Porches, decks

Published on November 4th, 2013 | by Henri

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How to cool a south-facing enclosed porch

Q.    Many years ago I built a porch that faces south, so it is in continuous sun all day. I have been trying to determine how I can cool off the inside but I have been unsuccessful. I have a 52-inch ceiling fan and a 24-inch two-way fan (exhaust and intake) to circulate the air but it doesn’t appear to be working. The temperature is constantly 90 to 100 degrees on sunny days.

I thought of putting a roof vent thinking this might release trapped air. I also thought of insulating the ceiling. I would like your opinion on these ideas and any other suggestions you may feel would help.

A.    The only thing the ceiling fan does is move hot air around. The exhaust fan draws in outside air that is also hot on those days and, since the ceiling assembly has become radiant under the sun, the fan does not do much for you.

If the roof is covered with a dark membrane or dark roll-roofing, the best thing you can do to improve the situation is to put on a white or reflective roof covering. Roll roofing comes in white and there are also white synthetic rubber and PVC membranes (Sika Sarnafil and Johns Manville are two manufacturers of such roof membranes). They cost more than roll-roofing but will last a lot longer. However, you may need to clean them from time to time, as air pollution may dull them and diminish their reflexivity.

If there is space to lay 2-inch thick rigid insulation on top of the roof sheathing before installing the new roofing, that is the ideal way to insulate the roof. However, if there isn’t, this is the best way to go: If the rafters are exposed, you can nail or screw 1-inch by 2-inch furring strips to the sides of the rafters and against the roof sheathing, tack 1- or 2-inch thick rigid polyiso insulation, with the aluminum reflective film facing up, to the bottom of the furring strips and fill the rest of the rafter depths with fiberglass.

Install a ceiling finish. Install Air Vent, Inc. Flash Filter Vent where the porch roof meets the house wall and off-the-shelf soffit vent strips in the porch roof overhang. This will provide some ventilation and a reflective surface to reflect solar heat back out.

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