Gutters and Downspouts

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Climate

The following are some climate-specific considerations:

  • Hot-Dry and Mixed-Dry Climate. Gutters are not necessary in dry climates. However, do install a wide roof overhang to keep the drip line from occasional rainwater and melted snow away from the structure and do slope the grade away from the building.
  • Marine Climate. In areas with potentially high winds and heavy rains, increase gutter and rain leader capacity to accommodate heavy rain and large roof areas. Use metal rather than vinyl gutters and downspouts in areas susceptible to forest fire (Baechler et al. 2010).
  • Cold and Very Cold Climates. Avoid the use of gutters in high snow load locations. Use metal rather than vinyl gutters and downspouts in areas susceptible to forest fire. (Baechler et al. 2011c).

ENERGY STAR Version 3, (Rev. 07)

Gutters and downspouts are not required in Dry (B) climates as shown in the IECC climate zone map (2009 IECC Figure 301.1 and Table 301.1).

climate zone map

International Energy Conservation Code (IECC) Climate Regions

Description

A few inches of rain falling on the roof of a house can produce several thousand gallons of water runoff (EPA 2013). This runoff must be channeled away from the building foundation to keep the basement or crawlspace dry and to prevent water from seeping into the building interior where it may create moisture problems. If not drained away from the house, the immense volume of water coming off the roof can quickly saturate the soil surrounding the building and wick through the foundation to the interior. Once inside, this moisture can lead to a variety of problems, including mold and rot. Moisture in homes is both a cause of indoor air quality problems and an important factor affecting the durability of the building (Lstiburek and Brennan 2001).

Saturated ground water. If not drained away from the house, the sheer volume of the water coming off a roof can quickly saturate the soil and wick through the foundation into the interior of a building
Figure 1 - Saturated ground water. If not drained away from the house, the sheer volume of the water coming off a roof can quickly saturate the soil and wick through the foundation into the interior of a building.  Reference

As a whole-house best practice, it is important to design the house exterior with climate-appropriate flashing, overhangs, gutters, downspouts, and drainage planes to shed rainwater and conduct it away from the house (Baechler et al. 2010). A system of gutters and downspouts is particularly important to keep water away from the building foundation in areas with expansive and/or collapsible soils.

Expansive soils swell when they get wet and can put extreme pressure on foundations, even to the point of causing cracking or uplift of foundation materials. Collapsible soils are lose soils that shrink in volume when they become wet, causing the ground to collapse. At the very least, when these soils get wet around a building, they can create a trough that collects water, increasing the likelihood of that water seeping into the foundation. In extreme cases, some collapsible soils can sink to the point of dislodging or cracking a building foundation (Colorado Geological Survey 2011). The assessment of whether the soil is expansive or collapsible needs to be completed by a certified hydrologist, soil scientist, or engineer.

Controlling Roof Runoff

As outlined in the scope, builders have four options for dealing with rain water runoff from a roof:

  • Install gutters and downspouts that terminate at least 5 feet away from foundations. OR
  • Install gutters and downspouts that terminate to an underground catchment system at least 10 feet away from foundations. OR
  • An alternative option to gutters is to deposit rainwater to a grade-level rock bed with a waterproof liner and a drain pipe where water terminates on a sloping finish grade at least 5 feet from the foundation. OR
  • If a rainwater harvesting system is installed, properly design the drain to adequately manage the overflow, and meet discharge-distance requirements.

Gutters System Basics

Gutter systems consist of two parts: 1) gutter channels that run horizontally along the roof edge to collect runoff and 2) the downspouts that carry the collected water down to grade level. Gutters are needed in all but the driest climates of the United States. In cold climates, gutters will freeze and should be avoided. Instead, in cold climates, grade-level drainage systems should be installed (as described below).

