Basement Insulation for Partial Finish

Old 12-22-15, 12:37 PM
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Basement Insulation for Partial Finish

I am in the planning phase of the finishing process and plan to start sometime in the spring. At this point I have everything mostly figured out, but I am debating on one last thing regarding insulation.

Some background: I am partially finishing my basement. I will have a ventilated room for the boiler, hot water heater, and oil tank, which are all on one wall of one side of the basement. Water purification is on the other side with the bulkhead door, which I plan to keep as storage. I plan on finishing most of the space in between. This means two sides will be up against the concrete, while the other two sides will not (minimum distance will be 4 ft. on boiler side side and at least 10 ft. on the other storage side).

Before moving forward I do want to mention I have a dehumidifier down there and it has a pump with drainage to the exterior of the home. I usually keep the moisture setting low (~40%), and I don't mind the cost of electric as a result. Better safe than sorry.

My original plan was to put up XPS foamboard along the two sides where the interior walls would run against the concrete. I would leave around a 1-2 inch gap between the foam board and framing to allow air flow, and then put up fiberglass insulation. The XPS on the concrete would only run the length of the interior wall, not the entire basement wall. If you can imagine, the entire unfinished portion of the basement, including the gap between the concrete/XPS wall and framing would be connected; air can circulate with the help of the dehumidifier on the unfinished side

My question is: is it necessary to even have the rigid XPS foam board if I plan on leaving a 1-2 inch gap (or more) between that and the framing for air circulation? Is it overkill? Anyone have any recommendations? Would the foam board even make any difference or add any benefit whatsoever?

Overall I plan on being a bit overcautious even though my basement has had no signs of water issues yet (been in the house for only a year so not all that much to go on).

I've attached a picture to illustrate. The pink is where I plan on putting up the XPS foam board and leaving a 1-2 inch gap. THe door in the middle leads upstairs to the main floor. Name:  Basement Layout example.jpg
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Old 12-22-15, 01:14 PM
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Welcome to the forums.

I would include the foam but omit the air gap between the stud wall/fiberglass insulation and the foam.

Hang tight and Bud will be here to chime in with more info.

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