How To Use Baffles On Uneven Rafter,ceiling Joist Spacings - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 07-22-2009, 01:07 AM   #1
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how to use baffles on uneven rafter,ceiling joist spacings

FIRST off,very small house--- that being said, My 2X4 roof rafters are reduced to about a 2" birdsmouth over the double top plate of the wall.

I have NO eaves or overhang but am adding that right now and going to use continous vent allum. soffit. Soffits will be about 10",,, birds mouth area still 2"

BUT issue is roof rafters are random spaced generally at 22-24" spacings and ceiling joist which is also attached to top plate is 16" OC ,,,so I have ceiling rafters right where the end of the baffle would be. OR do you cut those around ceiling rafters and staple fast to their sides?? (NO sheetrock anywhere,all open,for now.

So outside foot or so isnt going to have minimum insulation required,or do I have to do something else there to meet min insulation standards??

Borrowed this drawing from another thread. So have about 2 inches of 2X4 (in birdsmouth area) holding this outside 10 inches or so,,,about foot and a half or more sticking up sistered to existing rafters. Do I need further support in this area??

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Old 07-22-2009, 06:08 AM   #2
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You should be fine with baffles every 2-3 spaces but retain all insulation possible over the top plate, fully covering it otherwise the home could sweat at the corners of the ceiling.
When venting rooftop, use either box type or ridge vent , not both , you can over vent and negatively effect the air flow.
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Old 07-23-2009, 06:59 AM   #3
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Cut the baffles to width, if needed, to fit in the rafter cavities. Then cut a slot for them to slip over the joists. They should extend down far enough to get past your insulation. You need a baffle in every rafter cavity that will have insulation. Any insulation past your top plate isn't doing anything for you. You can install more insulation in the rest of the ceiling to compensate for the light values at the eave edge. If the average coverage meets the R-value requirement, that is acceptable per code.

Last edited by Maintenance 6; 07-23-2009 at 07:03 AM.
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Old 07-23-2009, 07:13 AM   #4
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I put rafter vents in every bay
If 24" OC I use 24" vents, 16" OC I use 16" vents
I have trimmed the sides in some cases
You could put 24" vents then switch to 16" for a short distance near the rafter ties

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Old 07-23-2009, 12:41 PM   #5
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Use this site to find your roof's requirements.

All house ceiling areas should be insulated. I would use some rigid insulation board, box stores sell it also. Install in the areas next to exterior walls to replace batt or blown-in that wouldn't be enough or get compressed. Just leave the air space required for ventilation next to the roof sheathing. If using batts, just angle-cut the edge of the foam board the roof's angle, then start your baffles. If blow-in, run the baffles first, then the foam. Because it is so easy to work on, you could cut a foam edge to match the baffle's contour, a 4" high piece on edge to seal the gap that blow-in insulation would travel to access the soffit area. Be safe, G
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