The Sixth Enemy Of Your Roof – Expansion and Contraction

The sixth enemy of your roof is expansion and contraction. This is the truly invisible enemy. It is the physical manifestation of forces and properties of physical matter that together cause your whole house to move back and forth. That sounded very “techno” but, it just means the house is obeying nature.

When I was in architecture school we studied the physical properties of materials and the effects of forces on materials. Here are two basic truths about all materials. First, they expand and contract as the temperature changes. Second, as a group they are affected by wind forces, earth shifting forces, mechanical forces and solar forces. When I studied large or tall building structures one of the most interesting things was learning how much they moved. Tall buildings could sway back and forth several inches. Large volume buildings could grow in any direction several inches. Control joints, expansion joints, flexible materials and other design features are some of the techniques Architects use to keep buildings from destroying themselves.

Your house is no different. When your house expands and contracts the nails tend to lose their grip. On your roof, if a nail backs out of the wood deck it causes a hole in the shingle it is holding. This causes a leak. Since an average residential roof has over 10,000 nails in it, there are lots of chances for nail “pops” and leaks.

Metal flashing is a part of your roof system that is greatly affected by expansion and contraction. Metal flashing is installed around chimneys, dormers, gables and other structures that penetrate your roof. Metal expands and contracts at a greater rate than wood. Therefore, when you nail a piece of metal flashing through the shingle and into the wood deck it is being pulled and pushed in different directions all day long. This is where more leaks occur due to expansion and contraction than anywhere else on your roof.

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Metal flashing is a critical part of your roof system but we recommend using metal flashing wisely. Specifically, we recommend not installing valley metal flashing under asphalt shingles. This practice causes lots of nail “pops” along each side of your valleys. Because the metal is moving more than the shingles and the wood deck, it causes nails to work their way up and “pop” through the shingle causing a leak at a very critical point. It is critical because a greater volume of water runs off at the valley. This is one of those hidden defects that can be devastating.

The invisible enemy, expansion and contraction, is common to everyone. There is no escape. To fight this monster you need to enlist Arrington Roofing’s trained roofing specialists and let them secure your home with an annual maintenance plan that will conquer the expansion and contraction enemy.