Gutters & Downspouts, common leak points (C) Carson Dunlop Associates Roof Gutters & Downspouts Home Page

  • GUTTERS & DOWNSPOUTS - CONTENTS: A complete guide to gutters, downspouts, & roof drainage systems. Types & photos of roof drainage systems: gutters, downspouts. Definition of eaves trough or integral roof gutter; Definition of yankee gutter. Comparison of aluminum gutters, copper gutters, plastic gutters, wood gutters. Gutter & downspout defects, clogging, overflowing, holes corrosion, leaks that cause wet basements or crawl areas. Gutter screens, types, uses, maintenance. How to avoid Snow & ice damage to roof gutters. Roof gutter installation & repair details: drip edge, slope, capacity, leak sealants, support, length & placement of leader & downspout extensions. Proper installation of buried downspout extensions. Proper installation of French drains & seepage pits at flat sites. Gutter & downspout defects cause wet basements & crawl areas
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Building gutters, leaders, roof drainage systems:

In this article series we describe good gutter and downspout installation details, the need for roof gutters and drainage systems, and we describe the types of roof gutters used on buildings. This article series discusses how to choose, install, diagnose & maintain roof gutters & downspouts, & roof drainage systems to prevent building leaks and water entry.

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Guide to Roof Gutter & Downspout Systems

No gutter installed (C) Daniel Friedman

Our page top sketch of common roof gutter leak causes is provided courtesy of Carson Dunlop Associates.

Quoting from Carson Dunlop Associates' Home Reference Book:

Gutters and downspouts have two major functions. Firstly, they protect the walls of a building from water that would ordinarily run off the roof. This water can damage the wall surfaces and cause localized erosion at ground level.

The most important function of gutters and downspouts in homes with basements or crawlspaces, however, is helping to ensure a dry basement.

Regardless of the foundation type, there is always the risk of water penetration. The less water there is in the soil near the foundation wall, the lower the risk of water penetration into the basement.

Gutters should collect all water run off, and downspouts should discharge the water into proper drains or onto the ground well away from the foundation walls

[Click any image or drawing to see an enlarged, detailed version.]

Are Gutters Really Necessary?

Raccoon outdoors on a downspout (C) Daniel Friedman

If your building is located where it rains or where there is snow-melt, your building probably needs a roof drainage system to carry water away from the building in order to prevent leaks into the building, especially if the building includes below-ground areas such as a basement or crawl area.

A very large percentage of basement or crawl space water entry, moisture, leaks, rot, and mold problems all begin at the building roof, with the failure to adequately capture roof runoff and to direct it away from the building.

We have met a few architects who never include gutters in their building design, arguing that "Gutters are ugly, and besides we've never had a water entry problem in our homes." Yet every home we inspected of that design had a wet basement within a short time of construction, sometimes even during construction, [excepting in arid climates of little rainfall, homes built on slabs with no basement or crawl area, or homes whose surrounding soils incorporate special subsurface drainage systems].

Even where a roof drainage system such as simple gutters and downspouts are installed, errors in their installation or failure to maintain (and clean out) clogged gutters remains a most common source of wet basements and crawl spaces.

Fix the Gutters Before Installing a Basement de-Watering System

Watch out: While on occasion we find a home that was built over a spring or stream bed, or was unfortunately located at the bottom of a hillside, even then, mis-handling of water coming off of the building roof is very often a major source of chronic basement leakage. Before installing a costly basement de-watering system to cure "rising damp" or "high water table flooding" at your building, making an expert inspection of the condition of the gutter and downspout system is worthwhile.

In some climates some roofs and buildings make it difficult to install and keep gutters on the roof. For example a standing seam metal roofed building in a climate subject to heavy snowfall or ice formation may keep losing its gutters to sliding snow and ice. Proper gutter installation details and snow guards can solve this problem on some buildings. See Snow & Ice Damage to Building Gutters for details.

Where those steps don't work, a more costly and extensive surface and subsurface installation of geotextiles and waterproof drainage mats below the soil surface (or below gravel) at the building eaves can be constructed to keep water away from the building foundation, draining it to a distant catch basin or lower site area. See BASEMENT WATERPROOFING.

