What is a dormer loft conversion?
A dormer loft conversion adds a box-shaped structure to the rear roof slope, creating vertical walls and full headroom across most of the new room. It is the most common loft conversion in the UK because it works on terraced, semi-detached and detached houses.
How much does a dormer loft conversion cost in St Helens?
In St Helens, a dormer loft conversion typically costs £45,000–£64,000 for a typical rear dormer with en-suite, including VAT at 20% (standard rate). Building costs in the North West run about 6% below the UK average, and the figures for St Helens are adjusted to reflect that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear dormer with en-suite | £45,000–£64,000 |
| Higher specification | £64,000–£80,000 |
The main things that change the cost:
- Staircase position
- Fire safety upgrades to the existing house
- En-suite or bathroom
- Dormer size and roof structure
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a dormer loft conversion in St Helens?
Approvals for a dormer loft conversion in St Helens follow the rules for England. In England a rear dormer is often permitted development if the extra roof volume is no more than 40 cubic metres on a terraced house or 50 on other houses, it does not face the road, sits no higher than the ridge and is set back from the eaves, with matching materials and obscure-glazed side windows. Balconies, front dormers and work in conservation areas need planning permission.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
What we take care of:
- Party wall notices for shared walls
- Insulation, plastering, electrics and plumbing
- New staircase and fire-safe escape route
- Steel beams and new floor joists
- Dormer structure, roof covering and windows
- Building control completion certificate
How long does it take?
Build time is typically 6 to 9 weeks on site. Before that, surveys, drawings and approvals usually take 6 to 12 weeks, longer if the council asks for changes.
Building in St Helens
The North West has many brick terraces and inter-war semis, where kitchen extensions and dormer loft conversions add space without moving.
Our St Helens coverage includes postcode districts WA10, and we also work in nearby places such as Prescot, Ashton in Makerfield and Huyton.
How it works
- 01
Free visit
We look at the property, talk through what you want and measure up. There is no charge and no obligation.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about dormer loft conversions in St Helens
What fire safety is required?
Building regulations require a safe escape route. Converting a two-storey house to three storeys usually means a protected stairway with fire doors to habitable rooms and mains-wired smoke alarms.
How long does it take?
Usually 6 to 9 weeks on site.
Who approves a dormer loft conversion in St Helens?
Planning matters in St Helens go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
Will I need to move out?
No. Most of the work is done from scaffolding and the roof. The new staircase is formed near the end, which causes a few days of disruption.
How much does a dormer loft conversion cost in St Helens?
In St Helens, a dormer loft conversion typically costs £45,000–£64,000 for a typical rear dormer with en-suite, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.