Capturing the Rain

Start with the end in sight, and expect the unexpected. (Stephen R. Covey). The best “end” for rain is to serve as watering for the landscape. The unexpected is when it lands in the basement.

Cricket to protect from snow shear

The roof design is the first critical decision. Simple “A“ frame roofs shed the water relatively evenly along the length of the roof. This is the easiest roof design to waterproof, as there are no penetration of pent-up water flow. The worst are the composite roofs with all sorts of extra gables, dormers, and pitches. Add snow to this, and you can get built up forces in the resulting snow and ice dams which can shear of entire dormers. They can be protected with “crickets,” which are designed to shear the snow to either side of the protrusion, like a chimney.

Dry "River"

The only other option is to not insulate your roof, and let the escaping heat of the house melt the snow. Not a very energy efficient option, but it should be noted that this may be the exact scenario in older houses. So before you air-tighten and insulate the attic, check to make sure this won’t be causing snow overload on the roof.

In warmer and drier climates, the roof can be used to capture the rain for irrigation purposes. A simple gutter works best when the roof edge is pretty straightforward. Collect the rain into a down spout, funnel into a rain barrel, or a dry river bed which is directed towards a garden area.

Scupper for Corner Valley Flushing

Indeed, rain capture may be a valid reason for some level of complex roof, such as a butterfly roof or a cross-gable roof, if carefully designed. Water can accumulate quickly in the valley. Wide valley flashing with an added “v” in the groove can help the water from splashing up the other side. But the biggest opportunity / problem area is the corner of the roof. Depending on the amount of rain, this can be a trickle, which falls close to the house, or a huge gush, which might shoot far out from the corner. Carefully designed and install a scupper to capture the water. The other risk with this type of roof design is ice damming, as snow melt makes its way down the valley, and may refreeze and start lifting the tiles as it backs up.

House designs have become increasingly more generic, and roof lines hopelessly complex. But rain and snow are two very good reasons to take a close look at the roof, and decide what “end” you have in mind before you start your design.