Vapor barrier in addition to paperbacked in MS??

2695 Views 15 Replies 4 Participants Last post by forcedreno2012, Apr 25, 2013

forcedreno2012

Discussion Starter · Dec 15, 2012

Is it advisable to add an additional plastic vapor barrier to the paper backed insulation for a house in MS? The exterior walls are wood siding then foam board then the insulation and then drywall.

When we put the insulation back is it worth putting a plastic vapor barrier between the insulation and the drywall? I know this is common up north with the winters but would anything be gained by doing this down south where it gets really humid.

THanks

1 - 16 of 16 Posts

Gary in WA

· #2 · Dec 15, 2012

No plastic vapor barrier or vapor retarder. Paper faced insulation is fine if not asphalt covered paper faced, keep it vapor open to dry inside, pp.14; http://www.buildingscience.com/documents/guides-and-manuals/gm-guide-insulating-sheathing

Other helpful hints, pp.31-33 and all the rest; http://www.buildingscience.com/documents/houseplans/hp-hot-humid-recommendations

Gary

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Windows on Wash

· #3 · Dec 15, 2012

Putting a vapor barrier in your climate on the cold side wall would be about the most disastrous thing you could do.

If you were going to have any vapor barrier, it would be on the outside wall and not the inside wall.

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forcedreno2012

Discussion Starter · #4 · Dec 16, 2012

Thanks guys,

So if I am interpreting this right, no plastic vapor barrier and for the paper backed insulation put the paperside to the outside of the house. If this is true how do you staple the stuff when installing? - smoosh it in then staple then fluff or have I really got it backwards?

Windows on Wash

· #5 · Dec 16, 2012

Whats the exterior of the home construction?

forcedreno2012

Discussion Starter · #6 · Dec 16, 2012

WOW , from the outside in....

Originally - it was wood siding, black brick board (some type of black board filled with almost like particle board cardboard) and then the framing and R-7 insulation then drywall and a million coats of paint etc.

Now - with the flood we have been replacing as much of the black board with a rigid foam as we have had to replace a bunch of siding. The foam board is white bout an inch thick and has silver backing on both sides. It has a whopping R value of 3. We are also replacing the R-7 we found with R-13 all the way up on the exterior walls, so I know this is an improvement. There is no house wrap of any kind. Not able to strip the walls at one time to put it on so we are doing as best we can.

Thanks

forcedreno2012

Discussion Starter · #7 · Apr 22, 2013

Getting ready to put the insulation back in and I don't think I got the final answer on where the paper on the insulation goes is it paper against the outside wall or the inside wall. They had it both ways.

Thanks

Nailbags

· #8 · Apr 22, 2013

You put it in paper facing to the warm side of the home in your case to outside wall. don't need to staple anything just put it in and don't squish the batts.

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forcedreno2012

Discussion Starter · #9 · Apr 23, 2013

Thanks.. that makes sense we had it the other way round in WV.

Gary in WA

· #10 · Apr 23, 2013

Page 14 in the first link given in Post 2 explains it well... what type of wood siding?

Gary

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forcedreno2012

Discussion Starter · #11 · Apr 24, 2013

Sorry WOW I did read the article back when you posted it and promptly forgot. We hoofed the bales of wall insulation into the house today. Heck those things weigh a ton when compacted.

The wall is from outside in

Wood siding 4 x 8 grooved sheets 1/2 inch thick.
Brick insulation (bout r - 3)
and then the studs and the soon to be insulation.

Robyn

Gary in WA

· #12 · Apr 24, 2013

Usually, the T-1-11 structural siding goes directly on the studs for for shear value. The black Celotex was under what?http://www.inspectapedia.com/structure/Fiberboard_Sheathing.htm

What siding was removed, brick veneer?

Gary

Reactions: 1

forcedreno2012

Discussion Starter · #13 · Apr 24, 2013 (Edited)

Gary the house was moved to its current location a few years ago. It was actually brick that was removed and not a veneer.

The fiberboard is behind the wood siding the fiberboard is nailed in and then the wood siding is over the top of that.

As we have replaced the siding with the flood issues we have replaced the brick board with a foil backed foam of the same thickness. I would say that over the last year we have replaced approximately 80 percent of the brickboard. As for the shear factor, you should by stock in screws...those panels are NOT coming off short of a tornado. We even went over where the other panels were nailed in and screwed those in as well for added protection. (And I have drill blisters to prove it :laughing

Robyn

forcedreno2012

Discussion Starter · #14 · Apr 24, 2013

And thanks for the link. Interesting that there are so many different kinds. was interesting to read that none of them like water..but I think we know that.

Gary in WA

· #15 · Apr 25, 2013 (Edited)

Is it T-1-11? That product requires installation directly on the studs/underlayment plywood. You cannot get shear value at the corners/every 25' through the foamboard. Foamboard, especially foil-faced is wrong in your proposed application;
"in the old days, before foam sheathings and OSB, moisture was redistributed into the exterior sheathing (board sheathing, plywood, and fiberboard) relieving the moisture stress on wood siding that happens when the front is really dry and the back is really wet.

This hydric redistribution does not happen with wood sidings over foam sheathings, especially ones with a foil facing. Airspace is necessary to help redistribute the moisture. Not much of an air space, 1/4 inch to 3/8 inch, will do." From; removed bad link.

You need sheathing at the corners for wall shear resistance and an air space between f.f. foam/T-1-11; http://www.buildingscience.com/docu...for-insulating-sheathing?searchterm=sheathing

http://www.buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh/?searchterm=foam%20board%20in%20walls

Fig.6, pp. 11, the foamboard will act as your drainage plane:http://www.buildingscience.com/documents/reports/rr-0412-insulations-sheathings-and-vapor-retarders

Gary

forcedreno2012

Discussion Starter · #16 · Apr 25, 2013

Gary thanks for the links - will review....just as an FYI, one of top two links has a Trojan virus on the page. My filter caught it. If you didn't get the warning you might want to run a virus scan.

I am not sure if we have the true t 1 11 or the other type, I know its 1/2 inch thick and weighs a freaking ton. I know its not the thin version that I have seen on houses. Hope that makes sense.

We have 1 x 4 trim at the top and corners of the house and we have 1 x 6 on the bottom. All of this trim is over the top of the siding and its all screwed in and not nailed. The trim is also PT. There is additional bracing inside the corners of the house as well. There are no exposed ends per se on any of the edges of the house or sheathing. Its very secure.

The bottom trim is sealed to the bottom plate with roof tar really thick and all seams, trim pieces, windows, screw holes etc have been caulked. The house has one coat of primer and two coats of latex paint. So I think its pretty waterproof... well as much as we can make it.

Also of note the studs in this house are not regular pine they are made of a hardwood - cant remember the name. This stuff is really heavy and really hard to cut.

Sorry for the ramble.

Robyn

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