Adjustable Deck Pedestals | Deck Support Blocks | Decking Pedestals New Zealand

A floating deck is a low platform that sits on supports rather than on posts set in concrete. Adjustable pedestals are the supports. This guide covers when a pedestal deck is the right choice, how to measure for the height range, how many pedestals to buy, how to lay them out and how to keep the finished deck level for years.

When a pedestal deck makes sense

Pedestals suit low decks, usually under 300mm off the ground, on a base that is firm but not perfectly level: a concrete slab, compacted road base, pavers or a bed of crushed rock. They also suit paver patios, walkways, shed floors and rooftop terraces where you cannot dig footings. For a deck high enough to walk under, or one attached to the house, you are into posts, bearers and building approval, and a pedestal is not the tool.

Measure for the height range

Decide where the top of your joists will sit. Then measure from the base to that line at the lowest point and the highest point of the area. The difference is the fall you need to take up. Pick the range that covers both figures with a little to spare at each end. The 18-30mm pack is for a near-level slab where you only want air and drainage under the joist. The 30-60mm pack covers most home decks and patios. The 60-135mm pack takes up a real slope or lifts a floor over a drain or a step.

If the fall across the area is more than one range covers, mix packs: shorter pedestals at the high end, taller ones at the low end. Each pedestal is set on its own, so there is no need for them all to match.

Work out how many to buy

Run joists at 450mm centres for standard decking boards and support each joist every 400mm to 600mm. A 3 metre by 3 metre deck with seven joists supported every 500mm needs about 49 pedestals, so four 12-packs. For pavers, put a pedestal under every corner where four pavers meet and one under each edge where two meet. Count from a sketch, then add a few spares.

Prepare the base

The pedestal spreads the load across its base, but it still needs something firm to sit on. A slab or pavers are ideal. On soil, dig out the turf, lay weed mat, then compact at least 50mm of crushed rock or road base. Never set a pedestal straight onto soft ground or mulch; it will sink and the deck will go out of level within a season.

Lay out and fix

Set a string line at the finished joist height. Place the pedestals on your grid, drop each joist into its top plates and wind the rings until the joist just kisses the string. Check with a long level across several joists, then drive two exterior-grade screws through the pre-drilled holes in each top plate into the joist. Screws are not supplied with the pedestals, so buy them with your timber. Fit joist tape over the top of each joist before the boards go on and the timber will last longer.

Fall for drainage

A deck should shed water. Set the string line with a fall of about 10mm per metre away from the house, and the pedestals will follow it. Because every support adjusts on its own, this is far easier than packing shims under fixed blocks.

Keeping it level

Walk the deck after the first heavy rain and again after the first summer. If a corner has dropped, lift one board, reach in and turn the ring under the low joist. That ten-minute job is the main reason to choose an adjustable pedestal over a fixed block.

Your buying checklist

Measure the lowest and highest points. Choose the height range that covers both. Count the supports from a sketch and round up. Buy exterior screws and joist tape with your timber. Check the delivery window suits your build date. Then order, knowing you have 14 days to change your mind.

The short version

Firm base, the right height range, a pedestal every half metre along each joist, two screws per plate and a string line with a little fall. Do that and the deck stays level and dry for years.