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How to upgrade downpipes?

Stormwater / Downpipe Upgrade Advice (QLD, 1985 House)

Hey everyone,

I’m planning on replacing my home’s downpipes and could use some advice.

The house was built around 1985 (QLD), and it currently has square downpipes. I’d like to swap them out for round PVC downpipes — partly for aesthetics, but mainly because the current system struggles with heavy rain.

There are 4 downpipes in total.
On the length of the house, 2 downpipes are spaced 21m apart.
On the width, the other 2 are 12m apart.
From what I understand, downpipes should be spaced every ~12m, so mine are definitely stretched.

My Questions:

Should I replace the square gutter adaptors riveted into the gutter (100x80x90) with round adaptors as well? Or is the hole too big to transition neatly?
Would you recommend running the pipes straight into stormwater, or leaving a small gap with a grill drain at ground level so I can see if it’s blocking up with leaves (we don’t have gutter guards)?
I’ve read that 90° PVC elbows can cause dripping noises — is that actually a problem?
We also have a decking area with a pitched roof that ties into the house. In torrential rain, water floods back into the eaves even though we’ve got catchers on the gutters. Any tips for fixing that?

The Plan:

Swap out all the downpipes for 90mm PVC, leave a gap above stormwater with grill drains for easier maintenance, and hopefully get better flow.

Has anyone here done something similar? Would love to hear your suggestions or pitfalls I should watch out for.

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Comments

JacobZ

Hi @bowmatty,

Thank you for your question about upgrading your downpipes.

You wouldn't be able to simply remove the rectangular downpipe pops and replace them with round ones, as the corners of the rectangle would remain open. In this situation, you should be able to use Holman 100 x 80 x 90mm PVC Stormwater Downpipe Adaptors to transition from the rectangular pops to the round pipe.

Running downpipes directly into stormwater is neat, but it hides blockages. Leaving a small gap with a grated drain (also called a "dry joint" or "inspection point") at ground level is a good practice. It lets you see if water is backing up, clear debris easily, and still connects to your stormwater. Since you don’t have gutter guards, this is what I would do.

Yes, 90° bends can cause dripping sounds, but considering you already have 90° bends in your downpipes, if they were going to annoy you, you would likely be aware of them already. I wouldn't really factor this into your decision-making. If it becomes a problem in future, there are options for addressing it.

The water backing up into the eaves near your deck suggests the gutter and downpipe there are undersized for the roof catchment area. Even with the rainhead you can see in the first photograph, once the inflow exceeds capacity, water can spill back. I'd consider adding an additional downpipe in that section or upgrading to a larger gutter profile.

Considering the complexity of the work and the potential for damage to your home from overflowing gutters, I would consider consulting with a roofing plumber for their assessment. Even if they don't carry out the work, they may be able to offer some guidance based on their experience.

Allow me to tag @AlanM52, @Nailbag and @Dave-1 for their thoughts.

Let me know what you think.

Jacob

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/56259#Comment_56259

Good Afternoon @bowmatty

I dont think changing over you downpipes to being round will help with the quantity of water they can carry. I am thinking of more downpipes installed to carry the load from your roof and decking roof. Thats a fair amount of space overall with only 4 downpipes all up. (The gazebo would definently be charging the system in a big way.)

I switched my downpipes over to the air gap system as I have a large amount of leaves that fall, end up in my gutter and downpipes. I think it has helped me out with less blockages but also something to note is you will need a dogs leg kink to get the down pipe to exit over the grilled base squarely.

Sound of drips, I have that sound on one of my downpipes lol and yeah its annoying, I intend to fix it but have not done so as yet. (its a rectangular downpipe btw)

Adding more downpipes will entail joining them into your existing piping and for that you will need a plumber. So Id suggest a quote first for the joining of pipes and see if they are happy for you to do the rest?

Dave

bowmatty

https://www.workshop.bunnings.com.au/discussion/comment/56259#Comment_56259

@JacobZthanks for the reply.

In regard to the water backing up... Where do you suggest I add another downpipe? Do you mean like a dual downpipe at one of the ends or in the middle of the gutter somewhere. Issue with the middle is that its enclosed and no room to install a downpipe unless I drill through the eave and then into the metal gutter. Additionally, could I replace the rain catcher with a larger one that's currently used?
Pictures attached of the gutter between house and deck area + raincatcher

bowmatty

https://www.workshop.bunnings.com.au/discussion/comment/56259#Comment_56259

What would you suggest i do with the front downpipes. Obviously, no room to install a 90 elbow, do you think it would look ok if i go straight down from the gutter and mount to wall or would you suggest I use a standoff mounting bracket that protrudes off the wall. I am in two minds...

