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How to modify pergola roof to stop house gutter overflowing?

Hi all, I'm wanting to modify my pergola roof to resolve two issues:

The pergola roof currently falls into one of my house gutters. This gutter tends to overflow in heavy rain. Underneath the gutter is a sliding door with no threshold so I'm concerned about water impacting the door or entering the house when this happens.
Even in light rain, drips of water come over the top of the gutter which means my alfresco area isn't water tight.

I've come up with the following options:

It looks like the previous owner siliconed the gap between the gutter and the underside of the corrugated roofing. I could add extra silicone to see if that fixes the drips.
Introduce some type of flashing which is attached to the top of the corrugated roofing and the inside wall of the gutter.
The fall of the roofing might be too flat causing water to flow back along the underside of the sheets. Maybe I could add some packers or something to the purlins to increase the fall.
I could fall the roof towards the fence instead of towards the house. This would reduce the load on the house gutter but create a few issues -
- This would create a bigger gap between the house gutter and pergola roofing. Although this would make it a lot easier to clean the gutters, I might still get rain coming through the gap into the alfresco.
- The pergola posts are quite close to the fence so I'd need to find a narrow gutter that doesn't overhang into the neighbour's property.
- Once I add in the gutter along the fence side of the pergola, I'm not sure what I would do with the rainwater. Cheapest option might be to direct a downpipe or rain chain into a large pot.

One more note, I know there's a fair bit of leaf litter in the gutters in the photo below. I still experience the issues listed above even after cleaning them out.

Thanks in advance for any suggestions you might have.

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Comments

JacobZ

Hi @DG11,

A warm welcome to the Bunnings Workshop community. It's wonderful to have you with us.

I would probably steer clear of any major changes at this point and try a few simpler solutions before altering the pitch or adding any additional gutters.

You mentioned that you still get the drip when the gutters are clear, which tells me it the water is likely rounding the end of the sheets and through surface tension coming back up under and over the edge of the gutter.

To prevent this, I would suggest you start by giving your gutters a good clean out and then wiping the top edge and inside edge of your gutter with isopropyl alcohol.

Once cleaned and prepared, you can attach a long strip of flashing tape to bridge the gap between the two surfaces. Ensure that the tape is securely attached to the top of the roof sheet and sits flush against the corrugation valleys.

This should create a barrier to prevent the water from rounding the bottom edge of the sheet and coming over the edge of the gutter.

With this in place, you can assess its effectiveness and look at further steps if required. The next step I would consider is having a larger capacity gutter installed on the house side of the pergola.

Allow me to tag @Nailbag, @Dave-1 and @Noyade to see what they think.

Jacob

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/54149#Comment_54149

Good Morning @DG11

I look at your gutters and think they look like mine 🙂 Mine do overflow as well even when i ahve cleaned them recently. I know the fall of my gutters isnt the greatest as the roofline does dip a little and so does the gutter creating a low spot which then overflows.

I was thinking of additional downpipes installed, in particular near the corner but not onthe corner, then arrowing the downpipe back to the one you can see in the second photo near the water heater.

Im not a fan of leafguard but you may find it helps, its just a pain when cleaning as leaves and dirt still get through.

The last idea I had was to either install a wider gutter to carry the load of water, and also meaning the pergolla roofing will definently be in range for it to drain even with that curling you describe. If you google "box gutter" you will see some examples. Tho that also means it will catch more leaves lol 🙂

Maybe an extra downpipe plus a more frequent clean of the existing gutters as a start. (yeah thats a pain but id rather the trees I have)

Dave

Nailbag

Hi @DG11

A very quick first step is to clean your gutters as @JacobZ has also pointed out. These are extremely full and as a result will also be holding dirt debris/mud and possibly water. Both of which will be deteriorating the guttering in particular all joins. This issue alone is a common one that I see very regularly causing internal wall and eve damage. Its the most likely cause of the rain water dripping between the gutter and facia board.

My solution, isn't the cheapest or easiest for the Alfresco roof, but potentially the best long term one.

I would remove the pergola roof sheets and replace the cross joists with taller ones. I would take the opportunity to then replace the sheets with new ones which will have a much higher UV rating and are not an expensive product. There are many profiles and colour profiles. Alternatively if the budget is tight, then it appears you could refit the existing sheets forward to the right of the photo so they overhang the roof tiles of the house and pass the guttering. You would then need to silicon seal all the old fastener holes.

This new profile will still allow you to access the gutters for future cleaning while pushing the Alfresco roof over to the house roof and back in to the gutter. You wouldn't need gutter guard, which I personally cause their own issues. they keep gutters clear of leaves, but dont stop the build up of dirt and mud.

Nailbag

Screenshot 2025-07-04 at 6.51.31 pm.png

DG11

https://www.workshop.bunnings.com.au/discussion/comment/54149#Comment_54149

Thanks @JacobZ for the reply. Just trying to picture how the tape would work with the corrugations in the sheets. Would I apply the tape to the inside of the gutter first and then fold it back towards the end of the sheets? If so, there would be a gap between the tape and the high point of each corrugation but would this not matter?

DG11

https://www.workshop.bunnings.com.au/discussion/comment/54171#Comment_54171

Hi @Nailbag , I do try to clean the gutters fairly regularly. When they're clean the overflow issue is certainly less frequent but the dripping still occurs in any level of rainfall.

Thanks for the suggestion though. I like the idea of being able to access the gutter from underneath the pergola. This will make it much easier to keep clean. I was thinking about replacing the sheets anyway since they're quite old.

One question, do I need to be concerned about how the run off from the pergola roof is hitting the house roof tiles? Is there a risk that the water could run up the tile it hits and underneath the tile above?

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/89311#Comment_89311

Hi @DG11

Thats a very good question. The pergola roof should only be around a 5deg angle. And of the overhang of the Alfresco sheet was just past the end of a row of tiles. Then the water should run off slow enough it wont creep up to the top off the tile and enter the roof space if that makes sense?

If you have anything doubts, you could get a couple of quotes from a roof plumber and find out how they would finish the sheets to get additional peace of mind.

Nailbag

JacobZ

Hi @DG11,

You could use something flexible like this T-Rex 101mm Strong Waterproof Tape.

Attach it to the corrugated iron first so that it sits flush on the ridges and valleys of the corrugation. You can then stretch it to attach to the gutter. As long as the tape is flush on the corrugated iron, it should direct any water that is running around the leading edge of the corrugated iron down into the gutter.

Let me know what you think.

Jacob

riziqbl

Hey @DG11 , did you find a solution to your problem? I'm having a similar issue.

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/58058#Comment_58058

Hi @riziqbl,

Did you have any photos of your gutter that you could share?

I'd be happy to have a look and see if there is anything that jumps out about your situation that might be a solution.

Let me know what you think.

Jacob

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