L-Shaped

L-Shaped Dormer

Two connected dormers forming an L-shape — ideal for Victorian terraces to create two loft rooms. Compare up to 3 free quotes — no obligation.

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L-Shaped Dormer

An L-shaped dormer is formed by two connected dormer extensions — one to the rear and one to the back addition roof — creating an L-shaped footprint in the loft. This is the most common conversion for Victorian and Edwardian terraced houses with a rear 'outrigger' or back addition, as it maximises the available loft space across both roof sections.

The result is typically two or three usable rooms in the loft — a master bedroom, en-suite and potentially a study or dressing room. Getting 3 quotes is particularly important for L-shaped dormers as complexity and pricing vary considerably between builders.

What’s involved

  • Structural survey of both roof sections and calculation of steelwork required
  • Building regulations application and staged inspections
  • Construction of both dormer structures and the connecting valley or junction
  • Waterproofing, roofing and window installation across both sections
  • Internal fitting out of two or three rooms including staircase, bathrooms and decoration

Typical costs

Typical cost: L-shaped dormer conversion £40,000–£60,000. L-shaped with two en-suites or high specification £55,000–£80,000.

Prices vary by region, subfloor condition and product choice. Compare 3 quotes for the most accurate price for your specific job.

FAQs — L-Shaped Dormer

Does an L-shaped dormer need planning permission?
Rear-facing L-shaped dormers on Victorian terraces frequently fall within Permitted Development, but the combined volume and height must stay within permitted development limits. Your specialist will confirm for your specific property.
How many rooms does an L-shaped dormer create?
Typically two to three usable rooms — most commonly a master bedroom, an en-suite bathroom and a small study, dressing room or second bedroom, depending on the size of the original loft.
What type of property suits an L-shaped dormer?
Victorian and Edwardian terraces with a rear back addition are the classic candidate. The back addition creates a second lower roof section that, when combined with the main rear roof, creates the L-shape.
How long does an L-shaped dormer take?
An L-shaped dormer typically takes 10–16 weeks from start to completion due to the complexity of two connected structures and the extent of internal fitting out.
Is an L-shaped dormer worth the extra cost over a standard dormer?
For Victorian terraces with a back addition, yes — the additional rooms and space created usually justify the extra cost, and the alternative (a single rear dormer only) leaves the back addition roof space unused.
What customers say
★★★★★ 4.9 / 5 from verified customers
★★★★★

“We had a rear dormer conversion done last summer — extra bedroom and en-suite for our teenage daughter. Got three quotes through this site, saved around £4,000 compared to the first firm we spoke to. The specialist handled planning permission and building regs start to finish. Highly recommend.”

Sarah M. Surrey
★★★★★

“Hip-to-gable conversion on our 1930s semi. I was nervous about the planning application but the specialist I found here had done dozens in our street and knew exactly what to submit. Project came in on time at 10 weeks. The new master bedroom is brilliant.”

James R. Leeds
★★★★★

“L-shaped dormer on our Victorian terrace — created two rooms and a bathroom from what was a completely unusable loft. The comparison process gave me confidence I was paying a fair price. Building control sign-off came through with no issues. Absolutely transformed the house.”

Helen T. Manchester
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