Gutters and Downspouts
Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
Showing changes from Rev 1
to Rev 2
in Gutters and Downspouts.
---
title: Gutters and Downspouts
…187 unchanged lines
## Coastal, industrial, and high-pollution exposures accelerate corrosion of bare and coated metals, and they govern the choice between a standard polyester finish and a premium PVDF finish as well as the choice of substrate. {note}
+## The exterior exposure severity shall be classified, and the finish and substrate selections shall account for the corrosion risk it presents.
+
```datasheet
label: Exterior exposure severity
…5 unchanged lines
```
−# Materials {toc}
+# Material selection is the first decision and it drives every downstream compatibility constraint: fastener metal, solder or sealant joint method, and contact with adjacent roof-edge metals. Prefinished aluminum is the usual commercial choice; galvanized steel and Galvalume are economical alternatives; copper and zinc are premium institutional, historic, and high-exposure choices. {note}
−## Material selection is the first decision and it drives every downstream compatibility constraint: fastener metal, solder or sealant joint method, and contact with adjacent roof-edge metals. Prefinished aluminum is the 80% commercial default; galvanized steel and Galvalume are economical alternatives; copper and zinc are premium institutional, historic, and high-exposure choices. {note}
+# The gutter and downspout substrate material shall be specified, and fastener metal and adjacent roof-edge metal contact shall be selected for compatibility with it.
```datasheet
…9 unchanged lines
```
−## Aluminum {toc}
+# Aluminum {toc}
−### Aluminum gutter and downspout coil shall be alloy 3105-H24 conforming to ASTM B209.
+## Aluminum gutter and downspout coil shall be alloy 3105-H24 conforming to ASTM B209.
−### Aluminum is specified by decimal thickness, not by gauge; stating a gauge for aluminum is ambiguous because the gauge-to-thickness relationship differs from steel. The commercial default is 0.032 in for 5 in and 6 in gutters, with 0.027 in acceptable for residential and light-commercial work and 0.040 in for heavy-commercial and built-in gutters. {note}
+## Aluminum is specified by decimal thickness, not by gauge; stating a gauge for aluminum is ambiguous because the gauge-to-thickness relationship differs from steel. The commercial default is 0.032 in for 5 in and 6 in gutters, with 0.027 in acceptable for residential and light-commercial work and 0.040 in for heavy-commercial and built-in gutters. {note}
−### Aluminum sheet thickness shall not be less than the value scheduled for the gutter size and exposure.
+## Aluminum sheet thickness shall not be less than the value scheduled for the gutter size and exposure.
```datasheet
…7 unchanged lines
```
−## Galvanized Steel {toc}
+# Galvanized Steel {toc}
−### Galvanized steel gutter and downspout sheet shall conform to ASTM A653/A653M with a G90 zinc coating designation.
+## Galvanized steel gutter and downspout sheet shall conform to ASTM A653/A653M with a G90 zinc coating designation.
−### A G60 coating is a residential minimum and shall not be used for commercial gutters; G90 is required for commercial durability because the heavier zinc coating substantially extends service life in the standing-water and debris environment of a gutter. {note}
+## A G60 coating is a residential minimum and shall not be used for commercial gutters; G90 is required for commercial durability because the heavier zinc coating substantially extends service life in the standing-water and debris environment of a gutter.
−### Prepainted galvanized steel gutter stock shall conform to ASTM A755/A755M for the coil-coating process.
+## Prepainted galvanized steel gutter stock shall conform to ASTM A755/A755M for the coil-coating process.
```datasheet
…7 unchanged lines
```
−## Galvalume {toc}
+# Galvalume {toc}
−### Galvalume gutter and downspout sheet shall conform to ASTM A792/A792M with an AZ50 coating class.
+## Galvalume gutter and downspout sheet shall conform to ASTM A792/A792M with an AZ50 coating class.
−### Galvalume offers longer corrosion life than galvanized steel at similar cost, but its cut edges and fastener penetrations require the same compatible-fastener discipline as any coated steel. {note}
+## Galvalume offers longer corrosion life than galvanized steel at similar cost, but its cut edges and fastener penetrations require the same compatible-fastener discipline as any coated steel. {note}
−## Copper {toc}
+# Copper {toc}
−### Copper gutter and downspout sheet shall conform to ASTM B370, minimum H00 temper.
+## Copper gutter and downspout sheet shall conform to ASTM B370, minimum H00 temper.
