Insulating the very cold bunker under the porch?
December 20, 2017 3:10 PM   Subscribe

In the basement of my Canadian house, there is a freezing cold, uninsulated "Cold Room" - it's the hollow interior of a concrete/cinderblock porch. How can it be insulated to create a nice living space?

The room is basically the "basement of the the porch"- it's a little box made of cinderblocks, topped by a concrete slab which serves as the porch floor. Room is about 7' x 15", ceiling is about 6'3".

Pics.
What's the best way to dry & insulate this bunker, and make it habitable as a bedroom?

About the room:
Inside, it's totally uninsulated and very cold. 2/3 underground, 1/3 above ground.
It's a later addition to the house- it's outside the main foundation wall.
3 exterior cinderblock walls. The fourth wall is rough brick, and it's the foundation of the rest of the basement, so its reverse side is warm.
Poured concrete floor. Concrete slab ceiling with 6 small metal tabs poking out of the slab (presumably to allow you to tie-into them).
Damp area (under the porch stairs), and some water leaking in from the old wood-framed window. But the dampness is not horrible- home inspection said that for what it is, the room is dryer-than-expected.
In the middle of the long exterior wall (beside the damp spot), there's a tiny little glass brick window roughly mortared in among the cinderblocks, about a foot above ground level.
10' of gas line runs through the room at the ceiling.
Freshly painted this past spring, so the visible damp is from 9 months of above-average rain.

The bad news is obvious.... it's a small, freezing-cold, slightly damp bunker. The good news is that it gets lovely light in the daytime, and will comfortably fit a double bed + dresser + desk.

Main concerns are:
(1) Condensation forming between the warm interior wall and the very cold exterior wall, and creating puddles or mold in the walls... will it need a floor drain?
(2) Keeping all insulating layers thin so the room stays as large as possible... drywall + spray foam?
(3) How to fix that damp spot? I guess that means ripping off the concrete porch stairs outside?
(4) Do we need to also insulate the 4th wall? It's the basement foundation, so it's heated on the other side.
(5) Adding new windows to replace the little glass brick and the old wood window. They'll be a few inches above ground, and one must double as an egress. What's the best kind of windows to use?
(6) Adding heat- we have a gas boiler, so it'll be a radiator- as it's cold as hell in there.

Definitely hiring a contractor, but want to go in with knowledge.
Ideas? Advice? Thanks!
posted by pseudostrabismus to Home & Garden (6 answers total)
 
I don't know if your codes for egress windows are the same IRC as the US but here you'd need a window well etc as the sill can't be more than 44" above finish floor for an egress window.
I'll leave the rest of it for someone from a cold climate.
posted by rudd135 at 3:23 PM on December 20, 2017 [5 favorites]


I'm not sure where in Canada you are (guessing Ontario from a previous question), but the four jurisdictions including Ontario I've lived in have had a minimum ceiling height of 2100mm or about 7' for any habitable room. This in addition to your egress issues are likely to mean any contractor will not be able to get a permit for the work which adds risk to you and whoever is going to sleep there.

I'd start with local building and fire codes for guidance on what the minimum standard is for other things even if you do this on the downlow. Most likely, it's at a minimum re-routing that gas line, roughing out a much larger egress window, and adding walls and insulation in addition to a heat source (I imagine it's sweltering in summertime too as it's likely not getting a lot of air circulation) which will reduce the room size to something like 6'4 x 14'4.
posted by notorious medium at 5:40 PM on December 20, 2017 [3 favorites]


I'm not a contractor but I've owned an older Toronto home with similar issues.

The damp is likely from poorly designed (blocked or leaking) downspouts and/or the ground needs to be raised under the stairs so that water doesn't pool there during a downpour. You can't deal with damp from the inside anyway...you'll be able to keep that section wall dry by digging on the outside, spraying it with a few cans of sealer and covering it with the black dimpled water proof shield they sell at building supply places. In a worst case scenario you'd install weeping tile below it that tied into the sewer line. Ripping off concrete stairs may not be a big deal. They're usually sectional and come off one step at a time. For insulation, assuming the walls are as flat/straight as they look in the photos, I'd mount wooden studs turned sideways with plastic behind them to keep any damp off. Between them, I'd glue sheets of rigid foam and then staple plastic over everything and drywall. I'd do the same for ceiling but on the floor I'd use those DriCore floor panels as a sub floor.

...but you know what? Keeping the cold and damp out in the winter is only half the battle - in the summer time you have to worry about basement humidity getting behind the plastic, condensing in the cool space and growing mould. One of the attractions of spray foam is that it eliminates any kind of air gap that can grow mould but the trade off is that you're creating the perfect conditions for a termite invasion.

