Patio paving

Building Regulations guidance in England sets the damp-proof course of an external wall at least 150mm above the adjoining ground. A patio laid higher than that lets rain splash and soak into the wall above the damp-proof course, which can cause damp inside. Raising the ground level with a new patio is one of the most common causes of damp in back rooms.

The patio should also fall gently away from the house, so water runs off rather than pooling at the wall. Air bricks that ventilate suspended timber floors must not be covered or blocked. If the only way to reach the level you want is to build up against the wall, a channel drain or a gap filled with gravel along the house, agreed with the contractor, may be needed. Ask how the design deals with this before work starts.

Source: planningportal.co.uk

Slabs can be laid on a full bed of mortar that supports the whole slab, or on five spots of mortar, one under each corner and one in the middle. Spot bedding is quicker and uses less material, but leaves voids under the slab. Water collects in them, slabs can crack under point loads, and gaps under the edges let weeds and ants in. For that reason many slab manufacturers and paving specialists call for a full bed.

Porcelain and dense natural stones need a priming slurry on the back of each slab to bond to the mortar, because they absorb very little water. Without it, slabs can come loose even on a full bed. Joints can be filled with mortar or with a proprietary jointing compound; ask which is used and whether it suits the width of joint.

• the area, shape and finished level, and its relation to the damp-proof course
• falls and where water runs off
• sub-base type and depth
• full mortar bed, and priming slurry for porcelain or dense stone
• joint width and jointing material
• steps, edges and how the patio meets the lawn
• treatment of air bricks, drains and manhole covers

Outdoor porcelain is dense, stain-resistant and consistent in thickness, which makes it neat but harder to cut and bond. Natural stone varies from piece to piece and has more character, but needs a laying method that suits the stone and may need sealing. Concrete slabs are the budget option and come in many finishes. Whatever you choose, ask about slip resistance when wet, particularly in shaded areas where algae grows.

In England, a patio at or near ground level in a back or side garden has no area limit under permitted development; the permeable surfacing rule applies only to front gardens. Significant work to embank or terrace the ground to support a patio can need planning permission, and any significant work at a listed building needs listed building consent.

A raised patio on a sloping garden also affects neighbours. Standing higher than the fence can overlook their garden and windows, which is why raised platforms are controlled. If yours needs retaining walls, they are structural and should be designed for the load of soil and water behind them. Talk to neighbours before building, and ask the council if you are unsure whether permission is needed.

A large impermeable patio sends rainwater somewhere. A gentle fall onto a lawn or border is usually enough for a small area. Larger patios, or those with no garden below them, may need a channel drain connected to a surface water drain or a soakaway. Water must not be sent onto a neighbour's land. Permeable paving systems and gravel joints are also possible behind the house, even though there is no legal requirement for them there.

Describe the area, the slabs you are considering and any level changes. We verify your phone number and email, then show the request without your contact details to paving contractors in your area. Exactly one of them can buy it and pays us for it; you pay nothing. Before the contractor sees your details, we email you its name, address and phone number. Offrano confirms the business is registered but does not inspect its patios, so ask how it will bed the slabs and set the levels.