Are you wondering if rooftop decks can actually handle Seattle’s weather without causing leaks or extensive damage? Are you confident that you’ve chosen a roofer who knows how to waterproof a rooftop deck the right way and won’t leave you to pay for costly repairs in a few years?
If you’re reading this, you’re probably considering a rooftop deck to enjoy Seattle’s limited sunshine and maximize your home’s space. But if it’s not built and waterproofed correctly, your dream deck can quickly turn into a nightmare of hidden leaks, mold growth, and costly structural damage.
At RoofSmart, we’ve helped many homeowners who were struggling with leaks, mold, and rotting wood caused by a poorly installed rooftop deck. We have seen how easy it is to cause widespread and expensive damage and have learned the most effective ways to waterproof a rooftop deck.
In this article, you’ll learn the two most common—and most expensive—problems Seattle homeowners face with rooftop decks and how to prevent them before you build.
Additionally, you’ll be able to confidently choose a roofer who can make your rooftop deck dreams come true (without any nightmares).
What should I know before getting a rooftop deck in the Greater Seattle area?
Many Seattle residents choose to install a rooftop deck on their homes to take advantage of their rooftop space during the summer.
Rooftop decks can be a beautiful addition to your home, but before you get one, make sure you’re aware of how to avoid the two biggest problems Seattle residents with rooftop decks face:
1.) Leaks
2.) Condensation build-up.
In a rainy area like Seattle, it is crucial that you talk to your roofing contractor about how to avoid leaks, mold, rotting wood, and extensive water damage that will cost you thousands of dollars to repair.
Need help identifying leaks, condensation, or rot in your rooftop deck? Want to make sure you don't face these issues after installation? Contact RoofSmart today!
1.) What happens if my rooftop deck is leaking?
In a rainy area like Seattle, having expert-level waterproofing on your roof is non-negotiable. If your rooftop deck is installed poorly or not waterproofed correctly, then you’re at risk of leaks.
The huge bummer about roof leaks is that they stay invisible for a long time. By the time you notice it, it’s probably already caused widespread mold or extensive rotting.
Unfortunately, this happens a lot more than you would think. Sometimes, too many contractors are working on the project, and certain areas don’t get waterproofed because they’re overlooked. Sometimes, the contractor doesn’t have enough experience and does a poor job installing the rooftop deck.
Either way, you’re stuck with leaks that cause thousands of dollars in damage. And then you also have to tear everything apart to reach the damage. It’s a major mistake with expensive consequences.
When a rooftop deck gets installed, these are the vulnerable areas that must be waterproofed to prevent leaks:
- Railing
- Siding
- Walls
- Doors
For example, we helped one customer by replacing their entire rooftop deck. Water had entered in through the railing and caused extensive rotting and mold in several sections of the roof deck.
Here’s what one of the railing posts looked like as we were removing it. You can see the rot and mold all around it:
We replaced areas that were rotting, treated other spots for mold, and made sure that everything was correctly waterproofed so that they don’t have a repeat of this costly mess.
2.) What happens if condensation builds up underneath my rooftop deck?
Aside from poor installation or waterproofing, the biggest issue that contractors overlook is the risk of condensation forming underneath the rooftop deck.
If your roof isn’t properly insulated (or ventilated!), you’ll have the same issues as you would with a leak: mold and rotting wood.
Here’s an example of a flat roof deck that was completely destroyed due to condensation build-up:
And so often, the same types of incompetent contractors win the bid to replace the assembly…putting it right back the way it was before. The definition of insanity is doing the same thing and expecting a different result. When critical elements of the roof assembly are missing, your price should definitely be cheap!
A rooftop deck is still a roof, so it needs to be insulated properly, just like you would with any other roof. You produce water vapor every day while going about your daily tasks. Cooking, cleaning, bathing, laundry, breathing—basically anything that involves water or moisture produces water vapor.
This water vapor rises up to the attic and collects on the ceiling of the attic. Without insulation, your roof will form condensation. This is because there’s a temperature difference between the cold roof deck and your warm interior, which will build up moisture and turn into mold. It also causes rotting wood. But with the right kind of insulation, your roof is protected.
