Rockwool batts insulation support
derekr
| Posted in General Questions on
https://www.lowes.com/pd/Common-23-5-in-Actual-23-5-in-100-Pack-Insulation-Support/1007637
will these work with rockwool insulation? If not what’s a similar price and easy to install alternative
do I even need any support since rockwool is a friction fit insulation?
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Replies
derekr,
You may want some support if the rock wool is going in a floor with nothing underneath. In those situations you can either cover it with a WRB, or run several lines of string stapled to the bottom of the joists.
Mineral wool will generally stay in place but can slowly wiggle out as the joist move over time. Some minimal support definitely helps. I've used poly webbing (the stuff for hanging ducts) for this that is simple to unroll and staple up.
I’m putting some in a 60 degree steep roof and it’s 24 OC so I’m going to be cutting the batts in half. I’m hoping the batts will be small enough and the roof steep enough that I wont have to secure them there, just in places where they are horizontal like my crawl space
Could I use canned spray foam around the edges of the batt? I think it could dry before the batt falls out
I wouldn’t trust that. While canned foam may hold the batt sufficiently that it doesn’t fall out completely, I think you’d still get sag. I would use something that supports the entire surface of the batt for best long term performance.
Bill
The spray foam wouldn’t hurt the batts though right if I did use it? Not concerned about sagging because drywall is going over it anyway, I just want it to be held in place for 3-4 months before drywall comes
I saw this video on YouTube and this guy didn’t use anything and all his batts are staying in place even 24 oc on the ceiling
https://youtu.be/_s9KwemrLkk
I've had no issues with mineral wool batts staying in place between dimensional lumber especially if you go up thicker.
With a 60 deg roof, it can't see it falling out. I'm not sure why you would cut them in half, you can wider batts for 24" spacing. The bigger issue is the dust from the batts which you don't want to be breathing, so best get a vapor barrier up right after the batts are installed.
I bought these at the end of 2021 during all the Covid shortages and it took 5 months for them to come in
The 16 oc was the only one I could get couldn’t get the 24 oc, so I said I guess I’ll just cut them in half, it’s good I bought them back then though because the r23 is almost double the price now from what I paid
I don’t need a vapor barrier at my location I’m in zone 3
The 14.5" tall strips of insulation most likely won't stay put. In that case, I would pick up a roll of the cheapest house wrap you can find and use that for support. Unroll and staple as you go along. As a bonus you can also tape the seams of the house wrap and caulk the perimeter as a backup air barrier.
Thanks, I’ll try it first without nothing to see if they stay, my thinking was since they will be cut in half they will be lighter weight and easier to hold themselves than if they were a full piece, they will be going deep between 2x12 rafters double stacked so it will take them awhile to fall out if they ever do I think
Wish I could have got the 24 OC now but at the time price increases were happening like every week it seemed like and they had no idea when they would be able to get the 24 oc batts, it could have been 10 months or 2 years and i didn’t want to imagine what the price for batts could be by then plus I was ready to build so I ordered what I could get even before my house was finished framing
I’ve used those supports with mixed results. The insulation batts tend to bulge or sag in the center between the joists, and the thin wire tends to do the same thing. If your batts are the same thickness as the joists are high, I would not use them. Where I did find them useful was under a radiant heated floor, to hold a layer of insulation to improve the heat transfer to the floor vs loss in the joist cavity. In that case the batts were only half the height of the space and I could bow the support upwards with a very thin cut in the insulation batt to keep the support from rotating out of position.
I'm finding that not all of the rafters in my attic are perfectly spaced, so friction holds most of the mineral wool batts in place but with some I've used the linked to insulation supports, and with some I've used poly webbing. The duct strapping is more flexible in that it can work for whatever width I need. I'm going through and doing a second layer of r15 now and it's going a little slower as I'm furring out the 2 by 6 rafters like a bonfiglioli wall, putting a 1 inch strip of EPS against the rafter and securing it with a rip cut of 3 inch wide plywood that then helps hold the next layer of rockwool friction in place. https://www.finehomebuilding.com/project-guides/insulation/breaking-the-thermal-bridge My house has two separate attics, one with vented soffits along the eaves and a ridge vent at the top. For that one I installed accuvent from eave to ridge to maintain the vented attic while adding insulation underneath.
I did 1 test section just to see what would happen, it’s been up for 6 hrs now, it might just be me but it feels like it wants to fall out, maybe not
I think the fact they are cut in half and stacked sideways is actually hurting, not helping, your cause.
I've used mesh style landscape fabric as insulation hold ups.
If what i did stays up for 1 month by itself I’m not going to add any support to it, I just need it to stay in place until drywall
I would have got the 24 oc batts but I couldn’t, I had no choice but to get 16 oc and cut them in half