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Insulating a concrete block bathroom addition

I'm in zone 5A. This is our second winter in our 1948 ranch built out of concrete block. In the master bedroom there was an addition put on, also concrete block but a slab on grade floor. Needless to say, the heat in that room could also use help.

Recently a few tiles fell off the shower wall reveiling wet, moldy cement board and EPS. We gutted the shower and have been avoiding that bathroom for over a month (busy with other big projects, new baby, holidays, birthdays, and of course lack of $). But its even colder now in the bedroom and there is a breeze in the bathroom, so we really need to at least seal and insulate ( and hope to not find more issues).

What do you think is the best way to insulate?
2.5 in of polyiso, vaporous barrier, green board, tile?
I think the slab floor is a lost cause at this point...even though I would love to insulate and install radiant electric heat there.

I'd love to insulate the exterior but there is a great rock facade on the front and new stucco on the rest (plus lack of funds).

Asked by Nick H
Posted Jan 7, 2013 9:08 AM ET
Edited Jan 7, 2013 10:00 AM ET


2 Answers

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Q. "What do you think is the best way to insulate?"

A. The best way to insulate would be from the exterior. Ideally the entire house would be insulated at the same time.

But it sounds like you can't insulate the best way.

The problem with this type of construction is that it makes little sense to insulate just one room. Your walls are giant thermal bridges that will suck away all of the heat that they absorb.

To do it right, I would either demolish the slab (one room at a time), or at least demolish a portion of the slab near the exterior wall, so that you can insert some vertical perimeter insulation there.

Alternatively, you can install a layer of rigid foam on top of the existing slab, and then install new flooring.

At the walls, you'll want to install a layer of rigid foam insulation -- the thicker, the better.

None of these details make any sense unless you think through the issues of thermal bridges and insulation continuity. For example, do you have insulation in the ceiling? Can you make your insulation continuous, from the floor insulation to the wall insulation to the ceiling insulation, without any interruptions or thermal bridges?

It's going to be difficult, but you have to think these issues through.

Answered by Martin Holladay
Posted Jan 7, 2013 10:10 AM ET
Edited Jan 7, 2013 10:12 AM ET.


luckily this is the only room with a slab, the rest of the house is crawlspace/basement

this isn't looking good. we're installing a woodstove so mayne we just need to crank it up...easier on the budget.

unfortunately this isn't the only addition, so the concrete block extends into the building in another area.

Are there viable ways to create thermal breaks along concrete walls? Insulating on the outside could work if there were options...I'm thinking like cutting a slice of wall out and inserting another medium.

In the bathroom I don't know if the ceiling is insulated, if it is then it cant be much. The exterior wall of the bedroom isn't but the ceiling is.

Answered by Nick H
Posted Jan 7, 2013 11:27 AM ET

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