How can I waterproof a hole in my vinyl deck to fit a downspout?

Question

I am wondering if anyone might have some suggestions on solving this drainage issue with our vinyl deck.

We used to have 2 separate decks but upon rebuild we have them joined with a narrow walkway. There was previously a downspout where the new walkway currently is. Initially, we were going to redirect this downspout to the other side of our roof gutter as our deck builder didn't think having the hole through the deck would look good. But after having a roofer and a gutter company here, we were told that due to the current slope of our roof, redirecting the downspout to the other side would not work without the risk of having our gutters overflow. We have temporarily attached a piece of downspout across our deck that then drains down into river rock for the time being, but of course, it cannot remain this way.

As a result, I now have to cut a hole in our deck for the downspout to fit through so that it can reach the storm drain below. The deck surface is the Deksmart vinyl product. I want to make sure that I do this as least invasively as possible while also being accurate. The last thing I want is for water to seep under the vinyl and potentially cause bubbling or rotting, so I want to shield the exposed edges in the subfloor once I cut out the hole. Almost all water will be inside of the downspout, but I want to protect the subfloor in case some water on the deck itself runs into the cut-out. I have attached some photos for reference.

Gutter Fix 1 - This is the current layout, as well as the proposed plan outlined in red.

Gutter Fix 2 - An alternative view from under the deck.

Gutter Fix 3 - This is a mock-up of how I was hoping to potentially protect the subfloor edges (the green tape represents vinyl decking that I would heat weld to the existing vinyl.

I have also been searching online for options, but I'm not sure that I have found a viable solution. Our gutters are 2x3" rectangles and the only PVC coated drain openings I could find online are 1.5" or 2" circles.

Could anyone suggest a product or PVC insert that will work with a 2x3" downspout? Or a better way to heat weld the vinyl to protect the cut-out opening? Or any other suggestions or ideas on how to accomplish this?

Any help would be greatly appreciated!

Answer 1

I finally completed the deck/downspout project and thought I would provide an update of how I ended up doing it. It was quite a bit of research & prep work but I am happy to say that it turned out great.

I ended up using an Amerimax 2x3 vinyl gutter drop outlet as an insert to put inside the hole I cut out of the deck. It had a very minimal footprint and came with a flange which helped in adhering it more securely to the deck. I've attached some images with more details for anyone interested, and also in hopes that it may be of use to someone else.

Picture 1 - A collage of all the various products that I found throughout the process that I could have potentially used for the project or as an insert in the deck. It also includes part numbers and locations where they can be purchased.

Picture 2 - The final product I chose to use as the insert for the hole I cut, along with a custom cutting template I made for that product in case someone else ends up using the same item. Just to reiterate, this was for a 2x3" downspout.

Picture 3 - For anyone else in a similar situation, here are all the steps I took to cut the hole and connect the downspout to the drain below, as well as some pictures of the final result.

Hopefully, this will help anyone who might run into this issue in the future. Again, thank you all so much for all the advice and suggestions!

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Answer 2

I wonder if you could use a Low Profile Dryer Vent like this one? (google that phrase for more options).

You might be able to seal it using the stuff they use to glue PVC pipes together but that might ruin your deck. Probably caulk is the way to go.