By Harry Schouten, ADVANCED Architectural Sheet Metal & Supply

There are many different ideas to consider regarding rain gutters - style, material, expansion, size, pitched or no pitch, downspout size and finish. The following are some ideas or suggestions that we have recommended during our years of supplying commercial and industrial gutters and downspouts.

Size and Style

If you have an architectural sheet-metal manual, there is a section about sizing for gutters and downspouts. We found very few contractors use it - including the people who design the roofs and metal. Designers leave it to the contractors or tell them to use the manual. Most contractors look at the roof size and use what is available - 4- or 5-inch (102- or 127-mm) K for residential and 6-inch (152-mm) K or box style for commercial and industrial. This usually works for them. Our suggestion is making sure you have enough downspout and that they are large enough. Remember the gutters are there to catch the water - not hold it. With today’s building designs, downspouts usually are put out of view so they do not obstruct the design of a building. This creates longer runs and less downspout. In this case, size of the downspout matters.

Material

Do you choose steel or aluminum? Location makes a difference. In coastal areas, aluminum is preferred because of the salt air. In the South, the choice can be aluminum or steel because there are no freeze/thaw cycles. In the North and Midwest, steel is used more because of freeze/thaw cycles and snow. Remember aluminum expands more than steel. This pertains to commercial and industrial - not residential, which is mainly aluminum. There also are uses for copper and stainless in special situations.

Expansion

The architectural sheet-metal manual has its recommendations. Today, with portable rollform gutter machines, we have seen these recommendations really stretched. The selling point is there are no seams to leak. Remember, you nail or screw this gutter in place thus restricting its expansion. We suggest roll forming gutters at 40- to 50-foot (12- to 15-m) maximum lengths. What we like is 40-foot (12-m) sections with end caps on each end, thus using the end caps back to back on each section with an 1/8 inch (3 mm) or so gap for expansion. The butted end caps are fitted with a cleat at the top so water does not leak between the gaps. This allows each section to expand separately, and the cleat holds the top evenly, giving the gutter a clean look.

The expansion system of slipping one gutter into the other about 3 inches (76 mm) and butting the end caps with a gap for expansion is not our preference, and this is why: With rollformed gutters, the profile matches and there is not a large or small end. The end caps have to be made one large and one small. One gutter has to slip over the other and cannot be riveted or screwed to make it fit properly. If you do, you no longer have expansion. We have done this many times and found it takes longer and patience runs thin because the customer wants a clean look. It just doesn’t look as good as the two end caps with a cleat. We talk to the designers and customers and show them the two systems. Ninety percent of the time they go with the two end caps and cleat system.

Pitched or No Pitch

We find out how old the building is and its construction type. Buildings, like people, tend to settle or sag with age. In most cases we find masonry and wood-framed older buildings tend to settle more than steel-framed structures. We like to build in pitch on older buildings. You need a little pitch just to get the water moving toward the downspouts. There are ways to do this with a roof flange on the rollformed gutters if your machine has an Alcoa hook. With new construction, the roof edge is pretty level. On long runs, we like 40-foot (12-m) sections or less (as already discussed in the expansion section) with a large enough downspout. In this case, we do not build in any pitch to our gutter.

Some plants or factories have a dust byproduct problem that settles on the roof, and when it rains, it gets washed into the gutter. We found in this case, by putting a greater pitch on the gutter and placing the downspout at the very end, the dust byproduct will be washed out of the gutter, depending on how much rain falls.

Downspouts

We like bigger, and more is better. Getting the water out of the gutter is the most important thing in our view. If your gutter is a little undersized for that seven-year downpour and your downspout is too small, the customer will be calling asking why their gutters are not working properly. We never know when this downpour will happen, so we like bigger downspouts or more of them. We find a 3 x 4 inch works well on 6-inch (152-mm) K, but a 4 x 5 inch also will fit for those long runs with fewer downspouts. For box gutters, we prefer 4 x 5 inch downspouts.

Finishes

With all the colors and materials available today, contractors must be going crazy. Being a commercial contractor your choice is probably Kynar 500 colors in steel or aluminum. Just remember your warranty is the same on steel as aluminum. When bidding, let your customer know steel, being more cost effective, carries the same warranty.

Good Ideas

There are many different ideas about gutters and downspouts, and these are a few of ours. Good or bad, we hope we started you thinking about some ideas of your own. We only grow and become better if we discuss our ideas with each other. A good rule of thumb is “You listen to all the ideas and theories people have, and then keep and apply the good ones that you think will work.”