Dormer loft conversion drawings in Harrow

Hipped roofs and gable ends in Harrow

Wherever a house has a hipped roof, the no-wrapping rule decides how far a dormer can spread. A hip-to-gable change is a different operation from a dormer and is judged separately, which we cover in our wider dormer loft conversion drawings guide.

Where a house has a hipped end, the usual route is a rear dormer inside the clearances, with a rooflight on the hip if more light is needed.

Conservation areas, listed buildings and green belt in Harrow

Harrow has 31 conservation areas, and Historic England lists 295 entries. Class B roof enlargements are not permitted development on article 2(3) land.

About 22 per cent of the borough is green belt. A house inside it is still judged as a householder project, but the surroundings matter more to the council, and we note them on the drawings. The borough's Harrow Local Plan 2021-2041 was adopted in 2,026, so we check the adopted wording rather than relying on older guidance.

How Harrow decides householder applications

Harrow decided 917 householder applications in its latest year and granted 81.7 per cent, with 93.7 per cent decided in time. This includes every kind of home project, so it tells you about the council's habits and not about your roof.

Permitted development or planning for a Harrow dormer

An unlisted house outside a conservation area can use permitted development, within a volume limit of 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume. The dormer must not extend beyond the principal slope facing a highway: No enlargement beyond the plane of a roof slope that forms the principal elevation and fronts a highway.

If the drawing fits, a Lawful Development Certificate records it. Even then, the council's clearances are a sound guide to what looks right, so we usually follow them.

Surveying a Harrow semi before drawing the dormer

Harrow's clearances are fixed distances, so accuracy matters. We measure the roof from inside and out, locating the party boundary, the gable end and the eaves line precisely, then lay the clearances onto the survey.

What remains is the true width and height available for the dormer. On a hipped semi this can be a good deal narrower than the roof looks from the garden, and it is better to learn that from a drawing than from a council officer's report.

We also record the chimney, any existing rooflights and the line of the stair below, since each of them affects where the dormer can sit.

Stairs, insulation and structure for a Harrow dormer

The stair rule for lofts is: Loft conversions where 2.0 m cannot be achieved: 1.9 m at the centre of the stair, 1.8 m at the side (half width). We test the stair position early, because it often dictates the dormer's position.

The thermal rule for the new roof elements is: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. The dormer's insulation thickness adds to its overall height, which we allow for within the council's clearances.

Structure follows: new beams across the roof, with bearings checked against the walls below. Our building regulations drawings set this out in detail for the engineer.

Drawings, price and related Harrow pages

A Harrow dormer set has existing and proposed plans, a section and four elevations. Price: £695. If the council asks for changes, we redraw at no charge until approval.

Compare roof forms in loft conversion drawings in Harrow, add a back room with house extension drawings in Harrow, or see architectural drawings in Harrow. Nearby, the rules differ in Brent and Hillingdon.