Sunday, August 2, 2015

The Stack Effect

Ah the stack effect. Anyone who has seen a 2 story house built before 1960 has seen this kind of design. 

Tall, narrow, almost floor to ceiling, double hung windows, vents in crawl spaces, and direct or indirect vents in the attic. Our project house was the apex of building engineering in the late 40's.

This was before modern-day air conditioning. And the bane of any modern building design. Air drafts in the winter become very significant, and the need for energy efficiency pushes the need for a tighter building envelope and greater insulation values.

In our project house we added 6-mil plastic sheeting to the living room and entryway on top of the paper vapor barrier of the r 30 insulation in the floors, as well as the walls.

This cut down on the ability of the house to produce a stack effect,  however it did reduce the permeability of cooler air rising up from the crawl space. This results very little air circulation within the area, and the formation of condensation within the crawl space. That condensation can lead to mold growth, falling insulation (reduced r values) and a host of other long term problems.

The ultimate solution is to include the crawl space into the building envelope. However this can be very costly and is labor intensive, especially when the crawl space is only about 12-16 inches deep, and is broken up into 4 different cells.