rafter baffle height for blown insulation
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    rafter baffle height for blown insulation

    Trying to figure how long to make my diy rafter battens (protected air space for eave vents into attic). Going to make them out of 1/2" foam board. Want them to extend high enough so that when installers blow insulation, it is unlikely that they will get the insulation into the "protected" air cavity, so I'd think it should be something like x inches above target insulation height. First time for me to use "blown", so no idea on how "controllable" it is. FWIW: no ceiling at this point - just framing; doing this pre-drywall.
    Last edited by dianedebuda; 02-11-2017 at 09:26 AM.
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    I just had a house built and the contractor used a cardboard premade barrier. It's about 2 feet high. I would go to a building supply and see how much they are before creating one. Time is money too. My insulation is blown as well and it appears it was highly controllable because they put it exactly where it was needed and there isn't much excess lying in the areas not needed. If you have not put on the roof, I would consider using boards that have metal foil on one side. It serves as insulation and really cuts down on the heat in the attic and reduces cooling costs. I moved from Texas in 2015 and a lot of new construction was doing that or installing a radiant barrier in existing homes.

    I looked in my attic and can't get over close enough to see what the brand name of the cardboard form is. Sorry about that. Good luck with your project.
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    You can get premade foam troughs from any home center for 16" or 24" on center rafters. They press fit into the void between the rafters and leave an air space for your ventilation. No need to make your own.

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    foam rafter baffles in Frederick, Md. they are 2.00 each for 23.5" x 48" .........if you have material laying around that you want to use up go for it . Are Insulators include this service when insulating a house or a retro attic job. Make sure you do it right. We also have an Insulation inspection in my county before drywall can be installed. Right strict here on application of ALL items involving insulation and air intrusion.
    Last edited by patchnball; 02-11-2017 at 10:20 AM.
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    Cannot use premade baffles because rafter spacing is non-standard (sistered 4x6 cedar rafter tails). Also about 4 ft of the eave end of some of the "rafter cavities" have to be partially filled with batts which means the protected air gap is lengthened - guessing 8 ft. Cause: sissor trusses with ridge & pitch not same as roof means space on one side is too small for installers to physically access - think partial vaulted ceiling. My installers do not do baffles. They were recommended to me by my long-time HVAC guy for my non-standard ducting design & install. I was happy with their duct work and think it'd be wise to use them for the insulation since they "know" my setup already. I'm kind of OCD about the ventillation anyhow.

    No inspections here, but I try to "do it right".

    Thanks for the thoughts.
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    Quote Originally Posted by dianedebuda View Post
    Cannot use premade baffles because rafter spacing is non-standard (sistered 4x6 cedar rafter tails). Also about 4 ft of the eave end of some of the "rafter cavities" have to be partially filled with batts which means the protected air gap is lengthened - guessing 8 ft. Cause: sissor trusses with ridge & pitch not same as roof means space on one side is too small for installers to physically access - think partial vaulted ceiling. My installers do not do baffles. They were recommended to me by my long-time HVAC guy for my non-standard ducting design & install. I was happy with their duct work and think it'd be wise to use them for the insulation since they "know" my setup already. I'm kind of OCD about the ventillation anyhow.

    No inspections here, but I try to "do it right".

    Thanks for the thoughts.
    You may be able to staple several ready made baffles side by side to get the width you need. They make the ready made ones for 16" and 24" centers. For 4', staple two 24"er's side by side.
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    If you make your own, I'd recommend at least 24" long.

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    Standard length is 48" to go into he eves and extend fully to any insulation depth.. The length depends on your roof pitch, (shallow requires more length up the rafters to compensate for the low pitch and I wouldn't go much less than 48" anyway). By the time you get the baffle into the soffits, install wind wash blockers to stop the blown in insulation from going into the soffits and wind blowing your blockers back you may end up with a very little amount showing.. It has been stated, to just use two baffles, I agree with that, making your own will cost you more than buying them and you don't need 1/2" foam to work. Think of how long it will take you to fashion a baffle so it's strong enough and also how you staple it to the sheathing.. Lots of bends to deal with on the make your own foam baffles.. never mind the staple length to hold them in place.. Remember you need to go to the outside of the wall with insulation not just to the top plate so you want to extend the baffle quiet far into the soffit. 24" may work but don't be fooled, the blowing of any insulation is messy and not a science to an exact spot, some may go into the baffle, best to get 48" and be safe and have no worries about that.. I would go with the 48" pre-made vents any brand will do as long as they are made of a foam product like expanded polystyrene.. or EPS foam or plastic. Good luck with your project..
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    IMHO, too much effort trying to use flimsy preformed battens compared to site-built for this situation. Bought a bunch of 1x2 for a project 30 years ago that didn't happen, so that makes it pretty easy. Have framing stapler, so just staple 1x2 to rafters as an upper stop, insert the foam board cut to size (18x48 or 18x48 + 22x48), then staple another 1x2 as a bottom holder. A sandwich! (wrong thread here?) Net result is 2" vent tunnel.

    Don't have soffits - venting is in eaves above top plate. Already have a pair of 2x4 as an inverted T nailed to top plate (no more 'coon invasions, please) leaving 2"+ for (screened) venting the entire length per side.

    Was able to contact my installer today & he said 10" beyond top of insulation was good for baffle extension, so my initial guess of 48" length for the flat ceilings is almost perfect.

    Thanks for brainstorming with me.

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