What kind of insulation does my roof need to protect it from condensation?
To achieve maximum protection, you need something that acts like a beer cooler or a foam insulator underneath that keeps the water vapor from migrating up to the bottom of that membrane. Usually, foam boards work well for this.
You also need an air barrier to keep air and moisture from traveling up through the roof deck and collecting condensation there. This can be plastic, ice and water shield underlayment, or spray foam.
Having those two layers ensures that moisture cannot collect and form condensation. But you have to assume that nothing is perfect, so the top of this insulation sandwich needs a rot-proof cover board (like a Densdeck gypsum board).
Here’s what Densdeck Gypsum Board looks like when installed:
Think of it like a tile backer. It’s a cement board that can’t rot and adds tremendous strength and rigidity to the roof system, even giving it an improved fire rating and impact resistance.
In summary, to build your insulation sandwich, you should:
- Repair the water damage on the roof
- Install an impermeable vapor barrier (like foam insulation boards)
- Install a condensation control layer (like a plastic sheet or spray foam)
- Install a rot-proof coverboard over the insulation
- Finally, install the new roof membrane. That could be textured like Duradek or smooth like Duro-Last (this would be in an application where there’s going to be a deck floated on top.
Here’s what the textured membrane looks like:
Here’s an example of a smooth membrane (like PVC) looks like installed underneath the deck tiles that are “floating” on top (they sit on pedestals:
Without the PVC underneath, these tiles would be at risk of leaking and damaging the roof below.
How Can I Find A Roofer Who Is Qualified to Install My Rooftop Deck?
Hiring a contractor who knows how to properly install a rooftop deck is the best way to protect your roof and prevent costly repairs in the future. An experienced, trustworthy roofing contractor will know about these issues and take steps to avoid them.
But how do you find a roofer you know you can trust? That’s the hard part! But don’t worry, we have a few tips to help you vet your options:
- Find a local roofer: We recommend looking for a local contractor who has been working in the Greater Seattle area for many years. That way, they’re familiar with the issues that Seattle area residents face.
- Find evidence that they’ve done MANY rooftop deck installations: You want a roofer who can back up their claims and show proof of the projects they’ve done. Luckily, many roofers publish pictures of completed jobs on their website, making it easy for you to see how much experience they have. So, if a roofer doesn’t have any pictures (or only 1 or 2 pictures) of rooftop deck projects they’ve done, then they might not have enough experience.
- Check their reviews: Check the reviews for each company on multiple different websites. See what each company’s ratings are across the board, and make sure to read both good and bad reviews. If you can, search for reviews specifically about rooftop decks.
- Ask how they plan on preventing condensation: If your roofer cannot answer this question or does not understand why you brought it up, do not trust them with your roof. It’s VERY important that your roofer is knowledgeable about preventing condensation and is willing to discuss it with you.
Here’s our final tip: Remember that you’re not just comparing prices—you’re looking for the roofer who is most competent and knowledgeable about rooftop decks.
Rooftop decks are expensive, and it can be tempting to choose the least expensive option to save money. However, you might end up paying thousands of dollars more down the line in repairs if you do that.
We encourage you to choose the contractor that makes you feel 200% sure that they can do the job correctly.
Want help evaluating roofers? Download our Qualified Roofer Checklist to use as a guide for assessing each roofer's qualifications.
What to Do Before You Build Your Rooftop Deck in Seattle
Leaks, rot, and condensation are expensive problems—and they’re surprisingly common with rooftop decks in the Seattle area. But now you know what causes them and how to avoid them with proper waterproofing and insulation.
Most importantly, you know how to find a reliable contractor who knows what they’re doing and can make sure you do not have issues with leaks or condensation.
If you’re seriously considering adding a rooftop deck to your home, your next step is to read the article “How Much Does it Cost to Install a Rooftop Deck in Seattle?”.
This will help you get a sense of the overall cost of a rooftop deck project and the factors that can increase costs.
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