Shed drainage: plan where the water goes

Draw the whole water picture

Begin with a simple site sketch showing the proposed shed, existing buildings, driveway, fences, tanks and visible drainage features. Mark which ground is higher and lower based on observations, while leaving surveyed levels to the relevant professional. Show places that become wet after rain and any paths water appears to follow across the property.

Separate observations from assumptions. A dry hollow does not prove water never passes through it. A pipe disappearing underground does not establish its destination or capacity. Label unknown connections as unknown and give the designer whatever existing plans you have. The aim is to make uncertainty visible before a building blocks an existing route.

For a rural block around Dubbo, include a wider area than the shed footprint. Vehicle tracks, nearby hardstand and disturbed ground can affect how water approaches the site. For a smaller town property, show the relationship to the house and neighbouring boundaries. Ask the designer what survey and site information is needed for the proposed work rather than relying on the sketch as a level plan.

Separate roof runoff from surface water

Roof runoff is collected from the shed itself. Surface water may approach from ground outside the building. They need to be considered together, but adding a larger downpipe does not resolve every problem around a doorway. Describe the source and route of each water issue so the drainage designer can assess the complete arrangement.

Ask the shed supplier to identify the roof catchment and the proposed gutter and downpipe locations. Ask the drainage contractor how those outlets connect to the rest of the system. If different people design those parts, nominate who checks the interface. A downpipe shown neatly on an elevation is not a completed drainage route.

Keep water collecting near a wall distinct from moisture appearing inside the roof. The condensation investigation guide explains how to record internal moisture patterns. A drainage inspection and a roof investigation may both be needed, but an owner should not assume that one visible symptom identifies the entire cause.

Resolve levels before building placement

The chosen floor level affects vehicle access, surrounding earthworks and the available routes for water. Ask for a drawing that relates finished floor level to the apron, adjacent ground and the designed drainage arrangement. If the shed position changes, have those relationships checked again rather than carrying the old level into the new location.

Consider what happens at every opening. A roller door, side entry door and open-front bay may have different threshold details and exposure. Identify which openings are used frequently and which equipment crosses them. The designer can then coordinate practical access with weather and surface-water management. Avoid asking the concreter to solve a poorly coordinated level arrangement with an improvised lip or ramp.

Changes outside the building can undo an otherwise sensible detail. Later paving, gravel top-ups or garden beds may raise the ground close to cladding or alter the route water follows. Ask for the finished external arrangement to be documented and explain which areas will be completed later. The slab planning guide provides the related questions for floor levels and concrete scope.

Coordinate gutters with doors and traffic

Downpipe locations need to work with machinery, doors, shelving and access for maintenance. Show the daily vehicle path on the same sketch as the drainage outlets. A pipe in a convenient place for the roofer may be exposed to damage from a trailer or occupy the space needed for an open door. Resolve the conflict through design rather than repeatedly replacing a damaged fitting.

Ask the designer to specify the gutter arrangement and the behaviour of the system when its normal route is obstructed or exceeded. The owner does not need to invent a sizing formula; the useful task is to ensure that overflow behaviour is part of the brief. Request clarification of where water is intended to go and which building openings or stored items could be affected.

Include safe inspection and maintenance access. A tank, fence or later extension can make an outlet difficult to reach. Ground-level observation points and an appropriate professional maintenance plan are more useful than a design that assumes the owner will climb onto the roof. Keep roof and drainage product information with the handover documents.

Plan the tank when it is already full

A rainwater tank may be part of the shed plan, but its inlet is not the end of the water route. Ask how overflow is handled when storage is full and where that water goes. Show the tank, base, pipes and maintenance access on the site layout. An attractive position beside the shed still needs to work with doors, footing design and the broader drainage arrangement.

Explain the intended water use to the supplier and designer. Different uses can require different equipment and advice, and this guide does not establish whether collected water is suitable for a particular purpose. Record what is included in the tank package and what another contractor must provide. Inlet treatment, pumps and connections should not disappear into a vague allowance for a tank later.

