Installing Eaves Gutters

Eaves gutters including fascia mounted eaves gutters, deck mounted eaves gutter and concealed gutters should comply as follows:

- Overflow Provision & Size:  Eaves gutters should, in the event of a total blockage of its downpipes or stormwater drains, discharge all excess roof water clear of the building via overflows. Eaves gutters with higher fronts than backs and guttering which potentially discharge overflow into any building should be provided with fixed overflows not smaller than the downpipes connected to the gutter.

- Mitres: Mitres fabricated from eaves gutter materials should, when complete, be true in size, shape and angle and have all beads reinforced with purpose made gussets or custom designed cast of pressed metal angles.

- Maximum length: Eaves gutters should not exceed 20m without provision of an appropriate expansion joint. Eaves gutters should be installed to permit expansion and contraction to protect the cast type bolted clamp angles.

- Cleating: Eaves gutters should be fastened using purpose made fittings to permit longitudinal expansion & contraction. The back of the gutter should be cleated by means of a lug or galvanised nail bent over the top at 500mm maximum intervals.

-Spacing: Eaves gutter brackets should be securely fastened to fascias at stopends and in between stopends at intervals not exceeding 1200mm

- Fall: Eaves gutter brackets should be installed with a uniform fall towards the outlets. A minimum fall of 1:500 will ensure complete drainage.

- Roof covers: Roof covers discharging water into an eaves gutter should enter the eaves gutter by not less than 50mm. Flat pans or valleys should have the lower edge turned down 20mm at 45 degrees into the eaves gutter.

- Lap joints: Lap joints should have a lap of not less than 25mm in the direction of flow and should be sealed and fastened.

Baffle: Where the low edge of a roof cover is subject to excessive direct wind forces, baffle flashings should be installed to prevent the entry of roof water under the roof cover

Sarking: Sarking should enter the eaves gutter by a minimum of 20mm

- Outlet: Eaves gutter outlets should be as follows:

  • They should have outlet nozzles of a size and at intervals to permit the efficient , effective discharge of all roof water.
  • The minimum size of the outlet should be 50% of the effective area of the gutter.
  • Eaves gutter outlets should be installed so that no part of the outlet is above the sole of the eaves gutter.
  • All outlets should be tapered to fit inside the upper end of the downpipe.

Sumps, Rainheads & Downpipes

Sumps

- The sump should be sealed to the box gutter on all sides. The centre line of the downpipe should not be further from the nearest vertical side of the sump than either:

  • The diameter of a circular downpipe. Or,
  • The average of the two side dimensions of a rectangular downpipe.

Rainheads

The purpose of a rainhead is to ensure that in the event of a blockage or extreme flow conditions, all excess flow is discharged to the outside of the building. The centre line of the downpipe should not be further from the nearest vertical side of the rainhead than either

  • The diameter of a circular downpipe. Or,
  • The average of the two side dimensions of a rectangular downpipe.

The width of the rainhead should be at least equal to the width of the box gutter.

Eaves gutter outlets

All parts of outlets including, flange, sealants and fasteners installed to the sole of the eaves gutter should be level with or below the sole of the eaves gutter.

Back Outlets

Back outlets at the back of the eaves gutters with falls less than 1 in 25, should be of a size equal to the effective cross sectional area of the eaves gutter it drains.

An outlet at the back of an eaves gutter with a fall of 1 in 15 or greater should be sized not less than 50% of the effective cross area of the eaves gutter it drains.

Downpipes

Downpipes must comply with the following:

Internal Gutters: Internal gutters with internal downpipes should be fitted with sumps and appropriate overflow provision or discharged into external rain heads.

- Fastening: Downpipes should be fastened to walls and structures so as to withstand movements due to thermal expansion and weight due to partial or total blockage.

- Spacing: Downpipe brackets should be spaced at intervals not exceeding 2m vertically and 1m on a slope.

- Thickness of brackets: Brackets should be manufactured of materials compatible with downpipes and of the same thickness. Downpipes should be sized to permit thermal expansion and contraction.

- Fixed points on PVC downpipes: PVC downpipes should have expansion joints at spaces not exceeding 6m. The expansion joints or coupling should be fixed to prevent lateral movement.

- Slip joints: External downpipes manufactured of sheet metal should incorporate unsealed slip joints of 75mm within 2m of the point of entry to the stormwater drain.

- Graded downpipes: Downpipes other than vertical downpipes should have a minimum gradient of 1 in 25. Downpipes with gradients less than 1 in 25 should have a minimum cross sectional area equal to the effective eaves gutter cross section it serves.

- Seams: Downpipes manufactured of sheet metal with seams should have the seams positioned uppermost on graded downpipes and concealed from front view on all other downpipes.

- Concealed downpipes: Concealed downpipes or downpipes with limited access made of sheet materials with seams, should have such seams sealed. Concealed downpipes should be made of copper, copper alloy, stainless steel or PVC. Incompatibility with gutter material should be avoided.

- Joints in PVC: Joints in downpipes made of PVC should be socket and spigot joints and sealed appropriately.

- Joints: Joints in downpipes should be lapped not less than 50mm and should be installed in the direction of flow.

- Jointing: when jointing a downpipe, consider:

  • Laps in offsets & branches should be manufactured to avoid partial obstruction to rainwater flow.
  • Circular downpipes should have their offsets lapped not less than 6mm
  • Straight, on grade downpipes should be sealed

- Overflow protection:  Downpipes connected to stormwater drains should have overflow protection.

- Heavy duty applications:  Downpipes exposed to heavy vehicular traffic should be manufactured using cast iron  or galvanised wrought iron.

- Shoes: Downpipes connecting to earthenware stormwater drains or where stormwater drains are off the wall should have shoes installed at an angle not exceeding 30 degrees to the vertical.

- Spreaders: Spreaders may be used to drain a roof surface with a catchment area not exceeding 15sq m, providing that the follow conditions are met:

  • The increased roof water volume should not enter the seam of the roof covering.
  • No spreader should discharge roof water onto or over ridge tiles, mortar jointed tiles, flashings, timber fascia or roof sheet side lap.
  • No spreader should have its discharge entering any part of the building.
  • Spreaders should discharge all roof water onto roof covers in the direction of roof flow.
  • When discharging one roof on to another, the additional catchment area should be considered when sizing the roofing gutters and downpipes.

 

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