Terminology

• Catchment surface: roof or other impervious area that intercepts rain
• Catchment potential: how much of the rain a surface passes on to the gutter
• Water safety: how little contamination a surface adds to runoff
• K-style gutter: common gutter profile, typically 5 in. or 6 in.
• Leader: vertical pipe that carries water from the gutter to the tank or storm system
• Slope: drop along the gutter run toward the outlet

Standards

Catchment surfaces

• Collection efficiency: about 0.95 for metal, 0.8 average, 0.75 for soil surfaces
• Cleanest roofs: unpainted galvanized and standing seam steel are generally considered the cleanest in a Texas study; shingle roofs can add more particulates and some chemical concern
• Other surfaces: ARCSA/ASPE/ANSI 63 addresses roofs and other hard surfaces; parking lots and walkways fall under ARCSA/ASPE/ANSI 78 for stormwater harvesting
• Plumbing code: collection surfaces, gutter slope and sizing, cleanouts, and joints follow the code provisions in the roofs and plumbing parent notes

Conveyance sizing

• Gutter cross-section rule of thumb: about 1 cm2 of gutter area per 1 m2 of catchment
• Example: a 23 m2 catchment needs at least 2.13 in. pipe diameter; the next common size is 2.5 in.
• Slope guidance: about 1/2 in. of drop per 10 ft in one design guide; a larger gutter allows less slope; check the minimum slope required by the adopted plumbing code
• Other methods: online calculators for K-style gutters, pipe friction tables, Hazen-Williams, and Manning's equation

Materials

• Aluminum, steel, zinc, vinyl, or copper K-style gutters: easy to mount, fittings easy to find
• Straight PVC: accessible and easy to work with; sizing must be more precise
• Half-round PVC: easy to slope, hard to mount
• Hand-shaped galvanized sheet metal: accessible, but joints are hard on long runs
• Bamboo: inexpensive, less durable

Detailing

• Slope: continuous toward the outlet to prevent clogging, sagging, mosquito breeding, and freeze damage
• Roof edge: gutter end should not sit so low it looks wrong, and a steep roof can overshoot a gutter
• Debris: fit leaf guards and a screen at each downspout; see the first-flush note
• Joints: watertight and compatible with the tank and filtration chain
• Cleanouts: provide access to downspouts and collection piping
• Test: pour water at the far end of each gutter run and check for leaks and standing water
• Coordination: roofing, flashing, and gutter attachment with the roofer; leaders with the plumbing engineer

Uses

Specific uses

• Residential and commercial rainwater harvesting
• Cistern and underground tank feed lines
• Rain gardens and landscape drains
• Retrofit of existing roofs with collection gutters

Pros and cons

Pros

• Roof drainage already exists on most buildings and needs few changes
• Metal roofs give high collection and good water safety
• Common gutters are widely available

Cons

• Asphalt and thatch roofs reduce water safety
• Roof coatings and treatments can affect water quality
• Debris, pollen, and bird droppings enter with the runoff

Manufacturing and cost

Construction

• Gutters are roll-formed or extruded and hung from the fascia; leaders are fastened to the wall and connected to underground or exposed collection piping

Main manufacturers and suppliers

• Rainwater Management Solutions
• Graf USA

Trade association: ARCSA, American Rainwater Catchment Systems Association.

Sources

• Grafman, L.: To Catch the Rain, section 2.1 catchment surface, https://eng.libretexts.org/Bookshelves/Environmental_Engineering_(Sustainability_and_Conservation)/Book%3A_To_Catch_the_Rain_(Grafman)/02%3A_Components/2.01%3A_Catchment_Surface
• Grafman, L.: To Catch the Rain, section 2.2 conveyance, https://eng.libretexts.org/Bookshelves/Environmental_Engineering_(Sustainability_and_Conservation)/Book%3A_To_Catch_the_Rain_(Grafman)/02%3A_Components/2.02%3A_Conveyance_(Gutters_and_Downspouts)
• Grafman, L.: To Catch the Rain, section 4.3 gutter and downspout sizing, https://eng.libretexts.org/Bookshelves/Environmental_Engineering_(Sustainability_and_Conservation)/Book%3A_To_Catch_the_Rain_(Grafman)/04%3A_Calculations/4.03%3A_Gutter_and_Downspout_Sizing
• Texas Water Development Board: effect of roof material on harvested rainwater quality, https://www.twdb.texas.gov/innovativewater/rainwater/projects/rainquality/index.asp
• American Society of Plumbing Engineers: ARCSA/ASPE/ANSI 63-2020 rainwater catchment systems, https://aspe.org/?p=6144
• Image: 20140530-AMS-LSC-9001 - Peoples Garden - Rain Barrel (15498316125).jpg, U.S. Department of Agriculture, Public domain, https://commons.wikimedia.org/wiki/File:20140530-AMS-LSC-9001_-_Peoples_Garden_-_Rain_Barrel_(15498316125).jpg