−### Copper weight is selected by application: 16 oz/sq ft (0.0216 in) is the default for hung gutters, and 20 oz/sq ft (0.0270 in) is required for built-in gutters, which carry more water and more structural and thermal stress. {note}
+## Copper weight is selected by application: 16 oz/sq ft (0.0216 in) is the default for hung gutters, and 20 oz/sq ft (0.0270 in) is required for built-in gutters, which carry more water and more structural and thermal stress. {note}
−### Hung copper gutters shall be a minimum of 16 oz/sq ft.
+## Hung copper gutters shall be a minimum of 16 oz/sq ft.
−### Built-in copper gutters shall be a minimum of 20 oz/sq ft.
+## Built-in copper gutters shall be a minimum of 20 oz/sq ft.
```datasheet
…6 unchanged lines
```
−## Fasteners and Accessories {toc}
+# Fasteners and Accessories {toc}
−### Fasteners, hangers, rivets, and solder shall be the same metal as the gutter or a metal that is galvanically compatible with it; carbon-steel fasteners shall not contact copper or aluminum.
+## Fasteners, hangers, rivets, and solder shall be the same metal as the gutter or a metal that is galvanically compatible with it; carbon-steel fasteners shall not contact copper or aluminum.
−### Aluminum gutters shall be fastened with aluminum or stainless steel fasteners.
−
−### Copper gutters shall be fastened with copper or copper-alloy fasteners and joined with lead-free solder suitable for copper.
−
−### Galvanic incompatibility is the dominant premature-failure mode for gutters: pairing aluminum gutters with copper downspouts or fasteners, or carbon-steel screws with either, sets up a corrosion cell that fails the joint long before the metal would otherwise wear out. Specifying a single metal family throughout, with stainless steel as the only mixed-metal fastener allowance, eliminates the risk. {note}
−
```datasheet
label: Fastener / hanger material
…5 unchanged lines
```
+## Aluminum gutters shall be fastened with aluminum or stainless steel fasteners.
+
+## Copper gutters shall be fastened with copper or copper-alloy fasteners and joined with lead-free solder suitable for copper.
+
+## Galvanic incompatibility is the dominant premature-failure mode for gutters: pairing aluminum gutters with copper downspouts or fasteners, or carbon-steel screws with either, sets up a corrosion cell that fails the joint long before the metal would otherwise wear out. Specifying a single metal family throughout, with stainless steel as the only mixed-metal fastener allowance, eliminates the risk. {note}
+
# Gutter Configuration {toc}
## The gutter profile sets capacity, appearance, fabrication method, and hanger type. K-style (ogee) is the commercial default and develops the most capacity per face height; half-round is favored for traditional and copper work and sheds debris well; box/built-in (yankee) gutters are custom shop-fabricated, often historic or institutional, and carry structural and overflow obligations addressed in their own section. {note}
+## The gutter profile shall be specified, and its capacity, fabrication method, and hanger type shall be coordinated with the selection.
+
```datasheet
label: Gutter profile
…8 unchanged lines
## Gutter width shall be sized to the governing rainfall intensity and projected roof area, with the larger of the SMACNA-table result and the code-required result governing.
−## A 5 in seamless K-style gutter on a 1% slope serves roughly 4,000 to 5,300 sq ft of projected roof area at a 4 in/hr intensity, and that area shrinks as intensity rises; published SMACNA tables, not rules of thumb, are the basis of record for each project. {note}
−
```datasheet
label: K-style gutter width
…19 unchanged lines
```
+## A 5 in seamless K-style gutter on a 1% slope serves roughly 4,000 to 5,300 sq ft of projected roof area at a 4 in/hr intensity, and that area shrinks as intensity rises; published SMACNA tables, not rules of thumb, are the basis of record for each project. {note}
+
## Seam Type {toc}
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### Gutter slope toward outlets shall be not less than 1/16 in per foot.
−### Gutter slope of 1/8 in per foot shall be the preferred default; for runs exceeding 50 ft, slope shall be not less than 1/4 in per foot.
−
−### Gutter slope shall be shown on the drawings and shall not be left to the installer's field determination.
−
−### Too little slope leaves standing water that accelerates corrosion and freezes, while inconsistent field slope produces low spots that overflow. {note}
−
```datasheet
label: Gutter slope to outlet
…6 unchanged lines
```
+### Gutter slope of 1/8 in per foot shall be the preferred default; for runs exceeding 50 ft, slope shall be not less than 1/4 in per foot.
+
+### Gutter slope shall be shown on the drawings and shall not be left to the installer's field determination.
