Why build over a patio?
Lifting a patio is heavy, noisy and creates a lot of waste. If the slabs are sound, they make a firm, level base. Building on top saves time and disposal, and keeps the ground undisturbed. It's especially common in Ingleby Barwick and Wynyard, where builders laid small patios outside the back doors of almost every house.
The height question
The first thing we measure is the gap between the patio surface and the bottom of your door sill. The deck needs room for the frame or pedestals plus the board thickness, and the finished surface should stay below the sill so rain doesn't run indoors. Low-profile frames and adjustable pedestals keep this as slim as possible, but if the patio sits right up against the sill, there may simply not be room.
Is the patio sound?
We walk the patio and check for rocking slabs, cracks, sunken areas and weeds pushing through. A few loose slabs can be re-bedded. A patio that's sinking or breaking up isn't a stable base, and building on it would only hide a problem that would come back through the deck.
Water, airbricks and the damp-proof course
Patios are usually laid with a slight fall away from the house so rain runs off. A deck on top must keep that path open, so we leave drainage gaps and never block channels or gullies. Just as important, the deck must stay well below the house's damp-proof course and must not cover airbricks, which ventilate the floor void. If a patio was laid too high against the wall in the first place, we'll point that out and may suggest lifting a strip next to the house.
How the deck sits on top
On a flat, sound patio we use low treated joists laid on packers, or adjustable pedestals that let us fine-tune the level on a patio that isn't quite flat. Either way the frame sits on the slabs without fixing through them, so water still flows underneath. Composite boards are the usual choice, because they're unaffected by the damp that collects at patio level.
Going beyond the patio
The old patio is rarely the size you want. We often build the deck over the patio and then extend it onto the lawn, using posts and concrete pads for the new part, so you get a bigger, level space with one surface throughout.
Questions we get asked
Do I need planning permission to deck over a patio?
Usually not, as a deck over a patio is low. Decking is normally permitted development if no part is more than 30cm above the ground. We'll check your levels.
Will weeds grow up through the deck?
Not through a sound patio. Where the deck extends onto soil, we lay membrane and gravel underneath to keep weeds down.