Floating Deck Over Flat A Roof: DIY How To


A flat roof deck can be an attractive addition to your home. The difficulty is that it will need some kind of supporting structure, and you will also need to take care of waterproofing and any penetrations. It is something that is a possible DIY thing, but remember, if you do go that way, there won’t be any warranty to fall back on should the rubber roof leak or something else unexpected happens that ends up flooding a downstairs floor area. If you are unsure, maybe the best option is to get someone in.

Nevertheless, if you are still brave to DIY, we are going to talk about how to build a deck over flat roofs. The process of building a deck surface on top of an existing roof top can be tricky, so it is important that you do your research before starting the project. We will cover some important considerations.

In many ways, installing a deck over a flat roof is similar to installing a floating composite or wood deck over a concrete deck on patio – instead, it’s a floating rooftop deck built on a floating deck frame. This type of deck is called a “floating deck” because it is not permanently fixed in place like a stand-alone structure. They can rather be regarded as an extra deck “placed” on top of another structure.

Unfortunately, typical flat roof specifications do not meet the minimum requirement for a deck to go on top. As a starter, the roof must be at least 16 inches high for a deck to rest on the surface without obstructing sunlight or ventilation needed between the roof and the deck. The good news is, that you can adapt your flat roof with some measures that will allow for an adequate height!

Professional Inspection Needed For A Rooftop Deck

So if you are thinking about installing a roof deck on an old flat roof, make sure it is professionally inspected by a contractor before proceeding with construction.

The roof you want to put a deck on must be able to support 55 pounds (25kg) of weight per square foot. If you are unsure, it is always best to consult an engineer.

Don’t Install Before You Confirm Integrity Of Existing Roof

Considerations should also include how you plan on finishing off your flat roof, such as water run-off, deck access for maintenance, drainage, etc.

You need to proceed with caution as flat roofs leak regardless of whether they are decked or not, as a result of design errors, insufficient materials, and poor installation. Many roof decks, when installed, further damage roofs, resulting in even more severe leaks and drainage problems.

The first consideration is that the posts on the deck can puncture through and damage your old flat roof if it’s not supported with additional blocks or beams.

You also need a platform that can support the weight of your deck and any furniture or equipment that might be on it and make sure this platform has enough room for power cables, pipes and other infrastructure such as vents.

What Is Best Used For Waterproofing A Floating Deck: A Membrane

Deck waterproofing entails flashing the deck supports and rail penetrations and installing an EPDM membrane. This is commonly done with boots made of EPDM rubber which are slipped over the openings. EPDM is a rubber-like sheet that is used to waterproof surfaces. In order to shed water, it is important that the roof slopes at a quarter of an inch every 12 inches. Poor drainage can lead to leaks.

Likely Professional Builder Approach

A professional builder would usually achieve this by creating two columns beneath the new deck – one at each end – and putting beams across the top. If you are doing this on your own, it will be necessary to find a way of supporting these columns using either post-tension cables or pier blocks.

Then you need a platform constructed from planks laid at right angles which is able to take the weight of your deck with enough space between each plank for water to run off and a layer of insulation.

If there are any penetrations in this new platform – for example, if you need to put in a post, column, or beam – you will have to make sure that these are sealed against leaks.

A water-tight EPMD rubber membrane should be installed on top of the roof deck to prevent water infiltration.

Afterward, you will ensure you have installed “sleepers” or flat 2x6s laid flat on the roof before working with the decking. This will provide the surface for you to install the decking. 

Approaches To Take With Deck Construction

With a deck on a flat roof, ensure you have adequate spacing between decking boards to allow drainage and aeration.

Rubber packers should be used to keep the decking off the roof membrane.

Make sure you use a high-quality waterproof membrane to ensure it is watertight and has long durability. It is not something you should skimp on to save a few dollars. PVC membranes are the way to go.

Possible Alternative To Consider

As a possible alternative to consider, there are proprietary pedestal systems that can provide very stable, level, and reliable decking over the roof membrane, however, they are relatively more expensive than conventional methods.

Allow Future Access

Deck panels should be built in a manner that makes it easy to lift them for cleaning and repairs of the membrane below. In other words, you need to be able to easily get to the membrane below for any required maintenance and repair. You don’t want to have to take your deck apart to gain access at some stage.

The roof below should be cleaned and inspected regularly to check for leaves and other debris. A deck placed on a roof under pine trees will need far more maintenance to keep debris from building up over time than a rooftop deck on top of a high-rise.

Frequently Asked Questions About Building A Deck Over A Flat Roof

Can my roof support a deck?

If your roof can safely support at least 55 pounds of weight per square foot, and is in optimal condition, it may be suitable for a deck.

Are rooftop decks worth it?

The answer is a resounding YES. A rooftop deck can be built for as little as $15,000 and the financial benefits are substantial. A rooftop deck will increase your home’s value by an average of 12%. That means more equity in your property.

Does a covered deck increase home value?

After seeing the benefits that a rooftop deck provides, it is clear that there are many reasons to construct one. The first reason is affordability: you can build a respectable and functional rooftop for just $15,000. The second benefit is the increased value of your home: Researches has found that a residential building with an amenity such as green space, a rooftop deck, or a private parking lot increases the home’s value by an average of 12%!

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