Which falls and drainage rules apply to your deck?
A pedestal deck needs somewhere for the water to go, and the rules on falls and drainage are split across a British Standard, a warranty body and a guidance note. This page is for anyone specifying or signing off a balcony or roof terrace build-up in the UK.
See corrections and updatesNHBC Standards clause 7.1.16: the joint width your pedestals need to produce
The gap left between adjacent paving units, the joint, is what lets surface water find its way down through the deck. How wide that joint needs to be is set out in NHBC Standards 2025, clause 7.1.16 (Accessible thresholds and upstands), which gives a joint width of 6 to 8 millimetres between individual paving units and 10 to 12 millimetres at perimeter upstands and thresholds, for paving laid on height-adjustable support pedestals under NHBC warranty.
Many pedestal heads carry moulded spacer tabs that set the joint automatically as the paving units are laid against them. The width those tabs produce is not stated consistently across datasheets in this category, so a tab alone is not something you can check against clause 7.1.16 without knowing what it actually leaves once the deck is laid.
What this means for sign-off
A warranty surveyor checking joint width against clause 7.1.16 is checking what is on the ground, and checking it in two places: the field joints between units and the wider gap required at perimeter upstands and thresholds. A deck built on spacer tabs alone, with no allowance made for the perimeter figure, risks failing the check at the edges even where the field joints are correct.
Ask the supplier, before the pedestals are ordered, what joint width their spacer tabs actually produce on a finished deck, and whether that figure meets 6 to 8 millimetres in the field and 10 to 12 millimetres at upstands and thresholds on its own, or needs packing to get there. Get the answer in writing.
NHBC Standards 7.1.16: the joint width your pedestals need to produce
The gap left between adjacent paving units, the joint, is what lets surface water find its way down through the deck. How wide that joint needs to be is set out in NHBC Standards 2025, clause 7.1.16 (Accessible thresholds and upstands), which gives a joint width of 6 to 8 millimetres between individual paving units, and a wider 10 to 12 millimetres at perimeter upstands and thresholds.
Those are two different figures for two different parts of the same deck. A width that satisfies clause 7.1.16 in the field of the paving will not satisfy it at the upstand, and the two need checking separately.
What this means for sign-off
A warranty surveyor checking joint width against clause 7.1.16 is checking what is on the ground, in both zones. Where the field joints and the perimeter joints are set by the same method, one of the two is likely to fall short unless it has been checked on its own terms.
Many pedestal heads carry moulded spacer tabs that set the joint automatically as the paving units are laid against them. Ask the supplier, before the pedestals are ordered, what joint width their spacer tabs actually produce on a finished deck, in the field and at the perimeter, and whether that figure meets 6 to 8 millimetres and 10 to 12 millimetres respectively or needs packing to get there. Get the answer in writing.
NHBC clause 7.1.16: the joint width your pedestals need to produce
The gap left between adjacent paving units, the joint, is what lets surface water find its way down through the deck. How wide that joint needs to be for paving laid on height-adjustable support pedestals is set out in NHBC Standards 2025, clause 7.1.16 (Accessible thresholds and upstands). It gives a joint width of 6 to 8 millimetres between individual paving units, and 10 to 12 millimetres at perimeter upstands and thresholds.
Many pedestal heads carry moulded spacer tabs that set the joint automatically as the paving units are laid against them. The width those tabs produce varies by manufacturer, and a tab that sets a narrower gap than clause 7.1.16 asks for will not meet it on its own.
What this means for sign-off
A warranty surveyor checking joint width against 7.1.16 is checking what is on the ground. Where the spacer tabs are the only thing setting the gap, the paving may need packing or repositioning to reach 6 to 8 millimetres between units, or 10 to 12 millimetres at upstands and thresholds, before the deck can be signed off against that clause.
Ask the supplier, before the pedestals are ordered, what joint width their spacer tabs actually produce on a finished deck, and whether that figure meets clause 7.1.16 on its own or needs packing to get there. Get the answer in writing.