Box (Gutters) Building Codes & Rules

- Learn how to install box gutters and rain heads with the weir design for optimal drainage and protection. Follow key steps for a reliable, flood-free solution.

Sump

Nozzle

Downpipe

Rain Water Head

Lap joint

Class 1

Roofing

Drip Edge

min

≥ 25

min

Capping

Overflow

HB 39:2015, 5.3.1

≥ 50^{HB 39:2015, 5.3.1}

HB 39:2015, 3.10

Blanket Insulation^{HB 39:2015, 3.10}

Cut back Insulation at Fascia / sheet end
Profiled foam filler strip or end cap to Roof Sheet

Fall

Support

Class 2 to 9

> 5°

Maximum length between Expansion Joints

HB 39:2015, 2.0

Material^{HB 39:2015, 2.0}

To be compatible to avoid galvanic reaction
Stainless steel in coastal or industrial environments
Joints soldered or sealed

AS/NZS 3500.3:2021, 4.5.4 (b)

HB 39:2015, 5.3.2 (k)

≥ 25^{AS/NZS 3500.3:2021, 4.5.4 (b)HB 39:2015, 5.3.2 (k)}

HB 39:2015, 5.3.2 (f)

≥ 50^{HB 39:2015, 5.3.2 (f)}

AS/NZS 3500.3:2021, 4.5.4 (b)

HB 39:2015, 5.3.2 (k)

AS/NZS 3500.3:2021, 4.7.2.3

Lap Joints

Sealed and fastened in direction of fall^{AS/NZS 3500.3:2021, 4.5.4 (b)}
2 off Sealant & Fastener rows^{HB 39:2015, 5.3.2 (k)}
≤ 40mm Fastener spacing at
≥ 10mm from Joint Edges^{AS/NZS 3500.3:2021, 4.7.2.3}

HB 39:2015, 5.3.1

≥ 25^{HB 39:2015, 5.3.1}

Informative

Cappings^Informative

Fall towards gutter
Avoid fixing through top
Drip edge to avoid wall staining

AS/NZS 3500.3:2021, 4.5.4

HB 39:2015, 5.3.2 (j)

Weather Folded Sides^{AS/NZS 3500.3:2021, 4.5.4}

Ensures strength to resist deformation^{HB 39:2015, 5.3.2 (j)}
Finish without gap to underside Roof Sheet

HB 39:2015, 5.3.2 (b)

≥ 50^{HB 39:2015, 5.3.2 (b)}

Tools™ Best Practice

Seal rivet heads^{Tools™ Best Practice}
Stagger where possible

AS/NZS 3500.3:2021, 4.9.4 (b)

AS/NZS 3500.3:2021, 4.9.4

AS/NZS 3500.3:2021, 4.9

Informative

Support^{AS/NZS 3500.3:2021, 4.9.4 (b)}

≤ 750mm centres to Gutter Support^{AS/NZS 3500.3:2021, 4.9.4}
≥ 450mm wide Gutter to have Continuous support^{AS/NZS 3500.3:2021, 4.9}
Trapezoidal profile Roof Deck Support to allow foot traffic^Informative
At stop ends, Rain Heads, both sides of Sumps or Expansion Joints^Informative

Tools™ Best Practice

Colour-matched Sealant^{Tools™ Best Practice}

Tools™ Best Practice

Sealant^{Tools™ Best Practice}

Neutral cure silicone
"Stitch" over end joints to improve watertightness

HB 39:2015, 5.3.3

≥ Ø DP^{HB 39:2015, 5.3.3}

HB 39:2015, 5.3.1

≥ 50^{HB 39:2015, 5.3.1}

Base of Overflow

below Gutter level

NCC 2022 Vol 2, H2D6 (1) (a)

NCC 2022 Vol 2, H2D6 (3) (b)

