Gutters and Downspouts:
Hung Gutters

Description: Hung gutters are formed from 8'-0" to 10'-0" long sheets of 20 oz. cold rolled copper. Adjacent sheets are joined by 1" lapped, riveted, and soldered seams.

Expansion joint spacing depends on gutter configuration and gauge, see Table 4.4.3. At inside or outside corners, expansion joints should be provided not more than 24' from the corner.

As shown in the details, there are many configurations for gutter assemblies. A few basic principles generally apply. For most climates, the supporting brackets or straps should not be spaced more than 30" O.C. The roof (upper) edge of the gutter is folded over. A continuous copper apron, edge strip or cleat, that extends onto the roof sheathing a minimum of 4", is locked into this fold to form a drip.

If straps are used, a reinforcing bar in the gutter bead is required. The straps are fastened through this reinforcing bar. The reinforcing bars or support brackets are made of copper, brass or bronze stock.

Special Conditions: In areas where severe ice or snow conditions exist, special steps must be taken to account for the effects of water back-up, and the weight of the ice or snow. A one-piece gutter and apron design, as shown in Detail B, helps reduce the chance of a leak from capillary action when ice and snow prevent positive drainage. The additional support, also described in Detail B, is required for these climates.

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A. Strap Hung Molded Gutter This is a typical detail of a gutter hung by straps. Straps are riveted or bolted to the outer edge at the gutter bead and attached to the roof with two brass screws. The straps should extend a minimum of 6" onto the roof.

The gutter is supported bybrackets spaced 30" O.C. The upper edge of the gutter is folded over 3/4" to form a lock. The separate apron flashing extends at least 4" onto the roof. Its upper edge is nailed, at 3" O.C., while its lower end hooks over the lock of the gutter.

A two-piece copper gutter and apron is not suitable for areas with severe ice and snow conditions or high winds. In such conditions, refer to the integral apron and gutter in Detail B.

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B. Bracket Hung Gutter with Copper Roof The detail shows the recommended method for use in areas with severe ice and snow as well as other conditions. In this example, use with a copper roof is illustrated.

A one-piece copper gutter and apron is supported by a brass bracket at 30" O.C. The upper edge of the gutter extends at least 6" onto the roof and is folded over and held by cleats at 12" O.C. A continuous locking strip is soldered to the apron at least 4" below its upper edge. The lower edge of the copper roof is hooked over the locking strip.

20 oz. copper braces at 30" O.C. are placed at the mid-points between brackets.

If the gutter width is more than 6", or in areas with ice and snow, brass straps should also be used. These must extend at least 6" onto the roof. If a copper roof is used, the area around screws and the strap must be soldered to ensure watertightness. Brackets, straps and braces are spaced alternately.

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C. Hung Gutter with Copper Fascia This detail illustrates a method of using a hung copper gutter in conjunction with built-up roofing with a copper fascia and gravel stop.

The gutter is secured to the wood fascia with cleats at the top edge and is supported by brass brackets spaced at 30". The brackets are fastened to the wood fascia by two brass screws. Install 20 oz. copper braces at the midpoints between the brackets.

A continuous copper apron strip extends onto the roof a maximum of 4". The copper gravel stop is fastened to the roof by nails spaced 3" in a staggered pattern, through the edge strip.

An optional copper soffit trim piece is also shown. It is attached to the wood fascia under the gutter brackets.

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D. Bracket Hung Molded Gutter This detail illustrates a gutter supported by brackets on an asphalt built-up roof with a gravel stop. Brackets and spacers, alternately spaced, are used to support and stiffen the gutter.

To divert any asphalt drippage, the top ply of roofing felt is extended over the back edge of the gutter.

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E. Strap Hung Molded Gutter This detail shows a copper gravel stop and a copper gutter supported by straps and brackets. They are loose locked together to allow the gutter to expand and contract independently of the gravel stop. The gravel stop is fastened to the roof at its back edge with nails 3" O.C. This detail is not recommended for areas with severe snow and ice conditions. In such areas use an integral gutter and apron detail. See Detail B, Plate 4.4.2.

