The hidden costs of a patio or decking
The headline rate per square metre is the surface layer. Here is what the quote leaves out below ground — and how to work out your true total before you sign.
What the sticker leaves out
The visible surface sits on a sub-base you never see. Digging out, disposing of spoil, and building a compacted stone base is often a large share of the real cost, and it scales with how much has to be removed and how uneven the ground is.
A patio or deck has to shed water away from the house, which typically means creating a slight fall and sometimes a channel or soakaway. Poor drainage is where a cheap job fails, so this is a real cost rather than an optional extra.
Restraint edging for a patio, or posts, footings and joists for decking, are structural work hidden beneath the finish. Ground-screw or concrete-footing requirements often surface only after the quote.
Excavated soil, old slabs and offcuts usually leave by skip or grab lorry, charged by volume. Removing an existing patio before the new one goes down is frequently a separate line.
If a machine can't reach the garden, materials and spoil move by barrow through the house or side return, which adds labour hours. Restricted access is one of the most common reasons a real cost lands above the headline.
Many surfaces want sealing or oiling on completion and periodically after, plus pointing, a weed membrane or a sub-frame vent. These recurring and finishing costs sit outside the build quote.
Why the per-square-metre rate misleads
Quotes are usually pitched as a rate per square metre for the finished surface, because that is the number that wins the comparison. But most of the cost and nearly all the risk lives below the surface: excavation, sub-base, drainage, edging and access. Two quotes at the same rate can be wildly different jobs once you account for how much has to be dug out, where the water goes, and whether a machine can reach the garden. A rate that looks like a bargain can quietly be the dearer choice once the groundworks are priced — which is exactly the comparison the headline rate prevents you from making.
How to work out your true total
Start from the surface area and its material rate, then add excavation and spoil disposal for your ground, the sub-base build-up, drainage and falls, edging or the deck sub-structure and footings, an access allowance if a machine can't get in, and any sealing or finishing. Add removal of the existing surface if there is one. For a sourced figure on a specific job — with each line dated and graded by how well we can verify it — run it through the TrueCost calculator rather than relying on a rate per square metre.
How we stay honest about this
We may earn a referral fee if you book a supplier or installer through a partner link, at no extra cost to you, and it never changes which option we rank first or the figures we show. Placement can't be bought — the order is decided by the true total and verifiable quality, never by who pays us. See our affiliate disclosure and methodology.
Rules of thumb only get you so far. Run a specific option through the calculator for a sourced, dated, confidence-graded figure.
Frequently asked
Because the finished surface is only the top layer. Beneath it sits excavation, spoil disposal, a compacted sub-base and drainage — all of which take labour and materials you never see, and all of which determine whether the job lasts. On many projects the groundwork rivals or exceeds the cost of the surface itself.
Often, yes. If a mini-digger and grab lorry can reach the work, excavation and spoil removal are quick. If everything has to be barrowed through the house or a narrow side return, the same job takes far more labour hours, which is why restricted access is a common reason a real cost lands above the headline rate.
Usually not. A build quote covers installation; sealing, oiling, re-pointing and periodic upkeep are typically separate and, for timber and some stone, recurring. Fold a realistic finishing and maintenance allowance into your true total rather than treating the build price as the whole cost.
Related guides
See the big picture in the Hidden-Fee Index — how much the advertised price hides across every category — or browse all buyer guides.
This guide explains typical, well-known cost mechanisms for general education — actual fees vary by operator, destination and date. Confirm live prices, fees and your consumer rights with the retailer and official sources before you buy. TrueTotal provides guidance, not financial or legal advice.