Block Paving in Harrow | Driveways & Permeable

Block paving in Harrow runs to a fairly consistent pattern because the housing does. Most frontages are inter-war semi-detached, which means a similar size, an original crossover that is often too narrow for a modern car, and a shallow fall from the house to the footway. The site visit measures all three. Two things then shape the programme. The first is the crossover: a car crossing the footway needs a vehicle crossover from the London Borough of Harrow, which is the council's approval on its timetable, so it is raised early rather than assumed. Northwood and Ruislip are in the London Borough of Hillingdon, which takes its own dropped kerb applications. The second is parking, because controlled parking zones cover parts of the borough and where a grab lorry or a delivery of blocks stands has to be agreed with the property in advance. Harrow is covered on the same round as Pinner, Northwood, Stanmore and Ruislip.

Block paving suits London Clay better than most surfaces do, and it is worth being clear about why rather than simply recommending it.

BMS Building lays block paving driveways across Harrow, Pinner, Northwood, Stanmore and Ruislip.

Units move, continuous surfaces crack

Clay shrinks through a dry summer and swells through a wet winter. A surface made of individual blocks can absorb a small amount of that by opening a joint fractionally. A continuous surface has nowhere to put it and shows it as a crack.

What block paving cannot survive is a sub-base too thin for the clay beneath it, because then the movement stops being small.

So the dig depth comes from what the ground shows on your frontage, and the base goes in and is compacted in layers. That is the whole of the difference between two quotes that look identical on paper.

Permeable, on ground that does not absorb

Permeable blocks take water through the joints. Clay cannot take much of it away.

So permeable block paving here only works if the stone layer below has the depth to store water and an outfall to release it. Permeable blocks over a shallow build up on clay just hold water where it is.

That gets designed from the dig rather than assumed from the product.

The crossover

A car crossing the footway needs a vehicle crossover, applied for from the London Borough of Harrow. The council's approval, its price, its timetable, and only its own contractors may build it. In Northwood and Ruislip the application goes to the London Borough of Hillingdon.

Raised at the site visit and started early. We will not build on the assumption it will be granted.

The shallow fall

Inter-war frontages usually leave little height between the damp proof course and the kerb. That makes the finished level a design decision rather than a copy of the old one, and it is measured before the blocks are chosen.

Edges

The edge course is what stops the field creeping outwards. Not properly haunched, the joints open and the blocks rock. It is the part most often skimped.

Parking

Controlled parking zones cover parts of the borough, so where a grab lorry or a delivery stands, and when, is agreed with the property before the first morning.

At two neighbouring houses in Ruislip, BMS Building laid 136 square metres of Marshalls Standard Block Paving in Charcoal across both driveways and the shared access between them, with a matching Savanna kerb. Key kerbs form the front door steps and hold back a planting area that was kept. It replaced tired red block paving and took about two weeks.

Block paving is actually well suited to London Clay, and it is worth saying why rather than just selling it. Clay shrinks and swells seasonally, and a surface made of individual units can take a small amount of that movement by opening a joint fractionally, where a continuous surface shows it as a crack. What block paving cannot survive is a sub-base that is too thin for the clay beneath it, because then the movement is not small. So the dig depth comes from what the ground shows on the frontage and the base is compacted in layers. The second local factor is drainage: clay holds water, so permeable block paving only works here if the build up below it has the depth to store water and an outfall to release it. The third is the shallow fall common on inter-war frontages, which leaves little height between the damp proof course and the kerb and makes the finished level a design decision rather than a copy of the old one.