CATHEDRAL CEILINGS: REDUCE HEAT GAIN WITH SOLAR POWERED ROOF FANS

GREEN SUSTAINABLE ARCHITECTS BUILDERS IMPROVE LEED SCORE

SOME POSSIBLE QUESTIONS AND ANSWERS

Having been in the business of providing attic ventilation for almost thirty years, one of the most difficult (and, in fact, impossible) situations to deal with in completed construction is heat buildup in rooms (or finished attics) with “up to the peak” cathedral ceilings. If you’re an architect, builder or homeowner contemplating using cathedral ceilings, I have some thoughts and recommendations you might consider. The present theory in attic ventilation, as reflected in most building codes, is that hot air will travel by convection up through the styrofoam “spacers” between the insulation and the roof sheathing, exiting through the ridge vent, thereby pulling fresh air in the soffit vents.

Our experience has been that this theory does not work well. In fact, the air below the roof sheathing can reach 150°F. That hot air is rapidly expanding. Unable to escape through the soffit and ridge vents quickly enough, it pushes through the porous insulation, heating up the ceiling and creating a tremendous heat gain in the living area. Very often even a well-designed air conditioning system can’t keep up.

SUGGESTION: Design a small attic over the cathedral ceiling. A solar-powered roof fan will exhaust heat from the “attic” creating a vacuum thereby pulling in cool air from the soffits through the spacers. This creates an envelope of cool air around the living space. (If you already have a flat ceiling, just add the solar fan)

These heat-gain forces are the same in a regular “stand-up” attic. (Same Solution).

The living area will be at least 10°F cooler before the air conditioning is even turned on. With proper insulation, soffit vents and a SOLAR POWERED ROOF FAN you can look forward to a cooler attic space. Note: Insulation contractors should ensure unobstructed airflow from soffit vents to “attic space”.

~ Steve Pineault