Dormer Loft Conversion Roof Cost Kent

Last updated: August 2026

If you're planning a loft conversion, the dormer is often the most cost-effective way to create proper headroom and usable space. But the roofing element — the dormer itself, the tile or slate covering, the leadwork at the cheeks, and the flat roof on top — is a significant part of the overall cost. Here's what to actually budget for the roofing side, based on our experience building dormers across Kent and South East London.

Dormer Roofing Costs

These are the roofing costs specifically — not the full loft conversion (which includes structural steel, stairs, electrics, plastering, and Building Regs sign-off). The roofing element typically makes up 25-35% of the total conversion cost.

Dormer Roofing Costs (2026, inc. VAT)

Small rear dormer (single room)£4,000–£7,000

Full-width rear dormer£6,000–£12,000

L-shaped dormer£8,000–£15,000

Side dormer£3,500–£6,000

Slate-clad cheeks (per dormer)£1,500–£3,000 extra

Velux windows in remaining roof£800–£1,500 each fitted

Completed slate-clad dormer with Velux windows by IKON Roofing

What Affects the Price

What Drives the Price

Size & typeFull-width rear dormer costs significantly more than a small box dormer for one bedroom

Cheek finishTile-hung, slate-clad, lead-clad, or rendered — slate-clad is the most expensive but looks the sharpest

Flat roof systemThe dormer top needs a flat roof — torch-on felt is standard, GRP or single ply costs more

Tile matchingDiscontinued tiles mean sourcing reclaimed or switching to a close match — adds cost and complexity

AccessFull scaffolding always required. Terraced houses and narrow side returns increase scaffold costs

LeadworkCheek flashings, back gutters, apron flashings — skilled work that takes time

Planning Permission

Most rear dormers fall under permitted development in Kent and don't need planning permission, provided they don't extend above the highest point of the existing roof and the materials match the existing house. Side dormers usually do need planning permission. If your property is in a conservation area (parts of Rochester, Sevenoaks, Bromley, Greenwich), you'll almost certainly need full planning approval.

Why Hire a Roofer Directly — Not Just the Loft Company

Most loft conversion companies subcontract the roofing work. That means your dormer is built by whoever was cheapest that week, with no direct accountability to you. The roofing element — the waterproofing, the leadwork, the tile matching — is the most critical part of the whole conversion. If the dormer leaks, everything underneath it is ruined.

When you use IKON directly for the roofing, you get Jordan on your roof doing the work, not an unknown subcontractor. And you get our 15-year workmanship guarantee and 10-year IBG on the roofing element — something no loft conversion company can offer on their subcontracted roofing work.

Aerial view of completed dormer and re-roof by IKON Roofing

Planning a dormer? Read our full guide to roof costs in Kent or book a roof survey to assess your existing roof before work starts.

Written by Jordan — Owner, IKON Roofing Ltd

18 years' hands-on roofing experience across Kent and South East London. Every article is based on real jobs, real materials, and real pricing — not guesswork.

How Much Does a Dormer Roof Cost in Kent?