Gutters are added to all houses built in Perth. It is a requirement of the Building Code of Australia (BCA). If we actually harvested this water into water tanks I could understand this need for gutters, but that can be another blog post in itself.
Anyway, these gutters are usually neglected by most home owners. Gutters can become blocked and then they overflow, but most home owners won't know - or care - because you just don't go outside when its raining heavy. And even if you did you may not notice the overflow from the actual rain falling.
What happens when you add a patio though? You very quickly notice the existing house gutters overflowing. This is because a patio is an ADDITION to a house, not a renovation to the house. So when the patio is added, the existing problem doesn't go away - it actually reveals itself for the first time.
Most of the time the issue is simply blocked gutters. It is surprising how very few leaves can impede water flow into a down pipe. Obviously lots of leaves means NO water flow to downpipes. If the water can't escape onto the down pipe it will find its way over the back of the gutters - the lowest point of the gutter.
This is NOT the time to call the patio builder. It is time to get on the roof and see what is going on. I would say 90% of callbacks we get about leaks are nothing to do with the patio. We are happy most of the time to come and have a look as part of good service practice. Most people are understating and happy to learn about this situation and take steps to prevent it happening again. Others think we are just trying to get out of fixing the problem. All we can do is be polite, try to educate and come to an agreement as to the best course of action. Extra downpipes added to a house are usually the best option although sometimes can be impractical due to existing paving or concrete below the gutter line.
Winter is a beautiful time of year - not many sounds are better than heavy rain on a colorbond roof - so make sure your gutters are clean to avoid avoidable water problems.