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How To Deck A Flat Roof

Roof Top Deck Construction

Deck Over A Flat Roof

There are proprietary pedestal systems that provide a very stable, level and serviceable deck over a roof membrane, though, they are relatively expensive compared to conventional methods.

In whatever manner a deck is constructed over a roof, maintenance for cleaning and repairs of the membrane below is recommended. Deck panels should be constructed that can be lifted with minimal effort or damage. The roof below should be cleaned and inspected at whatever intervals is found necessary for each deck. A deck located under pine trees will need much more maintenance to clean out debris than a rooftop deck above a high-rise.

Flat roofs are prone to leaking even without decks because of design errors, improper materials and improper installation. Many times when roof decks are installed, they further damage roofs causing more severe leaking and drainage problems. Proper waterproofing for a roof deck involves installing an EPDM membrane and flashing around deck supports and rail penetrations. This is often accomplished using EPDM boots that fit over the openings. EPDM is a rubber like sheet used for waterproofing surfaces. Roofs should be sloped about 1/4″ every 12″ to shed water. Drainage is very important because pooling water can cause leaks.

Average Cost To Build A Roof Over A Deck

Unfortunately, we wouldnt be able to tell you how much it would exactly cost to add a roof to your deck without scheduling a consultation and coming to your home. But we can give you an average range of prices that it would most likely fall within. They include:

  • Adding any deck covering or enclosure will typically cost between $1,000 $10,000.
  • Adding a covered roof to your deck will typically cost between $3,000 $10,000.

The cost will vary depending on the professionals hired, materials used, square footage, and weather conditions.

Not a real zip code.

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A Balcony With Wooden Floor Or Other

This option is generally quite popular given that it is an affordable one, not only due to the choice of materials, but also because costs related to construction are also quite low. Other than the structural changes that may be required, generally, all you will need to do is add a floor with proper drains in order to assist in water evacuation. Moreover, you will have the choice between different styles for your flooring: sequoia, cedar, yellow pine, etc. You can also opt for vinyl or composite.

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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 wont 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, its 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.

Modified Bitumen Vs Pvc Membranes Flat Roofs

RoofTop Deck Construction

The Modified Bitumen option is a single-ply rolled roof available in traditional torch-down systems and newer peel-and-stick systems. The peel-and-stick method is available as a do-it-yourself option. The torch-down method is a fire hazard and not recommended for occupied homes. Neither are good options as a walkable surface to make a flat roof usable space as a roof deck. If that is the goal of a flat roof, a modified bitumen roof would require an extra build up and product application to create useable deck space.

PVC Sheet Membranes are also a single ply application. While there are some brands available as a do-it-yourself option, the waterproofing reliability demands specialized installation techniques and professional application is recommended. However, in the case of the PVC membrane single-ply system, no additional product is needed to have it function as a leisure roof deck. It is designed as a pedestrian traffic coating in addition to its roofing properties and does two jobs in a single product solution. It is important to be sure to choose a PVC membrane that has been tested for use as both a roofing membrane and a pedestrian traffic coating.

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A List Of Materials For Flat Roof Installation

Depending on the type of roof youve chosen either warm flat roof or cold flat roof youll need to gather a number of important materials to build a flat roof.

In addition to basic tools such as a drill, utility knife and measuring tape, youll need the following basic materials, knowledge of local regulations, and a set of detailed instructions:

  • Roofing timber
  • Steel joists
  • Rubber EPDM membrane
  • Water-based adhesive
  • Insulation

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 of weight per square foot. If you are unsure, it is always best to consult an engineer.

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Average Costs Of Popular Roof Deck Coverings

The ranges given below are based on product quality and local costs. The most obvious information is the differences in the costs of the various coverings.

Type of Roof Covering
50 yrs./steel 100 yrs./aluminum

Shingles, shakes, and tiles can be a problem in high wind locations. Metal roofing, while initially more expensive, is resistant to severe weather. It is also energy efficient and has virtually no maintenance.

Metal roofing now also comes in various attractive shingle styles as well as standing seam and corrugated sheets. There are still other options for roof coverings, such as clear polycarbonate plastic sheeting, skylights, and a durable canvas-type material.

