Attic Air Sealing
Negative pressure caused by air leaking out of the attic sucks outside air in near the bottom of the house.
A house that hasn't been air-sealed has air leaks everywhere in basement and crawl space areas, in the main living space, and in the attic too. But sealing attic air leaks turns out to be especially important in improving a home's energy efficiency. Understanding the need to air seal the attic will help you appreciate what an experienced professional crew can accomplish to make your house more comfortable and more affordable to heat and cool.
Air-sealing the attic helps to minimize the Stack Effect.
More exfiltration (interior air leaking outside) occurs through the attic than anywhere else in the house. This isn't surprising when you consider how many leakage points there are into the attic and how convection causes warm air to rise. When warm interior air leaks out through cracks, gaps and openings near the top of the house, a similar amount of outside air needs to leak in - to avoid causing a vacuum. Exfiltration through the attic, combined with infiltration through lower parts of the house is called the Stack Effect - a major factor in poor energy performance. When we air seal the attic, we create a more effective attic air barrier to minimize the Stack Effect.
Attic Air Sealing Goes together with an Attic Insulation Upgrade
Since most houses have too much air leakage into the attic and too little attic insulation, these two improvements should always be completed together. Simply adding more attic insulation will not stop air leaks, because "fluffy" insulation like fiberglass batts and blown-in fiberglass will not stop air leakage. To properly air-seal your attic, energy technicians need to move aside existing attic insulation and expose all the wall framing, can lights, soffits, vent fans and other details; then they seal all the holes, gaps and cracks they can find. When a blower door test is performed after upgrading the attic air barrier, there will usually be a dramatic reduction in air leakage. Only then is it appropriate to proceed with adding attic insulation.
Don't forget the Attic Stair or Hatch
Whether attic access is provided by a drop-down stair, a hatch or (in historic houses) a conventional stairway, the opening that provides attic access needs to be air-sealed. Dr. Energy Saver can explain the different ways this opening can be made more airtight.
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