Most of us don't think a house roof is a thing of beauty. An asphalt tarmac that keeps the rain out is perhaps a more apt description. But with a steep gable or two, dormers, and varying roof slopes, a house can make a bold and unforgettable statement.

Striking as a roof design can be, the luster wears off quickly at the first sign of a leak. If your roof leaks, take solace in the fact you are in esteemed company. Homes of some of the most famous architects have failure-prone roofs. Cases of big egos putting form before function? Perhaps. But put today's sophisticated design software in the hands of an experienced design/building team, and ever-complex roof geometries will perform as well as they look for many years.

Architect Brian Lee, a partner in the Toronto-based firm The Ideal Environment, has been designing country and cottage homes for 15 years, says homebuyers shouldn't be intimidated by a complex roof, or one that is a bit unusual. "The technology is available to make a roof perform well in many geometries," he says.

In cottage country, Lee says there is a growing demand for traditional-style houses that feature dormers and "fairly complicated" roof lines. "Many of our clients tell us they want a cottage that looks like it has always been there. They don't want a home that looks like a city house."

Historically, cottages in regions like Ontario's Muskoka and Haliburton were often built with roofs punctuated by dormers, small gables, hips and varying slopes. While many builders have moved away from tradition, choosing to build bigger homes with simple roof geometries, designers like Lee say there is good reason to go back. A complex roof design poses a striking image and allows for unusual interior spaces and, if done right, will perform well for its expected lifespan.

The more complicated it is, the more it will cost to build. But Lee says some of that money can be recovered on the price of shingles. Make an unusually bold statement with your roof and then cover it with inexpensive conventional three-tab shingles, he suggests. Pricey cedar shakes are often a redundant expense (from the point of appearance) on a roof with curves, dormers and gables, he says.

If you are happy with a country home or cottage that has broad expanses of roof, Lee suggests using an overlay tab or laminated shingle with an imitation 'shake' appearance. Laminated shingles cost about 30 per cent more than conventional shingles, but that's still about a third of the price of cedar shingles or shakes.

Lee says he likes to design low, continuous horizontal roof lines. The idea is to create a home in harmony with wilderness, rather than a big-city suburban home with two-storey walls. His houses are often one-and-a-half storeys, punctuated by dormers and sometimes with gables.

The design is equally important on the inside as it is outside. "Increasingly, people want those kinds of odd-shaped spaces with sloping ceilings and things like built-in cupboards in kneewalls that remind them of older homes and cottages," he says. "These kinds of designs make that possible."

While sophisticated design software makes complex roof geometry relatively easy, many roofs fail prematurely due to poor design and/or improper installation. Things to avoid: dormers too close together, chimneys near valleys, inadequate or poorly installed flashing, inefficient attic ventilation and low-slope roofs.

Bruno Levesque has seen a lot of leaky roofs since he formed a roofing contracting firm distinctly named Let It Rain Inc. in 1989. One of the worst examples was a low-slope roof (flat roof) he recently replaced. The roof had been on the house for only 2 1/2 years. The problem was the previous contractor installed shingles on a slope of 2:12. Not surprisingly, the homeowner had water leaks every few months.

"The customer wasn't too happy about spending $6,000 to $7,000 on the original roof, only to find that he had to spend about $20,000 just 21/2 years later to get a proper low-slope roof," says Levesque.

Flat roofs typically cost up to three times as much as sloped roofs. Prices vary, based on a number of variables, including the regional dumping fees.

Flat roofs are a tricky beast best done by roofing contractors that specialize in them. One of the major reasons flat roofs fail early is that they literally are flat. Levesque says at least a one or two per cent slope is required for proper drainage. To achieve that grade on an existing flat roof, either a wood-frame structure or a tapered insulation system will do the job.

A two-ply modified bitumen with a one or two per cent minimum slope is recommended by most roofing manufacturers, says Levesque. But what is recommended by manufacturers is often not practiced by contractors. "I see a lot of single-ply roofs out there. The problem is that by 10 years they have often cracked from the heat and the sun."

A two-ply system offers protection from harmful UV rays, extending life by years. Traditionally, these membranes were torch applied, but due to a high incidence of fires, manufacturers have developed a peel-and-stick modified bitumen system.

