Roof Drainage System: Everything You NEED To Know

When you’re building your house an important factor to consider is your roof drainage system as this will be key to ensuring rainwater is effectively dispersed away from your property minimising the chance of damage.

Roof rainwater drainage system diagram

What is Roof Drainage System?

A roof drainage system consists of a number of components that work together to collect and effectively disperse rainwater from your property structure.

Based on the past rainfall intensity of your region (provided by your local councils or state), your roof drainage system will be scaled and configured to suit the amount of rainfall you experience over the year and also the intensity.

For example, if your yearly rainfall is an average of 600mm though this happens over a 1-2 week period, then the configuration of your roof drainage system will be different from those areas that get the same 600m rainfall evenly dispersed over the 12 months.

What does Roof Drainage System consist of?

There are a number of different parts that contribute to an effective roof drainage system.  Key components include:

  • Roof valleys
  • Gutters and downpipes
  • Soakwells and drainage

Roof valleys

The collection of your rainwater first starts at your roof valleys.  These are the metal trays that sit between two adjoining areas of your roof.  From here the water is collected and redirected to the gutters.

Gutters and downpipes

When rainwater flows from your roof, or valleys if your roof has them, your rainwater then collections in your roof’s gutters system.  

See also: Gutters: What are they and how do they work

From here the rainwater will flow out of your gutters and down into your drainage pits or what we know as soakwells in Western Australia.

See also: Downpipes: What you need to know

Soakwells and drainage

The final destination for rainwater as it ventures down through your roof drainage system is your drainage pit (aka soakwell).  leaving the downpipes water will flow into your drainage pipes that run underground to your soakwell.  From here the rainwater will then soak away into the soil, ensuring no damage to your property.

Note, in WA soakwells are the most common method of dispersing stormwater, however, some other states where soakwells are not suited will use connection pits to connect up and disperse the water via that area’s stormwater drainage network. 

This is what is known as an “offsite” disposal method, compared to a soakwell which is considered an “onsite” disposal method.

What Roof type has the most effective drainage system?

Generally, pitched four or two-sided roofs are the best when it comes to dispersing rainwater.  

Flat roofs or roofs with valleys, trays, or box gutters are known to be less efficient and more problematic as rainwater doesn’t disperse as quickly and can more easily pool and remain within areas of the roof’s drainage system.

Therefore, although it may not be as visually pleasing as other roof designs, if you do have the option of a pitched four or two-sided roof this would definitely be my choice.

Final thoughts

I hope you found the above article on Roof drainage systems helpful.  Be sure to check out the related links below for more roof and rainwater drainage-related information.

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