Reasonably Priced Materials for Site-Built Ventilation Baffles
I’m planning to do an air sealing and insulation retrofit project on my vented attic this spring (blown in cellulose insulation). Part of the job will be to build site built ventilation baffles.
With skyrocketing materials prices, I’m paying close attention to materials costs. Some options I have for the baffle material are (all CAD prices for 4×8 sheets):
1. 3/8″ sheathing plywood @ $42 / sheet
2. 5.2 (about 0.2″) mm lauan @ $16 / sheet
3. 1/4″ sanded plywood @ $27 / sheet
4. 3/4″ foil faced EPS @ 14 / sheet
4. 1″ Foil faced EPS @ $17 / sheet
5. 1″ Unfaced EPS @ $8 / (1/2 sheet)
Since I live in a cold climate (zone 6), I initially planned to use plywood for its vapor permeability but I balked when I saw the prices. Would the lauan be too flimsy?
The unfaced EPS seems like it would be easily damaged through handling in my cramped trus framed attic.
Anyone have experience with this? …or suggestions?
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Perhaps ease of install should be a priority?
https://www.adoproducts.com/vents
I'm not a fan of manufactured polystyrene baffles. I had to work with them a bit when installing some bathroom fans and they were very easily damaged during installation. Also, I plan to build-up rigid foam over the top plates to make-up for the insufficient heel in my trusses. This would be easier with a site built baffle approach.
Well you said that the area was cramped. You're still going to have to custom cut the spacers (creates the depth of the vent channel) as well as the width of whatever sheet good you want to use.
At least with this product you can still add insulation on top of the top-plate and you can easily cut/staple into place.
Patrick,
Are you sticking with blown-in cellulose on the attic floor? If so you only need baffles from the eaves to several inches above the cellulose, and the material's permeability doesn't matter.
Yes currently it's very settled and trampled fiberglass plus mouse droppings. We're going to get that all sucked out and replace with blown-in cellulose after air sealing and building new baffles.
Martin's article on site-built baffles makes the same point but he also says if there's any concern to use vapor open materials:
https://www.greenbuildingadvisor.com/article/site-built-ventilation-baffles-for-roofs#:~:text=Site%2Dbuilt%20ventilation%20baffles%20can,example%2C%20and%20can%20be%20sturdier.
I was thinking that the baffles might become a condensing surface with condensation forming on their underside that might then drip to areas where I wouldn't want it dripping. To be honest I'm not super concerned about it but if lauan would work, then it seems like a cost-effective approach that would also minimize the risks.
Patrick,
There's is next to no force on the baffles with blown cellulose on the floor. I don't think there are any bad choices among the ones you listed. Another option if done diligently is to simply use house-wrap.
For blown in cellulose, I've seen a few attics with just cardboard stapled in to keep the cellulose out of the soffit vents. I guess that was a standard practice in the 90's. Most of those installs held up, though a couple had gotten hammered by electricians and other trades doing remodel work later.
EPS probably isn't a good choice here -- it's not very sturdy and is likely to break.
Try hardboard, which is commonly available in 1/8" and 1/4" thicknesses. Hardboard is the same stuff pegboard is usually made of, just without the holes. A quick check shows 1/8" at about $9/sheet and 1/4" at a bit shy of $15/sheet. This material is pretty sturdy, and it's cheap. Hopefully it will stay cheap too :-)
Bill
Hardboard is a good option. I think the lauan should work well too if it is easier to get or cheaper.
Among pre-fab production Smart Baffle, made of corrugated plastic is much sturdier than others. You can also make your own equivalent from 4x8 sheets of corrugated plastic. There's some advantage to these in that they spring into place, so they needn't be cut to the exact dimensions.
Now if only I knew where the leftover political yard signs went, I’d collect these to go the corrugated plastic baffle route.
I think that would be the only way to make it work. I looked into those sheets and .157" x 4' x 8' sheets go for $50 a piece at the local big box building supply store #$@&%*!
I used 1/2" sheets of R-Max Polyiso, which I cut the long way into two 2x8 strips.
I then measured the width between each rafter bay at the approximate point I was installing the baffles - mine were not all the same, so I assigned each a unique number. I then added 3" to the width, and cut those pieces out of the 8' length of strips I had, numbering them with a Sharpie.
