Q: Whenever I hear some contractor saying residential buildings are built better today than in bygone days, it infuriates me. Take my 10-year-old house (please). I recently found out that all the windows are leaking because the builder did not install whatever is needed to prevent rain from seeping in, and now I can expect dry rot in the framing near the windows. Maybe you could explain how a proper window should be installed so it does not leak?

A: Rainwater is finding its way in behind the window trim, and you are probably right that the source of the problem is faulty installation.

On the whole though, we have to agree that today’s residential buildings are potentially better built than those of bygone days. Quantum advances in the development of engineered building materials and a heightened sense of the effects of sun, wind and rain on structures couple to make for tighter, better-built homes.

Each year we head to the Pacific Coast Builder’s show, where building industry suppliers display the latest building components. Over the years we’ve seen engineered lumber in the form of beams and floor joists. We’ve also seen energy-efficient windows, waterproofing products that breathe, and mold-resistant wallboard.

Engineered beams and joists are stronger and more stable than dimensional lumber. Housewrap allows the building to breathe, yet protect it from infiltration by water and wind. Modern windows are an integral part of today’s energy-efficient homes. When these components come together with countless others, they produce a superior building compared to the homes of yesteryear.

We also empathize with you, because all too often the high-tech materials of today are compromised by shoddy workmanship.

Before the 1950s, homes were most often built one at a time and craftsmanship was more at a premium. With the demand for houses spiking around the end of World War II, the concept of the housing tract was in full swing. Mass production and speed was the word of the day, and quality craftsmanship began to take a backseat.

Go to any subdivision under construction today and you’ll see a factory production line in full swing. Especially over the past several years, the push was to get the houses out of the ground and on the market. Sometimes, in the hurry, "best practices" slip through the cracks. Adding to the problem is that the skill of the modern production carpenter is less than his counterpart of years ago, so even when they are making a mistake, they don’t know it.

Any time the building envelope is penetrated, there is a potential for water to get in. Every window and every door exposed to the weather is a potential leak. To guard against this happening, proper installation is paramount. The guiding principle should be to channel any water away from the bones of the building.

Most windows these days come equipped with nailing flanges. These fins protrude from the window frame and are nailed to the building after building paper or housewrap has been applied over the plywood or OSB sheeting. These materials should wrap around and cover the framing of the window opening. A piece of flashing paper should be placed on the window sill. Flashing paper is most often a 6-inch-wide piece of asphalt-impregnated building paper.

Lay a bead of caulk on the outside edge of the opening. Next, install the window into the opening by nailing or screwing through the nailing flange into the framing. Make sure the window is level, plumb and square. With a hammer stapler, staple flashing paper on the sides of the window butting the paper to the sides of the window frame. Extend the paper 6 inches above and below the window. Finally, staple a piece of flashing paper on the top of the opening, making sure to overlap the paper on the two sides. Overlapping the paper in this way encourages water to move toward the outside and not into the building.

Either stucco or siding is applied over the flashing paper followed by any window trim. If the window is trimmed we recommend that a piece of "Z" flashing be installed to direct water running down the siding away from the joint where the siding meets the top of the window.

For a detailed description of window installation go to links.sfgate.com/ZVL on the Web.


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