What Can I Cover My Deck Floor With

Installing Flat Roof Deck

Interlocking deck tiles are a low-cost way to transform your deck into a safer, more attractive space while helping to protect the actual deck from wear and tear. Installing outdoor tile over a wood deck can help to protect you from splinters, while offering the deck protection from sun and wear and tear.

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Research Guidelines & Limitations

Depending on the area in which you live, you may realize there are guidelines and limitations regarding rooftop decks or additions. Two of the groups you will need to contact are your homeowners association or neighborhood board and your local building department.

If you have a homeowners association or neighborhood board, you will likely have to submit your rooftop deck design for approval. This may even include reaching out to your neighbors to inform them of your intent to build a deck on the roof.

Waterproof Flat Roof Decks: A Bit Different

Whats the difference between a regular roof and a flat roof deck, and why does it require different materials?

The key is in the word flat. When a roof is flat water is going to spend a lot more time in one place giving it more time to find a way underneath the roof surface and into the buildings structure. So rather than a roofing material that simply lets water run down it, you need a roofing material that offers a completely waterproof barrier. Hence, why waterproof vinyl decking is popular. As a multi-ply roof PVC membrane, the waterproof flat roof deck will hold up to the rigors of continued exposure to water, heat, wind, foot traffic, etc.

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Install The Intersected Beams

On top of the 8×2 rafter and aligned above each of the original beams, install the intersected beams of equivalent size in a calculated straight line one after the other in a pecking order. If they are 6×6, then install 6×6 beams in a standing position.

All new beams must be of exact height so that the lowest part of the roof will have an even surface to sit on.

The Six Ds Of Decking: Waterproofing Flat Roof Assemblies

Building a Deck on a Flat Roof

All images courtesy Duradek

When waterproofing a walkable roof deck, there are a number of important principles to consider in determining the ultimate performance of not only the decking assembly, but also the waterproofing and the overall building envelope. These can be thought of as the Six Ds:

deflection detailing and deconstruction.

Each plays a key role in the performance of the deck, waterproofing system, and building envelope.

DeflectionDeflection refers to a decks ability to control surface water. This is affected by numerous factors, including slope, drip edges, and diverters. In multi-storey buildings where decks or balconies are stacked, the structure below will benefit from the overhang provided by the balcony above.

When a deck is correctly designed, water will flow where it is supposed to gothat is, away from the building into a gutter system or over a drip edge away from the exterior wall system. A proper deck slope of ¼:12 helps reduce the possibility of ponding water, even with building shrinkage or settlement.

False fascia details can be used to hide gutter, fascia, railing mounts, and deck slope. Given the proper slope, a simple drip edge detail is typically the most expedient way of removing surface water from the deck surface.

tapes flashings and perimeter fastening devices.

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How To Build A Roof Over A Deck Attached To A House

This article covers building a roof over a deck attached to a house, but several plans and designs are available. Remember that these instructions may vary depending on your deck plan and roofing type.

The time has finally come to cover that deck, but before we get into the nitty-gritty of the detail, we first need the right tools and materials.

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Preparation For Adding A Deck

Before installing a roof deck, you must confirm the stability of the roof. As a deck, the roof will have to bear more weight, which you need to consider before construction begins. The roof must be able to support 55 pounds per square foot at a minimum. An expert roofer can help you determine if your flat roof can support whatever materials you decide to use and you can save yourself a lot of hassle and money later.

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The 3 Most Common Materials Used For Flat Roof Construction

There are several methods and materials for the design of the exterior surface of a warm or cold flat roof.

Material 1: Hot tar and gravel

Also known as the built-up roof , this type of flat roof features three or more layers of waterproof material, mixed in an alternating fashion with hot tar and a layer of smooth stone-like gravel.

As you might imagine, this is the cheapest version possible and good for covering a shed.

Material 2: Modified bitumen

This involves a single-ply rolled roof that creates a protective layer against ice and water. It can be made stronger with a mineral-based surface. To guarantee the material stays secure, most of these materials come as peel-and-stick systems that are easy to apply.

