The basis of any roof assembly is the roof deck. Its primary function is to provide structural support for the roofing system with adequate strength to support all anticipated live and dead loads. The deck must not deflect, must be secured to p
rovide resistance to wind uplift and should be a clean, uninterrupted surface that provides for insulation or membrane securement.
Why am I concerned with the roof deck type,” you might ask. Three reasons:
- The deck type determines if insulation is required and what load it may carry
- The deck type mandates mechanical attachment or adhesion of your roof.
- The deck type determines how difficult repairs will be as your system ages
We will include the relevant factors in our basic instruction on the following types of roof decks:
- Plywood or Wooden Plank
- Steel Deck
- Lightweight Insulating Concrete
- Structural Concrete
- Tecum/Cementitious Wood Fiber
Plywood/ Wooden Plank
Used most frequently in residential construction or in commercial sloped roof applications, wood decking is secured directly to wood or steel framework and is available in thickness from 1/2″ to 3″.
Pros
Readily accepts most fasteners, is quick and easy to cut and form and is relatively inexpensive.
Cons
Low wind uplift resistance when nailed and rapid deterioration when moisture is encountered.
Steel Deck
The most common form of deck on commercial projects is steel. Metal decking is puddle welded to the structural steel framework and is available in 18-22 gauge, with profiles 1″-1-1/2″ in height.
Pros
Rapid installation in 24″ x 3″ panels welded to a steel frame. It is also cost effective due to low labor resources needed at the time of installation. There is super wind uplift ratings and good long-term resistance to moisture.
Cons
Metal decking is costly to replace becaue of the need to remove the closest frame member. It also requires either structural concrete or lightweight insulation to perform properly.
Repair investigating is also difficult with a steel deck roof because of possible water migration under the roof through the lenght of each panel.
Lightweight Insulating Concrete
Another common form of decking for commercial projects is lightweight insulating concrete (LWC). It can be found on many buildings in the form of plank using gypsum, or monolithic pours over corrugated/fluted metal deck or a form board such as fiberglass. LWC is an air entrained mixture of cement, water, fly ash, sand, or other additives depending on density required. When poured over preformed foam, it allows drainage to be built into the deck.
Pros
Rapid installation with taper in deck to enhance drainage. It also has a high fire resistance. The lighter deck weight results in savings from footers thru the the wall structure due to less dead load at deck level.
Cons
LIC has low wind uplift resistance and fastener pull out values in comparison to steel or structural concrete. There is also rapid deterioration once moisture intrusion occurs.
Structural Concrete
The next form of decking in commercial applications in Florida is structural concrete. It is found in three common types:
- Monolithic Pour – uses “forms” and is poured in a slurry, similar to the foundation in residential construction.
- Pre-stress or “twin tees” – a pre-cast plank with steel reinforced built into the material at the plant and shipped in various lengths and widths.
- “Hollow Core” – also a factory formed plank, it is hollow inside with internal supports similar to masonry blocks
Pros
The most secure form of decking with superior wind uplift and fire ratings. Structural concrete is virtually indestructible and is found on most high-rise buildings and hurricate rated shelters.
Cons
Extremely heavy decking requires extensive supporting walls. Concrete decks allow water saturation, eventually deteriorating the reinforcing steel enough to require epoxy injections to restore.
Tectum/Cementitious Wood Fiber
The last form of commercial roof deck covered in this post will be tectum or CWF. These planks or panels are factory formed and comprised of wooden fibers bonded by hydraulic cement. CWF was used widely during the 1950s – 1970s but has since become a marginal player in commercial applications.
Pros
Superb sound absorbtion and acoustical properties. A Class A/I interior rating requires no additional finish for exposed deck applications. Fabricated from sustainable natural resources meets “green” building requirements.
Cons
Poor wind uplift ratings. Requires extensive 2-step fastening system to meet Florida wind loads. Deteriorates rapidly when wet.
For a more detailed examination of your roof deck and entire roofing system, please call us to set up an appointment..
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