Gutter channels are typically available in K-styles (also known as "ogee," as the shape resembles this molding type) and U-styles (or half round), and in 4-, 5-, and 6-inch sizes. The style is principally aesthetic; there is no substantial difference in performance. Size, however, does matter. A larger size will conduct more water at a faster rate, provided there are enough downspouts to drain the gutter channels (EPA 2013).

Gutter channel. Stock gutter material's found in building supply centers are often listed as "K" or "U" styles. The difference in styles is purely aesthetic

Figure 2 - Gutter channel. Stock gutter material's found in building supply centers are often listed as "K" or "U" styles. The difference in styles is purely aesthetic.  Reference

Both styles are readily available in vinyl, aluminum, galvanized steel, and copper. All materials weather well, although copper and galvanized steel have the advantage of withstanding impacts from ladders and tree branches better than vinyl and aluminum, which can crack or dent.

Install gutters along the roof eaves so they slope at least 1/16 inch per foot of run. This will provide positive drainage to direct water toward the downspouts.

Downspouts conduct water from the roof to grade-level. They should terminate at least 5 feet from the foundation, or to an underground catchment system located at least 10 feet from the foundation.

Downspout termination. Unless downspouts are connected to an underground catchment system or storm sewer system, they should drain to daylight at least 5 feet from the foundation

Figure 3 - Downspout termination. Unless downspouts are connected to an underground catchment system or storm sewer system, they should drain to daylight at least 5 feet from the foundation.  Reference 

How to Install Downspouts

  1. Install downspouts every 20 to 50 feet along the gutter. The more closely downspouts are spaced along the gutter, the more water can be conducted away during peak rainstorms. 
  2. Connect the end of the downspout to lateral piping made from non-perforated flexible ABS or Schedule 40 PVC pipe.
  3. Extend the lateral piping at least 5 feet from the building. Use a level and tape measure to ensure that the pipe is pitched away from the foundation at a minimum 5/8-inch per foot (a 5% slope).
  4. Terminate the lateral pipe to daylight (or to a catchment system or storm sewer). It is critical that a daylight drain empty onto a sloped grade that directs water away from the building, and does not allow water to drain back towards the building. A splash block placed at the end of the lateral pipe will help control erosion to this location (EPA 2012).

Grade-level drainage system. In cold and very cold climates, where snow can accumulate on roofs, the water in gutters can freeze; therefore, gutters should be avoided in cold and very cold climates. Instead, install a grade-level drainage system that conducts roof run-off away from the foundation.

Grade-level drainage. Gutters can freeze in cold and very cold climates. Therefore, in these climates, install a grade-level drainage system, as shown here

Figure 4 - Grade-level drainage. Gutters can freeze in cold and very cold climates. Therefore, in these climates, install a grade-level drainage system, as shown here.  Reference

How to Install Grade-Level Drainage

  1. Install a perimeter foundation drain at the footing level. The standard foundation drainage system shown in the graphic above consists of Schedule-40 perforated piping and clean stone that is isolated from the surrounding soils with filter fabric.
  2. Backfill the foundation drainage system with a well-draining backfill material.
  3. Stop backfilling 16 to 18 inches from grade level. 3a) Lay-in a piece of EPDM rubber roofing or other impervious membrane to isolate the grade-level drainage system from the foundation drainage system. 3b) Install Schedule-40 PVC or ABS perforated pipe, or similar perimeter drainage piping. This piping should extend past the corner of the foundation at least 5 feet and drain to daylight or connect to a catchment system or storm sewer. 3c) Backfill around the drainage pipe with clean stone surrounded by filter fabric. Bring the sides of the EPDM isolation membrane up the sides to create a contained channel so water is drained off by the perforated piping and does not overflow and saturate the foundation backfill.
  4. To finish off, cover the drainage system with 4 to 6 inches of clean stone.
  5. Leave 8 to 16 inches of space between the finished surface and the first course of siding to prevent splash back from damaging siding materials (EPA 2012).

