Ask the Architect

You have to think like water

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Q. Our rear porch was changed to a family room, and even though we noticed that the ceiling and floor got wet when it rained, we thought that making the porch a closed-in room would mean no more water. Unfortunately, after the room was finished, it still leaks. The contractor has sent people back three times, but it still leaks. Do you have any suggestions? We keep moving the new furniture, and now it’s under plastic sheets. We’re so frustrated, because we thought the work was done. It got a final inspection and we followed the rules, so why is this happening?

A. So you didn’t ask for the indoor waterfall feature? This common problem is frustrating. In my many years of construction design, I’ve observed that many people often assumed that it wasn’t necessary to develop redundant waterproofing at joints. Waterproofing must work under extremes, not just in an average rainfall.

Louis Sullivan, a Chicago architect who helped rebuild after the great fire, once said you have to “think like water.” Water follows the path of least resistance, and is acted on by five different means: positive pressure, negative pressure, gravity, capillary action and adhesion. Positive wind will force airborne rain into small openings; negative air movement inside the structure will move water by suction, like when a ventilation fan, cook-top hood or clothes dryer vent blows outward, using the room air to push outward; gravity allows water to gather at a low point and enter; capillary action allows materials to wick water in; and adhesion causes water to stay connected to a surface and be drawn down and into openings.

Detailing the roof-wall connection is complicated, because it involves another phenomenon of water, namely the ability to change its state from liquid to gas, gas to liquid and liquid to solid. You can completely waterproof the connection and still have leaks because of condensation due to humidity gathering inside construction. That’s why compressed wood chip beams, called “laminated beams,” aren’t recommended for exterior use (in crawl spaces, ceilings of porches or carports), even when wrapped inside metal or other synthetic covers. Humidity develops everywhere, and very slowly causes materials to fill with moisture, to the point at which the molecules separate, causing the solid material to fail.

In your case, the upper wall, above the roof, must be stripped and checked for staining and water damage. Window frames in the wall above must be waterproofed. Rain gutters should be sized and correctly directed away to prevent water from dropping onto the roof below — even covered to keep from clogging. This should all be done before the leaves begin to fall. I recommend installing a waterproofing membrane 2 feet up the wall and 2 feet onto the roof under siding and shingles. The ceiling should be cross-vented or foam-filled to either ventilate or create a solid water barrier. Even the smallest, pinhole-sized opening can be a problem. Cover correctly and redundantly. Good luck!

© 2019 Monte Leeper Readers are encouraged to send questions to yourhousedr@aol.com, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.