Mastering Roof Inspections: Roof Drainage Systems, Part 1

by Kenton Shepard and Nick Gromicko, CMI®



The purpose of the series “Mastering Roof Inspections” is to teach home inspectors, as well as insurance and roofing professionals, how to recognize proper and improper conditions while inspecting steep-slope, residential roofs. This series covers roof framing, roofing materials, the attic, and the conditions that affect the roofing materials and components, including wind and hail.


If runoff from the roof is allowed to discharge next to the home's foundation, serious structural problems can develop. Saturated soil can lose its ability to support the weight of the home, or seepage can undermine the foundation.

The most common roof-drainage control system in residential construction is gutters hung from the roof edge attached to downspouts.

The gutter problems you find may be related to the materials from which the gutters are made,  the quality of installation, the environmental conditions, or some combination of all three.

Gutter Materials

Vinyl gutters are fragile, and you may find them broken or disconnected.

Galvanized steel gutters are common, and you’ll see them all over North America. If they’re painted, it may be difficult to tell steel gutters  from aluminum just by looking, but you should be able to tell the difference by tapping them with your finger.

Copper gutters generally last a long time compared to steel and vinyl.


Problems with installation range from improperly sloped gutters to gutters that are loose or poorly attached. You may be able to identify improper slope by observing standing water in the gutter or the accumulation of sediment in portions of the gutter away from the downspouts.

You can check the slope from the ground by looking at the margins between the gutter and roof or the gutter and fascia.


Metal gutters are subject to corrosion, especially if debris has been allowed to accumulate. Debris holds moisture next to the metal, so watch for corrosion in gutters which have tree branches hanging over them. You may find advanced corrosion by probing. Corrosion often starts at seams.

On homes with steeper roofs, gutters may need to be installed using standoffs to help ensure that runoff doesn’t overshoot the gutter.

In areas with snowfall, it’s not unusual to find gutters bent from sliding snow, especially on homes with metal roofs.

Built-In Gutters

“Built-in” gutters are gutter systems that are built into the roof instead of hanging from the edge.
There are two types of built-in gutters.  One is usually installed a foot or so back from the edge. The installation method for these is crucial because leaks will allow moisture into the framing or home interior where it can cause decay or other damage.

The other type is built into the edge of the roof and is more common.

Roofs with this second type of gutter are easy to spot because the roof slope will not extend clear to the edge of the roof.


Do not probe these gutters. If you puncture the gutter, you may be responsible for damage caused by leakage. Look for signs of leakage in the soffit below the gutter.

On this particular home, it was decided that the best way to deal with failed built-in gutters and downspouts was to make them go away.


Learn how to master a roof inspection from beginning to end by reading the entire InterNACHI series: Mastering Roof Inspections.

 Take InterNACHI’s free, online 
Roofing Inspection Course
Mastering Roof Inspections
Roofing Underlayment Types
Inspecting Underlayment on Roofs
Fall-Arrest Systems
Roofing (consumer-targeted)
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