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In or Out!

May 11, 2013 | Posted by Mitt Jones

“Inside or out.” It’s a phrase I heard a lot as I was growing up—as I lingered too long in an open doorway or as the family dog simply stared at us blankly across the threshold. In the context of home performance, the phrase has a similar meaning: Every space in your house, whether it’s a side attic, a crawlspace, or a basement, should clearly be inside or outside. Too often these spaces are somewhere in between.


When we say a space is inside, we mean it’s inside the thermal and pressure boundaries of the house, which is a geeky way of saying that it’s reasonably well sealed and insulated from the outdoors. Think of it as being inside a really warm, zipped-up coat.

An attic area that’s been brought inside might be insulated and sealed on the roof deck and gable walls with spray foam. Without being intentionally heated or cooled, it won’t be the most comfortable area in your Portland home (or so we hope), but it won’t be so bad, either.


When we say a space is outside, we mean it’s outside the thermal and pressure boundaries. This is the more typical way of doing things in Oregon when we’re talking about attics and crawlspaces. For instance, most attic spaces have insulation on the floor of the attic—above the ceiling of space below. And most side attics should have insulation on the knee wall—the wall that separates the attic from the upstairs living space. The space should be isolated as much as practical from the inside of the house through both air sealing and insulation.

Here’s another key part of being outside: Attics and crawlspaces that are outside should be ventilated, partly to avoid moisture problems.

Inside or Out!

Unfortunately, it's not unusual to find side attics that have insulation on the roof deck and exterior gable walls but that are also ventilated, which makes no sense. In winter it’s like leaving your really warm jacket unzipped when it’s really cold out.

It's also common to find crawlspaces that are ventilated but still more or less open to the basement. Would you leave your basement windows open? Those openings to the basement should be closed! And insulation should be added to the subfloor above the crawlspace and to the little wall between the basement and crawlspace.

The bottom line: Any time you’re trying to figure out how to insulate some portion of your house, just remember—put it inside or out! A great many of a home’s comfort and energy problems can be solved by a thoughtful and careful application of this simple rule. 

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