How to Check Eavestrough Slope and Pitch Without a Professional

A trough that does not slope toward its downspout holds water, sags and freezes. You can test the pitch yourself with a bucket, a string and a tape measure. Here are three checks, a worked example and what to do with the result.

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What a good slope looks like

Every run should fall gently toward a downspout. Installers commonly aim for a drop in the ballpark of 6 millimetres over 3 metres (about 1/4 inch over 10 feet), and some go a little steeper. Follow your installer's spec if you have one. On a long run, the high point often sits in the middle, with both halves draining to a downspout at each end.

There is a second tilt too. The front lip should sit slightly lower than the back edge, so overflow spills outward and not into the fascia. A slope you can see by eye is usually a slope that is too steep or a trough that has sagged, so the tests below rely on water and measurement instead.

Clean the trough before you test. Leaves and muck dam the flow and give false readings.

Test one: the bucket test

This takes about ten minutes and one trip up a ladder at a single-storey eave.

1. Set the ladder on firm, level ground with a standoff, and keep clear of wires by 3 metres.
2. Pour a bucket of water into the trough at the end farthest from the downspout. Pour steadily, not in a rush.
3. Watch the water travel. It should move at a steady pace toward the outlet and drain down the downspout.
4. When the flow stops, look for what stays behind. A thin film is normal. Any puddle deep enough to wet a fingertip is a dip.
5. Note where each puddle sits. Dips near the middle mean a sag between hangers, and water flowing the wrong way means a reverse slope.

From the ground, you can run the same test with a hose only if the outlet is reachable. At a second-storey eave, skip it and use test three.

Test two: the string line

The string test gives you numbers. You need a length of string, two nails or clips, a line level and a tape measure.

1. Fix the string at the high end of the run, just above the trough, and stretch it along the run to the low end.
2. Pull it tight and slide the line level along it until the bubble centres. Fix the far end at that height.
3. Measure from the string down to the bottom of the trough at the high end, the middle and the low end.
4. Subtract. The low end should measure more than the high end by roughly the intended drop.

Here is a worked example. A 9 metre (30 foot) run at 6 millimetres per 3 metres should drop about 18 millimetres (3/4 inch) from the high end to the downspout. If your numbers show almost no change, the trough is nearly flat. If the middle measures deeper than the low end, the run has sagged. For the reasoning behind slope, read why gutter pitch matters.

Test three: read the evidence after rain

Rain runs the test for you. A day after a downpour, look from the ground, using binoculars if needed.

• Standing water in the trough, or a dark, wet line along the low spot.
• Silt and grit that collects in one place while the rest of the trough is clean.
• Seedlings or algae growing at a single spot.
• Overflow that begins mid-run, not at the outlet.
• Stains on the siding below a dip.

Also check the fascia. If the fascia board itself waves or slopes the wrong way, the trough will follow it. The guide to spotting gutter damage covers related signs.

What to do with the result

A small dip between two hangers can often be corrected by adding a hanger and re-fastening the trough to solid wood at the right height. A run with a reverse slope, a long sag or soft fascia behind it is a re-hang, and possibly a fascia repair.

Do this work only at single-storey eaves and only with a standoff, as described in the guide to ladder safety for exterior home maintenance. Anything higher, or any run you cannot fix in one visit, is a job for a crew.

D&D Home Services cleans and flushes eavestroughs and quotes eavestrough installation across Kitchener, Waterloo, Cambridge and Guelph. See gutter cleaning for the first step. Quotes are free and confirmed in writing before work begins.

Devon Moore, Operations Lead Co-Founder & Operations Lead, D&D Home Services

Devon Moore is the co-founder and Operations Lead at D&D Home Services, with hands-on experience cleaning hundreds of homes across Kitchener-Waterloo, Cambridge, and Guelph.