2mo ago

Best way to insulate attic with full plywood flooring?

My house entire attic has plywood flooring over the joists/insulation.

It is nailed in and a pain in the ass to remove.

What is the best way to add additional insulation to the attic? I worry the plywood/insulation underneath has a bad r value.

Do I need to take up all the plywood and re insulate the batts? Should I just loose fill on top of the plywood?

Ideally I want to air seal it to but taking the plywood up will be a nightmare.

10 comments

Get blown insulation. Cut a foot wide hole between each joist to insert the blower into.
You will need to feed the tube to the end and pull it out slowly while you blow. Blow more than you think you need.
Disclaimer: never done it before, good luck.

I mean, the majority of insulation should be on the roof/walls...
Even if you don't use the attic, it's better for that space to be insulated from the outside, not insulating the rest of the house from the attic.
- This is not always correct. Depending on the roof construction and the climate you're in the attic may need to breathe (for example if part of the house vents into it), in which case blowing in loose insulation onto the attic floor is the correct solution.
  
  Yeah, I said that to someone else...
  Even if it’s sealed (it shouldn’t be)
  But with climate change and how long roof lasts, lots of people need vents added or no longer need them.
  I believe there's even some with a temp and/or humidity switch these days so it only opens when necessary.
  Really tho, what matters is how much attic space we're talking here.
  Mine was renovated before I bought my house, and while I can walk down the middle I can't really take a step either side. But I'm abnormally tall. And the last owners used it for a teenagers bedroom. If someone was like 5'8 the space would be a lot more usable.
  But doing the bare minimum to make it "livable" drastically inflates the price even if you don't use it.
  Long run it's worth it, so it makes sense to plan ahead and when things like this come up to do it as if it was already a living space.
- Why would you want to heat non-living space? That is a waste of energy. The attic is outside of the house as far as your furnace is concerned.
  
  I'm not saying rip the existing insulation out and do the roof/ceiling
  I'm saying leave that, and add the insulation to the roof/ceiling.
  If it has plywood floors, it's usable for storage, and these days theyre often eventually remodeled to become a bedroom drastically increasing value of the home.
  So rather than remove the poor performing insulation in the attic floor, leave it and add more to help the attic become a living space eventually.
  It's just planning for the future, and achieves the same result.
  Even if it's sealed (it shouldn't be), the giant air pocket of slightly warmer air would be working as insulation as well.
  So from outside to lower level, there'd be more r factor and it would be more energy efficient
  Like, they're not "heating" it unless there's vents up there anyways...
  You made a short comment, but there's a lot wrong with it.

Depends if you wanna use it for storage or something.
If not, just use urethane to seal and top with loose fill.
If you wanna keep the surface provided by the plywood and specifically insulate underneath the plywood then it's a bit more work, though there are companies that insulate by drilling holes and adding expansion foam. I've mostly seen them do exterior walls, but I imagine the same concept can be done on the attic. If DIY, consider the risk of blowout if the foam expands too much.
If you end up removing the plywood... cut it up there with a circular saw set to a shallow depth as to not cut the joists.
Smaller pieces are easier to pry off, as well as easier to get out of the attic.
It's on the expensive side, but a battery circular saw is just fabulous.
If adding loose fill, use baffles so the soffit can still breathe.

So you have batt between the joists insulating the ceiling then plywood on top Seems fine, though unorthodox Are you having issues Just seal the plywood then if you don't use the attic space for storage or anything put your insulation of choice on top Just make sure to extend your attic access upward Is the attic space vented, with on the ends, roof line, or another way

Depends on the size of the building. If you have a large house with a big attic space ... then I'd look for professional help.
If you have just a small house and the attic is 30'x30' or less, I'd just pull up the boards and insulate.
When it comes to questions like this, it's better to do the proper work (even if it's going to be long and hard and complicated) now rather than take a shortcut. If you cheap out on this now, you'll pay way more fixing the problems it will cause a year or two from now.

Spray foam the underside of your roof deck (sorry, it's no cheap) unless you're going to pull the plywood. Be aware that if you live in a really hot climate the spray foam will shorten the life of your shingles unless you have something other than asphalt shingle roofing.

10 comments