The short answer
You can sometimes lay block paving over existing concrete or tarmac, but only if that base is sound, stable and well-drained — and it brings real complications. The big problems are levels (adding blocks and a bedding layer raises the surface, which can breach the damp-proof course or clash with thresholds and gulleys) and drainage (an impermeable old base sheds water sideways, so it must have falls and somewhere for water to escape, since it cannot soak through). A cracked, sinking or hollow old base must not be paved over — its faults will telegraph through. Where the base is poor or the levels do not work, the correct approach is to break it out and build a proper sub-base. Reusing a base saves money only when it is genuinely fit to keep.
Reusing an old concrete or tarmac base is tempting and occasionally sensible, but it raises level and drainage problems that often make digging out the better choice.
Over concrete/tarmac
- Possible ifBase sound, stable, drained
- Main risk 1Raised levels vs DPC
- Main risk 2No drainage through the base
- Never overCracked / sinking / hollow base
- Better option oftenBreak out, build sub-base
When laying over an existing base can work
It is possible to use a sound existing concrete or tarmac surface as the base for block paving, treating it like a rigid sub-base with a bedding layer and blocks on top. For this to be sensible, the old base must be genuinely fit for purpose: structurally stable and not moving, free of significant cracks, not hollow or drummy (which signals it has lost support beneath), and able to deal with water. A solid, well-laid concrete slab in good condition is the most plausible candidate. Where it stacks up, reusing the base avoids the cost and mess of excavation and spoil removal. But these conditions are demanding, and many old bases fail one or more of them, which is why this approach is the exception rather than the default.
The level and drainage problems
Even on a sound base, two problems frequently make laying-over impractical:
- Levels: block paving needs a bedding layer plus the block thickness on top of the existing base, raising the finished surface by a meaningful amount. That can push the surface too close to or above the house's damp-proof course (DPC), cover air bricks, or clash with door thresholds, garage floors, gulleys and the street. Raising a drive above the DPC risks damp in the house — a serious problem — so the level rise has to be checked carefully against every interface.
- Drainage: concrete and tarmac are impermeable, so water cannot soak down through them as it would through a granular sub-base. Any rain that gets through the joints sits on the old base and must be made to run off via correct falls to a drainage point. If the old base traps water, the bedding layer can stay saturated, weakening it and risking frost damage. Permeable block paving cannot perform as intended over a solid impermeable base, because the water has nowhere to go.
These issues are why simply tipping sand and blocks onto an old slab so often disappoints.
When to dig out and start again
The honest position is that breaking out the old base and building a proper sub-base is frequently the better route, even though it costs more. You should dig out rather than pave over whenever the existing surface is cracked, sinking, hollow or of unknown construction, whenever reusing it would raise the levels beyond what the DPC and surrounding features allow, or whenever drainage cannot be resolved on the old base. Building from scratch lets you set the correct depth, the right MOT Type 1 sub-base, proper falls and a drainage strategy — and, importantly, lets you choose permeable construction, which matters because a new front driveway that drains to the road can require planning permission unless it is permeable or drains to a soakaway. You cannot reliably achieve a permeable system by laying over solid concrete.
There are also some methods that change the picture. Where an existing concrete base is sound and the levels happen to work, a competent installer may bond a bedding layer to it and pave over with the right detailing and drainage falls. In other cases, contractors break out only the problem areas and reuse sound sections, or use the old base as a capping within a properly designed build. What you should be wary of is any quick, cheap offer to simply screed sand over an old drive and lay blocks without addressing the levels, the DPC, the drainage and the condition of the base — that is the recipe for damp problems, standing water and paving that fails early. The decision should be made on the specific base in front of you: assess its condition, work out the level rise against the house and surroundings, and confirm where water will go. If all three check out, reusing the base can be a reasonable saving; if any of them does not, excavating and building a correct foundation is the route that lasts.
How to assess the existing base
Whether reusing an old base is sensible comes down to a practical assessment, and it is worth knowing what to look for before deciding. The first question is condition. Walk the surface and look for cracking, especially wide, stepped or recurring cracks that suggest movement rather than surface crazing. Tap or look for areas that sound hollow or drummy, which indicate the slab has lost support beneath and could drop. Check for existing sinking, lifting or rocking, any of which means the base is already moving and is unfit to build on. With tarmac, look for potholes, ravelling (loss of surface stone) and soft spots, which signal it is past its serviceable life. A base that fails any of these tests should be broken out, because its defects will work up through new paving.
The second question is levels, and this catches many people out. Because laying blocks over the old surface adds a bedding layer plus the block thickness, measure how much the finished surface will rise and check that rise against everything it meets: the house's damp-proof course (the surface must stay well below it, clear of air bricks), door and garage thresholds, the level of the street and any gulleys, and neighbouring surfaces. If the rise would breach the DPC or leave awkward steps and trip points, reusing the base is the wrong call. The third question is drainage: since concrete and tarmac will not let water soak through, you must confirm the existing falls run to a drainage point and that water will not be trapped on the old surface beneath the blocks. Only when the base passes on condition, the levels work against the house and surroundings, and drainage can be resolved does laying over become a reasonable, money-saving option. If any of the three fails, excavating and building a proper sub-base is the route that avoids damp, standing water and early failure — and is the only way to achieve a genuinely permeable driveway.
Frequently asked questions
Can I just lay block paving on top of my old concrete drive?
Only if the concrete is sound, stable, uncracked and you can solve the level and drainage problems. Adding blocks raises the surface, which can breach the damp-proof course, and water cannot soak through concrete, so falls and a drainage point are essential.
Will cracks in the old base show through new paving?
They can. If the old concrete or tarmac is cracked, sinking or moving, those defects tend to telegraph up through the new paving over time. A base with structural faults should be broken out, not paved over.
Is it cheaper to lay over the old base than dig it out?
It can be, because you avoid excavation and spoil removal. But it is only a real saving if the base is genuinely fit to keep and the levels and drainage work. If not, the failures that follow cost more than digging out would have.
Sources & further reading
- Pavingexpert — laying over existing bases
- Planning Portal — paving your front garden
- HomeOwners Alliance — driveways advice
Figures on this page are typical UK ranges drawn from published sources and depend on your specific site. They are guidance, not a quotation.