Think about replacement and maintenance as well as first installation. Can equipment reach the tank location after the shed, fence and landscaping are complete? Can someone inspect the accessible parts without moving stored machinery? If the tank will be added in a later stage, have the interim roof-water arrangement designed too. Leaving an outlet temporarily discharging beside a building is not a substitute for that plan.

Establish the downstream connection

Ask the responsible designer to identify a suitable drainage destination and confirm what permissions, investigations or coordination the proposed connection needs. Do not assume that an existing roadside feature, nearby pipe or neighbouring property is an available outlet. Those decisions depend on the site and the applicable requirements, which need to be checked for the actual project.

For quote comparison, request a route drawing and a clear statement of where each contractor's work starts and ends. Is the price for downpipes only, for pipework to a nominated point, or for a complete arrangement including the connection? Identify who verifies the existing system if it is being reused. A connection shown as existing on an old plan may still need investigation.

Avoid selecting underground pipe sizes or trench positions from a general article. Their design and installation need to be coordinated with levels, services, access and the shed structure. Give the contractor the available service information and let the relevant professionals establish the required checks. The planning outcome should be an understood route and responsibility, not an owner-designed trench.

Example: a tank blocks the straight approach

This is an illustrative layout exercise rather than a completed project. An owner puts a proposed tank beside a new machinery shed because it is close to a downpipe. On the combined plan, the tank occupies the space the tow vehicle needs to straighten a trailer. Moving it to the rear would improve access, but changes the pipe route and the arrangement for overflow.

The owner asks for both layouts to be assessed with the same floor level, vehicle movement and drainage brief. One option may need more pipework; another may require a different door position or building setback assessment. The useful comparison includes those consequences instead of choosing the shortest visible pipe run.

The selected arrangement is recorded before concrete and earthworks begin. The machinery path remains clear, the tank is accessible and the relevant designer has confirmed the water route. This is why the door access plan and drainage plan should share a drawing. Solving them separately can produce two apparently sensible designs that do not fit the same site.

Keep drainage in the construction sequence

Ask how water will be managed during the work, including the period between earthworks, slab placement and connection of the roof drainage. The finished system may be well planned while the temporary site arrangement is unclear. The contractor should establish a suitable sequence and any temporary measures, particularly where excavations or stored materials change the way water moves.

Identify work that must happen before access becomes restricted. A drainage route beneath an apron or across a delivery area needs coordination with the concrete and shed programme. Mark inspection or documentation stages in the scope so buried work is recorded before it disappears. Photos should show context and location, supported by the final route drawing.

Keep variation decisions visible. If an unexpected service or unsuitable connection changes the plan, ask for the revised route and responsibilities to be agreed before covering the work. A verbal instruction passed between trades may not reach the person who later needs to maintain the system. The final record should show what was actually installed, including departures from the original quote.

Check the completed route and preserve it

At handover, walk the accessible parts of the system with the contractor. Identify each roof outlet, connection, tank overflow and maintenance point. Ask what should be inspected from the ground, what requires a professional and whom to contact if water appears in an unintended place. Keep that information with the drawings rather than relying on memory.

After rain, observe from a safe location and record any unexpected ponding, overtopping or water entry. Do not enter flowing water, open hazardous pits or climb onto a wet roof to investigate. Give the contractor photographs and timing information if the arrangement behaves differently from what was agreed. An observation during one event describes that event; it does not establish performance under every possible condition.

When adding paving, a fence, tank or extension later, revisit the drainage plan first. The extension planning guide explains why new work needs to preserve access and service routes. For a new farm shed, the best enquiry includes the site sketch, intended floor use, roof-water proposal and every known uncertainty about where the water can go.

Read alongside your drainage sketch

• Coordinate drainage with the slab
• Protect machinery approaches from layout conflicts
• Preserve drainage routes through later work
• Farm and machinery shed services

Request a final route drawing identifying the installed connections and maintenance points. Keep temporary drainage and later landscaping responsibilities visible in the agreed scope.