+
+### Too little slope leaves standing water that accelerates corrosion and freezes, while inconsistent field slope produces low spots that overflow. {note}
+
## Finish {toc}
### Prefinished gutter and downspout coatings shall be one of: a PVDF (70% resin) coating meeting AAMA 2605, a polyester coating meeting AAMA 2604, mill (bare) aluminum, or the natural patina finish of bare copper or zinc.
−### A PVDF coating with minimum 70% resin content per AAMA 2605 carries a 20-year color and chalk warranty and is the default for most commercial specifications; a polyester coating meeting AAMA 2604 is acceptable for moderate exposure at lower cost. The premium finish is justified wherever the gutter is architecturally exposed or the exposure is severe. {note}
−
```datasheet
label: Prefinish coating
…7 unchanged lines
```
+### A PVDF coating with minimum 70% resin content per AAMA 2605 carries a 20-year color and chalk warranty and is the default for most commercial specifications; a polyester coating meeting AAMA 2604 is acceptable for moderate exposure at lower cost. The premium finish is justified wherever the gutter is architecturally exposed or the exposure is severe. {note}
+
## Leaf Guards and Strainers {toc}
### A removable strainer or basket shall be provided at each outlet to keep leaves and debris from entering the downspout.
−### Whether continuous leaf protection is provided, and of what type, shall be specified explicitly rather than left to the installer, because the choice changes the maintenance interval and the assumed debris load. {note}
+### Whether continuous leaf protection is provided, and of what type, shall be specified explicitly rather than left to the installer, because the choice changes the maintenance interval and the assumed debris load.
```datasheet
…70 unchanged lines
### Each downspout shall terminate at grade in a splash block, at an underground connection to the storm system, at a through-wall fitting, or at a dry well, as scheduled for the project location [[drawing: downspout discharge locations]].
−### The responsible party for each downspout discharge termination shall be defined in the construction documents.
−
−### An undefined boundary between a splash block (this scope) and an underground storm connection (often site civil, not in this contract) is a recurring source of field RFIs about who furnishes and installs the connection fitting. {note}
−
```datasheet
label: Downspout discharge termination
…8 unchanged lines
```
+### The responsible party for each downspout discharge termination shall be defined in the construction documents.
+
+### An undefined boundary between a splash block (this scope) and an underground storm connection (often site civil, not in this contract) is a recurring source of field RFIs about who furnishes and installs the connection fitting. {note}
+
# Expansion Joints {toc}
…17 unchanged lines
# Hangers and Supports {toc}
−## Concealed hidden-hanger clips are the current standard; spike-and-ferrule hangers are obsolete and shall not be used. {note}
+## Concealed hidden-hanger clips are the current standard; spike-and-ferrule hangers are obsolete and shall not be used.
## Gutters shall be supported on concealed hidden-hanger clips, concealed brackets, fascia-mount straps, or standoff brackets matched to the eave condition and the gutter profile.
…49 unchanged lines
## Overflow scuppers shall be provided as a mandatory secondary drainage path for every built-in gutter, sized and located in coordination with [[sync/roof-drainage]].
−## Built-in gutters shall be lined continuously with the specified metal, with soldered or welded joints appropriate to the lining material, and shall not rely on sealant alone at the lining seams.
−
−## The combination of structural load, ponding risk, and concealed location makes a built-in gutter the highest-consequence configuration in this standard; the structural coordination and the overflow-scupper backup are not optional refinements but the conditions under which a built-in gutter may be used at all. {note}
−
```datasheet
label: Built-in gutter overflow provision
…9 unchanged lines
```
+## Built-in gutters shall be lined continuously with the specified metal, with soldered or welded joints appropriate to the lining material, and shall not rely on sealant alone at the lining seams.
+
+## The combination of structural load, ponding risk, and concealed location makes a built-in gutter the highest-consequence configuration in this standard; the structural coordination and the overflow-scupper backup are not optional refinements but the conditions under which a built-in gutter may be used at all. {note}
+
# Testing {toc}
## Completed gutters and downspouts shall be water-tested by flooding representative runs and confirming flow to the outlets and downspouts with no leakage at joints, miters, end caps, or outlets.
−## Slope shall be verified after installation by confirming that no standing water remains in the gutter after a water test drains, because a low spot that holds water is both a corrosion site and a freeze hazard. {note}
+## Slope shall be verified after installation by confirming that no standing water remains in the gutter after a water test drains, because a low spot that holds water is both a corrosion site and a freeze hazard.
## Soldered copper and zinc joints shall be visually inspected for full, continuous solder fill at every seam and outlet.
…66 unchanged lines
- Strainer baskets
```