@BCtriguy1 et al…I think I’ve made the decision to go this route.
We have a colonial and just central air and simple storage in the attic. I’m talking a few plywood boards laid down with storage boxes. Maybe 15 total.
High hats and canisters.
AC Unit & Duct work
Exposed joists and batt insulation laid between.
Roof lines already have baffles to vent the soffits
I get 30% tax rebate on materials.
Do I need to remove the existing rolled fiberglass batts? Some things I’ve read say yes. But I feel like I’d want to keep that.
I need 10-14" of blown material.
This is obviously a project that requires more research but hit me with what you’ve got as far as advice. Is this a relatively easy low skill level DIY ? If I rent a machine for a few hours and buy the materials why do I need to pay X more if I can do it myself? Especially if the baffles are already installed?
I will need to make a new elevated platform(s) for the storage area. And that seems like it would take the most planning.
I used to work in the insulation industry, so I have a bit of experience. Full disclosure, I was on the sales side not the install side.
As long as the glass bats are not water damaged or infested you don’t need to remove them.
ETA, I didn’t answer the second part of your question. Yes, this is something a DIY’er can do. We rented blow machines to homeowners that wanted to do the install themselves.
Excellent thanks for offering your experience! Ok so if I’m not removing the existing batts, would u subtract that height from the targeted 10-14"? Or do I still need that additional 10-14" on top of the existing joist lines?
I wouldn’t do it. I’d use 10 or 12 inch rolls going across the rafters.
If you blow the attic full of loose-fill insulation and you ever have to do anything up there, like run a wire or do ac work, you’ll have to go up there with a snow shovel.
Either way you do it, you have to get covers for your high-hat lights and foam them in place.
Then before you do either get two sheets of half inch plywood. Cut one into three 16’’ by 8’ pieces. Cut the other into two 16 x 48 and three 16 x 64. You’ll need these to lay across there rafters while you work and later if you ever go up there. It really makes it a lot easier and you won’t put your foot through the ceiling.
Excellent advise. Unless the existing batts are super old and compressed, in that case, I would not count that towards your final insulation depth.
Sweeney is right about the PITA factor of future work in the attic requiring a snow shovel, but a lot of that can be mitigated. Personally, I would blow it in. I don’t know about the cost savings of DIY. In my area you generally need a qualified installers registration number to be eligible for any efficiency rebates.
If you’re planning on making a plywood runway in the attic, I would build up the ceiling joists a bit so you can get 12" of insulation under it. Run some batts, put your plywood runway down and have blown in everywhere else. Running batts well in an attic space is a major PITA, especially if it’s a trussed roof. Heck, just getting the insulation in to the attic is a PITA.
BC, I asked you this before but maybe you didn’t see it. In the new house next to me, they didn’t insulate the second floor ceiling/attic floor. They spray foamed fully between the roof rafters with no ventilation. No soffit vents, gable vents or ridge vents. The builder told me that this is to meet the new high efficiency code and get a something-something rating on the house. I had never seen this before. Have you?
I’ve seen that but it’s generally a bad idea. If you eventually have a leak in your roof it becomes almost impossible to trace, and can trap moisture so you don’t even find the problem until you have a huge mold and rot issue.
I believe there is a massive problem with this in the UK right now. They pushed spray foamed rafters big time for a few years, and now the roofs are all failing, homeowners can’t insure their house and can’t sell them. Those homeowners are basically on the hook to rip off the roof of their house, trusses and all, and re do it. It can cost hundreds of thousands of dollars in those cases. ETA: I found this article that states that houses with such insulation won’t get mortgage approval. Removing the spray foam can be done if the roof hasn’t suffered rot damage, and the folks in the article were quoted thousands, but not hundreds of thousands to remove the whole roof.
What we are seeing now for high end efficiency in roofing for passive housing and such is actually exterior insulation on top of the plywood. I’m So you build your roof as normal, put 2" rigid insulation with foil over the sheathing, cross strapping then your shingle layer, combined with batt insulation between the rafters. The external insulation layer is excellent and preventing thermal bridging.
Yes, fiberglass between the rafters with no venting can always rot out the roof sheathing. I once showed this to a friend who was going to buy a house insulated like that. I pulled down a batt and I was able to flake off the plywood with my fingers. The seller had to replace all the roof plywood and do a new roof.
I thought they were crazy with the house next door. Glad you agree!
We are moving away from spray foam in general as it’s having hosts of problems. We now have to pass strict air tightness tests before lock up. Spray foam used to be heralded as the gold standard for airtightness. It’s your insulation and air barrier in one!
What they are finding now is that when installed in new homes, as the home naturally shifts and shrinks over the first few years, the spray foam doesn’t, and you get air cracks between every stud and the spray foam, rendering the air tightness essentially gone.
We only use spray foam sparingly in joist ends of floor systems, or in areas where you can’t get a high enough r value behind a pipe or something. People used to spray foam their entire basement. Those days are long gone here now.
Thanks to you and @Sweeney for the posts. Definitely learning more.
I do have a trussed roof and space is limited up there. I will need to build some basic walkways and storage platforms which should be easy enough.
I do like your idea of batts underneath them rather than blown. Seems easier to do that and then blow in the rest. @Sweeney I understand your point about future work. I did consider that. But we’re losing so much heat/cooling up there and I just want to make a solid step towards mitigating that.
My FIL is an HVAC guy so hopefully that’s sll we ever have to do up there. But I know that’s not realistic.
Maybe I should swap out all high hats and light fixtures now before I do this.
Home Depot has really nice modern fixtures the screw into the hight hat fixture then clip on to give you a modern flush light that’s better in every way. They also have the domes that you need to put over the high hats in the attic then seal with foam.
I did the rolls myself and thought it was easy, but I’ll leave that decision up to you. Which ever you choose, your heating bill will thank you!
I would hope that they aren’t doing that in hail prone areas. If so, I would think that it would allow for roof damage from smaller diameter hail since it is hitting a softer surface allowing it to penetrate further.
I say that because when I’m working a storm with marginal hail damage - I often find more hail damage in the valleys since the shingles are not laying flat on the sheathing.
That makes sense that it is used with metal roofs. I didn’t think about that. Are there issues/challenges with fastening the metal through 2 inches of the rigid insulation or do they put battens on top of the insulation? I guess that it would only be a major concern if you had a lot of strong wind that could get underneath it.
I don’t see a lot of open (exposed) valley metal anymore. I saw it quite a bit in Omaha Nebraska, but that’s the only place that I remember it being really common.
I probably see it underneath the shingles on 30-40% of the houses that have valleys.