Waterproof Your Roof Deck

A roof deck offers an enjoyable and functional outdoor living area and is a very attractive perk of any house, but it also requires maintenance and waterproofing for a long lasting, leak free service life. Waterproofing your deck will prevent water from entering the house’s structure and also provide the benefit of creating a dry and usable living space below. If you are experiencing problems with your roof deck and would like to waterproof it, its critical to find an experienced contractor who will use high quality materials and will get the job done right. Inexperienced contractors will actually exacerbate the existing problems and may cause a range of major issues such as: structural damage, sever dry rot, interior damage, mold and many other complications, all of which will be very costly to repair. The rule of thumb to follow with roof decks is that their construction and repair must be done with top notch materials and practices, otherwise leaks will inevitably occur.


Where do leaks come from?

Contrary to popular belief that leaks come from a defect in the deck itself, the reality is that the source of a leak is usually in the waterproofing material, used to keep water out, or one of the items near the deck, such as hose bibs and exterior electric boxes. Additionally, railings and walls are very common items to leak. All leaks typically occur because of poor flashing and wrapping techniques. To avoid the leaks in the first place, or to repair them properly all penetrations must be carefully flashed and caulked.

Another thing to watch out for is the fact that your roof deck must be properly vented. Otherwise condensation will start building up in the structure and with time it will begin to rot.

Options for Waterproof Deck Surfaces

When choosing a waterproofing surface, there are two general options to consider: 1. An integrated walking and waterproofing surface 2. A separate waterproofing surface with a raised walking surface (floating deck) above it.

In the first scenario, integrated walking and waterproofing surfaces (such as IB DeckShield material) are applied over a constructed plywood deck surface. This deck surface must slope toward drains at a minimum of 1/4 inch to 1 foot. In this type of a design it is crucial for the structure and plywood decking to be very solid, and for all joints to be properly aligned. Moreover, drains and scuppers, which are often a source of leaks, must also be adequately waterproofed.


Installing separate walking and waterproofing surfaces makes it possible to pick from a greater variety of decking and waterproofing products. Be sure to choose a roofing membrane that has a long life, welded seams, and a solid performance track record in low slope applications. You should also go for a system that includes heat welded drains and scuppers, which are an integral part of the membrane. This type of a system will provide years of leak free survice life in comparison to systems that combine parts from different companies. Next, you can construct wooden platforms with wood decking or other decking materials on top of this waterproofing surface. It is also possible to use a pedestal system that supports stone or concrete pavers. You need to make sure that the deck design will allow for the added depth and weight of this system.

If you would like your waterproofing system to last for many years, it is best to avoid an EPDM rubber roof or a Tar/BUR roof. This is because on a rubber roof, pieces of uncured flashing must be glued to the roof and the post to make the post penetration watertight. Similarly,on a Tar / BUR roof liquid tar or roof cement is used to seal around the post. The problem is that both rubber roof flashing and tar flashing around the post will begin to fail after 5-7 years, causing roof leaks. To stop the leaks you will have no choice but to disassemble the deck and repair the flashing, which is a very costly affair.

One disadvantage of a separate walking and waterproofing system is that you will periodically need to lift up the walking surface to clean under it. This may be an issue for homes that have trees overhead that drop leaves and pine needles on the deck, making it more labor intensive to clean. In these cases, you can go with an integrated walking surface with waterproofing, which can be easily cleaned off.

Another helpful tip is not to overload your deck surface with heavy potted plants or other heavy things. You should be able to easily remove everything from the deck so that you can quickly clean and inspect the waterproofing surface whenever necessary.


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