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gutters & downspouts

Gutters and Downspouts are utilized to minimize ground erosion by collecting rainwater from roofs. Gutters are installed below the slope line so that ice or snow can slide freely off the sloped roof without damaging gutter system. The amount of rain or melting snow discharged into the gutter system is influenced by the typical rainfall for a region and total roof area available. Gutters empty rainwater into downspouts or ‘leaders’ that deliver water to a drywell, sewer system, or ‘daylighted’ onto the ground to seep into the groundwater system. Gutters can be made of vinyl, galvanized steel, or aluminum. Copper and stainless steel is also available.

For this section we will explore common residential and light commercial gutters and downspouts made of aluminum and galvanized steel. Common steel gutter gauges are 24-30 gauge with 26 gauge being used most commonly in residential work. 26 gauge is often recommended as it is more resistant to warping under ice or ladder loads. Common steel downspout gauges are 26 or 28 gauge. Hot-dip galvanization is also recommended for steel. Aluminum gutters have become quite popular as they can be cold formed on site custom to the structure, allowing limited joints and easier transportation of stock material. Common aluminum gutter gauges are .019 – .032 ” thickness with .027″ being the industry standard. Warrantied gutter typically end up being 0.032″. Aluminum downspouts are usually 0.024-0.027″ thicnkess.

The most common gutter shapes are beveled, half-round, or K-Style.


K-style have become quite popular for residential applications and range in heights of 2-3/4″ – 6″, with widths of4″ – 8″. A good rule-of-thumb to use for sizing gutters is 4″ width for up to 750SF roof area, 5″ width for up to 1400SF roof area. Straight runs are commonly sloped a minimum of 1/16″ per foot. Joints in gutters are typically lapped and soldered or adhered together with mastic.


For runs over 40′, expansion joints are recommended for movement.

The dimension between the outer tip of the gutter and the imaginary slope line is; 1/4″ for 12:12 roof slope, 1/2″ for 7/12 roof slope, and 3/4″ for 5/12 roof slope.


An ‘inside miter’ is required for joints at inside corners, and likewise with outside miters.


For downspouts, a good rule of thumb is to have 1 square in of sectional area for each 100sf of roof area. Downspouts are commonly corrugated to provide additional strength and to provide resistance to bursting when plugged with expanding ice.


Gutters and downspouts are commonly installed after the roofing, fascia, soffits, and siding are in place.

The following are components that make up a typical gutter system:


Strap-Hangers – screwed or nailed to roof sheathing often to rafters for best support, often spaced every +/- 3′ depending on gutter size.


Spike and ferrule hangers can be utilized in addition to or in-lieu of strap hangers and are fastened through the fascia to the rafter tails. Also brackets may be utilized inside of which the gutter snaps into. Brackets are also fastened to the fascia board and/or the rafter tails.


Strainer – Prevents downspout clogging and is placed directly above downspouts inside gutter.

End Cap – Terminates a run, designated as ‘left’ or ‘right’


End Section w/Outlet – Standard gutter section with a ‘Tee’d’ outlet for downspout connection.

Leader – Offset section with +/- 45 degree bends on each end to provide routing of water from gutter to a downspout that is attached to the building


Downspout – Standpipe unit which receives gutter drainage and sends it down below into ground or sewer system. May require (leader) straps at top or bottom and at intermediate joints (if necessary) to attach to building.

Elbow – Utilized particulary when drainage empties onto a splash block to route water away from the building, foundation, or basement. Can be deisgnated by ‘A’ (sitting on wide side) or ‘B’ (sitting on narrow side)


Slip Joint Connector – Essentially a gutter coupler piece with 2 male connectors, one on each end, bringing two gutter pieces together.

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