Foam board and basement crawl space.

5 years ago

My house is a 1909 Craftsman in North Eastern Ohio. About 1924, a 2 story addition was added to the home that are upper and lower sunrooms. As typically seen in old homes, in the back of the basement there is a portion of the original foundation busted out to create access to a crawlspace under the above sunroom. This ~9'x12' room has a dirt floor the walls are red cinder block. There is a glass block window at the far end of this room.

As my workshop is adjacent to this area, I would like to roughly finish it so that I can store some plastic bins, tools, and wood. From looking around on the internet, I have found others who say put plastic vapor barrier on the walls, draping it a foot or so out onto the dirt, add another layer across the floor, overalapping all joints 12" and taping all seams. Following that, use rigid foam board on the walls. My plan is to put 2x2 furring strips down on the floor and add plywood. I am wondering what is the best type of rigid foam board to use (XPS, PolyIso?). I am aware that 1/2" drywall may be required, subsequently, as a flame barrier, but have also heard that foil faced fiberglass reinforced isocyanurate board, e.g. Thermax, can be used and left exposed. I have seen countering opinions regarding pink Foamular and blue Tuff-R.

This room is more for function than aesthetics. I have not seen any water intrusion. The floor to ceiling joists distance is about 5 feet, so I just need to be able to comfortably get in and out of there to grab things.

Any thoughts?

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Comments (4)

Bruce in Northern Virginia
5 years ago
From what I recall of my architect's drawing for an encapsulated crawl space, we leveled out the dirt and then added about 4" of stone/gravel chips, and leveled it out again. We then laid down thick plastic on the gravel, going up about 12 inches on the walls. Then we installed 2" thick XPS foam board and taped all the seams with Tyvek tape. On top of that we added 3/4" tongue and groove Advantech plywood tightly fit to the walls. When we had the house insulated they spray foamed all the walls with open cell foam and sealed them to the edges of the plywood floor.

By code, you need a flame barrier over foam if its a storage area. For the spray foam walls we had the option of adding a fire retardent coating, which would allow us to use the crawl space for storage. We decided to just leave it alone and not use the area for strorage.

Bruce
Rob F thanked Bruce in Northern Virginia
worthy
5 years ago
last modified: 5 years ago
See Dr. Joe's take on crawlspace detailing.

You may or may not have to provide an ignition barrier over the foam depending on your local jurisdiction and the intended use of the space.

If that's electrical wire dangling, that will have to be properly affixed. And scrap the k&t if it's in use.

I count five courses of brick. So I don't understand how the floor to ceiling distance is 5'.
Rob F thanked worthy
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Charles Ross Homes
5 years ago
Check with your local building code official before doing anything. I encourage you to rethink whether it will be a suitable storage area after investing the effort and the cash. Will it be a conditioned space? Will those conditions match the conditions in the workshop area?
Rob F thanked Charles Ross Homes
Rob F
Original Author
5 years ago
last modified: 5 years ago
Thanks for the comments, so far. @worthy That's a great article! I will definitely consult the local code before proceeding. The knob and tube is not live. I will rip it out. The dangling romex needs to be tacked up. The space could easily be conditioned, as there is a trunk from the AC/Furnace that I could branch off of, right above the front of the room.