Expansion Joints: Proper Allowance for Gutter Expansion
Expansion Joints are a component in seamless rain gutter systems designed to protect the gutters from the effects of thermal expansion. Thermal expansion is the tendency for a material to expand and contract when exposed to changes in temperature.
There are a couple of options when it comes to expansion joints in gutters. Your first option is a pre-made expansion joint (FIG 1: LEFT) consisting of a piece of rubber stamped between two separate pieces of metal. This option allows for plenty of movement however it is not the recommended approach.
FIG 1: (LEFT) PER-MADE EXPANSION JOINT. (RIGHT) TWO RUNS BUTTED TOGETHER
According to SMACNA, the best way to protect your gutter system from thermal expansion is to split any run of 50 Ft or more into two separate runs, capping both ends and leaving ¼” gap between the top edges of the end caps (FIG 1: RIGHT). It is recommended that you then secure a small piece of aluminum to one of the end caps and fold it over the gap so that all rainwater over that gap is directed into either gutter.
In most residential situations you will not have a single run of gutter longer than 50’ and will not need an expansion joint.
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