E1/AS1 Surface Water

These pointers are guidance from this tool, not part of E1/AS1. The building consent authority decides whether the evidence is sufficient.

Your project has no rainfall location or figure yet. Set the Appendix A location in the project (or, where no location fits, an intensity from elsewhere), and every clause that needs it reads the same one. Set the rainfall location

No drain runs yet.

No sumps yet.

Where E1/AS2 applies

1.0.2 sets the same four site conditions as E1/AS1 a) to d), and they are the ones ticked on the tool face. So a site outside E1/AS1 for one of those reasons is outside E1/AS2 for the same reason. What it does not restate is the 0.25 hectare catchment limit: E1/AS2's area scope comes from AS/NZS 3500.3 itself.

What E1/AS2 changes in the standard is under Reading, the names the two documents give the same component under Terminology, and the one part of E1/AS1 it keeps (Section 2.0, minimum floor level) is on the notes sheet with everything else.

1. Where E1/AS1 applies E1/AS1 applies to buildings and sitework with a catchment of no more than 0.25 hectares (2500 m²) on a site free from a history of flooding, not adjacent to a watercourse, not in a low lying area and not in a secondary flow path.

   E1/AS1 1.0.1, E1/AS1 1.0.1 a) to d)

2. Floor level Suspended floors and slabs on ground are at least 150 mm above the finished ground immediately adjacent to the building, and, for a site level with or above the road, no less than 150 mm above the road crown on at least one cross-section through the building.

   E1/AS1 2.0.1

3. Rainfall intensity Drains, gutters and sumps are sized on the rainfall intensity for a storm with a 10% probability of occurring annually and a 10 minute duration, from the territorial authority or from Appendix A.

   E1/AS1 3.2.2, E1/AS1 Appendix A

1. Gutter sections Every gutter is divided into sections, each the length of gutter between a downpipe and the adjacent high point on one side of that downpipe, and each section has a cross-sectional area no less than Figure 15 (external) or Figure 16 (internal) gives it, increased by I/100 where the intensity exceeds 100 mm/hr.

   E1/AS1 5.1.2, E1/AS1 5.1.3, E1/AS1 5.1.3

2. Minimum gutter size No gutter has a cross-sectional area of less than 4000 mm².

   E1/AS1 5.1.4

3. Gutter fall Roof gutters fall to an outlet.

   E1/AS1 5.3.1

4. External gutter overflow External gutters need no overflow outlet, and are installed so that any overflow spills to the outside of the building.

   E1/AS1 5.5.2

5. Gutter materials Roof gutter materials comply with the standards in Table 6.

   E1/AS1 5.2.1, E1/AS1 Table 6

6. Gutter thermal movement Allowance is made for the thermal expansion and contraction of the gutters, at the change in length Table 7 gives the material.

   E1/AS1 5.4.1, E1/AS1 Table 7

7. Valley gutters Valley gutters are designed to E2/AS1; E1/AS1 does not size them.

   E1/AS1 5.1.5 COMMENT, E2/AS1

1. Downpipe sizes Downpipes are sized to Table 5, or have a cross-sectional area no less than Table 5 requires and pass a 50 mm diameter sphere.

   E1/AS1 4.2.1, E1/AS1 Table 5

2. Downpipe materials Downpipe materials comply with Table 4.

   E1/AS1 4.1.1, E1/AS1 Table 4

3. Compatible materials Downpipes, gutters, roofing, fastenings and all adjoining components are of the same or a compatible material, so that nothing sets up galvanic corrosion.

   E1/AS1 4.1.2

4. Downpipe thermal movement Where thermal movement of the downpipes cannot be taken up by the gutters, the downpipes have expansion joints.

   E1/AS1 4.3.1

1. Drain sizes Every drain is sized from Figure 3 for its modified catchment area, 0.01 × the roof and paved area it carries × the rainfall intensity, and no drain has an internal diameter of less than 85 mm.

   E1/AS1 3.2.1, E1/AS1 3.2.2, E1/AS1 Figure 3

2. Drain gradients Drains are laid at no flatter than the gradient Table 2 gives their size.

   E1/AS1 3.4.1, E1/AS1 Table 2

3. Changes of direction A drain changes direction by no more than 90° at any point, and by less than 45° wherever practical.

   E1/AS1 3.3.1, E1/AS1 3.3.1, Figure 4

4. Junctions Where two drains meet, their directions of flow are at 60° or less.

   E1/AS1 3.3.2, Figure 5

5. Line and gradient Drains are laid on a uniform line and gradient between points of access.

   E1/AS1 3.3.1

6. Points of access A point of access (inspection point, rodding point, inspection chamber or access chamber) at every change of direction over 45°, every change of gradient over 45°, and every junction except where the joining drain serves a single downpipe and is shorter than 2000 mm (2 m).

   E1/AS1 3.7.3 a), E1/AS1 3.7.3 b), E1/AS1 3.7.3 c)

7. Chambers Where a change of direction and a change of gradient happen at the same point and either exceeds 22.5°, the point of access is an inspection chamber or an access chamber; an inspection chamber only where the depth to the invert is no more than 1000 mm (1 m).

