Insulating the bathtub.... Flyleft? Others?

staceyneilNovember 12, 2009

I just read flyleft's mention of insulating the tub on another post, and I would love some details of how folks have done this.

We're installing a soaking tub (no jets) into a tiled deck. The "alcove" is 6'4" long, so there's about 8" on each end a couple inches on each side of the tub. Two walls are exterior walls, and since we live in Maine, I want to be sure I insulate it as well as I can.

So, how did you do it?

I can't really picture how to get a good tight amount of insulation in there without it being in the way when you drop the tub in... because the deck and apron will be all tiled and finished before the tub gets dropped in. The only access will be through the tub's hole before it goes in, and through a panel on the short end (through an adjascent wall) that's the valve access panel.

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I'll usually foam tubs when I have access from below, I usually tack plastic sheeting in place against the tub and then spray foam (I have a spray rig, not talking about canned foam) against the plastic. That way the foam isn't sticking to the tub. I know people have used canned foam, but you'd need quite a few cans.

You could build a "box" out of rigid foam insulation. Sort of like the "box" being a burial vault, with the tub being the casket that gets lowered in. The sides can be straight or slightly sloped to match the rough contours of the tub. Polyisocyanurate (polyiso) is about R-7 per inch, a 2" thick, 4' by 8' foil-faced sheet would run maybe $40 retail. Expanded and extruded styrofoams have lower R-values, in the 3-5 per inch range. You can add lightweight framing under the deck to hold the sheets in place, or use canned foam to "glue" the sheets together at the butt joints and reinforce with duct tape.

Or you could just stuff the cavity full of fiberglass batts, leaving space for the tub, and drop the tub in place. You can gauge how much FG you can place in the hole by sloping the sides to match the rough slope of the sides of the tub.

Realize that an insulated space is an insulated space. The insulation doesn't necessarily have to be in contact with the tub to insulate the tub. Obviously the closer it is to the tub the better, but sometimes jobsite limitations force you into a work-a-round.

There's no one "true" way to do it. In your case you have limitations, so just have at it and have fun.

    Bookmark   November 12, 2009 at 9:59AM
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Mongo - Is your spray rig something special just for foam insulation? Or is it a multi-purpose spray rig that can be used for foam, then cleaned up and used for something else later? (We love spray foam insulation and Hubby's got a few spray rigs...)

    Bookmark   November 12, 2009 at 10:33AM
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Hey thanks so much, Mongo! That's great advice. We will actually have some 2" polyiso left over from insulating the floor, so maybe I will use that, or a combo. Thanks for the ideas!

    Bookmark   November 12, 2009 at 12:05PM
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Well, for those of us without mongo's advanced spray technology :), I just used two spray cans on the back and sides of our master bath tub as far as it would go, and then used other methods too. One was to fill all the gaps in the apron/deck framing with thick polyiso sheets (available at HD) cut to fit tightly, and then I filled the cavity from two open holes with loose cellulose I pushed in with long sticks until I could fit no more. There was probably some airspace left, but I gave it my best shot. I was determined :)

With DD's tub just yesterday, I sprayed two cans on the back, then put an R-13 fiberglass batt around the back and sides as far as it could go. The walls in the alcove (not a deck installation) were also insulated. That's about as much as I could do on that one.

    Bookmark   November 12, 2009 at 12:10PM
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NOTE: the spray expanding foam I got was the less-expanding type for gaps & cracks, not for huge spaces. You don't want to be potentially distorting the tub. I forgot to put that in my original reply.

    Bookmark   November 12, 2009 at 12:11PM
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I did our drop in tub with canned spray foam (5 or 6 cans) before installing it. Turned it upside down on some sawhorses and went to it. Took a couple of applications to get it uniform. I also lined the inside of the cavity with mineral wool (readily available and same price as fibreglass here in Canada). My wife seems to think it made a huge difference in the heat retention of the tub. We had the same model in our old place and it wasn't insulated.

    Bookmark   November 12, 2009 at 2:12PM
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That's a very interesting controlled kind of anecdotal evidence--thanks, advert.

    Bookmark   November 12, 2009 at 2:27PM
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sweeby, yes, it's a special gun and set-up just for shooting two-part closed cell polyurethane foam. It's actually a commercial rig that I bought years ago when I had an absolutely monstrous project to do.

Now if you have a lot of board feet of foam to shoot, there are smaller "DIY" spray systems out there, these two have been around for a while and have a good track record;

There are also some that shoot soy-based foams if you're into that "green" stuff. ;^\

Some have reusable guns, others have disposable ones, so read the fine print carefully.

    Bookmark   November 12, 2009 at 3:45PM
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