Compliance

Box gutters to AS/NZS 3500.3:2021^{NCC 2022 Vol 2, H2D6 (1) (a)}
NCC 2022, HP compliance excludes Box Gutters^{NCC 2022 Vol 2, H2D6 (3) (b)}

NCC 2022 HP, 7.5.8 (b)

≥ 5°^{NCC 2022 HP, 7.5.8 (b)}

NCC 2022 HP, 7.5.8 (a) (ii)

≥ 50^{NCC 2022 HP, 7.5.8 (a) (ii)}

AS/NZS 3500.3:2021, 4.3.2 (c)

AS/NZS 3500.3:2021, 4.4

HB 39:2015, 5.7

Downpipe^{AS/NZS 3500.3:2021, 4.3.2 (c)}

Rivet & seal Nozzle to Sump
Allow for Thermal Expansion^{AS/NZS 3500.3:2021, 4.4}
Ensure materials & sealants are compatible^{HB 39:2015, 5.7}

HB 39:2015, 5.3.2 (o)

≥ 25^{HB 39:2015, 5.3.2 (o)}

HB 39:2015, 5.3.2 (i)

Fall ≥ 1:200^{HB 39:2015, 5.3.2 (i)}

Tools™ Best Practice

Colour-matched Sealant^{Tools™ Best Practice}

HB 39:2015, 5.3.2 (g)

≥ 75^{HB 39:2015, 5.3.2 (g)}

HB 39:2015, 6.3

HB 39:2015, 5.3.2 (o)

Sarking

25mm turn down & seal over gutter^{HB 39:2015, 6.3}
Protect from UV^{HB 39:2015, 5.3.2 (o)}

HB 39:2015, 5.3.2 (g)

≥ 200^{HB 39:2015, 5.3.2 (g)}

HB 39:2015, 5.3.2 (g)

≥ 300^{HB 39:2015, 5.3.2 (g)}

Tools™ Best Practice

Paintable

Sealant^{Tools™ Best Practice}

Tools™ Best Practice

Colour-matched Sealant^{Tools™ Best Practice}

Tools™ Best Practice

Colour-matched Sealant^{Tools™ Best Practice}

Downturn & Seal

Roofing Durability

Tools™ Best Practice

75^{Tools™ Best Practice}

Sump

Sizing to AS 3500.3, Appendix H^[1]
≥ 150mm deep (if high capacity overflow)^[2]
400mm or ≥ 2 x Ø DP long^[3]

Hail Guard BEST PRACTICE

NCC 2022 V1

Sump RULES

NCC 2022 V3

All Building Classes

NCC 2022 F1D3 [2019 F1.1]

May 2023

AS/NZS 3500.3:2021, 3.7.6 (g)

AS/NZS 3500.3:2021, 3.7.6

Box Gutters must discharge rainwater via a Sump or Rainhead^{AS/NZS 3500.3:2021, 3.7.6 (g)}
Sumps must be paired with^{AS/NZS 3500.3:2021, 3.7.6}
Downpipe, &
Channel, Duct or High Capacity Overflow Device

AS/NZS 3500.3:2021, 3.7.6 (e)

AS/NZS 3500.3:2021, H (c)

AS/NZS 3500.3:2021, H

Sizing to AS 3500.3, Appendix H^{AS/NZS 3500.3:2021, 3.7.6 (e)}
≥ 150mm deep (if high capacity overflow)^{AS/NZS 3500.3:2021, H (c)}
400mm or ≥ 2 x Ø DP long^{AS/NZS 3500.3:2021, H}

Tools™ Best Practice

Paintable

Sealant^{Tools™ Best Practice}

Tools™ Best Practice

Paintable

Sealant^{Tools™ Best Practice}

Roof Sheeting

Spans & Fixings to manufacturer's specification^[1]
Profile to suit pitch & rainfall intensities^[2]
Install Hail Guard Angle above all Box Guttering^[3]

