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I have a newer home that the builder put a concrete vault in. It is basically the porch that was dug out fully to make a room under it with a steel security door. The concrete porch is the ceiling. There are vents into the room so I can keep circulation in it. I would like to finish it off without taking up much space so I can use it as secure storage. I don't need much insulation, just enough to help keep the temperature somewhat steady as I would like to store some art and guns in there. My plan is to prep the outside walls and ceiling by painting them with DryLoc and then finishing them.

One thought is to do 2x2 walls with foam insulation glued to the concrete and then putting either sheet rock or some kind of paneling over it.

Another thought was some kind of Foam backed OSB and securing it directly to the concrete with the foam against the concrete.

I am pretty much at a loss for what to do on the ceiling.

I am not overly concerned about electrical as I will only need one or two outlets at the most and I could do them as surface mounts.

Any suggestions or ideas?

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    What climate are you in? Beware of creating two water barriers.
    – Bryce
    Aug 28, 2014 at 4:33
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    I'd be worried about excessive humidity. Neither guns nor art are particular fond of it. Will this vault be part of the conditioned space?
    – DA01
    Aug 28, 2014 at 5:16
  • We are in eastern Washington, so we get a definite 4 seasons. The humidity is part of the issue I am trying to deal with. The vents into the room are 3 x 4" pipes. In two of them I have placed two inline vent fans blowing into the room which seems to help even out the humidity and temperature.
    – J. Clay
    Aug 28, 2014 at 17:53
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    My stock answer for how to finish a basement properly: diy.stackexchange.com/a/8644/1209
    – DA01
    Aug 29, 2014 at 15:33
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    But note: even with the system I suggest, you will have humidity issues. We essentially had the same setup--we had a 'vault' like closet under the front porch. We turned it into a closet with a door and a transom vent above it. We also heated the basement and had a dehumidifier. However, if we left that closet door closed for extended periods, you'd still end up with a slight musty smell. I'd strongly suggest making it part of the conditioned space if you can (by dropping an HVAC vent and return in the room if you can)
    – DA01
    Aug 29, 2014 at 15:37

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A hundred years ago, that would be called a 'root cellar', and considered a great place to keep your potato crop or smoked meats. The temperature will be relatively constant down there because of the ground contact. Insulating will actually reduce that thermal buffering effect given the vents.

Your problem for guns and art is humidity. I'd start by measuring the humidity to see where you stand. A USB hygrometer is an inexpensive tool for plotting humidity over time, and you'll want that even if you go all modern and try to seal the room.

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  • There are 3 - 4" vents. In two of them, I have put inline vent fans that blow into the room from the basement utility area. They are on a timer and they run most of the night and about 30 minutes every few hours during the day. This seems to help keep the humidity and temperature fairly even, but want to see if I can get it even more steady and finished off for useful storage.
    – J. Clay
    Aug 28, 2014 at 17:57
  • Your humidity start too high given that setup. Insulating perfectly would remove the primary advantage of the underground location, in terms of temperature stability.
    – Bryce
    Aug 28, 2014 at 18:17
  • I will probably have a small space heater in the vault along with the venting from the basement utility area. My question really is how to finish of the walls and ceiling taking the least amount of space possible.
    – J. Clay
    Aug 28, 2014 at 23:29
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To answer the how should I finish the room question:

I don't see insulation as a major necessity here. The room is surrounded by the ground and there is no better insulation than that. You could insulate the ceiling if you so choose. If you are fine with the concrete walls I would use a multi-poxy. I use this stuff on basement and garage floors. It is very very durable.

The nasty part of this is...well all of it really.

Step 1: Clean it. I use muratic acid, scrub with a push broom, then rinse. You'll want ventilation and a mask.

Step 2: Mix and paint. Again, ventilation and a mask. But now you're done. I usually apply at least two coats on floors, but generally three. You should be able to get away with two on the walls.

It can be tinted to color, it goes on easy and again, its (given proper preparation) never going anywhere.

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  • The ground is terribly cold in many regions of North America--especially during the winter. But even in the summer, the ground is typically cool enough to be below the dew point. This means constant condensation problems. Insulation on a basement wall is to keep the space warm--but perhaps more importantly--it's also there to keep excess moist air away from a condensation plane.
    – DA01
    Aug 29, 2014 at 15:40
  • I live in the northern half of north america. my basement walls are cinderblock, some are insulated by the ground, some are not (walk out basement). Terribly cold weather is also terribly DRY weather, you aren't going to have condensation issues in the winter. during the summer it is more of an issue but insulation wont help basement moisture during the summer, thats what a dehumidifier is for...well that and decent airflow. Insulation isn't the answer here and won't fix moisture problems.
    – James
    Aug 29, 2014 at 15:46
  • It won't fix it, it assists. An insulated wall moves the dew point away from the condensation plane to somewhere in the middle of the insulation--where moisture can't condense. I agree it doesn't completely fix the issue (as typically a bit of air can still flow around it) but it greatly reduces the issue.
    – DA01
    Aug 29, 2014 at 15:55

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