Insulation Information?
July 29, 2014 8:15 AM   Subscribe

Our house is a small Cape, with a crawlspace attic. We’re going to get a home energy audit in the next couple of weeks, and the insulation of the attic is of particular concern for us, as it really gets quite warm on our second floor. Can I get your insulation wisdom here?

Right now, we have fiberglass batts that are a total disarray—it’s just mounds of batts (although there could theoretically be order below the mounds). State incentives will defray some of the cost of re-doing the insulation, provided we re-install batts or use cellulose. It won’t cover spray foam insulation—but we’re thinking of putting in central air, with ducts and stuff in the attic, and I thought that spray foam in the rafters would be better for that, since the ducts would then be within the insulation envelope.

Is it possible to install both cellulose or batts in the joists AND spray foam in the rafters--insulating the attic on both sides? Would it make better sense to forgo the incentives (which are significant—the state will cover 75% of the cost, up to $2000), and get only the spray foam? Again, since we’re hoping to retrofit central air in the future, we’ll be running ducts and stuff through the attic, and obviously, I don’t want to pay to cool the crawlspace above the insulation barrier if we just end up with batts or cellulose in the joists.

If we use the incentives, would cellulose or fiberglass batts be better?

I’d ask the energy auditors, but the way the program works is that contractors who could end up doing the insulation job are doing the inspection, so I’m leery about their advice.

And any guess on what an insulation job like this would cost? Roof is about 45 long and probably about 12 feet from the ridge to the eaves (so, internal measurement probably a little bit less. This is in Boston’s western suburbs.
posted by Admiral Haddock to Home & Garden (3 answers total) 3 users marked this as a favorite
I can't remember what we did for ceiling insulation as it was a while back, but for sub-floor insulation we got several quotes, checked out the materials in the quotes and looked up their specifications and checked around home forums etc. it became pretty clear there was only one option suitable for our space.

Re your plans to put in air-con; I'd suggest you get ceiling fans instead. They use a LOT less electricity and installation is relatively simple. I live in a city that gets much hotter than Boston in summer, and our upstairs bedroom is very well cooled by the ceiling fan.
posted by 8k at 10:31 AM on July 29, 2014

We live in a little cape-style house, too, and the upstairs bedrooms have always been unbearably hot. That is, until we replaced our roof this spring, and the roofers cut ridge vents and eave vents to increase air flow -- the ridge vent allows the hot air to rise up and out, while the eave vents allow cooler air to enter. I was kind of skeptical, but the before/after difference has been truly amazing. So, just a suggestion that ventilation can play just as big a factor as insulation.
posted by fancyoats at 11:04 AM on July 29, 2014 [2 favorites]

I'm having foam done in my attic and kneewalls tomorrow. Foam is more expensive but much better. Weird that state incentives won't cover foam. Maybe check again? What I learned is that Air barrier in the kneewalls is key. Foam does that better than others. If you're not using foam make sure it happens. Also Getting ducts in the envelope is very good. Whatever insulation you get will make a big difference, but its hard to believe fans will be enough.

Green Building Advisor is the best site for general info and advice. Building Sciences Corporation if you really want to geek out on the details.
posted by RandlePatrickMcMurphy at 11:59 AM on July 29, 2014

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