Wednesday, August 24, 2011
My last post (posted an eon ago) focused on the drawbacks of having central air equipment in an uninsulated attic. Here are a couple photos of the attic in another house we're working on. This attic has had open-cell spray foam applied to the underside of the roof deck and rafters. The central air equipment will, therefore, be operating in a much less hostile environment. The equipment should run less, last longer, won't collect condensation, and if any ducts leak, no problem: they'll still be leaking into the house they are conditioning, rather than into an attic that's vented to the great outdoors.
However, I cannot unequivocally endorse this spray-foam approach. There are a few drawbacks. First, because the foam creates such an impermeable barrier between the interior and exterior of a house, any moisture released inside the house -- from breathing, showering, cooking, laundering -- is trapped inside. This has been known to cause mold problems and deterioration of drywall and wall, floor, or ceiling finishes. Thus, in addition to the relatively expensive foam insulation, extra money needs to be invested in ventilation systems, and a more sophisticated central air system.
The second drawback, from my point of view as a remodeler, is that spray-foam is far more difficult to work with than other types of insulation if a home needs an addition, or routine repairs.
My third concern about using foam on the underside of a roof is this: a tiny leak in shingles over a conventionally insulated attic will appear as a stain on the ceiling below it, but a roof leak over a foamed roof may not be evident until an entire section of your roof's framing and decking is so rotten that it sloughs off to the ground below. That is no doubt a paranoid, worst-case scenario, but it ought to be considered.
Much more about the missing months of posts coming soon.