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Home Work

A Primer on Roofs

Mike Denker, left, and Todd McPhee of Hopkins & Porter.

Mike Denker, left, and Todd McPhee of Hopkins & Porter.

— “At least we still have a roof over our heads.” This old saying causes me to muse about roofs. When the dark English philosopher Thomas Hobbes said, “Life is nasty, brutish, and short,” he might have also added “damp.” One of the miracles of contemporary life which we usually do not appreciate is our dry homes.

Some might say roofs are not a sexy topic. I beg to disagree. Roofs can be and often are the beautiful crowning glory of a home. Many roofs require careful craftsmanship and careful attention to detail. Roofs show pride or neglect; they reveal the owner’s wealth or poverty. Our modern roofs are made of every conceivable material from wood, to stone, to ceramic, to rubber, to metal, to asphalt, and they vary in color across the spectrum. A roof replacement, which may need to be done every 20 or more years in the life of a house, is one of the more expensive and predictable kinds of periodic maintenance. It is possible to delay replacing your roof by several years if you pay careful attention to the few areas that begin to have trouble first. Professional roofing companies would prefer of course to sell you a new roof.

Finding small leaks is challenging, time consuming, and they are not really possible to guarantee, while replacing a whole roof from their perspective enables them to provide a warranty. My company employs a roofing specialist who has become an expert in repairing old roofs, and his detective work often begins with a crawl in the attic searching for water stains.

Roofs shed water typically because they have a “pitch” or a degree of steepness. Roofers will designate a roof as a 6/12 or a 4/12. The first number in inches is the “fall” of the roof for every 12 horizontal inches. In a steep 12/12 pitch, for every 12” of horizontal distance the roof drops 12”, which describes a 45-degree angle roof. If you feel proud of your roof, it may be because you have a steep one. A steep roof is naturally more eye catching. If all you care about is water running off, then a less expensive lower pitch will suffice. Of course most people are never involved in choosing the pitch of their roof. They take what they get and deal with it. Usually the only choice you will have will be the type and brand of roofing materials and their corresponding predicted longevity. Most roofing companies offer no more than a 5-year warranty, although your roof may have a predicted life of 20 or more years.

Roofs keep out the water, and they work with gravity. No roof should have water sitting on it. Sooner or later that water is going to find a way into the building below. When rain falls on a pitched roof, the rain keeps running downwards. The steeper the pitch, the quicker and the more effectively the water runs off. Historically, older houses had steeper roofs (with the exception of desert structures). Our predecessors used hand made shingles that needed this steepness to work. Today we have amazing roofing materials that can waterproof even a flat roof. The trend in our modern age is toward a less steep roof. This is partly an economic choice. The steeper the roof, the more costly it is. Consider it. Steeper roofs have more surface area. The more roof surface, the longer the framing needs to be, the more sheets of plywood, and the more squares of roof. (A square is 100 square feet of roofing material.) Similarly, the pitch of a roof has a lot to do with the architectural style of the home. The older styles have the steeper pitches and visa versa. Think Tudor, and you picture a very steep roof, but think modern architecture, and you could imagine a flat roof.

The most common roof is made of shingles, small pieces of wood (cedar shingles or shakes), stone (slate), metal (stamped metal shingles were popular in the Victorian era), ceramic (roof tiles) or asphalt mixed with glass fibers (the most common roof in America today). Shingles are applied first at the bottom of the roof just above the gutter or “eave trough,” and each successive course overlaps upon the previous shingles like the scales of a fish. As long as the roof is steep enough, drops of water will always run off one shingle to the next one below. As a roof approaches a gentle 3/12 pitch, water falling on a shingle roof can work sideways and can be pulled uphill by capillary action between two singles and create a leak.

Roofs with lower pitches need a more continuous roofing material like sheets of metal or rubber. One of the most handsome roofs in this author’s opinion is the standing seam roof made of continuous long pans of metal with the edges folded up together in such a way as to keep water from penetrating. Rubber which comes in very wide rolls needs only a very slight pitch 1/12 to waterproof the building below. Sheets of modified bitumen (invented in Italy), a rolled asphalt sheet with additional rubber as an ingredient, are another option for waterproofing a low pitch roof. Both rubber and bitumen can be glued or heat fused to make large fields of continuous membranes to be used on flat commercial buildings and smaller flat residential roofs.

Flashing, a word used in reference to roofs, is a system of relatively small bent metal pieces used mostly on shingle roofs to waterproof areas when the shingles might run into trouble: at chimneys, where roofs hit walls, dormers or where roofs run into other roofs.

Flashing metal solves a multitude of potential waterproofing problems. A skillful roofer can make flashing a roof a decorative element. A common example of this is where the small roof of an entryway runs into the brick or clapboard vertical wall of the house.

Behind every roof is a roofer. Roofing is still a hands-on trade. It is one of the most dangerous and physically tiring of the building trades. Imagine working all day in the sun and wind, walking on a pitched surface, and climbing up and down ladders with tools or bundles in your arms. Many roofers are craftsman who take tremendous pride in their work. Much of roofing work is long, boring, and repetitive where production efficiency is vital.

My next column will continue the exploration of roofs, including different roof configurations, more on different roofing materials, their longevity and their relative costs, the new painted metal roofs, skylights and light tubes, and stories of some famous leaky roofs.

As our company celebrates its 35th year in business, we welcome your comments and questions about these and other topics related to house design, building, remodeling, repairs and maintenance at mike@hopkinsandporter.com.