If you remember what you learned in school, in general the circle is the strongest geometric form, followed by the triangle.
From a practical standpoint, though, most building frames and trusses are made strong by converting some of their naturally perpendicular rectangles into triangles through the addition of cross members.
Probably one of the major structural components with which everyone is familiar is the gable roof.
It, in itself, is a series of triangles that, when covered by the roof decking, becomes one large triangle.
The gable roof has two weak spots – the two ends. And that’s where strong winds, hurricanes and the like have a field day, and many breeches occur.
In years past, gable ends were strengthened with shiplap lumber, cut and nailed on the bias to the frame. Picture that in your mind. That then made each of the gable ends a series of triangles to which the siding was affixed; enormously strong.
Apparently to save money, builders began enclosing gable ends with ¾ inch plywood, veneered with the siding. While not as strong as the shiplap, nevertheless, plywood gave substantial strengh, too.
Today, gable ends on home after home are built with little thought given to shear stress. Instead of the end caps being made of shiplap on the bias or plywood, they are merely covered with fiber board underlayment which has very little shear or tensile strength.
The underlayment is then veneered with siding which also has very little shear and tensile strength.
If the strong wind blows-out either of the gable ends, the entire structure is seriously compromised – all the result of the builder’s putting first his own economy.
If you have a gable or a hip roof, you may want to go into the attic and investigate how the ends were strengthened, if at all. A structural engineer can advise you how to correct any weak spots. The "fix" will normally not cost more than an investment of a few hundred dollars.
It's a worthy exercise and investment. And your insurer should love you more as
well.
Actually, far fewer homes on the gulf coast would suffer significant damage in hurricanes if their roofs were closed-end, square hips like the one on the garage in this illustration.
BILL CHERRY, REAL ESTATE BROKER
Dallas – Park Cities
Since 1964
214 503-8563
