Adjustable timber deck pedestal

Frequently asked questions

How do you level a deck on pedestals?

First set the finished height of the deck, usually from the patio door threshold. Subtract the thickness of the board and of the joist: this gives you the pedestal height. Choose the range whose adjustment span covers this height, with some margin either side to absorb unevenness in the ground.

Then place the pedestals at both ends of each row and adjust them by turning the nut by hand: adjustment is to the millimetre and needs no tools. Stretch a string line between these two pedestals, or use a laser level, to set the intermediate pedestals to the same height.

Lay the joist, check it with a spirit level along its whole length and correct pedestal by pedestal if needed. Finally, screw the joist into the tab on the head of each pedestal so it stays put while you lay the boards.

What are the drawbacks of a timber deck on pedestals?

There are four, worth knowing before you choose. The first is the minimum height: pedestal, joist and board add up. Even with the lowest pedestal (8-20 mm), allow about 7 cm between the ground and the top of the boards. In front of a low threshold, this can rule out installation on pedestals.

The second is the base. A pedestal spreads the load, it does not remove it: it needs stable, load-bearing ground such as a concrete slab, a screed, or ground that has been stripped, compacted and covered with gravel. On loose soil, pedestals sink over time.

The third is cleaning underneath. Leaves and debris fall between the boards and build up under the deck. Lay a geotextile membrane before the pedestals to limit weeds, and keep an access point for occasional cleaning.

The fourth is noise: a deck on pedestals resonates a little more than a deck laid on the ground. Acoustic strips laid on the joists reduce this effect. On the plus side, installation on pedestals avoids concrete, ventilates the joists, which extends their life, and lets cables and pipes run under the deck.