Full-Width Rear Dormers in Carmarthenshire
We design, build and weatherproof full-width rear dormers for homeowners across Carmarthenshire, working from first survey through to building control sign-off.
Full-Width Rear Dormers — indicative geometry
Full-Width Rear Dormers for Carmarthenshire homes
The housing stock around Carmarthenshire runs to Victorian and Edwardian terraces, interwar semi-detached houses and post-war bungalows — so the first question at survey is always which of those you have, because the structure underneath differs completely.
A full-width rear dormer runs from party wall to party wall, squaring off the entire rear slope. On a standard terrace or semi it typically converts 12–18m² of crawl space into full-height room — enough for a double bedroom and an en-suite. Set back 200mm from the eaves and 500mm below the ridge, it usually falls inside permitted development on a house that has not been extended before.
Key specification
| Typical projection | 4.0m – 8.0m wide |
|---|---|
| Set-back | 200mm from eaves, 500mm below ridge |
| Structure | Steel ridge beam plus floor steels |
| Roof finish | GRP, EPDM or single-ply membrane |
Planning and building control in Carmarthenshire
Whether you need planning permission or a lawful development certificate depends on the elevation, the volume already used and the local authority's Article 4 position — all of which we confirm before design work starts.
Building regulations approval is separate and always required. We submit the application, book the inspections around the programme and hand you the completion certificate at the end — the document a buyer's surveyor will ask to see.
Why homeowners in Carmarthenshire use us
One quotation covers scaffold, structure, weatherproofing, glazing, plastering and sign-off. You are not coordinating four trades who each blame the last one.
Send us the address and roughly what you are hoping to gain, and we will come back with a realistic answer rather than an optimistic one.
Other dormer work in Carmarthenshire
- Dormer Cladding in Carmarthenshire
- Dormer Window Repairs in Carmarthenshire
- Gable-Fronted Dormers in Carmarthenshire
- L-Shaped Dormers in Carmarthenshire
- Cat Slide Dormers in Carmarthenshire
- Velux to Dormer Conversions in Carmarthenshire
- uPVC Dormer Windows in Carmarthenshire
- Sash Dormer Windows in Carmarthenshire
FAQs
Full-Width Rear Dormers in Carmarthenshire — FAQs
Do I need planning permission for a dormer window?
Rear dormers on a house often fall under permitted development, provided the dormer is set at least 200mm back from the eaves, sits below the ridge line, uses materials similar in appearance to the existing house, and stays within the volume allowance — 40m³ for a terrace, 50m³ for a semi or detached. Front-facing dormers, flats and maisonettes, listed buildings, conservation areas and any property with an Article 4 direction all need a full planning application. We check the constraints on your specific address before we quote.
Will my roof be open to the weather?
No. The roof is only opened once the scaffold, temporary weather protection and materials are all on site, and the dormer is made weathertight — structure, deck, membrane and temporary glazing — before the crew leaves at the end of the opening-up phase. We do not open a roof on a Friday afternoon.
What is the best roof covering for a flat dormer?
GRP fibreglass and EPDM rubber are the two we specify most. GRP cures into a single seamless laminate with bonded trims and suits small tops with several upstands. EPDM is a one-piece membrane that copes better with movement on larger spans. Both carry twenty-year guarantees; mineral felt is cheaper but has a materially shorter life.
What insulation do dormers need?
Current building regulations want around 0.15–0.18 W/m²K for a new dormer roof and 0.18 W/m²K for the cheeks and front. In practice that is a warm-roof build-up using 100–150mm of PIR insulation above or between the structure, with a continuous vapour control layer on the warm side. Getting the VCL continuous matters more than the insulation thickness.
Can you match my existing roof tiles?
Usually. Most common clay and concrete profiles are still in production or available reclaimed, and we source a match at survey stage so you see it before work starts. Where a discontinued profile cannot be matched exactly, we normally recommend taking tiles from a less visible slope for the dormer and using the closest new match on the hidden elevation.
Find out what your roof will take
A free measured survey in Carmarthenshire tells you what is achievable, what it needs, and what it costs — before you commit to anything.