*
I’m putting up a small addition in Mass. I’ve heard that blown cellulose is cheaper and thermally fighter than batts, so I want to blow cellulose in the walls and roof. There is no basement; the floor is three feet above grade. I plan to install radiant heat tubing between the joists,cover with plywood and thin-set ceramic tile over (tile manufacturer says that ceramic tile disperses heat better than quarry tile). I was thinking of hanging Masonite below the joists, in the crawl space, and blowing in cellulose there, and laying a vapor barrier over the insulation.
Is this a foolish idea? Would it be even more foolish to put batts under the floor and cellulose everywhere else–it is a small job, after all, and I don’t want to make more trouble for the (as yet unchosen) builder. Thanks!
Replies
*
I think generally the thinking is floor insulation is not as critical because you don't lose as much heat there, since heat rises. But energy always flows from the hotter to the colder area, so you will get some loss. I am using cellulose in the walls and ceilings, but am undecided about how I'll treat the floor. Putting sheathing on the underside of your floor is doable but will cost a fair amount. Then your framer has to wait while the insulator blows in the cellulose, which if you fill the bays full is going to be pretty expensive. If you don't fill the bay full, you'll have a sizeable air space between the cellolose and the floor which is not a good thing. Usually, fiberglass batts are put in the floor.
Another option to consider, which can be done after the house is framed (or finished out for that matter) is sprayed on urethane foam (or other types) that can be applied to any desired thickness and which will make the floor nearly air tight. Again, cost is a consideration, but it will not interrupt the work flow (builders really hate that).
Just some things to consider.
*Kate,I see a possible opportunity for foil-faced polyiso board here because of the radiant floor option. If you are going to go under the subfloor with the radiant tubes, you could space rigid foil faced polyiso board a few inches away from the tubing. This would allow you to skip the aluminum heat plates that are recommended for under-floor tubing setups (with Wirsbo, anyway).Actually, if you are going with ceramic tile or some other masonry floor, I would set the tubing in a lightwight gypcrete on top of the sublfoor for better heat transfer. I would still use cells in the floor bays. Dense-packed for air-tightness. Actually the places dense-packing makes the biggest improvement are the areas under the greatest pressure differential ie: at the top of the house, where heated air is trying to get out, and at the bottom of the house where cold makeup air is trying to get in.Best of luck,Steve
*after you have your radiant floor in place...nail sheathing to the bottom on the joists and blow the joist bays thru the band joist..a lot of cellulose insulators are familiar with this..they'll use a solid two inch plastic pipe extension...and get a nice dense-pak....and it shouldn't cost a lot either... especially if you have all the holes drilled..if you preplan.. you can make the band joist out of 3/4 ply to facilitate drilling..then cover the holes with your sheathing..
*Mike,If I nail sheathing to the bottom of the joists, what do I do about a vapor barrier? Thank you to you and averyone else who has responded so far--this is very helpful.Kate
*Crusty, can you please describe what the urethane would be sprayed onto? thanks, Kate
*the vapor barrier goes on the ground...you can cover it with pea stone or mason's sand to keep it neat and hidden..or if there are no curtain walls to enclose it.. you could dispense with the ground vapor barrier altogether...with dense pak cellulose and your radiant floor .. you don't need a vapor barrier on the heated side..
*If you're going to have radiant floor heating, then I don't know about spraying foam. It looks a little like the "expanding foam" in a can that you use to fill cracks, penetrations, etc. It is sprayed on, and then it expands. It is sprayed just about like paint (different equipment, but same idea). This would be sprayed on the underside of the floor, right onto the plywood decking. It can be sprayed to any thickness desired, depending on the R-factor you want and what you want to spend.Mike's suggestions on cellulose are good. (If you are new to this board, pay close attention to Mike Smith -- no B.S. and he knows his stuff). But assuming you use 10" floor joists, you're going to have way more R-value than recommended, and it will cost. But you're going to have about 10" of cellulose in your ceilings also. Now that I think about it, the cost difference between 10" of cells in your floor and anything else you do is not going to be that much. Darn, why didn't I think of that a year ago??I worked with some fiberglass insulation today in the top of my entry (where cellulose is impractical -- or so I thought). You do not want to mess with this stuff, if you're doing it yourself. I think cellulose is the best material considering human factors, cost, and thermal efficiency.
*
I'm putting up a small addition in Mass. I've heard that blown cellulose is cheaper and thermally fighter than batts, so I want to blow cellulose in the walls and roof. There is no basement; the floor is three feet above grade. I plan to install radiant heat tubing between the joists,cover with plywood and thin-set ceramic tile over (tile manufacturer says that ceramic tile disperses heat better than quarry tile). I was thinking of hanging Masonite below the joists, in the crawl space, and blowing in cellulose there, and laying a vapor barrier over the insulation.
Is this a foolish idea? Would it be even more foolish to put batts under the floor and cellulose everywhere else--it is a small job, after all, and I don't want to make more trouble for the (as yet unchosen) builder. Thanks!