Building a home from scratch? Consider using a pre-engineered roof truss system, rather than conventional rafters. Truss systems have several advantages. Being pre-manufactured, they install quicker - a big plus in the world of home building where roof construction can be the most time-consuming phase of construction.

Another advantage is price. With today's design software, custom truss systems specified for such complex geometries as roof curves and odd angles won't cost the small fortune that the same design in rafters would.

Trusses, moreover, are made of smaller dimensional lumber than rafters. That can be a big plus because they allow for more attic space to be used for insulation. In many regions of Canada, a gap in the attic of at least 14 inches is required between the roof trusses or rafters and the ceiling joists, to accommodate insulation (R-40 typically requires 12-inches) and a two-inch air space for ventilation from the eaves up to the roof peak. The air space helps to prevent ice dams (ice build-up near eaves) and improves insulation efficiency, says Levesque. Trusses are also often made with high heels to allow for maximum air flow in attics.

Going a step beyond conventional roof truss systems, a roof can be designed with an engineered truss system that offers strength and longer spans. Frank Cohn, of Mississauga-based Cohn Construction Ltd., says engineered wood truss systems have found a niche in industrial/commercial applications, and despite the higher cost, are being used more frequently in residential construction as well.

To ensure proper attic ventilation, insulation chutes, made of extruded polystyrene, should be stapled to the inside of the roof sheathing. The idea is to maintain a cold space and good air flow above the insulation, which helps prevent ice dams. Ice dams are caused by heat loss through the roof. The snow melts and then freezes again and forms ice. Ice dams shorten shingle lifespan, rot sheathing and wreak havoc on rafters or trusses, says Lee.

Adequate airflow in attics is also paramount in summer, says Levesque. During hot summer spells, attic temperatures can rise dramatically, causing shingles to "cook" from inside and wear out prematurely. For optimum shingle performance, attic temperatures should be within a couple of degrees of the outdoor temperatures during all seasons.

The contractor says properly ventilated attic spaces have soffit vents and roof vents (60 per cent intake/40 per cent exhaust). "It's something that many roofing contractors don't address properly," Levesque says.

Equally important is the use of bituminous eave protection, commonly known as ice and water shield. It is a peel-and-stick, gummy asphalt layer applied under metal flashings along valleys and along the eaves extending up the roof about two feet past the outside wall. Levesque recommends ice and water shield under valleys, and around chimneys and dormers that are especially close to each other. "It's a remarkably inexpensive product for what it does," he says.

It is also a good idea to install ice and water shield around skylights underneath metal step flashing, says Shawn Hamill of Velux Canada Inc. Step flashing is essentially the same method of flashing chimneys, dormers or anywhere a roof butts against an object. It involves weaving metal step flashing pieces between the shingles.

To do this, shingles are nailed to the bottom of the skylight. Next, on the high side of the skylight, an L-shaped metal pan or flashing is installed overtop and fixed tightly to the top of the wood skylight frame (on the low side the skylight overlaps the flashing). This flashing should extend a minimum of four inches beyond the skylight. Shingles are installed over the flashing. Water getting under a shingle simply runs over the flashing to a shingle below it, says Hamill. Flashing methods may vary depending on roofing material type.

Levesque recommends a 26-gauge painted steel flashing, rather than the standard aluminum, because it expands and contracts less than aluminum. Large amounts of expansion and contraction causes nails to pull out, and reduces the life expectancy of the product. Consequently, steel flashing lasts longer than aluminum. For chimneys, flashings should be tucked into mortar joints and caulked into place or fastened with rawl plugs. When caulking is required, he suggests using a single urethane product such as Dymonic by Tremco because it is made to seal dynamically moving joints such as expansion and control joints.

For roof valleys, while metal is a good choice, for esthetic reasons Levesque suggests that homeowners consider a "closed valley", which consists of a three-foot-wide layer of ice and water shield, topped by pre-painted steel metal flashing, then by shingles.

Levesque, who has two building science experts on staff, says there are a lot of reasons for premature roof failure. Sometimes the cause is not easy to determine. When looking for a roofing contractor, steer clear of roofers who are reluctant to install ice and water shield membrane.

More advice? Buy a specification, not a price. Don't be fooled by low quotes. And, look around for a detailed contract that covers everything, he says. There is no reason these days that a roof can't look as good as it performs.
-Photography by Don Procter, May/June 2005