From my experience, I think it's a hell of a lot of expense and work for such a tiny, cut off space. I'd MUCH rather use it for storage or set it up with on demand heat to serve as a work shop.
posted by bonobothegreat at 5:45 PM on December 20, 2017 [6 favorites]


I wouldn't do this for a whole lot of reasons, but here's what I know about exterior cold rooms: They're mostly mouldy because of condensation and because concrete is porous. When I was house shopping I saw one completely black with mould and got the chapter and verse on it from our contractor. This is a tough nut to crack so you want to be sure your contractor can explain why there is going to be an amazing vapour barrier, insulation, proper venting, etc. so that you don't end up with a worse mess -- and that's just for the room, before you make a bedroom.

Here's a link
posted by warriorqueen at 5:48 PM on December 20, 2017 [3 favorites]


The proper way to do this is to excavate the outside of the block wall down to the foundation; install 2.5" of EPS foam board from footing to top of the wall (possibly stepped at the lower level); apply a dimpled foundation wall drainage membrane properly sealed to the brick; cover the above grade foam with a weather resistant covering that matches the rest of your house; back fill. You then need to apply a layer of foam to the ceiling; the thicker the better but at least R-11 and cover that with flame barrier like gyproc. Your contractor might also recommend coming down the block wall on the inside to grade level (you've got the problem that there isn't any realistic way to insulate the top of the block wall and you are going leak heat there).

The above isn't all that tricky if you are a DIYer. Can be hard work depending on what your local back fill is.

While you have the excavation dug you'll also want to cut the block wall to install at a minimum a single code minimum window (I'd go with vinyl or fibreglass rather than wood) whose bottom edge is no higher than the code maximum for an egress window and a window well on the outside with a drain to your perimeter drain, sump or a french well. Window wells are commonly of corrugated steel but I've seen some really nice ones made from Allen block.

If you didn't have the leak you could apply all the foam on the inside.

Is that white plastic vent for the dryer or a bathroom fan? If the former it's illegal and a serious fire hazard. Either way it should be replaced with standard metal ducting. If it's a dryer you'll save money with reduced dry times and if it's a bathroom fan the fan will work better with smooth ducting.

The metal tabs sticking out of the concrete are probably a left over from the construction process of the slab. If so they can be removed to prevent someone ripping their scalp open on them.

notorious medium: "I'm not sure where in Canada you are (guessing Ontario from a previous question), but the four jurisdictions including Ontario I've lived in have had a minimum ceiling height of 2100mm or about 7' for any habitable room. This in addition to your egress issues are likely to mean any contractor will not be able to get a permit for the work which adds risk to you and whoever is going to sleep there. "

This is only really a concern if you want to officially call it a bed room (if you were renting or selling the place) or are trying to meet square footage minimums/maximums with the space. Call it a reading nook or a storage room when talking to the planning/zoning people and then use it how ever you want and you are fine. Personally if it was my space that I planned to unofficially use as a bedroom I'd make sure the window opening was large enough (and the sill was low enough) to meet the egress requirements and then just enjoy the space. There are all sorts of spaces in homes that are used this way.

On the window, every home improvement borg and window place sells code minimum windows. I like the ones that hinge at the top and are designed to lay flat against the ceiling when you are exiting. Note that the code for exit windows has both a minimum area and minimum widths/lengths. IE: a window that barely meets the width and length measurements won't have sufficient area; and a 6' tall window that is only 12" wide, while having plenty of area, fails the minimum dimension requirements.

I don't have my code book here or I'd let you know what the minimum measurements for that stuff is.
posted by Mitheral at 7:31 PM on December 20, 2017 [3 favorites]


The proper way to do this is to excavate the outside of the block wall down to the foundation; install 2.5" of EPS foam board from footing to top of the wall (possibly stepped at the lower level); apply a dimpled foundation wall drainage membrane properly sealed to the brick; cover the above grade foam with a weather resistant covering that matches the rest of your house; back fill.

Seconded.

Concrete is a bastard of a thing to keep dry if significant areas of it have access to dampness. With your insulating blanket and moisture barrier on the outside, you will no longer be fighting your concrete walls to keep the inside of the room dry and at a stable comfortable temperature; instead, they will be helping you achieve both aims.

As a bonus, once the concrete basically wants to stay dry you could just whitewash the inside instead of needing to take even more space out of that already small space with the thickness of interior wall finishings.
posted by flabdablet at 10:38 PM on December 20, 2017 [1 favorite]


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