Pedestals are designed to support heavy stone, wood or concrete pavers over any waterproofed structural surface with pedestrian traffic only, such as balconies, terraces, rooftops, patios, walkways, courtyards, pool decks and pool surrounds. The purpose of pedestal support systems is to allow for deck drainage and air circulation, both which are critical to the health of any deck system. The elevated position of the pavers also helps to reduce heat conductance to and subsequent expansion of the waterproof membrane. Other benefits of using a pedestal support system include lower energy costs and noise reduction.
Pedestals allow fast, accurate leveling of pavers, and allow conventional wood or stone decks to be elevated from the roof, all while protecting the roofing membrane. In large cities where space is limited, maximizing living space is a high priority to building managers as well as homeowners, and using pedestal support systems is a way to transform an otherwise unusable roof deck into a beautiful, livable area suitable for a variety of functions.
Installation requirements vary for each individual project site. Before choosing which type of pedestal to use, factors that need to be taken into consideration are paver size, pattern, grid layout, starting point and finished deck surface elevation, which should be shown on shop drawings that have been approved by the architect, installing contractor and owner. Measurements from the construction site should be used for final selection.
In order to calculate how many and what type of pedestals you are going to need, first determine how high your deck is going to be from the bearing surface, then subtract the thickness of the decking material. That provides you with 'deck cavity height'. Then choose which pedestal matches your deck cavity height. Use basically the same number of pedestals as pavers on square or rectangular decks. Columns and other protrusions, where pavers are cut and fit, will increase the number of pedestals required.
There are two basic types of pedestal supports. There is the screw jack adjustable pedestal, which has a threaded shaft that enables contractors to adjust paver height by simply rotating the base of the pedestal. Then there is the fixed height pedestal which is raised by adding leveler plates or shims to increase to the desired height. Fixed height pedestals are recommended for heights lower than 1-1/4". Screw jack pedestals are somewhat easier to use than fixed height pedestals because you can adjust the height by rotating the base of the pedestal, as opposed to fixed height pedestals which require stacking shims on top of one-another to achieve the proper height and slope. Most pedestals are made from high density polypropylene or polyethylene, which is impervious to water, mold and resistant to freeze thaw cycles.
Some of the companies that manufacture fixed height pedestals are Envirospec, Appian Way System, Hanover and Tile Tech. Appian Way System manufactures an interlocking pedestal support with a smooth, flanged, bottom cap can be applied directly to a roofing membrane using the bottom cap with or without a bottom shim (1/16" or 1/8"). Hanover manufactures pedestals for projects which require paver heights above 3" and up to 24" and can provide a padded top plate that provides quiet installations and eliminates paver movement. Rigid-to-rigid (pedestal-to-paver) hard surfaces can create noise and paver movement when pedestrians walk across. The pads will eliminate both conditions. A coupler can be added to increase the paver height by 2 1/2" - 4". Bracing is required for elevations above 16" and up to 24". Hanover's coupler includes a circular flange with multiple holes, or eyelets, for ease of tie bracing. Envirospec makes PAVE-EL brand pedestals with a grid-like structure and integral spacer ribs located on the upper surface to ensure even joint spacing. These pedestals are easily sub-divided to support corner and edge pavers and 1/8" plates enable perfect leveling of pavers.
One recommended method for installing fixed height pedestal supports is to determine the first row of paver stones at an exterior edge of the deck, using 1/2 pedestals at the edges and 1/4 pedestals at the corners and at partial angled paver locations. Lower paver stones horizontally rather than nosing them into position to eliminate possible indentation of insulation on a protected membrane roofing system. Align and shim as required as work progresses. Run subsequent rows of pavers parallel to the first row. Where multiple stacking of pedestals is employed, locate leveling plates on top of the upper pedestal, never in-between or below pedestals. On the deck perimeter and around protrusions where it is not practical to cut pavers to fit, such as canted roof-wall junctures, fill the voids with coarse gravel and binder. For access to substrate areas, pavers simply lift out of position, so it is easy to replace damaged pavers as well.
Some of the companies that manufacture screw jack pedestals are Westile, Bison and VersiJack. With all screw jack type pedestal supports, it is easy to adjust partially loaded pedestals by rotating the base, allowing contractors, designers and installers to accurately plan, precisely align, and uniformly install level decks with a combination of ease, speed and accuracy. Bison manufactures pedestals that range in height from 1/2" to 16", and for heights over 1¼, the threaded design allows precise vertical adjustment with a simple turn of the wrist. Simple accessories are offered to adjust for slope, and the screw-to-adjust height setting assures a perfectly level deck. A maximum 1,000 pound/pedestal load bearing capacity with FS:2 exceeds most requirements.
A recommended method for installing screw jack pedestals is to install the shortest pedestals at the door threshold and the tallest at the roof drains. To obtain pedestal elevation, subtract the paver thickness from the finish deck surface elevation. Installing the first row of pavers at the perimeter wall is not recommended. Instead, begin the installation of full pavers at the second row in the roof field. Mark perpendicular guidelines on the substrate surface to ensure a square layout. Install initial pavers along the guidelines to form a "T" pattern, and then install the remaining field pavers outward from "T". Install the perimeter pavers last, as they are usually cut and less than full size to ensure proper layout and fit.
Using pedestal support systems allows architects to create unique deck designs with a variety of materials, such as concrete pavers, wood tiles or certain types of natural stone. With a compressive strength of over 19,000 psi, Glacier Blue® Devonian Sandstone is perfectly suited for use with pedestal paving systems. When Atlantic Testing Laboratories, Ltd. in Albany, NY tested a 48" x 18" x 2" thick Devonian Sandstone paver supported on four corners with a concentrated load applied at the center, the paver withstood over 3,000 lbs.
Devonian Stone of New York, Inc. recently provided Glacier Blue® Devonian Sandstone pavers for a project completed by Interior Foliage Design, Inc. that involved using pedestal pavers on the terraces of a building on Madison Avenue in New York City. The stone pavers measured 2' x 2' x 1.5" and Bison screw jack pedestals were used.
Aside from its strength, Glacier Blue® Devonian Sandstone was chosen because of its capacity for accuracy in cut tolerances. Stu Schecter of Interior Foliage Design, Inc. explains, "The trick with all of the paving systems is to find the stones that you can purchase plus or minus 1/16th of an inch, and the reason why that's so helpful is because if the stone is off more than that amount, then you can never get the lines perfectly straight. And on the Madison Avenue job, the lines are beautiful and straight, both the long ways and the short ways, and that's because the tolerances are so minimal, the cut is so precise."
Pedestal support systems have become more popular in the last three years or so because of their ease of use. It makes it possible to get any kind of elevation you want and get that elevation exactly level. If precision is what you want, properly installed pedestals are a perfect choice.
Educational Topic for Next Month:
Cleaning & Sealing