JacobZ

Hi @bowmatty,

Is the decked area the 21m side of the house?

A larger rainhead might help, but if it is not the choke point in the system, your focus might be better elsewhere. Have you noticed it overflowing when you have a large downpour?

At present, it looks like that gutter is servicing two separate roofs with two downpipes spaced, what I assume to be 21m apart. I just can't see it being able to handle a large downpour without adding a downpipe to the middle of that span.

Drilling through the eave to connect up an additional downpipe seems like it would be the most effective option on that side of the house.

For the front downpipes where you don't have space for a 90° bend, I'd just use two Holman 90mm 45° Elbows instead. You can always orient them slightly off square if there is not enough room.

Let me know if you have any further questions.

Jacob

Nailbag

Hi @bowmatty

Personally I prefer the look of the lower profile of square downpipes and using a colour closest to the house colour so not to make a feature out of them.

That aside, as far as the functionality of a more efficient drainage system, I'm going to leave that to the professionals which I advise you do as well. In Qld like all other states, it's a legal requirement to use a licensed plumber to perform all plumbing works other than whats outlined in this article.

Thats not to take away the simplicity of being able to do the work yourself. But it could raise its ugly head when there is an insurance claim or come time to sell the property and it's brought up in an inspection report. Though not highly likely scenarios, but one to be aware of.

Nailbag

bowmatty

https://www.workshop.bunnings.com.au/discussion/comment/56267#Comment_56267

Hi Jacob, no this side that runs with the deck is the shorter 12m apart. What raincatcher would you recommend as an upgrade that would connect to the stormwater.

i have not seen it overflow but i am only assuming its over flowing due to the metal grills rusted (connected underneath the eave) and water pooling below the eave. This only occurs when we have torrential rain though.

bowmatty

https://www.workshop.bunnings.com.au/discussion/comment/56271#Comment_56271

Thanks @snail.
Funny thing with this house is when we had the initial building inspection they found nothing wring with it.

We have since done many projects one looking at the drainage. we found there was no stormwater connected, all 4 main downpipes were connected to terracotta pipes coming 1m out from the house into a mud pit, not even gravel. Since then i have dug a 42m

trench and laid stormwater pipes which i have successfully diverted away from my house into an exit point.

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/56271#Comment_56271

Hi @bowmatty,

Rainheads are custom-made products that are outside my area of expertise.

You'd have to speak with a manufacturer for their advice on that one.

Jacob

AlanM52

Hi @bowmatty

CC: @JacobZ, @Nailbag, @Dave-1

We live in 3150 and the (inherited) 2 story house was built in 1970 and has the smaller downpipes and yep... got sick of going up the extension ladder to clear the pops.

Downpipes are now 90mm PVC stormwater and in the last 12 years not had any blockages.

Mini Soldering Torch Kit 135W.jpg

Pops were soldered so I used that Mini Soldering Torch Kit 135W purchased from ALDI to remove them.

Then enlarged the opening using Aviation snips for the 100 x 80 pop and also soldered them in (3 x pops).

Holman 100 x 80 x 90mm PVC Stormwater Downpipe Adaptor.jpeg

I purchased those (as @JacobZ mentioned) secured either side with pan head self drilling screws.

Similar to what @JacobZ mentioned these are my 'dry joints' with some chook wire to block the rats for the back corners.

This is the 3rd downpipe at the front porch corner on the utility side of the house and if you look closely that's the gas main coming in from the street. Thanks to a plumber mate who cautioned me to be careful digging there, concrete slab with the gas meter just over the other side.

Cheers

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/56299#Comment_56299

Nice work @AlanM52 👍

AlanM52

https://www.workshop.bunnings.com.au/discussion/comment/90431#Comment_90431

Thanks mate,

They are still waiting to be painted 🙄

Cheers

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/111089#Comment_111089

Morning @bowmatty

For a 21m run of gutter I still think there needs to be an extra dpownpipe in the middle. I would suggest to have a chat to a plumber/roofer to get the connection through the eve done properly. It dosnthave to be bang in the middle of the run, just somewhere "ish" to help carry that quantity of water you have going into the gutter.

Dave

bowmatty

Also, what ground drainage crates do you recommend? Circular or square and metal or plastic. I am indecisive as to what 🙂

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/56517#Comment_56517

Hi @bowmatty,

There's not a whole lot of difference to tell you the truth, but a square pit would be a bit harder to clog.

If you don't have to mow around them, I would use the Everhard EasyDRAIN Aluminium Grate And Flo-Way Pits.

If you had to mow around them, so you want them to be a bit lower profile, I'd use Holman 100 x 90mm Storm ABS Finishing Collar With Grate.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

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