How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What’s the difference between a gable and hip roof for my insurance?
Tuesday, October 9, 2018
A gable roof slopes inward on two sides, and the other two sides have a wall with a triangle shape at the top; whereas, a hip roof slopes in on all four sides. The photo above shows intersecting gable and hip roofs: the hip roof is in the back on the main part of the house, and gable roof at the protruding garage.
And here they are again below, represented in diagrams along with other popular roof styles. Hip roofs are more complicated and labor-intensive to build, but are also more wind-resistant in a storm. Gable roofs are easier and less expensive to build, but the triangle-shaped “gable end” is prone to collapse in a hurricane force wind if not properly braced, with a domino-effect knocking down a row of roof framing members once the gable end collapses.
Because hip roofs have been proven in wind tunnel tests to be significantly more hurricane-resistant than gable roofs, there is a windstorm insurance discount for homeowners in Florida that have a roof shape that is at least 90% hip. The calculation is made by measuring the length of the perimeter (edge at fascia) of the roof that is a hip shape as a proportion of the total perimeter. The big gable end at the garage door in the home above would disqualify it for the hip roof discount.
As you might expect with an insurance industry calculation, there are several complicating factors. A gable roof that covers an open entry area, and a porch roof that is attached to the main structure only at the fascia and is not over an enclosed living space, are both not considered as deductions in the calculation of hip perimeter length. Also, a very low-slope or flat roof that is more than 10% of the total roof area over the living space of the home overrides all the other calculations and eliminates the discount.
While engineers and insurance companies evaluate these two most common roof structures based on strength and cost parameters, architects see the two types of roofs as part of their design vocabulary, and it is currently popular to have the main mass of the house topped with a hip roof, with smaller gables added as a kind of embellishment for entry porches, dormers, and garages.
Also, see our blog post Why didn't I get the hip roof discount on my wind mitigation inspection?
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To learn more about roofs and attics, see these other blog posts:
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