Attic insulation soffit baffling

[ROBZ71LM7]

Hey all, I just bought a new house with an oversized, attached 3-car garage. The PO installed insulated garage doors and had it built with insulated walls, but did not insulate the attic. The ceiling joists are 2x12's and I intend to blow-in cellulose to a depth about 6" above the top of the joists. So where I'm at is I need to vent the soffits and block cellulose from falling into them. I was thinking of installing the baffles one of two ways shown, both with gaps in red that need to be sealed/blocked. Any suggestions? I was thinking of cutting 2' sections of unfaced batt insulation standign them up vertically and making contact with the soffit baffle/sheathing. Would this work? Do I need to vent every rafter opening?

 

[rburke65]

No expert here, but I don’t think you need to do every truss. They do make styrofoam baffles for this

 

[Notgrownup]

There should be wider foam baffle dams available and you can cut them and staple them 8n place ...

 

[CombatNinja]

I don't understand why you need a baffle. Those look like 2 x 8 joists, no? Just blow in up to the top of the joists and that is 7.5" of insulation, or are you trying to go 6" above the top of the joists for a total of of 13" of insulation? That is a LOT of insulation, up over R40. Where do you live?

Just reread your original post. So yeah, you are going for the 6" above the joists. With those being 2 x 12s, you realize that is going to be around R60. That is massive overkill, especially in a triple garage that has a huge amount of poorly sealed overhead doors to contend with. I would fill to the top of those joists for R40 and call it good.

That said, if you insist, you need to get the proper product, not those stupid styrofoam baffles. Those are for a completely different application than what you are looking to do. They sell cardboard dams for what you need. Barring that, get yourself some rigid foam board and make your own then seal with expanding foam along the edges.

 

[zak77]

I'd fill to the top of the joists and call it good. No need for baffles. My garage is completely uninsulated and it doesnt cost much to heat it for the season.

 

[CraigStu]

I think the main point of the baffles is to keep from blowing insulation onto the top of the soffit. I am imagining a guy w/ a nozzle would have too easy a chance of not being able to control the flow of insulation accurately enough for it to stop at exactly the right spot. This would be especially true when going for a depth that much above the tops of the joists. The baffle should sit somewhat like your second pic but w/ it being wide enough to staple to the bottom edge of the roof joists.

 

[Doug19]

I'm not expert but why no get a couple sheets of plywood and rip them down to a few inch strips and lay them down to cover a few openings with each strip.

 

[mike93lx]

my understanding is that code requires baffles in every bay, regardless of venting. As a lot of soffits are fully vented anyway, it just makes sense.

i would install the proper size styrofoam baffles and get to blowing in insulation. I'd go quite thick as well, as long as you don't need to use the space for storage.

before doing the insulation, do air sealing. otherwise you are going to have warm, moist air going up into the attic, building up in the insulation. that's even more important than the insulation itself. you can buy spray foam setups that use what looks like a 20lb propane cylinder...way more economical than the small cans.

to the OP, please add your location in your profile. it helps a ton when people are trying to offer advice that might be specific to your region

 

[welder4956]

I used the foam baffles from Lowes and found them to be a pain to install without tearing. If I had to do it over, I would rip 4 x 8 sheets of 1/4" plywood down the center lengthwise, lay them up against the face of the rafters and shoot 1" staples. You would need to remove those 2x4 kickers or notch the plywood around them. Heavy cardboard would be easier to work with if you can find it.

 

[dfiler2]

What we always did was staple the baffle in, then block the rest of the hole with a piece of fiberglass insulation. They do make baffles with a flap at the bottom too.

https://www.homedepot.com/p/ADO-Pro...O_c3efl7iU06KCC7jFRoCbKEQAvD_BwE&gclsrc=aw.ds

 

[1500hd]

Here is one type of baffle that is available that you DO need. Accuvent. Not sure why some are telling you that they are not needed?

 

[SundayFunday]

Looks like your trusses are on 24" centers and your pictures show a rafter vent made for 16" on center.
You can get 24" vents with a built in bend to cover the entire opening, but they are a bit pricey. Cheap way is to just get the plain 24" model and stuff the opening with unfaced fiberglass batt.

Here is a link for the bent version.
https://www.lowes.com/pd/ADO-Produc...VER6tBh0y9w-pEAQYAiABEgKs7PD_BwE&gclsrc=aw.ds


As for how many you need, you can never have too many. There is a real way to calculate what you need. Google attic vent calculator for many hours of fun reading.


Wow do I type slow! see the above posts for the same thing!

