Vapor Barriers - US West Coast

[NorthCivil]

I am wondering what is standard practice for residential wood frame construction on the US west coast. Are vapor barriers or vapor retarders required? if so, in which areas?

Vapor barriers are always meant to be on the warm side. In Canada and other cold dominated climates, where interior heating is common, vapor barriers are required on the inside. In florida, I assume vapor barriers are required at the exterior face?

I am wondering what standard practice around the US west coast, particularily between seattle and southern california, marine, humid environments where the weather is mild and there is not a drastic demand for heating or cooling, or (usually) a very large differential of temperature between inside and outside. what do your codes require? what do you see on projects where you have a dedicated envelope engineer?

Apologies if this is not the appropriate forum, this site could really use a dedicated building envelope/building science/building enclosure engineering forum.

 

[msquared48]

Definitely in crawlspaces and against exterior concrete basement walls retaining earth.

Mike McCann, PE, SE (WA, HI)

 

[DBronson]

NorthCivil:

You might want to investigate this web site:
Link They have dozens of papers on best practices in these climate zones. Note that Seattle(Marine)and Southern California(Hot-Dry) have very different climate regimes and construction practices.

Regards,
DB

 

[Earth314159]

On the "wet" (the west coast) coast of Canada (same climate as Seattle), it is on the inside by code but that is not necessarily the best practice. There were huge problems on the wet coast for buildings without a rain screen and the poly on the inside. The poly is still on the inside but new buildings almost always have a rain screen. Rain screens are added where ever possible on existing buildings.

 

[NorthCivil]

Good day all, thanks for the responses

I am aware that BC requires vapour barriers, and that they are likely not required in LA. I am aware of cavity construction (rain-screens). My primary interest is with what climates internal moisture becomes a problem that a vapour barrier solves, and where on the map the line is drawn on using or not using a vapor barrier. I am sure there is a large grey area somewhere between Portland and Santa Barbara where you may be able to get away with or without using one.

I have opened up quite a few older 2x4 timber frame homes in the lower mainland of BC, built before vapour barriers were used, and rarely have i seen damage from interstitial condensation. might not see the same thing if you opened up walls built without vapour barriers in winnipeg though.

 

[Earth314159]

I happened to live in an old house (built cira 1930) in Winnipeg a long time ago. The walls were lath and plaster, studs and newspaper, sheathing, paper, thick stucco with heavy wire mesh. They are very leaky (air leaky)and bone dry. There is not nearly as much insulation as you would expect for Winnipeg. The climate is bit different now but the cold air would leak through the walls and get really dry (skin irritatingly uncomfortably dry all winter long). This was typical construction for the neighbourhood and rot was not an issue.

 

[jayrod12]

I can confirm that older homes in Winnipeg have no such vapour barrier. Even up to the late 50's all they used was the kraft paper lined insulation stapled to the studs. But due to the fact there was nothing but black felt paper on the outside, diagonal 1x6 wall sheathing etc. the amount of air movement has minimized any damage I have seen in my years renovating and consulting.

Today's construction methods almost make matters worse if they are not constructed perfectly. Now we have interior poly, batt insulation, fluid applied vapour-permeable exterior membranes, rain screens etc. Once moist air gets into the wall cavity it has almost no way out. But damn are these new homes less drafty and cheaper to heat in comparison. Personally, I'd prefer the draftiness to never having to replace a rotten piece of wood again.