Downpipes move water off your roof, away from your home.
The legal requirement for downpipes may vary from council to council, but as a general rule, downpipes must move rainwater from gutters to stormwater drains or water storage tanks, and never to sewer pipes or septic tanks.
How many downpipes do you need?
The number of downpipes required depends on the:
- Surface area of the roof
- Diameter of the downpipes
- Fall of the gutter
- Average annual rainfall
One 100ml downpipe usually caters for 70 square metres of roof in South East Queensland, and so if your house is of average size (around 160 square metres), you will probably need 3 downpipes to cope with summer storms.
This is an example of why you need adequate downpipes:
- If your roof area is 160 square metres (i.e. 16m long x 10m wide)
- And rain fell at a rate of 50 ml per hour
- This would equal 8000 litres of water coming off your roof in one hour!
- Imagine 8000 litres of water pouring and puddling through your yard, eroding away your soil.
Where should you put your downpipes?
The position of downpipes is usually determined by the location of your storm water pipes or your water storage tanks, but you may choose to alter this to better suit the appearance of your house.
Deciding what downpipes to buy
Downpipes come in square, rectangular or round shapes, so this could be your first choice. The downpipes that are the most popular shape are also the cheapest, because more of them are manufactured and this brings the cost down.
For instance, a 100ml x 75ml x 1.8m ColorBond downpipe costs around $20 to buy, but a 100ml x 50ml x 1.8m ColorBond downpipe costs around $56, even though it contains less material. This is because the smaller pipe is less popular and needs to be specially made, making it more expensive.
While paying an extra $35 is not a lot for one length, the extra cost can make quite a difference because each downpipe on a low-set house is almost 4 metres long. For every story above this, you need to add an extra 2.6 metres. Downpipes taper so that they fit neatly when joined together to make a whole downpipe, but this means that it is not always possible to use a piece that is left over in another installation.
PVC vs. Metal
The second choice you need to make is whether to use PVC downpipes, or metal. Both have advantages that are listed below.
Advantages of PVC Downpipes:
- PVC is quieter when it is raining as there is less vibration or dripping sounds
- They are approximately half the price of a metal downpipe.
- Installation is easy for almost anyone with some degree of handyman skills because it is just a matter of cutting to size and gluing together.
Advantages of ColorBond or Zincalume Downpipes:
- ColorBond downpipes are pre-painted and so you just need to choose your preferred colour, rather than paint them yourself.
- Metal is more durable than PVC because it is stronger and less brittle.
- There are several different sizes to choose from.
In addition to shape, size and colour, other points to consider when deciding on your new or replacement downpipes include:
- Proximity to windows. For instance, if the downpipe is right near a bedroom, the noise may be a problem when it is raining.
- In very heavy rain, occasionally downpipes will overflow and this may be a problem at times if they are positioned close to footpaths or where you and your family usually walk.
- Aesthetic value of kerb-side appeal.
- Position of storm water or water storage inlets.
The philosophy of Stark Roofing in regard to installing roofs, gutters or downpipes, has been the same for the past thirty years: plan your work and then work your plan. This means that we discuss with you the practicalities of downpipe locations before we start installing them, and we try to fall the gutters accordingly.