Here’s Why Your Deck Keeps Leaking.
Hey there,
Got some photos from a client whose deck started leaking and yeah, it’s not a fun surprise. Let’s break down what’s likely going on, why this kind of thing happens, and how to fix it (without it happening again down the road).
First, What’s a Membrane Deck?
A membrane deck is basically a deck that’s been coated in a waterproof system – something like Gaco, which is one of the most popular options. The idea is that marine-grade plywood gets covered with four layers of this flexible, rubbery coating, and when it’s done right, it creates a seamless waterproof surface.
It’s tough. It holds up against rain, snow, sun – all of it.
So Why Is It Leaking?
From what I can see in the photos, it looks like the railings were top-mounted – meaning someone drilled straight through the membrane to install them. Screws go in, and boom: that watertight surface is no longer watertight.
Maybe it held up at first, but over time, decks expand and contract with the weather. Those tiny holes around the screws get bigger, water sneaks in, and eventually you get leaks. Then comes rot. Then mold. Then it’s just a mess.
FYI: If you’re seeing rot on the outer edge of a deck, chances are it goes 3–4 feet further than what’s visible.
If the damage is on an outside edge, it’s usually manageable.
If it’s in an inside corner or near living space, repairs get trickier (and pricier).
What Should You Do?
Yes, the leak can be repaired. But here’s the big thing:
Don’t reinstall railings the same way.
Instead of top-mounting them (aka drilling down into the waterproof surface), go with fascia-mounted railings – these attach to the side of the deck. You’ll see an example of this in the background of one of your photos – same look, better function, way less chance of leaks later.
Can We Help?
This kind of work isn’t our main specialty, but we have done similar repairs and would be happy to help if you want to move forward. Just so you know:
Gaco requires four separate coats, which means four visits to site, even for a small repair.
If there’s rot in the plywood, it may need to be replaced.
The more complex the location (inner corners, living areas), the more time and materials it’ll take.
What you need to know:
- Membrane decks are awesome – until someone drills holes in them
- If your deck’s leaking, it’s likely from something that punctured the membrane
- Avoid top-mounted railings – fascia-mounted is the way to go
- We’re happy to help if you’re ready to dive into a proper repair
Let me know if you’ve got questions or want to talk next steps. Always happy to chat!
-Luke
