Cat Slide Dormers in Gwynedd
We design, build and weatherproof cat slide dormers for homeowners across Gwynedd, working from first survey through to building control sign-off.
Cat Slide Dormers — indicative geometry
Cat Slide Dormers for Gwynedd homes
Most of the dormer work we take on around Gwynedd is on Victorian and Edwardian terraces, interwar semi-detached houses and post-war bungalows, where the ridge height and the position of the existing purlins set the limits.
A cat slide (or 'sweeping') dormer lets the main roof plane run on below the dormer sill, so the dormer appears to emerge from the roof rather than to be planted on it. It is a rural and cottage idiom, and it works beautifully on long, low roofs where a box dormer would look brutal. Detailing at the sill and the sweeping valley is the whole job.
Key specification
| Typical width | 1.2m – 3.0m |
|---|---|
| Sweep | Main roof continues below sill line |
| Roof finish | Plain tile, slate or pantile |
| Critical detail | Swept valley and sill flashing |
Planning and building control in Gwynedd
Rear dormers on houses often sit inside permitted development, but the volume allowance is consumed by any previous loft or rear extension — so we check the planning history for the address before we say yes.
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 Gwynedd use us
We would rather tell you at survey that your ridge height will not take what you want than take a deposit and find out in week three.
If you want to know what your roof will actually take, the survey is free and there is no obligation attached to it.
Other dormer work in Gwynedd
FAQs
Cat Slide Dormers in Gwynedd — FAQs
How disruptive is a dormer build?
Less than people expect, because most of the work happens above your ceilings and is reached from the scaffold. The noisy phases are opening up and installing steels, typically two to four days. Once the staircase is cut in there is dust and traffic through the house, and we sheet and protect the route for that period.
Do dormer windows need to be fire escape windows?
In a loft conversion, at least one window in each habitable room generally needs to meet escape requirements — a clear opening of at least 0.33m², minimum 450mm in both height and width, with the bottom of the opening between 800mm and 1100mm above floor level. We specify the opening lights to meet this as standard.
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.
Find out what your roof will take
A free measured survey in Gwynedd tells you what is achievable, what it needs, and what it costs — before you commit to anything.