Skylights and rooflights in Desborough

Desborough sits in North Northamptonshire: planning questions are answered by North Northamptonshire Council, never by a Leicestershire body. For the usual case, a house with its own front door, Class C allows glass rising 150mm at most above the slope's surface. It must never climb past the roof's highest point. And in a side-facing slope it is either obscure and fixed, or opens only above 1.7m from the floor.

A conservation area for the town, designated on 30 March 2007, is on the national planning register, centred on the middle of Desborough. Inside it the register logs a single Grade II listing. So the larger part of the housing probably sits outside any special control, though we never assume. A designation does not itself cancel Class C, though an Article 4 direction could; whether one applies to a given address is for the council to settle.

Building Control is a separate matter. The cut itself is building work. If notification is needed, we lodge it with the council or an independent approver and hand over the certificate at the end. A buyer's solicitor will want to see it when the house is sold.

One practical point on the planning side: two rooflights count as two openings, each within the same limits. If a single large unit would crowd the ridge, a pair of smaller ones can sometimes do the same job within permitted development, and we can price both options so you can compare them before you decide.

Timing is the other thing people ask about. A rooflight that needs no application can go ahead once the survey and quote are agreed. One that needs consent waits for the council's decision, and we would rather you heard that at the start than halfway through a booked fortnight. We keep the dates honest and the order of work simple: paperwork first, then the roof.

Desborough, a town and civil parish, lies in the Ise Valley between Market Harborough and Kettering. In the nineteenth century it was an industrial centre for weaving and shoe-making, and it kept a long association with the Co-operative movement. Silk weaving developed in a factory on Paddock Lane, and shoe-making gained ground beside it. The Co-op began with local shops and a corset and lingerie factory, and grew until it ran a department store, a bank, a supermarket, a travel agent and a ladies' shoe and clothing shop among a number of corner stores. The Victorian factory is still there, with warehousing and a factory shop across the road from it.

A town that employed itself in this way built homes for the people who worked in its factories, and a place like that tends to carry rows of similar houses with similar roofs. We cannot name which streets belong to which decade from the records, and an invented answer is worse than a plain gap. What we do know is the way we handle a run of similar houses: we survey each one on its own. Two neighbours with the same front can have different loft timbers, a different extension behind and a different set of limits on what will fit.

Take a factory warehouse and a terraced house side by side and the lesson is the same: the roof tells you what it will take. A broad brick slope with sound timber underneath will accept a generous opening. A tired one with patched felt and sagging battens needs the opening kept small until the structure behind it has been seen. Both can end with daylight in the room below, and the difference lies in the order of work. Look first, draw second, quote third, and only then cut.

The sums of daylight are worth a minute. A roof window set in the slope receives light from a wide patch of sky, so it brightens a room more than a window set in a wall would. That matters in a terrace, where the side walls are shared and the only outside walls are the front and the back. A loft room lit from the roof can have its two long walls left free for beds, shelves and wardrobes.

Big roofs, simple answers

Factory buildings and their warehouses have large, plain roof planes, and so do many of the houses that grew around them. Large planes are forgiving: there is room to place a rooflight where the room below needs it, not where the rafters happen to leave a gap. A VELUX window is a common choice in a loft like that. A code like MK04 reads width first (M) then height (04), a handy way to match a new unit to an old opening or pick one for a fresh gap.

An old roof window that has misted between its panes has failed at its seal, and the answer is a new sealed unit in the same opening. The replacing misted rooflights page explains what that involves. Part L sets the target for new glass: 2.2 W/m²K applies to a rooflight, while a roof window may be judged on band B of the WER scale or on 1.4 W/m²K. Both sit well ahead of anything that went in a generation ago.

When a two-storey house gains a loft room, Approved Document B draws the line: where a window is the escape, 4.5m above ground is the ceiling. A roof window up there is for light and air. The way out in a fire is a protected stair, and we make sure the plans you are given are honest about that.

Allow 35 minutes for the 20.5 road miles heading south-east out of Leicester. The B576 and B669 both run near the town centre, and the A6 Rothwell to Desborough bypass, opened on 14 August 2003, carries the through traffic round it. Desborough had a railway station from 1857 until 1968, run by the Midland Railway and its successors, and OSM records no station inside 2 km. Visits are by van, then, and we build a morning around two or three surveys in a town before moving on.

The River Ise runs through the valley the town lies in, and the map names two nature reserves close by: Tailby Meadow, 1.3 km out, and Rothwell Gullet, 1.6 km. Woodland Valley appears as a neighbourhood 1.8 km out. Houses near open land get a different kind of light from those packed into old terraces. Fewer neighbours overlooking the roof means fewer worries about privacy, and more freedom on where to put the glass.

Bypasses change how a town sits in its landscape. With the A6 taking through traffic round Desborough, through traffic no longer has to cross the centre, and a quieter street suits a loft bedroom whose roof window may be open on a summer night. If a window faces the road, mention it when we visit and we will propose glazing that keeps the evenings calm without shutting out the sky.

Houses where the roof joins a neighbour's need extra attention at the party wall. A rooflight cut close to the line of the wall has to leave the wall itself alone, and the flashing has to be dressed so rain cannot find the join. That is a detail you cannot see from the ground, which is one reason we want to be on the roof and not just look at it from the road.

On a sunny slope, solar-control glass stops a bedroom turning into a hot box in July, and a blind does the rest. We talk through which side of the house the slope faces before we suggest a specification, because a north-facing roof window wants something quite different from a south-facing one.

Landings and bathrooms under a loft, not a slope, suit a sun tunnel. Its dome caps the roof, a mirrored tube crosses the loft, and a ceiling diffuser scatters the light below. It needs a clear run between roof and ceiling, which we confirm in the loft before ordering anything.