Raise the Roof

A major part of your home inspection includes evaluating the roof.  As homeowners, we often don’t give our roof any consideration until we spot a leak, or something major happens, such a tree damage. The cost to replace a roof can be substantial, so it is important to find out what kind of shape the roof is in before you purchase your prospective home.

There are three main functions of a roof. First, they are designed to protect the home from rain, snow, wind, hail, and in some cases, fire. Second, roofs often support some of the mechanical equipment for the house. Third, some roofs make a strong architectural statement.

Contrary to popular thought, most roofs are not intended to provide insulation for the building. Additionally, the roof covering itself has no structural role, although most roofs are installed over sheathing, which does have a structural role.

However, when designing the building, the roofing materials must be considered because the weight of the materials adds to the dead load of the building and must be supported by the rest of the structure.  A dead load is the load of the structure plus the building materials. The dead load is constant. A live load is a load that varies and is exerted by outside forces such as wind, rain, and snow. In North Carolina, Hurricane Matthew just made its presence known. The ability of roofs to withstand hurricane winds is an important factor in building design.

So what are some of the strategies used when designing a roof?  While you will see many different variations of roofs in architecture, there are two fundamental types of roofs: steep roofs and flat roofs. Steep roofs shed water, relying on gravity and capillary action. They are not watertight. Steep roofs act more like a series of umbrellas than a weather-tight skin.  Flat roofs use a waterproof membrane or skin to protect the building. Generally speaking, flat roofs are more expensive to install and less tolerant of minor imperfections.

roof-types-diagram

Due to price and maintenance, most homes in the Triad are built with steep roofs. What constitutes a steep roof? Not to bore you with math, but when speaking with a roofer or home inspector, you may hear the term pitch discussed. The pitch is the slope of the roof, expressed as a ratio of the rise over the run. The run is usually expressed as 12, and a typical slope might be 4 in 12 or 8 in 12. A 45o roof would have a pitch or slope of 12 in 12. By standard definition, a roof with a conventional slope have slopes of 4 in 12 or greater. A low slope roof has a pitch between 2 in 12 or 4 in 12.  Roofs are considered flat when the pitch is below 2 in 12. The pitch of the roof determines the kinds of roofing materials that may be used on your home. At Parkwood, our home inspectors walk most roofs, however it is important to know that not all roofs are walkable and beyond the scope of the home inspection. A walkable roof for most roofing professionals is 8 in 12 and below. Anything above that requires special aids. While we know a lot about roofs, we let the inspectors use their discretion when evaluating if they can navigate a roof safely.

roof-pitch-in-degreesYou may also hear the terminology ‘square’ when speaking with a roofer or a home inspector. A square is a 100 square foot area of roofing material installed with its intended exposure. It is important to understand that it is not 100 square feet of the roofing material, but it is enough of the roofing material installed with its intended overlap to cover 100 square feet. In 1 square of asphalt shingle roofing, all the shingles would cover more than 200 square feet if they were laid side by side. When roofers quote work, they typically quote a job as being so many squares.

A Parkwood Home Inspection first evaluates the roof from a distance. This is an opportunity to look for sagging of the ridge, or bucking/ bowing along the roof surface.  While these indicate structural issues rather than roof covering issues, they may have an impact of the performance of the covering itself.  Our inspection also includes a close look at the roofing surface. This is often done at the eaves while on a ladder and by walking the roof surface. No roofing inspection is complete until the interior wall, ceiling and attic surfaces below the roof area are examined.  Because of the nature of roofing, inspectors cannot see everything. On a typical roof, at least half of the roofing materials are covered, which is why it is so important to assess from inside underneath the roof.

When we find evidence of leaks, often minor leaks are worse than major ones. A major roof leak is usually quickly identified and corrected. A minor leak may cause considerable damage before noticed and there may be concealed damage. Roof leaks often do not appear on the interior surface directly below the problem. Water coming through a roof can run along rafters or ceilings a considerable distance before it drips down, especially if there is a vapor barrier above the ceiling finish. We’ve mentioned before how important home maintenance inspections can be to finding minor issues before they become major ones. Small roofing leaks are a prime example of something we would discover.

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