   E1/AS1 3.7.4, E1/AS1 3.7.5

8. Spacing of access Points of access are no more than 50000 mm (50 m) apart where rodding points are used, and no more than 100000 mm (100 m) apart where inspection points or chambers are used.

   E1/AS1 3.7.2 a), E1/AS1 3.7.2 b)

9. Drains under buildings A drain under a building runs straight from one side to the other, with a point of access immediately outside within 2000 mm (2 m) of an exterior wall at each end, and takes no inlets under the building other than sealed roof-water downpipes.

   E1/AS1 3.7.6, E1/AS1 3.7.7, E1/AS1 3.7.8

10. Flexible joints Concrete, ceramic, vitrified clay, and rubber ring jointed steel or uPVC drains have a flexible joint within 225 mm of the face of any wall or foundation they pass through.

    E1/AS1 3.5.3

1. Sumps All surface water except that collected directly from a roof enters the drain through a sump with a hinged or removable grating of at least 35% openings, none wider than 35 mm in its smaller dimension, capacity at the bottom for silt and debris, and a submerged or trapped outlet.

   E1/AS1 3.6.1

2. Roof water Surface water collected directly from a roof discharges directly to a drain, not through a sump.

   E1/AS1 3.6.1 COMMENT

3. Sump types Each sump is a Type-one sump (Figure 8) where the area it serves is no more than 4500/I m², and a Type-two sump (Figure 9) up to 40,000/I m², I being the rainfall intensity.

   E1/AS1 3.6.2, E1/AS1 Figures 8 and 9

Gutter section5.1.2

The length of gutter between a downpipe and the adjacent high point on one side only of that downpipe; every gutter is divided into sections and each is sized on its own.

Internal gutter5.1.5, E1/AS2 1.0.1

A gutter within the roof, where overtopping can enter the building: a box gutter in AS/NZS 3500.3's words. Sized from Figure 16, at least 300 mm wide, with an overflow outlet.

External gutter5.5.2, E1/AS2 1.0.1

A gutter at the edge of the roof outside the building: an eaves gutter in AS/NZS 3500.3's words. Sized from Figure 15; any overflow spills outside.

Annual exceedance probability (AEP)E1/VM1 & AS1/AS2 Definitions, 3.2.2

The probability that a given rainfall intensity will be exceeded in any one year, as a percentage. E1/AS1 sizes on the 10% AEP, 10 minute storm.

Rainfall intensity, I3.2.2, Appendix A

The intensity of a storm with a 10% probability of occurring annually and a 10 minute duration, in mm/hr, from the territorial authority or Appendix A.

Modified catchment area3.2.2

0.01 × the plan roof area plus the paved area, in m², × the rainfall intensity in mm/hr: the figure Figure 3 reads a drain size from. Paved area includes paving blocks, concrete, asphalt and metalled surfaces.

Surface waterE1/VM1 & AS1/AS2 Definitions

All naturally occurring water other than sub-surface water that results from rainfall on the site or flows onto it, including from a drain, stream, river, lake or sea.

DrainE1/VM1 & AS1/AS2 Definitions

A pipe normally laid below ground, with its fittings and equipment, carrying foul water or surface water to an outfall.

OutfallE1/VM1 & AS1/AS2 Definitions

The part of the disposal system that receives the drainage system's water: for surface water, a natural watercourse, kerb and channel, or a soakage system.

SumpE1/VM1 & AS1/AS2 Definitions, 3.6.1

A chamber in the drain with features to intercept and retain silt, gravel and other debris: a grating, capacity for settlement, and a submerged or trapped outlet.

Type-one and Type-two sump3.6.2, Figures 8 and 9

The two sumps E1/AS1 draws: Figure 8's, for an area of up to 4500/I m², and Figure 9's, for up to 40,000/I m².

Inspection pointE1/VM1 & AS1/AS2 Definitions

A removable cap at drain level through which the drain can be cleaned and inspected.

Rodding pointE1/VM1 & AS1/AS2 Definitions

A removable cap at ground level through which the drain can be cleaned and inspected.

Inspection chamberE1/VM1 & AS1/AS2 Definitions

A chamber with working space at ground level through which the drain passes, as an open channel or as a pipe with an inspection point.

Access chamberE1/VM1 & AS1/AS2 Definitions

A chamber with working space at drain level through which the drain passes, as an open channel or as a pipe with an inspection point.

Secondary flow pathE1/VM1 & AS1/AS2 Definitions, 1.0.1 d)

The path surface water follows if the drainage system is overloaded or stops working. A site in one is outside E1/AS1.

Eaves gutter (AS/NZS 3500.3)E1/AS2 1.0.1

What E1/AS1 calls a External gutter. E1/AS2 prints the pairs because the standard and E1/AS1 name the same components differently, and it is the first thing to get wrong when reading one with the other open.

Box gutter (AS/NZS 3500.3)E1/AS2 1.0.1

What E1/AS1 calls a Internal gutter. E1/AS2 prints the pairs because the standard and E1/AS1 name the same components differently, and it is the first thing to get wrong when reading one with the other open.

