problems.  He definitely supports air sealing as you mentioned.  jueston: Makes sense - build it "right" so that moisture stays out whenever possible.  I lived all but the last 9 years of my life up North (including 26 years located 12 miles from Canada in northern Vermont), so I understand the northern climate.  If I'm correct, the Building Science Corp research says yes for vapor barrier on the inside of wall assembly in northern locations, but in southern (hot/humid or mixed/humid) climates, the vapor barrier should be on the opposite side of the wall assembly, i.e. the exterior.  Joe L rants about this when he talks about something he calls the top ten problems in building design or something like that.  One of his 10 is the fact that lots of homes in the South have been designed by folks from the North. By trying to apply principles that are good for the North, homes were designed that failed to perform in the South.  Some people say that the building codes in the South often contain ideas that are more applicable in the North.