Rooftop Deck Construction

Floating Roof Decks vs. Over-Concrete Decks

The technique of installing a deck over a level roof and the process of constructing a deck over a concrete patio are pretty comparable to one another. People sometimes refer to these decks as "floating" because they are not tied to the ship in any manner, and this is the reason why. This is due to the fact that they do not operate as a distinct structure on their own. They are not "constructed" into the other structure; rather, they are only "positioned" on top of it. They are not part of the other structure in any way.

Your first order of business is to determine whether or not the roof has the structural strength to support 55 pounds per square foot of weight. After that, in place of the roofing materials, you will need to put a watertight EPDM rubber membrane over the top of the roof deck as a barrier against water infiltration. This will need to be done. This membrane ought to be completely impermeable to water all the way through. Installing "sleepers," which are just 2x6s that have been laid flat every 16 inches, is the next step after the surface of the roof has finished being covered. You will then have a surface on which to install the decking planks as a result of doing this.

Read more: How to Decorate Deck Support Columns 

Even though they provide a very solid, level, and serviceable deck over a roof membrane, the proprietary pedestal systems that are available on the market today are considerably more expensive than the more traditional methods. This is the case despite the fact that they are currently available. It is recommended that the membrane that is positioned below any deck that is built on top of a roof get routine maintenance in the form of cleaning and repairs. This maintenance should be performed as often as necessary. It is essential that the "panels" of the deck be able to be raised with a minimum of difficulty and damage in order to facilitate easy access. In addition to being inspected and cleaned at whatever intervals are judged to be necessary for each deck, the roof that is located below it should also be inspected. A deck that is placed in an area that is dominated by pine trees will call for substantially more maintenance to keep it clear of debris than a deck that is located on top of a high-rise structure.

Even without decks, flat roofs have a higher chance of leaking due to design problems, inferior materials, and faulty construction. This is especially true of older homes with flat roofs. When roof decks are installed, they frequently cause more damage to the roofs, which in turn leads to more serious concerns with leaking and drainage. This cycle continues until the roof is completely destroyed.

When it comes to providing adequate waterproofing for a roof deck, two of the most important components are the installation of an EPDM membrane and flashing around deck supports and rail penetrations. EPDM boots are usually utilized to achieve this objective. These boots are designed to fit over the openings in the pipe. EPDM is a sheet that is utilized in the process of waterproofing surfaces. It has the consistency of rubber. Roofs should have a slope of about a quarter of an inch for every 12 inches in order to provide the most efficient drainage of rainwater. It is essential to have sufficient drainage since standing water can cause harm to the structure of the building.

FAQs about Rooftop Deck Construction

Do I need a permit, and which code applies to a rooftop deck?

• Yes, almost always. In commercial/multifamily projects the IBC treats a roof used by people as an “occupied roof” with egress and occupancy rules (e.g., §503.1.4 and §1006.3); one- and two-family homes typically follow the IRC, but your AHJ may still apply “occupied roof” provisions. Check with your building department before design.

Can my roof structure carry a deck? What loads apply?

• Have a licensed structural engineer verify capacity. Loads are taken per IBC Ch. 16 / ASCE 7 based on the occupancy; occupied roofs are typically designed to floor-type live loads (not the usual 20 psf roof live load), plus snow/wind where applicable.

How do I waterproof correctly—sleepers or pedestals?

• Never damage the membrane. Use pedestal systems (level, serviceable) or sleepers over a protection layer, and coordinate every detail with the roofing manufacturer; many specs require protection sheets/pads beneath pedestals and explicit approval so the roof warranty remains valid. 

What roof slope/drainage is required under a rooftop deck?

• Provide positive drainage—industry/code guidance targets ¼ in/ft (2%) on low-slope membranes, and NRCA/IIBEC emphasize no ponding. Use tapered insulation or shims/pedestals to maintain slope to drains/scuppers. 

Pedestals vs. sleepers—when to use which?

• Pedestals excel for leveling, airflow, and service access; many systems require a floating insulation base/protection pad to spread loads. Sleepers are useful for deck-board layouts but must sit on manufacturer-approved separation/protection layers.

How tall do guards/railings have to be on a roof deck?

• Under the IBC, required guards are 42 in minimum. Under the IRC (one- and two-family), guards are 36 in; confirm which code your project is under. Parapets can count as guards only if they meet guard criteria.
  
  

Can I avoid penetrating the roof for railings and planters?

• Often yes—use non-penetrating, weighted guardrail systems or anchor to parapets/curbs detailed by the roofer; penetrations (if any) must be flashed per the membrane manufacturer.
  
  

What deck surfaces work best on roofs (and what about wind)?

• Common choices: concrete/porcelain pavers, rubber/wood pavers, or modular tiles on pedestals. In wind zones, use assemblies with tested uplift resistance and follow SPRI/ANSI WD-1 or manufacturer wind-uplift guidance (ballast, clips, interlocks).

How do egress and occupant-load rules affect the design?

• Occupied roofs must provide exits based on aggregate occupant load and may affect whether the building counts as a high-rise (≥ 75 ft to the occupied level). Plan stairs/doors and exit paths early with your code official.

What about maintenance and access to the membrane?

• Design the deck in removable panels/tiles so the roof can be inspected and repaired; keep drains clear and follow the roofer’s overburden guidance to protect the membrane from traffic/impact.