 

[rvieceli]

they make a 1/4 inch thin Styrofoam insulation sheet that is typically used under vinyl siding. Generally available most lumber or big box lumber stores. Usually 4 feet wide by 50 feet. Here is an example.

https://www.lowes.com/pd/Kingspan-I...d-Polystyrene-Foam-Board-Insulation/999972970

Cut it into strips the width you need and then install. You would run a strip perpendicular to your rafters. Staple the bottom of the piece to that double plate on top of your ceiling joists and then staple to the facing edge of the of the rafter. Installing that way leaves the whole rafter bay open to the soffit. If your rafters are on 2 foot centers you should be able to work off the 4 foot edge of the foam or split the pack down the middle and use whatever length you can manage easily.

This stuff has the advantage of being light and easy to work with and will do the job keeping the insulation where you want it.

Ron

 

[redidbull]

My understanding is if the soffit vent opening is covered you will not get air flow and the roof sheeting will rot. I am not sure it is as big a problem with blown in as it is with batting. The batting, 9.25" here in CT, will push up against the sheeting as you get closer to the soffit. Jim

 

[mike93lx]

My understanding is if the soffit vent opening is covered you will not get air flow and the roof sheeting will rot. I am not sure it is as big a problem with blown in as it is with batting. The batting, 9.25" here in CT, will push up against the sheeting as you get closer to the soffit. Jim

with blow in, the wind will wash out the insulation, leaving the top plate exposed to outside temps. that's why baffles are needed

 

[burleyfarm]

It appears that your rafters are less than 24” on center. I would first do an adequate sealing of all air intrusion points as previously mentioned. This can’t be emphasized enough.

I agree with a previous post to use a rigid under siding foam, 1/4” under siding foam would be rigid enough and rip it to fit between the bottom of your rafter sill plate and the first diagonal truss brace. Half inch foam would also work as would double bubble Reflex. I would avoid the cardboard baffles as I’ve seen a lot of failures with this product. Install it perpendicular to the rafters to reduce gaps and staple or nail to underside of rafter and firmly attach to rafter sill plate. This will allow you to go as high an r-value that you want. For proper venting make sure all rafter channels are vented.

Good luck.


Dave

 

[Raisedonadeere]

I filled the opening the OP circled in red with 2 foot lengths of R30 bat insulation folded in half, paper side out and paper toward the outside stuffed gently into that opening paper so as not to crush the Styrofoam baffle. Fit perfectly and the paper takes care of incoming air infiltration but is not long enough to trap moisture. Then blew cellulose.

I used that method because my roof pitch being lower than OP's would preclude working in that space to get a good fit of the baffles that fold to cover that opening.

This spring I had to remove some soffit to run some electrical and got a good view inside the soffit area. Clean as a whistle and those top plates are well covered with the insulation I stuffed in there. I stuffed it in so it actually protruded into the soffit space a bit so it would cover the top plate well.

I wised up on my matching garage build this spring by filling that space with pieces attached from the outside before soffit installed with 1.5" gap to roof sheeting. I am attaching permeable radiant barrier (for this purpose the impermeable might be better) to the osb pieces and then the rafters to within a foot of the roof vent. That keeps the blown in stuff at bay and my garage is going to be better insulated than my house

 

[Notgrownup]

I don't understand why you need a baffle. Those look like 2 x 8 joists, no? Just blow in up to the top of the joists and that is 7.5" of insulation, or are you trying to go 6" above the top of the joists for a total of of 13" of insulation? That is a LOT of insulation, up over R40. Where do you live?

Just reread your original post. So yeah, you are going for the 6" above the joists. With those being 2 x 12s, you realize that is going to be around R60. That is massive overkill, especially in a triple garage that has a huge amount of poorly sealed overhead doors to contend with. I would fill to the top of those joists for R40 and call it good.

That said, if you insist, you need to get the proper product, not those stupid styrofoam baffles. Those are for a completely different application than what you are looking to do. They sell cardboard dams for what you need. Barring that, get yourself some rigid foam board and make your own then seal with expanding foam along the edges.

Good point...that is a lot of thickness

 

[CombatNinja]

Yeah, way too much insulation for a garage unless he makes his living in it and it is located where temps get way below zero.

That said, there are a lot of people in this thread confused as to what those styrofoam baffles are for. They are 100% the wrong product for this application. They are for keeping an air channel open under the decking if the insulation (usually fiberglass batts) is getting installed under the roof decking between the rafters. This is usually done when finishing an attic or bonus room and will ensure airflow from the eaves up to the roof peak where a ridge vent or gable vents can vent it out. They are pretty terrible but allow contractors to meet code quick and cheap.
The OP is not finishing this space with drywall and flooring. He just want s to put blown-in insulation up on top of his garage ceiling.

