Converting your loft is often one of the easiest and cheapest ways to boost the square footage of your home. Depending on the structural requirements and the floor area and access, costs typically range from around £20,000 up to about £70,000. But, if you’re thinking of expanding upwards, it is good to know what you should be paying.
Costs by size of conversion
- Consider how much light and head room you need. Raising the height of your roof, adding skylights and windows, and other structural changes will considerably increase the cost of your conversion. So, if you’ve already got enough standing room in your attic for a habitable space, you could save by constraining your new room to its current dimensions. Think carefully about what you’ll use the space for – adding a bathroom with a shower, for example, may require a higher ceiling height than you have available. While adding windows may be an extra expense, it could also be the difference between a bright, welcoming space and a dark, stuffy room you don’t often use. Often, choosing the wrong layout and not including dormers and rooflights can be top of the list of regrets.
| Type of conversion | Average cost |
| Velux | £18,000 – £20,000 |
| Dormer | £42,000- £60,000 |
| Hip to gable | £45,000 – £55,000 |
| Mansard | £52,000 – £70,000 |
| Type of windows fitted | Size (M) | Average Cost |
| 2 Roof Light | 5*4 | £38,000 – £42,000 |
| 4 Roof Light | 5*4 | £42,000 – £49,000 |
| 1 dormer, 1 roof light | 5*6 | £41,000 – £45,000 |
| 2 Roof Light | 5*6 | £43,000 – £45,000 |
| 4 Roof Light | 5*6 | £45,000 – £49,000 |
| 1 dormer, 1 roof light | 5*6 | £39,000 – £41,000 |
| 2 dormer, 2 roof light | 8*12 | £43,000 – £45,000 |
| 2 Roof Light | 8*12 | £40,000 – £42,000 |
| 4 Roof Light | 8*12 | £44,000 – £49,000 |
| 1 dormer, 1 roof light | 8*12 | £57,000 – £59,000 |
| 2 dormer, 2 roof light | 8*12 | £62,000 – £64,000 |
- Limiting the size of your conversion to 50 cubic metres (40 cubic metres for terraced houses) and ensuring that it doesn’t extend higher than the current highest point of the roof will negate the need for planning permission. If you do require planning permission, make sure your plans are finalised and sent off for planning approval early to avoid delaying work. It’s important to ensure your plans are finalised before submitting them, as you’ll have to reapply if anything changes. Applying for detailed or full planning permission for a new house or a conversion in England is currently £462.
- Project manage your loft conversion yourself, this can be an economic way of cutting your build costs, with the added benefit of managing all of the tradesmen and timings on the project yourself. The cost of project management including building control costs is around £8,800, however, you’ll need to be clear on exactly what needs to be done and when, ensure everyone is kept in the loop who needs to be, and manage timings, logistics and budgets for deliveries, contractors and the day-to-day running of the site. You’ll also need to be available when key decisions need to be made, to avoid costly delays. Managing a project of this size is no small task, so make sure you feel confident before committing to the job. There are a lot of jobs involved in a loft conversion. The table below gives the cost breakdown for £44,550conversion. This is to put in about 20m2of loft space and includes a dormer and a roof light over the new staircase. This would cover the electrics and plumbing for a master bedroom with an ensuite.
| JOB | COST FOR 20M2 LOFT |
| Project Management – including building control costs | £8,800 |
| Scaffolding | £3,000 |
| Plumbing and electrics | £6,500 |
| Alterations to Roof Structure | £4.400 |
| Steelwork to support structural changes | £3,200 |
| Roof Coverings | £6,400 |
| Guttering and lead work | £2,850 |
| Joinery – excluding staircase | £3,800 |
| Staircase | £2,000 |
| Plastering | £2,400 |
| Decoration | £1,200 |
| Total | £44,550 |
- Consider the position of plumbing If you’re thinking of adding a bathroom to your loft, its position could greatly impact the cost. If at all possible, position it directly above the pipework on the floor below. This will require a lot less work than re-routing plumbing across the building, so will therefore be cheaper.