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Vapour Barrier on House Overhang

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Posted by: from Coquitlam
1/15/2012 at 12:22:31 AM

My house is a 1 story with front door entrance on the main level. My living room is over top of the front door entrance. There is an area 10'X6' overhang covering my front door entrance. The overhang at one time used to be part of a wrap around sun deck but previous owners enclosed this area and extended part of the living room.

I replaced all of my soffits last year and when I removed the original wooden soffit underneath this overhang there was no insulation and no vapour barrier. I poked my head up between the joists and I could see completely through my house down the joists from a ladder at my front door.

Question, I want to add Roxul exterior wall insulation between the joists in the outside underhang part and then add a 6 mm vapour barrier attached to the bottom side of the joists on the outside overhang area only, then cover with a non-perferated vinyl soffit. I am wondering if this will trap moisture with the vapour barrier on the bottom of the joists between the soffit and the joists. Thoughts on what I need to do on this area?

REPLIES (6)
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Date/Time1/16/2012 at 9:54:21 AM

Hi there,

Sounds like the original contractor didnt know what he was doing when he closed in the porch. Installing batt insulation is the cheapest, least effective way of insulating it from the cold.

Best and really only solution is to spray foam it, costly but outweight the performance of batt any day.

Cheers

Good luck

Joe

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Mark in Coquitlam
Date/Time1/16/2012 at 11:49:32 PM

Joe,

Thanks. When I removed the original soffit there was no insulation at all. I installed Roxul insulation and then a vapour barrier on the bottom of the joists, then cover the area with new vinyl soffit material.

My question was should I have placed a vapour barrier or not. I was thinking perhpas I should have used insulation with the hard card board on one side that acts like a barrier and would be placed first up into the joists?

Thanks

Mark

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Date/Time1/17/2012 at 12:56:45 PM

Hi Mark, sorry to be the one to tell you this as it could mean a lot of work for you. The vapour barrier should be on the warm side of the insulation to stop warm, moist air from reaching the cold and turning into condensation which could then turn into mould if there are any organics. You may be able to re use the Roxul if you pull it out and apply the vapour barrier first, then re install the insulation. Another way is to open everything up and have 1.5 - 2" of closed cell spray foam applied on the underside and in the joist cavities, then re install the Roxul. This would give you the best possible air / moisture barrier and about R8 to R12 insulation to start with.

I know it is a PITA to re do your work but it really is the only way to go.

Good Luck with it!

Jim Kuzma

Kettleby Handyman Services

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Mark in Coquitlam
Date/Time1/17/2012 at 2:09:56 PM

Jim,

Thanks and this is what I supected may be required. Not a big job to redo fortunately and hope it is not too late (4 months ago I installed the vapour barrier).

I have another similar job to do in my covered garage with living space above but htis one was from a previous owner. I pulled down a section of drywall as I installed a garage door opener and noticed on the garage ceiling and noticed that there was a vapour barrier in place.

Sounds like I should be spray foaming the entire garage ceiling between the joists and then adding Roxul, and then dry wall. No vapour barrier along the joists correct even underneath the living area in the gargae and even underneath the non-living area of the garage?

Thanks again.

Mark

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Date/Time1/18/2012 at 1:37:25 AM

Hi Mark,

You are correct. If you spray foam, that is the vapour barrier and you don't need another one. If you can do the garage and the overhang at the same time, you may save a few bucks by getting the foam done all at once. If you have ductwork running through your garage ceiling, get the foam guys to encapsulate it with at least 2".

When you re install your drywall in the garage, make sure you seal it completely. Any penetration could be a huge safety issue.

Good Luck with it!

Jim Kuzma

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Date/Time1/24/2012 at 12:42:41 AM

Hi Mark,

I sent another reply with a reference to a great website for info on this kind of stuff. Apparently that is not allowed on this site as it never got publicly posted.

If you want, you can go to my profile and request a quote with your e-mail in it. I can then get the link directly to you. The company I was going to point you to is called Building Sciences Corporation. If a search gets you to their site, you can spend a long time reading more than you will ever need to know in their information section.

Good Luck with it!

Jim Kuzma

Kettleby Handyman Services

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