Once each piece was cut, I scored each side of each piece, about 1/4" + deep through the foil side, parallel to the 2' length, 2" from each edge. Then I snapped the pieces at the score line. This gave me a 2" high spacer on each side, and an attached piece of baffle (1" narrower than the rafter spacing to account for the 1/2" thickness of the polyiso.) These were admittedly a bit flimsy and I was somewhat worried if they would hold where I scored them as the plastic on the non foils side was all that was holding them
I then retreated to the attic. I inserted them into the spaces between the rafters, 2" side up to act as a spacer, foil side down to reflect. Most fit fairly tight with enough tension to temporarily hold. I used canned spray foam (red can) on the underside to secure them in place more permanently. The spray foam is applied at the upper end of the baffle on each side, so the bead hits the rafter, the 1/2" scored & exposed part of the 2" vertical leg and horizontal baffle, and the underside of the baffle. The bead extends as far as I could reach. Once cured, they are VERY secure, and the bead of spray foam makes up for any weakness where I scored them.
So far so good. They did not deflect when the cellulose was blown in.
Thanks for the advice. I don't know why but polyiso is not widely available and super expensive in my area. It runs about $40 for 1" thickness sheets. I wasn't able to find anything thinner anywhere. Might be because of the cold temperatures we get here and the drop-off in R-value.
I suspect that the score and snap approach probably works a lot better with foil faced polyiso than with foil faced EPS.
I think I'm pretty much settled on using the lauan and then I'll use some kind of foam to close at the top plate. My house has low heel trusses so I plan to also stack up foam at the top plates until I get enough height to get full r-value with the cellulose.
Scoring and snapping foil face polyiso still risks tearing the foil facer on the side opposite the scored line. I usually score, snap, then finish off the other facer with my knife before trying to seperate the pieces. It's somewhat similar to scoring and snapping drywall and being careful not to tear the paper on the opposite side of the sheet.
I've found the foil facers on polyiso are thicker than the facers I've seen on EPS too.
Bill
For our recent cellulose blow-in, I made my own baffles out of tyvek house wrap, and used an electric stapler to put it up. I stapled it on one side, then held it pretty tight against the other side, and gave myself a full 2" gap between the tyvek-baffle and the sheathing above.
It was cheap and very fast to install, not as resource intensive as plywood/rigid foam... but more importantly it's worked PERFECTLY.
We did initially purchase some pre-made baffles (3 brands) and they were so crappy. This was cheaper, stronger and the same install time.
Cellulose settles, so... although in some places our installer blew extra cellulose against the baffles, and I worried it was limiting the air gap it settled down pretty quickly, and my air gap was restored while not allowing any cellulose to blow into the soffit.
Although the (surprisingly) high power cellulose blower was shooting right at my baffles not a SINGLE baffle blew out. Admittedly, I used a lot of staples!
I bought a cheap plug in electric stapler just for this job. Yellow. Stanley maybe? And it was so fast and easy to use that... I could really go staple crazy!
**Side note**
During the cellulose blow I became quite friendly with out cellulose installer.
I spent the entire time in the attic with him (in full respirator.)
I'll tell you why:
They had to get TWO trucks to come up and bring more cellulose (compared to their estimate which I knew was spot-on because I built the house myself and knew the EXACT square footage of that attic). It wasn't hard to figure the AMOUNT of insulation they needed, it's printed on the bags!
So... how did they underestimate so badly. As we became more friendly, on a break, the installer explained exactly how they are incentivized.... he also explained that their estimates are always "right" because.... uh.... NO ONE hangs out in the attic with them for the entire blow. It's impossible to tell how much you've blown. He said, as a practice they've stopped using pre-markings for height. (I pre-marked heights, but even that... he could have just "drifted" up near the markers. You really can't tell). I used a rather ridiculous number of markers!)
He'd been blowing for years, and he said it never once happened to him that a customer hung out in the attic the whole time. This is a huge, national company and their incentive structure makes it so that EVERYONE is getting a lot less "blow" than they think they are paying for.
Just saying... if you really care about how much insulation you get up there, make sure you put in a LOT of markers and even then *either* pay for a lot more inches more than you actually want *or* hang out during the blow.
And... it's not a lot of fun hanging out up there (I was up there for 6 hours).