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Old 11-19-2012, 07:11 AM  
drewdin
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Default Lets talk about vapor barrier!

So it is required by the code in my town that I have to have a vapor barrier between the sheetrock and insulation. BUT, everyone I talk to tells me that vapor barriers are bad and they don't let the house breath, if I install it I will have nothing but problems.

SO my question is, who is right? What steps do I need to take to make sure I don't get problems since it is required by code or is it an old wives tale? Thanks!



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Old 11-19-2012, 10:33 AM  
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In some areas it is not a good idea, but if your code wants you need it. Breathing can also be called air lose, or drafts. Out here we put outlets and swithches and lightfixture boxes in a plastic covers on the outside walls and ceilings. Our houses do breath, we are required to have a hole in the outside sheeting in every stud bay behind the house wrap.



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Old 11-19-2012, 11:41 AM  
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Posting your location would help. The general rule is the vapour barrier goes on the warm side. So if you are down south the vapour barrier should be on the outside.

If code requires it you don't have much choice . In stall it as they require.

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Old 11-19-2012, 07:52 PM  
nealtw
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drewdin; Anything else you want to talk about?

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Old 11-21-2012, 08:07 AM  
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I am in Boston MA, so it gets hot and humid in the summer and very cold in the winter. The house was built in 1927 so there are holes and drafts all over since the outside board is in 12" strips. I tried my best to use spray foam and close as many gaps and holes I could but there are still a ton.

I just wanted to see if there are any tips or tricks since I have the house gutted down to studs. I have the insulation 90% up and I am about to put up the vapor barrier since it is required by code.

The plumber, electrician, father and others keep telling me to poke holes in the vapor barrier to prevent the house from getting extremely humid in the summer, but I don't understand how the vapor barrier would make the house humid. If the windows are open or the AC is on, what does it matter if there is a vapor barrier? Thanks

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Old 11-21-2012, 10:07 AM  
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Its the winter that is the problem. The warm air inside will be warm and holds moisture and there will always be gaps in insulation like studs and air leaks. When your warm air meets cold moisture will condence, you want to keep it that out of the framing and insulation. The biggest problem area is around windows, people often don't do enough to keep moisture out of the framing. When they find mold or rot they think the the had rain infiltration but likely it was condenstion. Old house did breath, get wet and dry out but now with the insulation we do it just cannot dry out fast enough.

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Old 11-21-2012, 11:10 AM  
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This will give a better explanation.
http://www.energybooks.com/pdf/D1142.pdf

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Old 11-21-2012, 01:59 PM  
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Thanks, that's a good read, i feel more comfortable about installing it. I don't understand why the electrician and plumber are so much against it. I will have to ask them their reasons or maybe they didn't install it right

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Old 11-21-2012, 04:42 PM  
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Old timers remember when, houses didn't have freash air for fire places and furnaces and the sort. The fire drew air from outside with the many leaks in the uninsulated walls and leaky windows and doors. Now we don't notice cold drafts because we have warm moist air trying to get out.

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Old 11-29-2012, 07:44 PM  
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Zone 5, this earlier answer on another forum will help you:

With Roxul or f.g., you need a vapor retarder, per code for your location;

"R601.3 Vapor retarders. Class I or II vapor retarders are required on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4.

Exceptions:

1. Basement walls. 2. Below grade portion of any wall. 3. Construction where moisture or its freezing will not damage the materials." Underline is mine. From: http://publicecodes.cyberregs.com/ic...001_par003.htm

Since the wall is above grade (daylight basement) add the asphalt- faced f.g. or "Membrain" with Roxul; http://www.bestofbuildingscience.com...3-4_p37-40.pdf

The degree of vapor retarder depends on the cladding and foamboard, what do you have for siding? http://publicecodes.cyberregs.com/ic...9_6_par005.htm

May get by with just latex paint on drywall; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_6_par006.htm

Gary
P.S. Depends on the RH in the room as WoW said, cover the studs with a Class 2 against high humidity. ADA the drywall: http://www.buildingscience.com/docum...wall-approach/



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