Types of Gutter & Roof Drainage Systems

Gutter Types by Profile or Shape

By examining the shape or "profile" of a gutter from the ground we can often determine whether it is made of aluminum (below), galvanized steel, or plastic. It's also usually easy to identify copper gutters even from ground-level inspection, as we illustrate below.

Gutter and Downspout Details (C) Carson Dunlop Associates

The sketch at left shows a traditional "K" profile aluminum gutter at left, and a more-rounded galvanized steel gutter at right.

Sketch courtesy of Carson Dunlop Associates.

Gutter Size & Capacity: the gutter size needed at a building depends on the total roof area being drained and the length of gutter available to collect that water. The most common gutter sizes are 4-inch and 5-inch widths. Details are at GUTTER SIZES

Types of Gutter Hangers or Supports: are discussed at Types of Gutter Hangers

Aluminum K-Gutter Shape & Profile photos

The aluminum gutter shown below is commonly referred to as a "K" gutter because of its gutter profile, as shown in the gutter profile sketch above. Aluminum gutters are widely used in North America as they are light, easy to install, and corrosion resistant. The outer gutter surface is a baked enamel finish available in white, brown, green, and black. The interior surface may be a silver or bronze color depending on plating.

Aluminum K Gutter (C) Daniel Friedman Aluminum K Gutter (C) Daniel Friedman

Aluminum gutters are easily bent such as by an inspector's ladder or by careless chopping of ice at the roof edge. Connections among gutter sections are made using a combination of slip-joint connectors and sealant, often butyl caulk. See Types of Gutter Hangers for a discussion of how aluminum gutters are secured to the roof edge.

Copper Gutter Shape & Profile photos

Copper gutters are readily identifiable by their characteristic colors (red, brown, or marked with a green patina). Copper gutters are provided in a variety of profiles including the "K" shape (shown below), a rectangular or "box" shape that may be custom fabricated for the building, and traditional half-round design. The copper gutter shown at below right was custom fabricated to fit at the wall top of the building. You will notice the brown oxidized copper interior of the gutter and the green copper patina on the gutter's exterior and upper edge.

Copper Gutter (C) Daniel Friedman Copper Gutter (C) Daniel Friedman

New half-round copper gutters and rectangular copper downspout are shown at below left. At below right we show an underside-view of traditional half-round copper gutters and a recently-installed round copper downspout.

Copper Gutter (C) Daniel Friedman Copper Gutter (C) Daniel Friedman<

Galvanized Roof Gutters Shape & Profile photos

Galvanized roof gutters are provided in both "K" and half-round profiles, though the half-round profile is perhaps most common. Our galvanized half-round gutter photo at below left shows that the gutter is rusted and overflowing.

Galvanized half round gutters (C) Daniel Friedman Galvanized half round gutters  (C) Daniel Friedman

At above right the half-round galvanized gutters were painted but have rusted through, sagged, and are at end of their useful life.

Plastic Roof Gutters Shape & Profile photos

Plastic roof gutters are popular with "do-it-yourself" homeowners, perhaps because the connecting gutter and downspout parts appear to snap together nicely and may include built-in gaskets in the gutter connectors. We often find that plastic roof gutter systems are under-sized, inadequately supported, and loose.

Plastic gutters (C) Daniel Friedman Plastic gutters (C) Daniel Friedman

Hung Wood Gutters Shape & Profile photos

Our hung wood gutter photo (below left) shows a common type of gutter used in North America: the gutter was actually carved out of a solid piece of wood. You can also see that while wood gutters may have lasted a very long time, sometimes up to 50 years, eventually the gutter is both rotted and filled with moss.

Wood gutters are more attractive than some metal alternatives but require considerable maintenance if they are un-lined: annual inspection, caulking at seams, and treatment with a preservative oil. The heavy moss found in this hung-wood gutter makes clear that it had not been inspected nor cleaned for a long time.

Sod roof (C) Daniel Friedman Sod roof (C) Daniel Friedman

Our second wood gutter photo (above right) was observed on a sod roof in Molde, Norway. This wood gutter approach is similar to a Yankee gutter but without brackets and using a larger timber to form the gutter side. The larger timber is used to help keep sod from sliding down or washing off of the roof surface.

Roof Gutter & Downspout Articles


Continue reading at GUTTER DEFECTS LIST or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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