Ask Jon Eakes

Last Updated: Friday, October 15th, 1999, Created: Friday, October 15th, 1999

MY CONTRACTOR SAYS I MUST HAVE AN AIR SPACE BETWEEN THE INSULATION AND THE SHEATHING INSIDE THE WALL CAVITY. IS HE RIGHT?

No. For many years houses have been built like this, and the air space did in fact help circulate air inside the wall and ventilate humidity through the wall. Now, as we increase the quality of air tightness -- sealing air leaks inside the house -- and increase insulation levels, this air space no longer serves a ventilating function. Being on the outside of heavy insulation, it is too cold to help much with ventilation, and the convection currents in this air space can actually make condensation problems worse. In addition, the air space is not a very good insulator. The Canada Mortgage and Housing Corporation and the National Research Council now recommend that all the space between the inside plaster wall and the outside sheathing be filled with insulation, leaving no air space. Despite this recommendation, it is often not economically feasible to open up the wall just to fill a small air space. However, when insulating an open wall, don't leave any air space. I say this confidently despite the protests of many contractors who simply are not used to working with modern levels of thermal insulation. In the same vein, do not leave an air space between basement insulation and the basement wall! (search the keyword "basement" for the title "MYTH: LEAVE AN AIR SPACE BEHIND THE INSULATION IN THE BASEMENT TO AVOID CONDENSATION.")

To avoid even further confusion see Air space behind brick (search keyword "brick" for the title "CAN I SHOOT INSULATION INTO THE AIR SPACE BEHIND THE BRICK FACING?") and Air space behind siding (search keyword "siding" for the title "SHOULD THE AIR SPACE UNDER THE SIDING BE FILLED?").

Keywords: Moisture, Siding, Ventilation, Walls

Print Send To A Friend

Article 742

Privacy | Ruby on Rails Development by Isnor Creative