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What would be the best way to add insulation to an attic floor? My attic has insulation already, the owens/corning kind, in between the joists. It’s as high as the joists and has plywood on top of the joists so that you can walk and store stuff up there. Would you just add more between the joists and press them together so that you could put the plywood back down? Please let me know what you think?
Thanks
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i'm almost sure that compressing FG insulation is not a good thing!
but not too sure, anyone else?
good stuff
*Is the attic space a walk in? If not, why would you want to store stuff up there. If the ceiling joist weren't designed for a specific live load, you will just keep adding stuff untill you create a structural problem for yourself. Take out the plywood and add as much fg insulation as you want, only run it across the joist. Do not block acess to your soffit vents if you have them.Dave
*Compressing the batts isn't a useful thing to do. It is the air pockets (still air -> R-5.6) not the glass fibers (R-0.14) that does the insulating.From the chart I'm looking at, a R-19 batt meant for a 2x6 walls squeezed into a 2x4 cavity ends up being R-14. And squeezing an R-30 2x10 batt down to 5.5" makes it R-21.So Dave's comments on laying more batts crosswise are right on. Of course if it is a walk-up attic and you insulate the floor a lot, then you'll also need to have an insulated & weather-stripped door.
*Hey Jim,If you do the math you will realize that compressing a fiberglass batt is actually a good thing. The R-value per inch goes up.That is what R-15 and R-21 batts are, higher density. The air pockets thing is a nice idea, except that they are big enough to let the air in and out as well. Compressing a batt increases it's density and slows convection within the batt.Now on the other hand. I would never be caught dead adding fiberglass batts to an existing attic. I would use an insulation better suited for attics - like cellulose. I would air seal first so the added insulation is not in the way.-Rob
*I am with you Rob, but from the post,I assumed he just wants more insulation that is expediant and cost effective.I don't like to see stuff store in an attic. I've done enough remodeling work over the years to see what excess weight does to ceiling joist. Beside the fact that anything that is put up there usually get toasted in about a year or two. I have experienced temperatures in excess of 160 degrees, that makes cardboard boxes turn to brittle paper in no time. I keep thinking of it as tinder for a fire. Fiberglass and cellulose at least have fire retartants in them.Dave