A comparison of deck support systems

Adjustable or fixed height pedestal supports used in conjunction with wood, porcelain or concrete pavers are without doubt the easiest way of constructing a perfectly level raised deck over a sloping surface. The majority of deck support systems rely on a screwed column to provide height adjustment with multiple sizes of pedestals being required to cover different height ranges, but a few alternative systems are also available, either based on fixed height columns or blocks or hybrid systems which combine both support methods.  We have summarized below the similarities or difference between the various options.

The pedestal support system utilizing the concept of a screwed column with separate base and head was first developed by Buzon in Belgium in 1992. Since that time, other producers have developed similar system, referred to in some European countries a ‘plots’. In fact there are now around 40 different makers of adjustable height pedestals in the world, with the vast majority being based in Europe. In its simplest form, the adjustable height pedestal comprises a flat circular base, a central screwed column to provide continuous height adjustment within the range of the specific pedestal and a circular head designed to support the pavers on each corner. The pedestal head typically includes either inbuilt tile spacers or has the ability to insert spacers of different thicknesses or placement in different position on the head. To add additional height, multiple threaded extension columns may be added between the head and the central screwed column. Typically pedestals are produced from high density injection molded polypropylene.

To ensure the top of the pedestal head is perfectly horizontal irrespective of the slope or unevenness of the substrate the pedestals are sitting on, three basic approaches are used.

1. A slope adjusting plate is placed under the base of the pedestal, which may either be a single unit comprising two rotating discs of variable thickness or more simply, single discs of variable thickness across the disc which are stacked to provide increasing compensation.  With this type of slope compensation, the pedestal itself remains in a perfectly vertical aspect.
2. The slope adjuster is situated on the head of the pedestal, in which case the top of the head itself is perfectly horizontal but the pedestal column will be on a slight incline. Again this might be either a single unit with rotating discs or single stackable discs.
3. A self-compensating head where the underside of the head is concave and moves inside a corresponding ‘cup’, allowing the head to swivel to a degree in all directions.  A device may be included to lock the head in a fixed position if required, although typically the head can only be locked perpendicular to the support column.

Typically these adjustment devices provide compensate for pitches up to 5 deg, although with some systems, additional slope adjusters can be stacked to offer extra adjustment.

The basic drawback of the this type of adjustable height decking support system is that you need to use a number of pedestal models (typically 4 or move) plus extenders to cover a full height range up to 12” and the lowest height achievable is around 1”.

A slightly modified version of the screwjack pedestal is now available to overcome the need for multiple models of pedestals in the 2” to 6” height range.  This involves using just two pedestals and adding ‘collars’ to build up the height, so just three basic components are required in this height range. At higher elevations though, the more conventional screwed pedestal becomes more cost effective.

As well the above screwjack type of adjustable height support system, some makers supply a system using 6” PVC pipe which is cut to the required height and inserted between a flat circular pedestal base and the pedestal head. The disadvantage of this type of system is that you can’t make height adjustments after the pedestal has been set in position other than by removing and cutting the PVC pipe, or cutting a completely new section of pipe . It is possible to add shims, but this only enables small height adjustments to be made. The PVC pipe system can however have cost advantages for very high deck elevations.

To overcome the issue of limited height adjustment with the pre-cut PVC pipe system, a few makers offer a hybrid system which combines a cut PVC with a head that includes a limited screwed section, offering an adjustment up to around 1”-1.5”.

Naturally, various makers offer their own unique features such as heads with inbuilt soft rubber material for extra shock absorption and sound deadening, loops to attach guy wires to stabilize the pedestals at higher pedestal elevations, and locking screws to keep the column from moving once it has been adjusted. Some pedestals also are also capable of using a screw and washer system which is used to secure Ipe wood pavers to the pedestal head when they are used on windy locations such as roof decks.

At the very lowest elevations below approx. 1.5” fixed height support pads are normally used. These might be square blocks, rings or circles and constructed of recycled rubber, neoprene rubber or plastic. Typically the pads will be stackable and minor height adjustments made with thin shims. Generally speaking, rubber pads are preferable because of their reduced noise transmission, additional shock resistance and slip resistance.

In passing, we should also make note that some installers choose to use a system of stacked. polystyrene blocks. Whilst it may have the advantage of lower cost, especially at higher elevations, this is not a system of deck supports we recommend.