Loft Conversions in South London

Before drawings, before planning, go up the loft ladder with a tape measure. Measure from the top of a ceiling joist to the underside of the ridge, in the middle of the loft. That one figure decides more about the conversion than anything else on this page.

The number you measure is not the number you get. The new floor is deeper than the ceiling joists there now, and the insulation in the roof takes more off the top. A loft that feels roomy empty can lose a good deal of height by the time it is a room.

The staircase is the second measurement. As the rules stand, Building Regulations ask for 2 m of clear headroom over a stair, relaxed in a loft conversion to 1.9 m at the centre of the stair and 1.8 m at the side. Where the new flight can rise under the slope often fixes the layout of the floor below it.

If the height is not there, it can be found by raising the roof, which takes the job out of permitted development and into a planning application, or by lowering the ceilings of the rooms below. Both are big decisions, and worth knowing about before any drawings are done.

The shape of the roof you have decides the shape of the conversion more than taste does. Most South London lofts end up as one of these.

A loft conversion is a run of separate jobs that have to arrive in the right order. These are the parts of a dormer conversion, from the roof down.

Many loft conversions on houses in England need no planning application, because they fall under householder permitted development. As the rules stand, a roof enlargement may add up to 40 cubic metres of roof space to a terraced house and 50 to a semi-detached or detached house. Anything added to the roof before, by you or an earlier owner, counts towards it.

The other conditions are about where it sits and what it looks like. Nothing may project beyond the plane of the roof slope on the principal elevation where it faces a highway, which in most streets rules out a front dormer. No higher than the highest part of the existing roof. Dormers set back at least 20 cm from the eaves, measured up the slope, where practicable. Materials similar in appearance to the house. A side-facing window obscure-glazed, and fixed shut below 1.7 m above the floor. No balconies, verandas or raised platforms.

Then the exceptions. Permitted development does not apply to flats or maisonettes. A listed building needs listed building consent. A conservation area removes permitted development for roof enlargements, and an Article 4 direction can remove more. Large parts of Southwark, Lambeth, Lewisham and Wandsworth are conservation areas, so check that first, not last.

The council or the Planning Portal has the final word for your house. Where a conversion does fall within permitted development, the council can issue a lawful development certificate that says so — worth having when you sell.

Planning decides whether you may build it. Building Regulations decide whether it is built safely, and a loft conversion needs Building Regulations approval whether or not it needs planning. Building control inspects the work at stages and issues a completion certificate at the end. Keep it: a buyer's solicitor will ask for it.

Structure comes first. The ceiling joists in a loft were sized to hold up a ceiling, not a room, so a new floor goes in, often with steel beams carrying it. A structural engineer's calculations set the sizes of all of it, and building control will want to see them.

Fire is the one people underestimate. A loft room adds a storey, and the rules want a protected escape route down the stairs to a final exit, fire doors onto it and mains-wired, interconnected smoke alarms. That can mean new doors on the floors below, not only at the top.

Then the staircase headroom above, and insulation to Part L. In a loft room the insulation sits in the roof itself, not on the floor, which is part of why the room loses height from the top.

The room inside a loft conversion is forgiving. The weather side is not. A dormer is a small flat roof with two walls and a window, cut into a slope where the rain is already running, and every joint between new work and old is somewhere for water to go.

The details that decide it are roofing details. The flat top needs a real fall, and its covering taken up and under the main roof at the back rather than stopped against it with mastic. The lead on the cheeks has to be cut in pieces small enough to move with the sun without splitting. The slates or tiles either side have to be cut and tied back in so every course still laps the one below. A roof window needs the flashing kit made for its covering, and the membrane dressed round it.

That is our own trade, and on a dormer that leaks it is nearly always one of those details that has failed, not the room.

Where the dormer goes, the old covering comes off, and what is left around it is cut in to meet the new work. If the front slope is shedding slates or the underlay has perished, the scaffold is already up — ask for re-covering to be priced as its own line.

On a terrace or a semi, the steels for the new floor often bear on the party wall, and cutting them in is work under the Party Wall etc. Act 1996. As the Act stands, that needs two months' notice to the neighbour. They can consent in writing, or a surveyor settles an award setting out how the work is done. Ask who serves the notice, and get it served early.

Bats and their roosts are protected. If there is any sign of them — droppings in the loft, bats leaving the roof at dusk — an ecologist's survey may be needed before the roof is opened.

Then put these questions to anyone quoting for a loft conversion, us included, and get the answers in writing.