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F. Strap Hung Gutter on Sloping Roof This detail illustrates an alternate method of attaching copper gutters on sloped roofs. The continuous copper apron strip is fastened to the gutter with a single lock seam and is nailed to the roof with copper nails 12" O.C. Copper braces of 32 oz. copper are alternately spaced with copper brackets at 30" O.C. Straps, extending at least 6" onto the roof, are fastened to these braces and screwed to the roof with two brass screws. Sealant should be applied between the straps and copper apron at fastenings. Abar is required in the outer edge of the gutter for stiffness.

This detail is not recommended for areas with ice and snow conditions.

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G. Expansion Joint Sections Expansion joints should be provided on gutters to allow movement caused by thermal changes. Long straight runs should have joints spaced a maximum of 48' apart. They should also be provided no more than 24' from any corner. See the expansion calculation example in Table 4.4.3.1.

This detail illustrates two types of expansion joints. For the butt type gutter expansion joint, gutter ends are flanged, then riveted and soldered into the ends of gutter sections to be joined. A cover plate is then placed over the expansion joint to improve the appearance of the gutter. Installation of the cover plate should not restrict the movement of gutter sections.

An expansion joint cap is placed on top, over the gutter-end flanges and the cover plate.

For the lap type gutter expansion joint, a gutter-end is recessed 2-1/2" minimum into the gutter on one gutter section and fitted flush on the other. Gutter-ends are flanged, then riveted and soldered into the gutter sections. The flush end of the gutter section is then slipped into the recessed end of the next section. The expansion joint cap is then placed on top, in a manner similar to the fabrication of butt type gutter expansion joints.

Table 4.4.3.1 - Example Gutter Expansion Calculation

A 60 foot copper hung gutter is being installed in 65 degree weather in a locality where the maximum temperature range is from 0 degrees to 100 degrees Fahrenheit. The ends are fixed because they contain downspouts. One end is at a corner the other is at another wall.

Expansion joints must be spaced a maximum of 48' on a straight run, but not more than 24' from a corner. Conforming to these limits results in two sections of gutter, 36' and 24'. The calculations should be based on the dimensions of the longer section.

Min. design temperature = 0 degrees Fahrenheit
Max. design temperature = 100 + 50 (superheat) degrees F.

Contraction temperature difference = dTc = 65 - 0 = 65
Expansion temperature difference = dTe = 150 - 65 = 85

The general formula for calculating the change in Length is (see Plate 4.1.3 for more information):

dL = Length x Expansion coef. x Temperature change
dL = L x 0.0000098 x dT

For the longer section:

Amount of contraction,
dLc = 36 x .0000098 x 65 = .0229' = .28" say 1/4"

Amount of expansion,
dLe = 36 x .0000098 x 85 = .0300' = .36" say 3/8"

For both sections combined:

Total contraction = dLc x 2 = 1/4" x 2 = 1/2"
Total expansion = dLe x 2 = 3/8" x 2 = 3/4"
Total relative movement = dLc + dLe = 1/2" + 3/4" = 1 1/4"

Allowing 1/4" clearance with heads expanded
Min. C = 1/4",

Clearance of heads at installation,
C = Min. Clearance + Total Expansion
C = 1/4" + 3/4"= 1"

Clearance when contracted,
Max. C = C at installation + Total Contraction
Max. C = 1" + 1/2" = 1 1/2"

Amount of movement in long section,
dL = dLe + dLc = 1/4 + 3/8 = 5/8"

Allowing 1/4" laps (dimension E) with cap at top angles when expanded, and 1/8" clearances (dimension D) when contracted,

Leg of each top angle,
B = D + E + dL = 1/4" + 1/8" + 5/8" = 1"
Fold-back of cap, also = 1"

Total width of cap,
A = Max. C + 2 x B + 2 x D
= 1 1/2" + 2 x 1" + 2 x 1/8"
= 3 3/4"