Inlet pit (AS/NZS 3500.3)E1/AS2 1.0.1

What E1/AS1 calls a Surface water sump. E1/AS2 prints the pairs because the standard and E1/AS1 name the same components differently, and it is the first thing to get wrong when reading one with the other open.

Stormwater pit (AS/NZS 3500.3)E1/AS2 1.0.1

What E1/AS1 calls a Access/Inspection chamber. E1/AS2 prints the pairs because the standard and E1/AS1 name the same components differently, and it is the first thing to get wrong when reading one with the other open.

Two intensities on the sheetE1/AS1 3.2.2, E1/AS1 5.1.3, E1/AS1 Appendix A

Appendix A prints a 2% AEP intensity beside the 10% AEP one, and a drainage sheet is read beside E1/VM1 and the council's secondary flow requirements, so the page shows both. Nothing in E1/AS1 sizes on the 2% figure: 3.2.2 and 5.1.3 name the 10% AEP, 10 minute storm.

Where sources differE1/AS1 3.2.2 COMMENT

3.2.2's comment says that where the territorial authority's figure and Appendix A differ for a location, the more conservative one should be used, so the page takes the higher of the two and says which it took. It does not replace the Appendix A figure with a lower published one.

A pitch on a band boundaryE1/AS1 Table 5, E1/AS1 Figures 15 and 16

Table 5 and Figures 15 and 16 are in pitch bands, and the document does not say which band a pitch exactly on a boundary belongs to. The page answers for both bands rather than picking one silently; the choice is the building consent authority's.

One gutter, two downpipesE1/AS1 5.5.1

5.5.1 sizes an internal gutter's overflow outlet at no less than the cross-sectional area of the downpipes serving the gutter, and does not say whether an outlet matches one downpipe or all of them where more than one serves the same gutter. The page sizes it to the downpipe on its card; confirm the reading with the building consent authority.

Reading the figuresE1/AS1 Figures 3, 15 and 16

Figures 3, 15 and 16 are curves, and the page reads them from its own digitisation of the published vector paths, checked against the PDF on every build. A value read from a curve is rounded up to the next 100 mm², never down, and a plan area past the end of a curve is refused rather than extrapolated.

E1/AS2, the other routeE1/AS2 1.0.1, E1/AS2 1.0.4

E1/AS2 makes AS/NZS 3500.3 the Acceptable Solution as its own 1.0.4 modifies it, keeps E1/AS1's Section 2.0 for floor levels, and restates site limitations a) to d) but not the 0.25 hectare catchment limit. So a site outside E1/AS1 on the catchment alone can still be inside E1/AS2. The modified text is printed in E1/AS2 under a permission that is MBIE's, so the page says what each change is about and not what it says.

Clause 3.6: replacedE1/AS2 1.0.4

Valley gutters are not designed by this route at all: they go to E2/AS1.

Clause 4.5.6: added toE1/AS2 1.0.4

Downpipes discharge straight into the site stormwater drain, and should not go in through an inlet pit.

Clause 5.4.5 (b): added toE1/AS2 1.0.4

Where two sources give different design rainfall intensities for a location, the more conservative one should be used.

Clause 6.2.3: added toE1/AS2 1.0.4

An alternative minimum trench width for the smaller pipe sizes.

Clause 6.3.1.1 (d): replacedE1/AS2 1.0.4

Which junctions may be used, and a limit on how far a drain may change direction at any one point.

Clause 6.4 Subsoil drains: added toE1/AS2 1.0.4

The subsoil drain clause is informative in New Zealand, not a requirement.

Clause 6.4.1 NOTES: added toE1/AS2 1.0.4

Added guidance on where a subsoil drain should discharge and how flat it may be laid.

Clause 7.4.1: replacedE1/AS2 1.0.4

Where inspection openings go, and their spacing, for anything other than a single dwelling.

Clause 7.4.3: replacedE1/AS2 1.0.4

How a below-ground inspection opening is reached, and the depth past which the easier options stop being preferred.

Clause 7.5.1.1 (b): deletedE1/AS2 1.0.4

Deleted outright, so whatever the standard requires there does not apply here.

Clause 7.5.1.2: replacedE1/AS2 1.0.4

What an inlet pit has to do (silt capacity and a submerged outlet), and a pointer to E1/AS1's own sump figures.

Clause 7.7.1 (a): replacedE1/AS2 1.0.4

The junction types and the upstream angle permitted at a connection.

Clause 7.10 On-Site Stormwater Detention (OSD) Systems: added toE1/AS2 1.0.4

On-site stormwater detention is informative in New Zealand, not a requirement.

Section 8 Pumped Systems: added toE1/AS2 1.0.4

The pumped systems section is informative in New Zealand, not a requirement.

Section 10 Siphonic Drainage Systems: added toE1/AS2 1.0.4

The siphonic drainage section is informative in New Zealand, not a requirement.

Appendix C – C.2.2 New Zealand: replacedE1/AS2 1.0.4

Where the design rainfall intensity comes from: the territorial authority, the standard's own Table E.1, or NIWA's HIRDS, and the most conservative of them where they differ.