Attic Flat Best Practices
Check out photos from HERS rating projects in Western Massachusetts, with detailed descriptions.
A vented attic, with an airtight attic flat, is the easiest, most cost effective way to achieve a warm hat for the home. Blown cellulose is the most popular insulation material as it is low in cost and low in embodied energy. Fiberglass batts do not belong in vented attic flats, nor do storage decks!
Air sealing is critical - Ensure the insulation contractor or general contractor is responsible for detailed air sealing of the attic flat, including after sheetrock is installed and before insulation is blown. This includes all penetrations and interior wall top plates. Ensure the ‘chute vents’ (falsely called proper vents) at the eaves are airtight to prevent ‘wind washing’ through the perimeter insulation. Wind washing is the movement of unconditioned air through a home and is a recipe for ice-dams.
More fluffy stuff, the better - 2012-2018 IECC (International Energy Conservation Code) calls for R49 (in zone 5) in an attic flat. There is no reason not to install R60. Once the attic is prepped, the additional 3 inches is a marginal cost.
Hatch/access should be simple, tight, and insulated - Forego the pull down stairs to avoid many headaches and energy waste. A simple 20” x 30” hatch, with rigid board glued to the top, made airtight, is the best approach.
No storage deck - vented attics are ‘outside’. Don’t store anything up there. Use your insulated basement instead!
No mechanical equipment - No efficient, high quality home built to the 2012-2018 IECC should have an air handler in a vented attic. Full stop.