Material 3: Rubber membrane

Also known as EPDM , this is natural rubber the kind you might find on a car tire or an inner tube. Its durable, and can be fastened to the roof with fasteners and glue. This is probably one of the easiest versions for a DIY project.

Access To The Rooftop Deck Over An Attached Garage

Installing a Lean-to Roof on an existing Deck

This could be rather easy or a bit complicated. It really depends on the floor plan of the 2nd floor of your house.


It would be just fantastic if a common area such as a living room, a dining room or even a hallway adjoins the Rooftop that you are planning to build.

In this case you could have a simple door or more grandiose French Windows as the way to access the Deck.

PROS: Easy Access, Easy Construction, Quick move back into the house if the weather changes.

CONS: Your guests will need to go through your house before they can get to the Deck.


Another option would be to build a staircase, along one of the wall, inside or outside the garage, leading to the rooftop deck over the garage,

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Whats The Finest Materials For A Flat Roof

Excessive-Performing Industrial Roofing Materials Varieties

  • PVC Roofing. For a lot of initiatives, PVC roofing is our most well-liked alternative as one of the best flat roof materials on the market.
  • Steel Roofing. A business standing seam steel roof is the perfect alternative for a constructing with a roof slope higher than 2 inches.
  • TPO.

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How Do You Build A Deck Over An Existing Roof

A deck built on top of an existing roof might be a lovely addition to your home. The challenge is that it will require some form of supporting structure, as well as waterproofing and any penetrations. Well go through how to build a in this guide. Because installing a deck on top of an existing roof might be difficult, its important to do your homework before getting started. As a result, we will go over a few key points.

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Choose Your Deck Team Wisely

Architects, landscape architects, engineers, green roof professionals, master builders all have their specialties. You may want to interview several of them before deciding on your rooftop deck team. Green roof professionals often have many these resources in house. If not, they will likely consult with an architect or engineer first anyway. Ask them about their process. Find out how experienced they are. Its well worth it.

What Types Of Flat Roofs Are There

Building a rooftop deck

The two classic types of flat roof designs are the warm flat roof and the cold flat roof. In addition, theres a third type the warm flat roof with airflow thats essentially a hybrid version of the warm flat roof and the cold flat roof.

There are design differences for each type.

The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers that help to hold up the roof.

In the warm flat roof construction, there is insulation packed into every possible space where air can flow. In creating the cold flat roof, air is allowed to circulate freely between the joists and there is no insulation.

Its important to keep in mind that installing a flat roof is a largely an either/or proposition: EITHER no air is allowed to circulate OR there is constant airflow throughout.

Problems can arise if air is allowed to move, but not freely. This creates the potential for condensation due to the gaps in temperature if too much condensation builds up, it can cause the wood to rot away, especially with an outdoor shed.

For that reason, cold flat roof construction needs to keep in mind the need for unblocked airflow.

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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.

Rebuilding A Rotted Deck On A Flat Roof

A client recently asked if I would replace her badly worn-out roof deck. This wooden deck was built over her screen porch and on top of a flat roof.

Its not really flat: Its pitched 1/4 inch per foot, but without a spirit level you cant really tell.

Years of neglect and lack of gutter coverage above the deck had destroyed not only the deck but a window and the sidewall as well.

The Value of a Roof Deck

Besides being a great place to take the love of your life for a romantic interlude, flat roof decks are very popular among homeowners because you can use your otherwise unused roof space to create a private retreat and increase your outdoor living space. Many condos and apartment buildings have roof-top decks, patios and balconies instead of backyards or ground-level patios and decks.

First Things First: Replace the Rot

First order of business was to remove the old deck and repair the rotted house wall and replace the window in the same process. The window was in a corner where two roofs met and formed a valley. Water runoff from the roof valley was overshooting a damaged gutter and soaking the window. Water eventually entered the window sill area and rotted the 2×4 sill-framing and plywood sheathing behind the cedar clapboards.

Luckily we only had to replace a few 2×4 studs and window framing since the water damage stopped at the house rim joist. Once the framing and 1/2-in.

Repairing the Water-damaged Roof Framing

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