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vapor barrier

woodandiron's picture

vapor barrier (post #205595)

woodandiron on Mon, 01/09/2012 - 07:42
in

   I am planning to build a new house.  Location is the Puget Sound area.  It's pretty damp here about half the year.  If I use dense pack, sprayed in celulose insulation, should I use a visqueen vapor barrier on the inside walls and ceiling?  I have read both yes and no to this question.  What are your thoughts and exoperience?  Thanks, Jim

-A +A

You're in what the building (post #205595, reply #1 of 11)

by rdesigns in reply to woodandiron [original] on Mon, 01/09/2012 - 09:28

You're in what the building code classifes as a 4-C climate zone. (the "C" means marine), and this means you will be required to have a vapor retarder on the inside of the wall assembly. (ref:  2009 IRC, section R601.3) 

This requires a Class I or Class II vapor retarder. (Class I retarder example:  Sheet polyethylene, unperforated aluminum foil; Class II example:  Kraft-faced FG batts.)

However, you could use a Class III vapor retarder (Latex or enamel pain) if your outside cladding/sheathing meets certain requirements:

     Vented cladding over OSB

     Vented claddng over plywood

     Inslulated sheathing with R-value at least 2.5 over a 2 x 4 wall

     Insulated sheathing with R-value at least 3.75 over a 2 x 6 wall

If I were you, I would not (post #205595, reply #2 of 11)

by Piffin in reply to woodandiron [original] on Mon, 01/09/2012 - 17:36

If I were you, I would not use a VB, but a vapor retarder only.

Another ? is if you will use AC or whole house air exchanger system or not.

 

You might want to study up at the building science site before deciding on all the details

 

 


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I am also in the Puget Sound (post #205595, reply #3 of 11)

by sapwood in reply to woodandiron [original] on Tue, 01/10/2012 - 09:29

I am also in the Puget Sound area. Having come here from a very different climate, I did a lot of research regarding the vapor barrier issue. My conclusion is to not use one. Let the wall dry to the inside. 

I hope you are also looking into using a rainscreen on the exterior of your new construction. 

      I would like to use 1" (post #205595, reply #4 of 11)

by woodandiron in reply to sapwood [original] on Wed, 01/11/2012 - 14:55

      I would like to use 1" of ridgid foam board over osb then a rain screen with verticle cedar 1x6 for the finish siding.  Any ideas on how to do this properly?  Thanks,  Jim

In that case, you DEFINITLY (post #205595, reply #5 of 11)

by Piffin in reply to woodandiron [original] on Thu, 01/12/2012 - 04:52

In that case, you DEFINITLY don't want a VB on the interior

Lots of ways to do it. I like four foot long lathe strips run horizontally with spaces 1/2" to 1" betweem them to create the space. Some places sell them in PT lumber. With a table saw, it is not hard to make good use of scrap

 

 


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When doing a horizontal (post #205595, reply #6 of 11)

by xxPaulCPxx in reply to Piffin [original] on Thu, 01/12/2012 - 10:32

When doing a horizontal rainscreen lath strips, how do you ensure water has a path out instead of puddling on the board?  Do you gap and stager them like bricks, or do you kerf weep slots, or do you angle them so water has direction back off th board?

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Notice I wrote to keep 1/2 to (post #205595, reply #7 of 11)

by Piffin in reply to xxPaulCPxx [original] on Thu, 01/12/2012 - 11:37

Notice I wrote to keep 1/2 to 1" spaces between

 

 


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What about using 1" horizonal (post #205595, reply #8 of 11)

by woodandiron in reply to Piffin [original] on Thu, 01/12/2012 - 18:31

What about using 1" horizonal naiing strips between the 1" foam boards, then covering the whole thing with "Rain Slicker", or some equal product for the water shedding surface?  I must mention that I have no experience with these methods and products.  I last built a house 22 years ago, in a totally different eco system.  I have a very limited budget and will act as my own general contractor.  I'll sub out the foundation, framing, plumbing, and electrical.  The house will be 1600 sq. ft., +or- a few.  Jim 

Yes, I saw that... I was (post #205595, reply #10 of 11)

by xxPaulCPxx in reply to Piffin [original] on Fri, 01/13/2012 - 10:39

Yes, I saw that... I was wondering if you had to do anything else though.  Part of my curiosity is that I don't know how much water actually gets back there.

It sounds like "So little gets back there that you don't have to treat it like a gutter"

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Yes (post #205595, reply #11 of 11)

by Piffin in reply to xxPaulCPxx [original] on Fri, 01/13/2012 - 14:37

If you get a tremendous amt of water there you have a much larger problem.

The idea is just to let siding dry to the back side. It will deform less that way and not stain of feed rot or provide a better damp spot for wood destroying insects like ants and powderpost beetles.

 

Some water will get behind siding in a hard driving rain as wind pushes it htru and that will find a way to drain down. A lot depends on siding type. B&B has gaps behind thebatten and cedar shakes or shingles have hundreds of gaps.

 

 


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I believe that Cor-A-Vent and (post #205595, reply #9 of 11)

by sapwood in reply to woodandiron [original] on Fri, 01/13/2012 - 09:23

I believe that Cor-A-Vent and others make plastic batten material that drains vertically. Piffins idea is less costly, I think. Personally, I like the battens to be vertical with horizontal siding. I used green 1x4 cedar as battens with cedar over for cladding. My wrb (Vapro-Shield) was behind the battens and over the xps foam.

For economy's sake here in the PNW, think cedar. It's readily available in many forms. Some mills sell direct.