Underground catchment system.  As an alternative to draining roof runoff to daylight, the downspout can connect to a catchment system, storm sewer or rainwater-harvesting system. The illustration below depicts one type, known as a drywell, that can be installed, but many types of both underground and above-grade catchment systems are available. When designed to collect roof runoff and properly drain overflow, rainwater harvesting systems, which retain the water in a tank for use in watering landscaping, may also be used to meet roof drainage requirements.

Catchment system. A roof runoff catchment system, such as the drywell shown here, must be located at least 10 feet from the building foundation.

Figure 5 - Catchment system. A roof runoff catchment system, such as the drywell shown here, must be located at least 10 feet from the building foundation.  Reference 

How to Install a Catchment System

  1. Connect downspouts to lateral piping that extends at least 10 feet from the foundation.
  2. Provide overflow protection to alleviate the water load during peak rain events. Locate overflow pipe at a branch in the downspout, or tee-off near the top of the catchment basin. If it branches off the downspout, as shown in this illustration, it must extend at least 5 feet from the building foundation and drain to daylight.
  3. 3a. Install a clean-out in the catchment basin. In a drywell, as shown here, this clean-out consists of a perforated pipe through the center of the gravel that allows the basin to be flushed out periodically. The clean-out should also connect to the lateral pipe to allow leaves and other debris to be removed.
    3b. Isolate the catchment basin with a geotextile filter fabric to prevent soil intrusion from clogging the system.
    3c. Fill the basin area with coarse gravel. One to 1½-inch gravel is typical. Small gravel will tend to clog too quickly (EPA 2012).

A Note about Kick-Out Diverters for Climates with Heavy Rainfalls

In climate zones that have heavy rainfalls which can overwhelm gutter capacity, a diverter (also known as “kick-out flashing”) should be integrated with the house wrap. Step-by-step instructions for kick-out diverters can be found in Chapter 12 of Baechler et al. (2010).

Ensuring Success

Gutters and downspouts need to be sized to accommodate anticipated water loads. The number of downspouts will depend on the cross-section dimension of the downspout material. Allow 1-inch-squared of downspout cross-section for every 100 square feet of roof area. Place downspouts at least 20 feet apart but no more than 50 feet apart. Foresight in the design of the building façade may be necessary to accommodate this downspout spacing (JLC 2003). Lateral piping at the end of each downspout should also be given careful design consideration because typically a 5-foot lateral channel will get in the way of lawn mowing and other yard activities. 

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Scope

Gutters and downspouts empty to piping depositing water on sloping final grade ≥ 5 ft. from foundation or to underground catchment system ≥ 10 ft. from foundation

Install adequately sized gutters and downspouts to carry water away from foundations.

DOE Zero Energy Ready Home Notes

The U.S. Department of Energy’s Zero Energy Ready Home Program requires that builders comply with the ENERGY STAR Certified Homes requirements as described below and in the Compliance tab. Builders must also meet the requirements of the U.S. Environmental Protection Agency’s Indoor airPLUS Program. The Indoor airPLUS checklist (Item 1.7) dictates that builders provide protection from water splash damage if there are no gutters.

The Indoor airPLUS Construction Specifications document notes that completion of the ENERGY STAR Water Management System checklist now satisfies the following Indoor airPLUS requirements: Direct roof water away from the house using gutters and downspouts that empty into lateral piping on a sloping finish grade; OR Direct roof water to an underground catchment system not connected to the foundation drain system that discharges water >= 10 ft. from the foundation.

However, Indoor airPLUS requires that builders provide extra protection against water splash damage on homes that don’t have gutters and downspouts. Only homes that meet certain ENERGY STAR exceptions are exempt from having gutters (slab on grade homes, homes that deposit rainwater to a grade-level rock bed with a waterproof liner and drain pipe, or homes that use a continuous rubber membrane system). For houses that don’t have gutters, builders must provide protection against water splash damage in one of the following ways:

  • Extend the foundation walls at least 16 in. above final grade; OR
  • Provide a drip line that is horizontally 16 in. away from the edge of the foundation wall; OR
  • Use cladding material that can tolerate regular wetting and install a well-sealed, continuous drainage plane that extends at least 16 in. above final grade (e.g., brick veneer or stone cladding with self-adhering moisture control membrane).

