May 23, 2008

Building Envelope

Roofs get attention they deserve — usually after a failure occurs

DAN O’REILLY

correspondent

What should be the most visible element of a building is often the one receiving the least amount of attention, says a professional roofing consultant.

“No one component receives less attention than the roof. It’s usually a case of out of sight, out of mind,” says Zen Szewczyk, national director of marketing and sales with Mississauga-based IRC Building Sciences Group Inc. and a former president of the Ontario Chapter of The Institute for Roofing, Waterproofing and Building Envelope Professionals (RCI) Inc.

The roofing system is often assembled under the worst weather conditions, applied by some of the least technically oriented trades in construction and is the first area considered when budgets have to be cut, says Szewcyzk.

In spite of those conditions, roofs are required to minimize thermal transfer in and out of the building, bear constant unwanted foot traffic and still keep the building weather-tight.

“No one is aware of its existence until water begins to drip down on the heads of the unsuspecting,” Szewczyk.

“Only when tenants and patrons raise the issues of expensive damage to their equipment and goods and the cost of business downtime, does the roof gain the attention properly due to it.”

Those problems can be avoided, or least minimized if the roof is designed by consultants who understand what the owner needs and wants and properly built by qualified contractors. “It’s sort of a circle between the contractor, the owner and the designer.”

The simplest two types of roof assembles are the conventional roof assembly and the protected membrane roof, he explains.

In the conventional assembly, the waterproofing membrane is placed on the top of the thermal insulation and the roof deck — protecting the thermal insulation from external moisture and allowing it to maintain its thermal and structural properties.

In the protected membrane assembly, the membrane is applied to the deck and the insulation is placed over it and kept in place with suitable ballast.

“The insulation must be water resistant in order to maintain its thermal and structural properties. But it will effectively eliminate harm to the membrane caused by solar radiation.”

Membranes are the water protection element of the roofing assembly and can be divided into four major classifications: asphalt saturated built Up Roofing felts; modified bitumen roofing felts; EPDM single-ply; and thermal plastic single ply.

“Each of these membrane categories has its own benefits and its own weaknesses often related or accentuated by the role it is required to play in the building envelope.”

Asphalt-saturated built-up roofing felt, for example, is the oldest commonly applied system and can last 15 to 20 years when properly maintained.

But these systems can fail from problems ranging from moisture being trapped, weathering due to loss of gravel or when the membrane has been stressed by movement of the substrate, says Szewczyk.

Clogged drains, perimeter flashings and ponding are some of the contributing factors to roof problems. Some of the solutions include installing or relocating drains, using tapered insulation and constructing sloped light weight concrete super decks.

Other measures include inspecting insulation for moisture egress and replacing if required; checking the vapour retarder for damage; and repairing or replacing felts that may have been damaged.

While property owners and managers and owners don’t have to be experts, a basic understanding of their roofing system and a willingness to hire professional consultants will go a long way in protecting their buildings, says Szewczyk.

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