By:Monte Leeper
Q. I read your column every week. I have a problem in my den, which is an extension of the house and has a flat roof. I had the drop ceiling, which was loose, redone. Since then, I see stains at multiple places. Though water collects on the roof, the roofer states the roof is okay. He states the roof has no ventilation and that's why there are more stains where water stands, as sun reflects more heat, etc. Also, I have a microwave with a ventilation fan. The pipe opening is on this roof and there is a stain there, too. My construction guy says it is due to condensation of hot vapor, etc. He tells me to put in at least two solar ventilators (cost, $750 each) and no electric ones. My roofer has not come up with a plan yet.
I would like your opinion on this. The roofer had taken out a tile from the drop roof and it was wet inside. The roof never leaks, only stains at multiple places; mostly where water stands.
A. Like so many of the questions I get, there is a time lag between the receipt and the answer being printed. I hope that you have waited for an
answer, because there are many ideas about what causes the sort of problem you have. Your contractor is right about the ventilation being necessary in between the ceiling insulation and the bottom side of the roof assembly.
Air must flow freely through that entire space. People used to believe that creating dead spaces contained more heat, which is partially true. But it also locked in moisture, a medium that can wreck the roof structure over
time, by causing rotting and lowering the dew point inside your home, making it humid and uncomfortable in summer and chilly in the winter. I am curious about the standing water on your roof. Water should not pond on the roof.
The roof is obviously either too flat or not uniformly pitched. The roof is also more susceptible to being penetrated by standing water through any cracks that open up in the roof surface. At the edges of the roof, is there complete covering of the perimeter and is it flashed in such a way that water runs away but air can still get into the membrane? The reason for asking, and many more questions ought to be asked, is that condensation rarely causes large accumulations, to the point of ponding in the ceiling and staining the tiles. There would have to be a high humidity in the room and extreme cold on the exterior, for a prolonged period of time. Ventilating and keeping the room warm in the winter would be necessary, since your contractor says the roof is not the cause.
But as you can begin to realize, the problem is not solved by one simple fix, but by a series of exercises that must be done to control the problem. The solar vent fans cost about $400 to $450 to the trade, and the remainder of the cost is labor and repairs to the roof. Without complete air flow between the roof rafters and inlets for the air to flow from so that it is pulled across the entire area of the roof assembly interior, the fans will be ineffective.
Good luck!