Hail Guard BEST PRACTICE

NCC 2022 V1

Roof Sheeting INSTALLATION

NCC 2022 V1

Roof Sheeting RULES

NCC 2022 V3

All Building Classes

NCC 2022 F3, H2D6, J4D4, & HP7 [2019 3.5.1-3.5.5, J1.3, 3.5]

May 2023

HB 39:2015, 5.1

Roofing detailed and built to the NCC
Weathering fold on ends^{HB 39:2015, 5.1}
Refer to detail below for roof ≤ 5°

AS 1562.1:2018, 2.2.1

AS 1562.1:2018, 3.3.1 (b)

Tools™ Best Practice

Spans & Fixings to manufacturer's specification^{AS 1562.1:2018, 2.2.1}
Profile to suit pitch & rainfall intensities^{AS 1562.1:2018, 3.3.1 (b)}
Install Hail Guard Angle above all Box Guttering^{Tools™ Best Practice}

Side Overflow

Direct water away from building^[1]
To surface stormwater within property^[2]
Capacity no less than design flow of Downpipe^[3]
Flange sealed to Wall and Overflow^[4]
Drip edges to Cappings, Overflows & Rainheads^[5]

Overflow RULES

NCC 2022 V3

All Building Classes

NCC 2022 F1D3 [2019 F1.1]

NCC 2022 H2D2 HP 3.3.5, & 7.4 [2019 3.1.3, 3.5.3]

May 2023

NCC 2022 Vol 1, F1D3

NCC 2022 Vol 2, H2D2

AS/NZS 3500.3:2021, 3.2 (a)

AS/NZS 3500.3:2021, 3.5.2

Stormwater Drainage designed & constructed to NCC F1D3, H2D2, Parts 3.3.5 & 7.4, including AS/NZS 3500.3^{NCC 2022 Vol 1, F1D3NCC 2022 Vol 2, H2D2AS/NZS 3500.3:2021, 3.2 (a)}
To calculate Overflows^{AS/NZS 3500.3:2021, 3.5.2}
Determine ARI (Average Recurrence Incidence)
Determine rainfall intensity
Measure Roof Catchment area
Calculate design flow
Overflow size as per AS/NZS 3500.3

Overflow BEST PRACTICE

NCC 2022 V1

HB 39:2015, 5.3.1 (c)

HB 39:2015, 5.3.1

Direct water away from building^{HB 39:2015, 5.3.1 (c)}
To surface stormwater within property^{HB 39:2015, 5.3.1}
Capacity no less than design flow of Downpipe^{HB 39:2015, 5.3.1}
Flange sealed to Wall and Overflow^{HB 39:2015, 5.3.1}
Drip edges to Cappings, Overflows & Rainheads^{HB 39:2015, 5.3.1}

Expansion

≤ 20m CTS for 0.55 BMT steel^[1]

Expansion Joint RULES

NCC 2022 V1

All Building Classes

NCC 2022 F1D3, H2D2, Parts 3.3.5, & 7.4

[2019 F1.1, 3.1.3.0-3.1.3.1, 3.1.3.5, 3.5.3]

May 2023

HB 39:2015, 5.3.2 (b)

≤ 20m CTS for 0.55 BMT steel^{HB 39:2015, 5.3.2 (b)}

Overflow Weir

Direct water away from building^[1]
To surface stormwater within property^[2]
Capacity no less than design flow of Downpipe^[3]
Flange sealed to Wall and Overflow^[4]
Drip edges to Cappings, Overflows & Rainheads^[5]

Overflow RULES

NCC 2022 V3

All Building Classes

NCC 2022 F1D3 [2019 F1.1]

NCC 2022 H2D2 HP 3.3.5, & 7.4 [2019 3.1.3, 3.5.3]

May 2023

NCC 2022 Vol 1, F1D3

NCC 2022 Vol 2, H2D2

AS/NZS 3500.3:2021, 3.2 (a)