Edit: in looking at it a 3rd time, if the OP fills the whole cavity of the 2x12 (11.5") and goes pretty much to the top of those 2x4s that make up that 'sill plate' (3"), that is a total of 14.5" of blown in cellulose which is about R50. OP, you are nuts if you insulate beyond that. Complete waste of time and money. But if you are bored because of Corona virus and stuck at home, knock yourself out.

 

[HotrodHR]

Just fill to the top of the joists. As someone already stated those crappy styrofoam baffles are just to allow air to make it into the attic because people layer insulation that blocks the air.

If you insist on putting something similar, just go to Lowes and buy some vinyl soffit material (of all things, go figure)... this stuff is 12" wide by 12 feet long. Run it along the top plate and staple or tack up against the rafters. This will help keep your insulation from blowing or falling into your soffit if you go above the joists. At $10 to $13 bucks each they will be cheaper and easier than those styrofoam baffles.

Just FYI, I installed those baffles in the attached space above my wife's garage in order to blow in more insulation. What a pain in the **** depending on the pitch of the roof... they're hold to hold and staple without breaking...

 

[ROBZ71LM7]

Thanks everyone, I'm in Louisville, KY actually. The rafters are actually on a 16" center but the baffles I bought were multi-use, unfortunately that meant 22" ones you split down the middle-useless. I did not pay attention to that until I went up to work.

The ceiling joists are actually 2x12". To get an R-38 rating that I want I would need ~70 bags of cellulose. Well ironically at 100 bags you get a price break of 30%, so 100 bags is the same price as 70 bags. So I'm going to end up with about ~R57. Overkill yes, but I have insulated overhead doors and am going to try to do double door seals. I intend to install a mini-split and run it most of the year.

I just sealed the outlet boxes, wiring penetrations and top outer sill plate with expanding foam.


The folded, 1/4" R-1 XPS foam board was a great idea. I picked up two 50' packages and roughly ripped it to 18" wide and stapled to the rafters with 1/2" T-50 staples. Super easy and will allow more than enough insulation to be installed. I just butted up the bottom against the wall top plate as the hurricane ties made it difficult to get completely flush.

 

[yeldogt]

Thanks everyone, I'm in Louisville, KY actually. The rafters are actually on a 16" center but the baffles I bought were multi-use, unfortunately that meant 22" ones you split down the middle-useless. I did not pay attention to that until I went up to work.

The ceiling joists are actually 2x12". To get an R-38 rating that I want I would need ~70 bags of cellulose. Well ironically at 100 bags you get a price break of 30%, so 100 bags is the same price as 70 bags. So I'm going to end up with about ~R57. Overkill yes, but I have insulated overhead doors and am going to try to do double door seals. I intend to install a mini-split and run it most of the year.

I just sealed the outlet boxes, wiring penetrations and top outer sill plate with expanding foam.


The folded, 1/4" R-1 XPS foam board was a great idea. I picked up two 50' packages and roughly ripped it to 18" wide and stapled to the rafters with 1/2" T-50 staples. Super easy and will allow more than enough insulation to be installed. I just butted up the bottom against the wall top plate as the hurricane ties made it difficult to get completely flush.

I was going to recommend plywood .. but, thick enough foam board will do the trick. Those vents are not needed for your application .... they don't really work for the application they say they are made for anyway.

That's another story ....

If you even want to use the space -- spray foam the roof deck and you will be good to go.

 

[paredown]

My favorite thing for blocking the end of joist bays are the plastic election signs that seem to sprout like mushrooms around here. Rip them to a good height--and then score and bend tails and staple those facing to the interior. I like to set them so that they line up with the outside of the plate so you are insulating the top of the wall cavity.

Use in conjunction with the styrofoam ones to keep some circulation on the underside of the roof deck if the insulation is going high enough that it will block air circulation.

You do want to keep the soffit vents clean and free of your loose pack.

 

[ROBZ71LM7]

110 bags of cellulose and a fiancé that still talks to me, for now anyways.

 

[burleyfarm]

110 bags of cellulose and a fiancé that still talks to me, for now anyways.

Looks like it worked out good for you. [emoji122]


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[burleyfarm]

Just finished installing the soffit baffles in my garage ceiling also and planning on blowing cellulose next week.


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[Notgrownup]

Went up in my attic above the shop yesterday and it was warm and dry...Rob, that looks good.

 

[Joemctag]

What I did was cut pieces of foamboard to stand upright. Try to get them snug. I used some dabs of latex caulk anyway. Really solid. I had a lot of 2” foam but 1-1/2 or even 1” would work. You could score and break off long strips of board 8”” or whatever wide and then cut them to fit with a handsaw.

 

[i4ni]

Don't over think it. Staple in the soffit vent. Fold a piece of fiberglass insulation over and tuck it in under the soffit vent then you're good. Works great