DOT Extension vs Loft Conversion: Which Is Right for You?
Both add real space, but they solve different problems. Here’s how we help customers choose, with real prices from our own jobs. All prices are plus VAT.
If it’s…
Bedrooms & bathrooms
Consider a loft conversion. If you’re short on bedrooms, or want a bedroom with its own en-suite, a loft conversion uses space you already have above your head — without touching the garden.
- Doesn’t reduce garden size
- Usually 8–12 weeks on site, and you can stay living at home
- Often needs no planning permission
- Can be cheaper than an extension
If it’s…
Kitchen, living or dining space
Consider an extension. If your ground floor feels cramped — small kitchen, no separate dining area, nowhere to entertain — an extension builds outward into space a loft conversion simply can’t reach.
- Opens up ground-floor living
- Usually 8–12 weeks on site, often under permitted development
- Can be combined with a loft later
- Uses garden space (worth checking how much you can spare)
How do an extension and a loft conversion compare?
| Extension | Loft Conversion | |
|---|---|---|
| Typical cost (+ VAT) | £30,000 – £65,000 single-storey rear, under permitted development | £32,000 – £65,000 dormer or hip-to-gable. Velux windows alone from about £6,000 |
| Time on site | 8–12 weeks | 8–12 weeks, up to 14 for a complex full planning job |
| Planning | Often permitted development (3m out, or 4m on a detached house) | Often permitted development, if it’s a rear dormer or hip-to-gable |
| Garden | Uses some of it | None used |
| Living at home | Yes | Yes, usually with a scaffold canopy |
| Best for | Kitchen, dining, living space, or a downstairs bedroom | An extra bedroom or office upstairs |
See our Extension Cost Guide and Loft Conversion Cost Guide for the full breakdown by type.
Is a loft conversion cheaper than an extension?
It can be. Depending on what you want, a loft conversion can come in cheaper than an extension. Here’s what four of our recent jobs cost, all plus VAT:
Little Haywood hip-to-gable: about £32,000
Permitted development, all new tiles, about 10–12 weeks. Case study
Leicester new roof and dormer: about £38,000
A terraced house where the family stayed at home, so it needed a full scaffold canopy. Case study
Nottingham kitchen extension: about £35,000
3m by about 6m, tiled pitched roof with two Veluxes. The customer did their own plasterboard and plastering.
Sinfin, Derby kitchen and office: about £42,000
Tiled lean-to with two rooflights, permitted development, around 11–12 weeks. Case study
How do you decide between an extension and a loft?
When we visit, we look at three things first: how much garden you’ve got, how much space is in the loft, and which works out more cost-effective for what you need. These are the details behind that.
Is there enough head height in the loft?
As a rule of thumb, you want about 2.2m or more from the top of the ceiling joists to the underside of the ridge. Less than that and a loft gets expensive (or impossible) without raising the roof, so an extension often wins.
Where would the stairs go?
A loft needs a proper staircase with enough headroom: normally 2.0m, although loft stairs are allowed 1.9m in the middle and 1.8m at the side. On a small landing that can be the deciding factor.
How much garden can you spare?
Under Permitted Development, a single-storey rear extension can go out 3m on a semi or terrace (4m on a detached house), or up to 6m (8m detached) with prior approval. On a small plot, losing that space may matter more than the room you gain.
Are you in a conservation area?
Roof extensions such as dormers don’t get Permitted Development rights in conservation areas, National Parks or National Landscapes. A rear extension may still be possible, so the planning picture can push you one way or the other.
What are you actually short of?
A bedroom or office upstairs points to a loft. Kitchen, dining and family space point to an extension. If you’re happy with a downstairs bedroom, an extension can do that too, like our Bedford bungalow job.
Can you do both?
Plenty of families do one now and the other later. If that’s the plan, it’s worth thinking about the order.
Plan the stairs early
If a loft is likely later, we can position steels and leave room on the landing during an extension, so the loft is easier and cheaper when you get to it.
One scaffold, one disruption
Doing both at once means one set of scaffolding, one Building Control process and one period of mess, which usually saves money overall. Our Little Haywood customer is doing it the other way round: a loft conversion first, then a permitted development extension on the back in the new year.
Watch the Permitted Development allowances
Extensions and lofts each have their own limits, and earlier additions count towards them. We check what your house has already used before you commit to either.
Common questions
The things people ask most when deciding between the two.
Which is cheaper, an extension or a loft conversion?
They’re often close, and a loft can come in cheaper. With us, a single-storey rear extension under permitted development is usually £30,000 to £65,000, and a dormer or hip-to-gable loft £32,000 to £65,000, all plus VAT. Our Little Haywood loft cost about £32,000, and our Nottingham extension about £35,000.
Which adds more value?
It depends on what buyers in your area want. An extra bedroom often adds the most, which can favour a loft. A big kitchen-diner can matter just as much in family areas. See our value guide.
Can I stay at home during the build?
Yes, for both. On a loft conversion you’ll usually need a canopy on the scaffolding to keep the weather out, which adds to the cost, and heating bills may go up a little while the roof is open.
Do I need planning permission?
Many rear extensions and rear dormer lofts fall under Permitted Development, but not in conservation areas or on designated land, and not if your house has already used its allowance. See our extension planning guide and loft planning checklist.
Still not sure which fits your house?
We’ll assess your property at a free site visit and give you an honest recommendation either way.
Call 01889 725765 Ask Us