AS/NZS 3500.3:2021, 3.5.2

Stormwater Drainage designed & constructed to NCC F1D3, H2D2, Parts 3.3.5 & 7.4, including AS/NZS 3500.3^{NCC 2022 Vol 1, F1D3NCC 2022 Vol 2, H2D2AS/NZS 3500.3:2021, 3.2 (a)}
To calculate Overflows^{AS/NZS 3500.3:2021, 3.5.2}
Determine ARI (Average Recurrence Incidence)
Determine rainfall intensity
Measure Roof Catchment area
Calculate design flow
Overflow size as per AS/NZS 3500.3

Overflow BEST PRACTICE

NCC 2022 V1

HB 39:2015, 5.3.1 (c)

HB 39:2015, 5.3.1

Direct water away from building^{HB 39:2015, 5.3.1 (c)}
To surface stormwater within property^{HB 39:2015, 5.3.1}
Capacity no less than design flow of Downpipe^{HB 39:2015, 5.3.1}
Flange sealed to Wall and Overflow^{HB 39:2015, 5.3.1}
Drip edges to Cappings, Overflows & Rainheads^{HB 39:2015, 5.3.1}

Box Gutter

≥ 300mm (W) x 75mm (H)^[1]
≥ 200mm (W) allowed for residential, ensure hand space for maintenance^[2]
Straight, constant width + vertical sides^[3]
Calculate minimum size or seek advice from Hydraulic Engineer^[4]
Size must include for secondary roofs / spreader volumes

Box Gutter RULES

NCC 2022 V1

All Building Classes

NCC 2022 F1D3, H2D2, Parts 3.3.5, & 7.4

[2019 F1.1, 3.1.3.0-3.1.3.1, 3.1.3.5, 3.5.3]

May 2023

HB 39:2015, 5.6 (j)

HB 39:2015, 5.3.2 (g)

HB 39:2015, 5.3.2 (i)

HB 39:2015, 5.3.2 (m)

HB 39:2015, 5.3.2 (j)

HB 39:2015, 5.3.2 (m)

HB 39:2015, 5.3.2

NCC 2022 Vol 1, F1D3

NCC 2022 Vol 2, H2D2

Stormwater Drainage designed & constructed to NCC F1D3, H2D2, Parts 3.3.5 & 7.4, including AS/NZS 3500.3^{HB 39:2015, 5.6 (j)HB 39:2015, 5.3.2 (g)HB 39:2015, 5.3.2 (i)}
Sizing^{HB 39:2015, 5.3.2 (m)}
≥ 300mm (W) x 75mm (H)
May be reduced to 200mm (W) for domestic installations
≥ 1 : 200 fall to Outlet^{HB 39:2015, 5.3.2 (j)}
Straight & without any turns or corners
Size designed for 1 in 100 year storm (ARI 100)(AEP 1%)
Upstand to be installed^{HB 39:2015, 5.3.2 (m)}
Without gaps to underside of Roof Sheet, or
Provided with hanging Flashing with weather fold
≥ 25mm lap of Sarking into the Gutter^{HB 39:2015, 5.3.2}
Protect Overflows from blockages
Lear & double lear box gutters allowed^{NCC 2022 Vol 1, F1D3}
May extend up behind roof coverings, if Gutter effective area is not reduced
"V" shaped Gutters are not allowed^{NCC 2022 Vol 2, H2D2}

AS/NZS 3500.3:2021, 3.7.6 (b)

HB 39:2015, 5.3.2 (g)

HB 39:2015, 5.3.2 (l)

≥ 300mm (W) x 75mm (H)^{AS/NZS 3500.3:2021, 3.7.6 (b)}
≥ 200mm (W) allowed for residential, ensure hand space for maintenance^{HB 39:2015, 5.3.2 (g)}
Straight, constant width + vertical sides^{HB 39:2015, 5.3.2 (g)}
Calculate minimum size or seek advice from Hydraulic Engineer^{HB 39:2015, 5.3.2 (l)}
Size must include for secondary roofs / spreader volumes

Downpipes