Loft conversions for terraced houses

The five types

Each drawing is a section through a typical two-storey Victorian terrace, front on the left. Grey dashed lines are the roof as it is now; blue is new work.

FIG. 2 · Rooflight conversion, section A-A

Rooflight conversion

The simplest loft: the roof keeps its shape and we set rooflights into the slopes. It works where the loft is already tall enough to stand in, which on our streets usually means the taller Edwardian roofs or houses where the ridge runs front to back. You get one room, often a study or a child's bedroom, with low eaves you can use for storage.

Suits	Taller roofs, tight budgets, conservation areas without an Article 4 direction
Typical floor area added	14 to 20 m²
Planning route	Usually permitted development
Price with us	£42,000 to £56,000 including VAT
On site	6 to 8 weeks

FIG. 3 · Rear dormer, section A-A

Rear dormer

We take off the back slope of the roof and build it out as a flat-roofed box, set back from the gutter line, with a window across the back. It turns a triangle of attic into a room you can stand up in across most of its width. This is the loft we build most often, and on a mid-terrace it usually fits inside the 40 cubic metre allowance with room to spare for a shower room.

Suits	Most Victorian and Edwardian terraces
Typical floor area added	22 to 28 m²
Planning route	Usually permitted development
Price with us	£64,000 to £80,000 including VAT
On site	9 to 11 weeks

FIG. 4 · L-shaped dormer, section A-A

L-shaped dormer

A rear dormer across the main roof, joined to a second dormer over the two-storey back addition, so the plan makes an L. The main dormer gives you the bedroom; the back-addition dormer is usually the shower room or bathroom, which puts it near the existing soil stack. Getting both under 40 cubic metres takes careful drawing, and we'll show you the calculation.

Suits	Terraces with a two-storey back addition (most of the Harringay Ladder, Crouch End and Walthamstow)
Typical floor area added	30 to 38 m²
Planning route	Usually permitted development
Price with us	£80,000 to £98,000 including VAT
On site	11 to 13 weeks

FIG. 5 · Hip-to-gable, roof plans

Hip-to-gable

On an end of terrace or semi-detached house with a hipped end, the roof slopes down on the side as well as front and back. We build that side up into a vertical brick gable, which extends the ridge and the usable floor, and usually add a rear dormer at the same time. The new gable is built in brick matched to the house. Worth knowing: an end of terrace still counts as a terrace house under the rules, so the allowance is 40 cubic metres, not 50.

Suits	End of terrace, semi-detached and detached houses with a hipped roof
Typical floor area added	28 to 36 m²
Planning route	Usually permitted development
Price with us	£84,000 to £104,000 including VAT (end of terrace)
On site	11 to 14 weeks

FIG. 6 · Mansard, section A-A

Mansard

The back of the roof is rebuilt as a near-vertical slope, about 70 degrees, with a flat roof on top and windows set into the slope. The party walls on each side are usually built up to match. It gives the most floor area and the most head height, and it is the one to consider when the loft is too low for anything else. It always needs planning permission, and your council will have views about how it looks.

Suits	Low roofs, houses with a butterfly or valley roof behind a parapet, streets with existing mansards
Typical floor area added	30 to 38 m²
Planning route	Planning permission
Price with us	£108,000 to £135,000 including VAT
On site	14 to 17 weeks

Estimate your loft

Is there enough height?

Go up into the loft with a tape. Measure from the top of a ceiling joist (the timbers you would stand on) to the underside of the ridge board at the highest point. As a rule of thumb we look for about 2.2 m. The new floor sits higher than the old joists, and insulation goes under the rafters, so you lose somewhere between 150 and 250 mm before we start.

2.2 m or more	Most loft types work, including a rooflight conversion
2.0 to 2.2 m	A rear dormer or L-shaped dormer usually works, because the dormer gives you full height across the back
Under 2.0 m	A mansard, or lowering the first-floor ceilings. Lowering ceilings is disruptive and we rarely recommend it

The stair takes height too

Building regulations ask for 2 m of clear headroom over a stair. For loft conversions there is a concession: 1.9 m at the centre of the stair, reducing to 1.8 m at the side. Most of our stairs rise over the existing flight, under the dormer, where the height is. When they can't, a turn at the top or a quarter landing usually solves it.

