Stormwater is easy to overlook during the early stages of a building project. But once building layout, levels and external spaces are established, changing the drainage strategy can become far more difficult.
Stormwater design is not simply about deciding where water will go after it falls on a roof or paved surface.
The design may need to work with the site’s levels, building footprint, roof layout, external works, drainage infrastructure and applicable authority requirements. Decisions made in one area of the project can affect what is possible in another.
When stormwater considerations are left until later in the design process, the available options may already be limited.
Stormwater Design Starts With Understanding the Site
Every site presents different conditions.
The slope of the land, available drainage points, existing infrastructure, soil conditions and surrounding development can all influence how stormwater needs to be managed.
For example, a relatively flat site may require careful consideration of levels to ensure water drains as intended. On a more constrained site, there may be limited space available for drainage infrastructure or on-site stormwater measures.
Before a stormwater solution is developed, it is important to understand the conditions the design needs to respond to.
This early assessment can help identify potential constraints before other parts of the building design become fixed.
Building Layout Can Affect Where Water Goes
The building itself has a direct impact on stormwater design.
Roof areas collect significant volumes of water, while driveways, car parks, pathways and other hard surfaces can reduce the amount of water that naturally soaks into the ground.
The location and arrangement of these surfaces can influence:
- Where water is collected
- How it moves across the site
- Where drainage infrastructure can be located
- The capacity required within the stormwater system
- How stormwater can be directed or managed
If the building footprint or external layout changes late in the project, the stormwater design may also need to change with it.
Considering these relationships early can help avoid designing major parts of the project independently and then trying to resolve conflicts later.
Site Levels Need to Work With the Drainage Strategy
Stormwater does not move independently of the rest of the site design.
Finished floor levels, driveway gradients, landscaping levels and surrounding ground levels can all affect how water flows across and away from the building.
A change to one level may create a new low point elsewhere. Water may then need to be redirected, collected or managed differently.
This is particularly important where a project involves:
- Sloping or irregular sites
- Basements or below-ground areas
- Large paved areas
- Car parks
- Building extensions
- Significant changes to existing site levels
If stormwater is only considered after levels have been established, resolving drainage issues may require changes to other parts of the design.
Early coordination makes it easier to assess how levels and drainage will work together.
Stormwater Infrastructure Needs Space
Stormwater systems can involve more than just downpipes and underground pipes.
Depending on the project, the design may require pits, pipes, drainage structures, detention or retention measures, pumps or other infrastructure.
These elements need physical space within the site.
On a constrained development, that space may compete with:
- Building areas
- Parking
- Landscaping
- Access ways
- Other building services
- Structural elements
- Existing underground infrastructure
If these requirements are not identified until later, suitable locations may already have been allocated to other parts of the project.
This can lead to redesign or additional coordination once services begin competing for the same space.
Existing Infrastructure Can Create Constraints
For refurbishment and redevelopment projects, existing conditions can add another layer of complexity.
There may already be stormwater infrastructure on the site, but its location, condition or capacity may not be suitable for the proposed development.
Existing services may also affect where new stormwater infrastructure can be installed.
Understanding these conditions early can help answer important questions before the design progresses, such as:
- Can the existing system be used?
- Does additional infrastructure need to be installed?
- Are there conflicts with other underground services?
- Is there sufficient capacity for the proposed development?
- Will new works require changes to existing drainage?
These issues can be more difficult to resolve once building design and construction planning are already underway.
Stormwater Design Often Requires Coordination With Other Disciplines
Stormwater design does not sit in isolation.
It can interact with civil design, hydraulic services, architecture, structural engineering, landscaping and electrical or mechanical infrastructure.
For example, the location of a drainage route may conflict with structural footings or underground services. Changes to landscaping levels may affect surface drainage. A proposed building extension may change the amount of roof area contributing to the system.
Without coordination, each design discipline may develop its own solution without fully understanding the requirements of the others.
This does not necessarily create a problem immediately.
The issue may only become apparent when designs are brought together, by which point changes can affect completed documentation.
Considering stormwater early provides more opportunity to coordinate these requirements before they become difficult to change.
Late Stormwater Decisions Can Lead to Redesign
When stormwater requirements are identified late, the problem is not always the drainage system itself.
The challenge is that other parts of the project may already be designed around assumptions that no longer work.
For example, a drainage route may require space that has already been allocated to another service. A required change in levels may affect access or external works. Additional infrastructure may need to be accommodated in an area that has already been designed for another purpose.
This can result in:
- Changes to documentation
- Additional coordination between consultants
- Design revisions
- Construction delays
- Unanticipated changes during delivery
The earlier potential stormwater constraints are identified, the more options are generally available for addressing them.
Stormwater Considerations Can Change as the Project Develops
Early planning does not mean the stormwater design is completely fixed from the beginning.
Building projects evolve. Roof areas may change, external spaces may be redesigned and the overall development may change as design progresses.
The important point is to establish stormwater requirements early enough that these changes can be assessed as part of the wider project.
A coordinated approach allows the stormwater design to develop alongside the building rather than being treated as a separate requirement that needs to be resolved once everything else is already in place.
Why Early Coordination Matters
Stormwater design is often most effective when it is considered as part of the overall site and building strategy.
Understanding site conditions, anticipated building layout, levels and infrastructure requirements early can help identify potential issues before they affect other parts of the project.
This gives the project team more opportunity to consider available options, coordinate services and make decisions before changes become more disruptive.
The goal is not simply to design a system that manages stormwater.
It is to make sure the stormwater strategy works with the building and the site as the project develops.
Stormwater and Building Services Coordination With Decobu
At Decobu, we work across building services engineering disciplines and consider how different services and infrastructure requirements interact within a project.
Stormwater requirements can affect site design, building layout and the coordination of other services. Identifying these requirements early can help the project team understand potential constraints before they become more difficult to resolve.
By coordinating engineering considerations as part of the wider design process, potential conflicts and requirements can be identified before they have a greater impact on the project.
Frequently Asked Questions
Why should stormwater be considered early in a building project?
Stormwater design can be affected by site conditions, building layout, levels, external works and available space for infrastructure. Considering these factors early can help identify constraints before other design decisions become difficult to change.
Can changes to a building design affect the stormwater system?
Yes. Changes to roof areas, paved surfaces, site levels or the overall building layout can affect how stormwater is collected and managed. These changes may require the stormwater design to be reviewed.
What can happen if stormwater requirements are identified late?
Late changes may require redesign or additional coordination if drainage infrastructure conflicts with completed building, structural, landscaping or services designs.
Does stormwater design need to be coordinated with other engineering services?
Stormwater infrastructure can share space with other building and site services. Coordination can help identify potential conflicts between drainage, structural elements and other underground or external infrastructure.
Is stormwater design only important for new buildings?
No. Refurbishments, extensions and redevelopment projects can also affect existing drainage systems. Changes to building areas, site conditions or external works may require the existing stormwater arrangement to be reviewed.
Final Thoughts
Stormwater may not always be one of the first things considered when planning a building project, but it can influence many decisions that follow.
Site levels, building layout, external works and available infrastructure all play a role in determining how stormwater can be managed.
Considering stormwater early gives project teams more opportunity to identify constraints, coordinate requirements and develop solutions that work with the overall building design rather than trying to resolve conflicts later.
Need Stormwater Planning for Your Project? Discuss Your Project With Decobu