Indoor airPLUS Exceptions: These requirements don’t apply to:

  • homes in dry climates, as defined by the 2009 International Energy Conservation Code (IECC) Figure 301.1
  • homes with rainwater harvesting systems that are designed to properly drain overflow, meeting discharge-distance requirements outlined in the ENERGY STAR Water Management System (WMS) Checklist, Item 3.2.

ENERGY STAR Certified Homes Notes

The ENERGY STAR Certified Homes Water Management System Checklist dictates the following (Item 3.2):

For homes that don’t have a slab-on-grade foundation and do have expansive or collapsible soils, gutters and downspouts are provided that empty to lateral piping that discharges water on sloping final grade >= 5 ft. from the foundation or to an underground catchment system not connected to the foundation drain system that discharges water >= 10 ft. from the foundation.

Footnotes:

(4) Not required in Dry (B) climates as shown in the 2009 IECC Figure 301.1 and Table 301.1.

(14) The assessment of whether the soil is expansive or collapsible shall be completed by a certified hydrologist, soil scientist, or engineer.  As an alternative, a roof design is permitted to be used that deposits rainwater to a grade-level rock bed with a waterproof liner and a lateral drain pipe that meets discharge requirements per Item 3.2. As another alternative, the builder can install a rainwater harvesting system that drains overflow to meet discharge requirements per Item 3.2.

Training

Right and Wrong Images

Presentations

  1. Presentation: Gutters and Downspouts Training
    (2 MB)
    Author(s): Steve Easley & Associates
    Organization(s): Steve Easley & Associates

Videos

None Available

CAD Images

None Available

Compliance

DOE Zero Energy Ready Home Notes

The U.S. Department of Energy’s Zero Energy Ready Home Program requires that builders comply with the ENERGY STAR Certified Homes requirements as described below and in the Compliance tab. Builders must also meet the requirements of the U.S. Environmental Protection Agency’s Indoor airPLUS Program. The Indoor airPLUS checklist (Item 1.7) dictates that builders provide protection from water splash damage if there are no gutters.

The Indoor airPLUS Construction Specifications document notes that completion of the ENERGY STAR Water Management System checklist now satisfies the following Indoor airPLUS requirements: Direct roof water away from the house using gutters and downspouts that empty into lateral piping on a sloping finish grade; OR Direct roof water to an underground catchment system not connected to the foundation drain system that discharges water >= 10 ft. from the foundation.

However, Indoor airPLUS requires that builders provide extra protection against water splash damage on homes that don’t have gutters and downspouts. Only homes that meet certain ENERGY STAR exceptions are exempt from having gutters (slab on grade homes, homes that deposit rainwater to a grade-level rock bed with a waterproof liner and drain pipe, or homes that use a continuous rubber membrane system). For houses that don’t have gutters, builders must provide protection against water splash damage in one of the following ways:

  • Extend the foundation walls at least 16 in. above final grade; OR
  • Provide a drip line that is horizontally 16 in. away from the edge of the foundation wall; OR
  • Use cladding material that can tolerate regular wetting and install a well-sealed, continuous drainage plane that extends at least 16 in. above final grade (e.g., brick veneer or stone cladding with self-adhering moisture control membrane).

Indoor airPLUS Exceptions: These requirements don’t apply to:

  • homes in dry climates, as defined by the 2009 International Energy Conservation Code (IECC) Figure 301.1
  • homes with rainwater harvesting systems that are designed to properly drain overflow, meeting discharge-distance requirements outlined in the ENERGY STAR Water Management System (WMS) Checklist, Item 3.2.