FIG. 07 · Measuring the height

Fire safety and the stair

Adding a loft to a two-storey house makes it a three-storey house, with the top floor more than 4.5 m above the ground. At that height a window is no longer a safe way out, so the rules change for the whole house, not only the loft.

A protected route to the front door

The stair from the loft down to the front door becomes a protected escape route. Every door onto it from a habitable room (bedrooms, living rooms, the kitchen if it opens onto the hall) becomes a fire door rated to hold back fire for at least 20 minutes, and the walls around the stair must give 30 minutes. If your ground floor is open-plan, we either put a partition and a fire door back in, or use the alternative the guidance allows: sprinklers in the open-plan area, a fire-resisting partition and door separating the ground floor from the floors above, and a cooking area separated off, with access from the loft to a first-floor escape window.

Alarms and floors

We fit mains-powered smoke alarms, linked so that one sets off all of them, in the stair at every level. The new loft floor is built to resist fire for 30 minutes, and the floor below is checked and upgraded where it needs it.

Old doors

If your panelled doors are original and you want to keep them, the guidance allows us to look at upgrading them instead of replacing them. It isn't always possible, and it costs more than a new door, but it's often worth asking.

The stair itself

Each step can rise up to 220 mm, the tread must be at least 220 mm deep, and the stair can be no steeper than 42 degrees. Space-saving paddle stairs are allowed only when the loft has one habitable room, with or without a bathroom, and they need the full 2 m of headroom. We make most of our stairs in the workshop, in softwood with an oak handrail, and fit them over two days near the end of the job.

FIG. 08 · A straight stair to the loft, thirteen risers

From Approved Document B (fire safety), Volume 1, paragraphs 2.5 and 2.21 to 2.23, and Approved Document K (stairs), paragraphs 1.13 and 1.29, Table 1.1. Your building control body has the final say on your own house.

Bathrooms in the loft

Most of our dormer lofts have a shower room. The easiest place for it is over the back addition or right beside the existing soil stack, because waste pipes need a fall and the stack is where they have to end up. A shower needs about 1.8 m by 1.2 m of full-height floor for the tray and the door swing; a basin and WC can sit further under the slope. We fit an extractor ducted outside, an electric underfloor heating mat or a towel radiator, and tile to full height in the shower. Pumped waste units are the last resort. They work, they hum, and we'll only fit one when there's no other way.

Shower room add £9,500 to £14,000 · Bathroom with bath add £13,500 to £19,000

What's in every Quinlan loft

Design, drawings and structural engineer's calculations
The lawful development certificate or planning application, including the council fee
Building regulations application and every inspection, including the council fee
Party wall notices drafted and served for you
Scaffold with a full temporary roof, alarmed, with the council's scaffold licence where it stands on the pavement
Steels, new floor joists, and 100 mm of acoustic mineral wool in the new floor
Insulation to current standards: 0.15 for the roof, 0.18 for the dormer walls (U-values, W/m²K)
Double-glazed windows and rooflights to current standards
A new stair made in our workshop, with an oak handrail
Fire doors on the protected stair, and linked mains smoke alarms on every level
Electrics with a certificate, radiators on your heating system where the boiler can take them
Plasterboard and skim, skirting and architrave to suit the house, decorated in white
All waste taken away by us, and the house cleaned before we hand back
A six-month defects visit

Not included. Party wall surveyors' fees, if a neighbour wants a surveyor. Flooring. Paint colours other than white. Blinds and furniture.

Loft conversions for terraced houses

The five types

Rooflight conversion

Rear dormer

L-shaped dormer

Hip-to-gable

Mansard

Is there enough height?

The stair takes height too

Do I need planning permission?

The permitted development rules for lofts

Conservation areas and Article 4 directions

Why we still apply for a lawful development certificate

When you do need planning permission

Which route is your loft likely to take?