Leading the Way in Energy Efficient Building Design & Construction
Building a High Performance Home II - Overview
December 15, 2013
So if you're building a home and want to make it more affordable to condition and more comfortable to live in, what do you do?
First, seal out the air leaks. Require the architectural plans to properly define the air barrier completely around the building - under the basement and crawlspace floors, up the walls, around any bumpouts and up through to the attic.
There are now many ways to seal up a building. We're finding that just using Tyvek building paper (or similar) as an air barrier isn't enough. We can use specialty plywood to sheathe it and then tape all the seams. We can wrap it in rigid foam sheets and tape those seams. We caulk all the joints in the lumber making up the exterior shell. We spray foam on the inside of the wall cavities. We have new liquid applied products that "paint" onto the outside of the building's plywood skin, that block air but allow water vapor transmission.
Next, insulate properly. Have the plans call out a specific type of insulation for foundation walls, underslab, above-ground walls and for the attic/roof structure.
Keep in mind that new codes are requiring a high R-value in the attic. If you choose to leave your attic "cold" and lay fiberglass insulation on the top of the ceiling, you need to be mindful of several important details. Thoroughly seal the home from the attic. Seal all electrical and plumbing penetrations that come up walls and enter the attic space. Weatherstrip and insulate attic doors and hatches. Allow plenty of exterior air to ventilate into the attic - it should be as cold as the outside. Use vent chutes to keep the insulation from blocking the air path from soffit to attic, and use ridge vents, not "mushroom" type vents. Lastly, if you must have a furnace in a cold attic, make sure all ductwork is insulated, under the attic insulation, and sealed well to prevent leakage. If possible, build an insulated and sealed room to house the furnace.
If it seems like it would be tough to build a house with a properly performing "cold" attic, that's because it is. Check the next post for the new and better way to do it.