Loft conversion builders in London and Essex
We design and build loft conversions across North London, Brentwood, Chingford and the wider Essex area. Velux, dormer, L-shaped, hip-to-gable and mansard, drawn, engineered, approved and built by one team.
Most people come to us with a room in mind rather than a conversion type. A fourth bedroom. A home office that is not the corner of the dining room. A bathroom that stops the morning queue. Which conversion delivers that depends on your roof, and that is the first thing we look at.
Which loft conversion suits your roof
| Conversion | Your roof | What you gain | Typical cost | Planning |
|---|---|---|---|---|
| Velux | 2.4m or more head height | One room, roofline unchanged | £40,000 to £50,000 | Usually not needed |
| Rear dormer | 2.2m or more, most terraces and semis | A double bedroom with standing width | £50,000 to £65,000 | Usually not needed |
| L-shaped dormer | Victorian or Edwardian terrace with an outrigger | Bedroom plus a separate bathroom | £65,000 to £85,000 | Usually not needed |
| Hip-to-gable | Hipped side roof, semi or detached | Recovered volume on the side slope | £60,000 to £75,000 | Often needed |
| Mansard | Period terrace, steep roof, low head height | A full extra storey | £70,000 to £95,000 and above | Almost always needed |
Costs are London and Essex ranges for 2026 and exclude VAT and professional fees. Full breakdowns sit on the loft conversion cost page.
Velux and rooflight conversions
The simplest conversion available. Rooflights are fitted into the existing roof slope, the floor is strengthened, insulation and a staircase go in, and the roofline does not change at all.
Because nothing structural alters, it is the cheapest route and the quickest, at four to six weeks on site. It almost always falls under Permitted Development.
The condition is head height. You need roughly 2.4 metres from ceiling joist to ridge for a Velux conversion to give you a room you can stand up in properly. If you have that, this is the sensible starting point.
Dormer loft conversions
A dormer builds a box out from the roof slope with a flat or pitched roof of its own, turning the pitched triangle into a room with usable width. It is the most common conversion in London, because it works on the terraces and semis the city is built from.
A rear dormer typically produces a double bedroom. An L-shaped dormer, which wraps around the rear outrigger on Victorian and Edwardian terraces, usually produces a bedroom plus a separate bathroom.
Read the full guide to dormer loft conversions, including types, costs and planning rules.
Hip-to-gable conversions
Where a roof slopes inward on the side, a hipped roof, a large amount of internal volume is lost to the slope. A hip-to-gable squares that side off, building the wall up vertically to create a gable end and recovering the space.
It suits semi-detached and detached houses, and it is often combined with a rear dormer to open up the whole floor. It usually needs planning permission where the gable faces a highway or sits in a conservation area.
Mansard loft conversions
The largest conversion a house will take. The roof is rebuilt so the rear wall rises almost vertically and a near-flat roof sits on top, producing a full extra storey with consistent ceiling height rather than a converted attic.
It suits period terraces with steep roofs and poor head height, and it is the right answer when you are adding a floor rather than a room. It costs more, takes longer, and almost always needs planning permission.
Read the full guide to mansard loft conversions, including costs and the planning position.
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Velux/Roof Light Conversion
A simple and cost-effective option that uses strategically placed skylights to bring light and ventilation into the loft space. This typically doesn't require major structural changes but may have limitations on headroom and floor space.
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Luxury Dormer Loft Conversion
A popular choice that involves adding a box-shaped extension with windows (dormers) that protrude from the existing roof slope. This creates more headroom and usable floor space compared to a Velux conversion.
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L-Shaped Dormer Loft Conversion
A variation of the dormer loft, incorporating dormers on two sides of the roof for additional light and maximizing available space.
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Hip to Gable Loft Conversion
This option involves completely transforming a hipped roof (sloping on all sides) into a gable roof (with a vertical wall at each end). This creates a more spacious and versatile loft area but can be more expensive due to the significant structural changes required.
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Mansard Loft Conversion
A complex and architecturally striking conversion that adds a raised section with a steeper roof pitch on the existing roof. This maximizes space but comes with a hefty price tag and may require planning permission approval.
How the work runs
We look at the roof first. Head height, roof structure, pitch and the position of the staircase below. That determines which conversions are actually available to you, and we would rather tell you a Velux will do than sell you a dormer.
Design and structure together. Architectural drawings and structural calculations are produced in-house, so the design that goes to Building Control is the design that gets built.
Approvals. We handle Building Regulations on every project, and the planning application where one is needed. Party wall notices too, on terraced and semi-detached properties.
Build. One team, one project manager, a fixed price agreed before work starts, and a payment schedule tied to stages of work rather than dates.
What it costs
A loft conversion in London and Essex runs between £40,000 and £95,000 in 2026, depending on type, size and specification. A Velux sits at the bottom, a mansard at the top.
That figure is the build. Architectural drawings, structural calculations, Building Regulations, a party wall surveyor where needed, VAT and any en-suite sit on top, and together they are usually 20 to 30 percent again. We set all of it out before you commit to anything.
The full breakdown by conversion type, including what is inside a quote and what is not, is on the loft conversion cost page.
Do you need planning permission?
Most rear Velux and rear dormer conversions fall under Permitted Development within the volume limits: 40 cubic metres on a terraced house, 50 on a semi or detached.
Mansards, most hip-to-gables, front dormers, anything in a conservation area, and any conversion on a flat will need full planning permission.
Every loft conversion needs Building Regulations approval whichever route applies, covering fire safety, the staircase, floor loading, insulation and ventilation. More detail sits in our guide to building regulations for loft conversions.
Areas we cover
We work across North London, North West London, East London and South London, and throughout Essex including Brentwood, Chingford, Romford and Gidea Park.
If you are not sure whether you are in our area, ask. We will tell you honestly rather than quote for a job we cannot service properly.
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Why choose us
✔️ A dedicated Account Manager to help you through the process
✔️ Keep your project on time & budget
✔️ Qualified and experienced team
☎️ Speak to an expert
Still not sure? Book a free 30-minute phone consultation and see how your project can come to life with Mammoth Design and Build.
E: hello@mammoth-builds.co.uk
M: 07878 719 909
