House extensions in Hythe, Folkestone and Kent

Many single storey extensions can be built without a planning application, under what are called permitted development rights. Those rights come with limits on size, height, position and materials, and the limits change from time to time, so check the current rules on the Planning Portal, or with the council, before relying on them.

Permitted development does not apply to flats or maisonettes, an earlier planning condition can remove it from a particular house, and it is tighter in conservation areas, where side extensions and some finishes need permission. Hythe's historic centre and several parts of Folkestone are conservation areas, and a listed building needs listed building consent for almost any extension.

The council for all of this is Folkestone and Hythe District Council. For anything close to the line, a lawful development certificate is worth having: it confirms in writing that the extension does not need planning permission.

Almost every extension needs Building Regulations approval, even when it needs no planning permission at all. Building control checks the foundations, the structure, insulation, drainage, fire safety and ventilation, and inspects the work at set stages as it goes up. Without a completion certificate you will have questions to answer when you come to sell.

If you are building on or near the boundary with a neighbour, or digging foundations close to theirs, the Party Wall etc. Act 1996 probably applies, and notice has to be served on them before work starts. On a terrace or a semi that is more often the case than not.

A flat roof keeps an extension low, suits a wide single storey room and leaves room under first floor windows, which on a lot of terraces is the only way an extension fits. Done in EPDM rubber or fibreglass on a properly laid fall, with the edges and the wall junction detailed for coastal weather, a modern flat roof is a long lived roof, not the weak point its reputation suggests.

A pitched roof sheds water faster and can be tiled to match the house, but it needs height, and a lean to against the back wall has to clear the windows above it. Every tile has a minimum pitch it is made for, and a lean to built shallower than its tiles allow is one of the commonest reasons an extension roof leaks.

This joint is where extensions leak most. On a flat roof the covering turns up the wall as an upstand, and a lead flashing is cut into the brickwork above it to cover the top. On a lean to, the lead is stepped into the wall down each side, or set in as an apron along the top. Sealant along the joint instead of a proper flashing lasts a year or two and then lets go.

If the house wall is cavity brick, a cavity tray is usually needed above the new roof, so that water running down inside the cavity is turned outwards rather than into the extension. It is one of those details that cannot be seen once the job is finished and is expensive to put right if it was left out.

The price is agreed in writing before work starts. If anything changes once the ground is dug or a wall is opened up, you hear about it before the work goes ahead, not on the invoice.

We are also straight about the parts that need other professionals. Where planning is needed, the drawings come from an architect or designer, and steels and foundations need a structural engineer's calculations. Building control will ask for both, and it is far better to have them before the build than to stop halfway for them.