ENERGY STAR Certified Homes Notes

The ENERGY STAR Certified Homes Water Management System Checklist dictates the following (Item 3.2):

For homes that don’t have a slab-on-grade foundation and do have expansive or collapsible soils, gutters and downspouts are provided that empty to lateral piping that discharges water on sloping final grade >= 5 ft. from the foundation or to an underground catchment system not connected to the foundation drain system that discharges water >= 10 ft. from the foundation.

Footnotes:

(4) Not required in Dry (B) climates as shown in the 2009 IECC Figure 301.1 and Table 301.1.

(14) The assessment of whether the soil is expansive or collapsible shall be completed by a certified hydrologist, soil scientist, or engineer.  As an alternative, a roof design is permitted to be used that deposits rainwater to a grade-level rock bed with a waterproof liner and a lateral drain pipe that meets discharge requirements per Item 3.2. As another alternative, the builder can install a rainwater harvesting system that drains overflow to meet discharge requirements per Item 3.2.

More Info.

Case Studies

  1. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: September, 2013

    Case study of a DOE Zero Energy Ready Home in west Connecticut that scored HERS 39 without solar PV. The 3,000 ft2 two-story home has R-33 double-walls, R-72 flat roof with closed-cell foam and blown cellulose, an ERV, and LED lighting.

  2. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: September, 2013

    Case study of a DOE Zero Energy Ready Home in Downers Grove IL that scored HERS 35 without PV. This 3,600 ft2 custom home has advanced framed walls with R-23 dense-packed fiberglass plus R-13 rigid polyiso, a sealed attic with open-cell spray foam, a pier foundation, and 95% efficient gas furnace.

References and Resources*

  1. Author(s): Baechler, Gilbride, Hefty, Cole, Adams, Noonan, Love
    Organization(s): PNNL, ORNL
    Publication Date: September, 2011

    Report describing measures that builders in mixed-humid climates can use to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

  2. Author(s): Baechler, Gilbride, Hefty, Cole, Adams, Butner, Oritz, Love
    Organization(s): PNNL, ORNL
    Publication Date: September, 2011

    Report describing measures that builders in mixed-humid climates can use to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

  3. Author(s): Baechler, Gilbride, Hefty, Cole, Williamson, Love
    Organization(s): PNNL, ORNL
    Publication Date: September, 2010

    Report providing builders in marine climates with guidance for building homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

  4. Author(s): Baechler, Gilbride, Hefty, Cole, Love
    Organization(s): PNNL, ORNL
    Publication Date: February, 2011

    Guide describing measures that builders in the cold and very cold climates can take to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

  5. Author(s): Colorado Geological Survey
    Organization(s): Colorado Geological Survey
    Publication Date: April, 2011

    Information sheet discussing building foundation problems caused by settling soil in Colorado.

  6. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2014

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  7. Author(s): EPA
    Organization(s): EPA
    Publication Date: June, 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

  8. Author(s): EPA
    Organization(s): EPA
    Publication Date: November, 2013

    Document outlining specifications that were developed by the U.S. Environmental Protection Agency (EPA) to recognize new homes equipped with a comprehensive set of indoor air quality (IAQ) features.

  9. Author(s): Journal of Light Construction
    Organization(s): Journal of Light Construction
  10. Author(s): Lstiburek, Brennan
    Organization(s): BSC
    Publication Date: December, 2006

    Document with important building science considerations, designed for members of the residential construction and remodeling industries, as well as owners and managers who work in affordable housing.

  11. Author(s): EPA
    Organization(s): EPA
    Publication Date: February, 2013

    Website providing technical guidance to help home builders and their subcontractors, architects, and other housing professionals understand the intent and implementation of the specification requirements of the IAQ labeling program.

  12. Author(s): EPA
    Organization(s): EPA
    Publication Date: February, 2011

    Guide describing details that serve as a visual reference for each of the line items in the Water Management System Builder Checklist.

Last Updated: 06/12/2014

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