What is a rooflight loft conversion?
A rooflight loft conversion (sometimes called a roof window conversion) keeps the existing roof shape and adds roof windows that sit flush with the slope. The floor is strengthened, a staircase is added and the space is insulated and finished.
How much does a rooflight loft conversion cost in South Glamorgan?
In South Glamorgan, a rooflight loft conversion typically costs £27,500–£41,500 for a typical rooflight conversion, including VAT at 20% (standard rate). Building costs in Wales run about 8% below the UK average, and the figures for South Glamorgan are adjusted to reflect that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rooflight conversion | £27,500–£41,500 |
| Higher specification | £41,500–£52,000 |
The main things that change the cost:
- Number of roof windows
- Floor and roof strengthening
- Bathroom or not
- Storage and finishes
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 rooflight loft conversion in South Glamorgan?
Approvals for a rooflight loft conversion in South Glamorgan follow the rules for Wales. In Wales roof windows that sit close to the roof slope are generally permitted development outside protected areas.
Building regulations in Wales are set by the Welsh Government. Approval comes from the council’s building control service or a registered building control approver, with inspections during the work and a completion certificate at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
On a typical rooflight loft conversion we handle:
- Head-height survey
- Building control sign-off
- Floor joists and any steel beams
- Staircase and fire-safe escape route
- Roof windows installed
- Electrics, heating and plastering
How long does it take?
Expect 4 to 6 weeks on site. Before that, surveys, drawings and approvals usually take 6 to 12 weeks, longer if the council asks for changes.
Building in South Glamorgan
Wales has many terraced valley streets, stone cottages and post-war estates, so extension designs are shaped by slopes, materials and local character.
Towns we cover in South Glamorgan include Cardiff, Barry and Penarth.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about rooflight loft conversions in South Glamorgan
How much does a rooflight loft conversion cost in South Glamorgan?
In South Glamorgan, a rooflight loft conversion typically costs £27,500–£41,500 for a typical rooflight conversion, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.
Do you build rooflight loft conversions in South Glamorgan?
Yes. We build rooflight loft conversions across South Glamorgan, including postcodes CF3, CF32, CF35, CF5 and CF61. Every project starts with a free home visit.
Do I need planning permission for a rooflight loft conversion in South Glamorgan?
In Wales roof windows that sit close to the roof slope are generally permitted development outside protected areas.
How long does it take?
Usually 4 to 6 weeks on site.
How much head height do I need?
Around 2.2 metres or more from the top of the ceiling joists to the ridge is a good starting point. Insulation and new floor joists reduce the height.
Is it cheaper than a dormer?
Yes, usually, because the roof shape stays the same. But you gain less full-height floor space.