# Insulating a valley



## altann (Dec 20, 2011)

I have an exposed valley in the master bath about (5 square feet) that I need to insulate what would be the best way? There are 4 rafter bays in this the ends are not open to soffit vents. Also this is on the north side of house so no sun to heat up the roof. Cold climate area.
Thanks


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## joecaption (Nov 30, 2011)

Not sure what your really asking. Since a valley is on the roof what does that have to do with insulating the ceiling in that area?
In that small an area it should be fine if there's no soffit vents as long as the rest of the roof is vented properly.


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## altann (Dec 20, 2011)

*valley*

Ten foot ceilings in bathroom and in one corner the valley is exposed running up through to attic. 
Thanks


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## joecaption (Nov 30, 2011)

A picture may help on this one.


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## seeyou (Dec 12, 2008)

joecaption said:


> A picture may help on this one.



He's got a vaulted ceiling with a valley in it. 

I'd say closed cell foam would be the best bet. Is the ceiling down?


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## altann (Dec 20, 2011)

Valley is in corner over bathtub 10 foot ceilings through out. I was wondering if I was to use pink fiberglass should proper vents be put in just to keep insulation away from underside of roof plywood? Attic is well vented other than valley areas. Also 2x10 rafters


Thanks


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## glkirk (Jan 5, 2012)

Yes, keep insulation from touching underside of roof sheathing. I don't think you need to worry about ventilation. It sounds like its a small area not ending at cornice or ridge.
As a builder I am supposed to tell you that you need R38 insulation. I don't know if 2x10s will work. You may have to fur down.
BTW Why are you having to do this? Why didn't the builder do it? Are you aware of all the sealing and insulation requirements?


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## jmiller (Nov 19, 2010)

glkirk said:


> Yes, keep insulation from touching underside of roof sheathing. I don't think you need to worry about ventilation. It sounds like its a small area not ending at cornice or ridge.
> As a builder I am supposed to tell you that you need R38 insulation. I don't know if 2x10s will work. You may have to fur down.


As a builder you should also know that IRC code requires ventilation, and there is no exception for being a small area or not ending at the eave/ridge. r806.1 http://publicecodes.citation.com/icod/irc/2012/icod_irc_2012_8_sec006.htm

A cathedral valley (yes I made that up) over a bathroom on the N side in a cold climate == ice damming.

CC spray foam applied directly to the underside of the roof sheathing would be the best solution, partly because it's one of the few options you have, but also because it is the best guarantee (IMO) that none of the warm humid air from the bathroom will get to the underside of the roof sheathing to melt accumulated snow and cause ice.
http://publicecodes.citation.com/icod/irc/2012/icod_irc_2012_8_sec006_par004.htm 

My only concern would be that valleys tend to be one of the most leak prone areas of the house, and a leak could go unnoticed for longer due to the foam.


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## altann (Dec 20, 2011)

*insulate valley*

This area of valley is about 25 square feet. I'm looking into spray foam sprayed on the underside of roof plywood. There are no soffit vent in this area because of valley. Only 4 rafter bays 4 feet long until they reach attic space. If I spray foam this area should I back it up with fiberglass insulation to meet sheetrock or fill the 2x10 rafter bays with spray foam? Also before sheetrock should a plastic vaper barrier be installed? And blocking where rafters meet cold attic?

Thanks


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