Most materials are subject to thermal expansion – a tendency to expand when heated and to contract when cooled. What is happening scientifically when heat is added to the material is the average amplitude of the atoms vibrating within the material increases. This increases the separation between the atoms causing the material to expand.
Aluminum, like most other material, will expand and contract. In fact, aluminum can expand or contract 13.1 micro inches per linear foot for each 1 degree change in temperature1. To put this in perspective, a 50 ft run of aluminum gutter subject to a 51 degree change in temperature could expand or contract .401 inches (just over 3/8”). 50ft X 12 inches = 600 inches x .0000131 X 51 degrees = .401”.
It is important to note that wood material used on the fascia or soffit can expand or contract even more than aluminum material. For example, new construction using western species of lumber may shrink longitudinally (lengthwise) by .2% as it dries (moisture content declines from 30% to 0%)2. Shrinkage on a 50’ run of wood can be as much as 1.2”. 50ft x 12 inches = 600 inches x .002 = 1.2”.
The expansion or contraction of either of these materials may be enough individually to cause heat buckling of gutter material if precautions are not taken during gutter installation. However, when both materials experience expansion and contraction simultaneously, the almost 2″ combined effect could have severe consequences to the gutter material.
Through decades of experience, we have determined the following precautions should be taken at the time of installation to reduce the possibility of heat buckling:
Gutter Machine Adjustment
Gutter machines must be regularly adjusted to ensure that the gutter coming out of the machine is straight with no curving or rippling which could increase the chance of heat buckling during thermal expansion.
Use of Run Out Stands
Gutter coming out of a gutter machine should be supported with run out stands to level the gutter so that the gutter does not stretch or get deformed. Run out stands should support the gutter at intervals of 15′ or less for the entire run.
Length of Gutter Run
The international trade association for the industry, the Sheet Metal and Air Conditioning Contractor’s National Association (SMACNA), recommends against installing seamless gutter in runs longer than 50 ft long. For runs that require longer than 50ft, an expansion joint can be used or two shorter runs of gutter with end caps can be butted together with a piece of aluminum folded over the joint.
Gutters installed during extreme temperatures, below 30 degrees where the aluminum is contracted fully and above 100 degrees where the aluminum is fully expanded, could exhibit heat buckling in the opposite extreme temperature. The optimal temperature for installing gutter is 60-90°F.
Expansion and contraction of aluminum is a natural property of the material and may occur regardless of the manufacturer. It is important for the homeowner to know that heat buckling can and does occur, although very rarely. One or more of the factors above lead to the material expanding or contracting so much that a deformity is the inevitable outcome.