Insulating behind upstairs tub (to prevent pipe refreeze)

[wahoowad]

I had a pipe freeze & burst during our foray into zero degree temps 2 nights ago. It was the cold water feed to an upstairs tub/shower. I looked in my crawl space and can see there is no insulation between the fiberglass shower unit and the exterior walls. But I'm thinking the coldest air likely came in from roof soffets from the crawl space under the gabled (sloping) part of my roof and one of the pictures shows how I can see the tub from the crawl space. I do not see how I can insulate between the shower unit and the side of the house because I just can't reach that area. But I can at least put some insulation and/or a block-off board to prevent the soffett air from reaching the tub.

I only have access to the end of the tub shown which is opposite of the end with the water controls. And the silver pipe shown is my dryer vent pipe.

Thoughts? This is new territory for me.

This is what I can see from my crawl space access

Close up of the shower unit showing the rectangular "cutaway" where the tub was left exposed to the crawl space. I'm thinking I can just block this off with a sheet of plywood cut to fit, although the shower wall will still be adjacent to the exposed/uninsulated exterior wall that I can not access to add any insulation.

 

[Dune]

Ya, your plumber did you a nasty. Stuff as much insulation in there as you posibly can, then block the space off with plywood, then insulate outside the plywood as well.

 

[wahoowad]

Actually, I need to quickly correct myself. Upon looking at the exterior wall from the new hole I have in my dining room ceiling (where we accessed the pipe for repair) I can see the exterior wall is insulated. It just must not be insulated down near the triangular access via my crawl space. Maybe they left a strip of insulation out down there for some reason? So that is good. I'm thinking a block off plate of plywood will fix me up....?

 

[wahoowad]

Dang, wish I had seen this earlier as I just came back from Lowes! I did not think of using foamboard so did not look at it too closely. But I did walk by that section and only recall these large sheets of like 3 or 4 inch thick foam. Is that what you were recommending, or a different size or type of foamboard?

 

[ansehnlich1]

Unusual that wall is not insulated down to the floor that shower stall sits on. Wonder if that pipe ever busted there before? Don't make sense to me, I'd think that outside wall would be insulated.

I think I'd have to get all twisted in an knot and try and look in there, maybe with a mirror, and see how much insulation is on that outside wall, and if I could get it properly insulated somehow.

At the least, insulate the area where you plan to close up between crawlspace and shower stall.

 

[dave11]

Actually, my vote is for plywood cut to cover the hole, then cover the plywood with insulating foamboard. Use foamboard adhesive. Caulk the edges of the plywood to make a seal, using 100% silicone.

Foamboard by itself is too flimsy, in my opinion, and if it ever gets wet, will deform and pull away.

Air seal the space where the pipe froze. That will do far more than just adding insulation. Seal off every crack where air can get in to that area.

The heat coming through the shower wall should keep those pipes from freezing, if there is no draft to the attic.

 

[Gooserider]

I could be way off base, but my gut instinct would be to try and make some sort of baffle to keep the plumbing pipes clear on the shower side of the wall, and then fill the space between the pipes and the outside wall w/ some sort of spray foam insulation... Possibly also throw a length of heat tape on the pipes as well just on general principles....

Gooserider