Why a well detailed dormer matters in Arundel
A dormer can unlock valuable headroom, light and views across Arundel, yet its success rests on careful planning, robust structure and weatherproof detailing. With our local climate bringing coastal winds and driving rain, the right specification protects your home and preserves the town’s distinctive character.
Planning and permissions
Check local constraints early
Much of Arundel sits within a Conservation Area and many homes are listed. Even where permitted development may apply, it is wise to confirm with Arun District Council before work begins. Key points include dormer size, position, materials and how the addition affects the street scene and roofline.
Form and proportion
Keep the dormer scale in balance with the roof. Set it back from the eaves and below the ridge to reduce visual mass. Align the window with openings below where possible. Use finishes that reflect local character such as slate hung or tile hung cheeks with lead flashings.
Structure and load paths
Openings and trimming
Cutting a roof requires a designed trimming arrangement that redistributes loads to sound supports. Typically this involves double trimmers and trimmer rafters bolted to joist hangers or coachescrews, sized by a structural engineer. Avoid notching or drilling in ways that weaken members.
Dormer roof build-up
Choose a simple roof form that sheds water well. A modest mono-pitch or a small hipped dormer often suits Arundel homes. Ensure the dormer front and cheeks have studs at appropriate centres, proper sheathing and fixings that meet wind uplift requirements in BS 5534.
Weathering and waterproofing
Tie-ins to the main roof
Water finds weakness at junctions, so detailing is critical. Use step flashing where the dormer cheek meets slates or tiles, with soakers to each course on pitched roofs. At the dormer front, form an apron flashing and chase it into the masonry or cladding. At abutments maintain a clear 150 mm upstand on flat surfaces.
Coverings that last
For pitched dormer roofs, continue the main covering in matching slate or tile. For low-pitch or near-flat dormers, consider a warm roof with high quality single ply, GRP or built-up felt. Leadwork remains a benchmark for longevity when correctly designed with drips, laps and allowance for thermal movement. Select the right lead code and follow the Lead Sheet Association guidance.
Membranes and fixings
Use a BS 5534 compliant underlay, counterbattens where needed and nails or clips suited to local wind exposure. In Arundel’s exposed spots, enhanced fixings reduce the risk of storm damage.
Thermal, moisture and air control
Insulation and Part L
Aim for a continuous insulation line around the dormer to limit cold bridges. A warm roof build-up places rigid insulation above the deck and works well on small dormers. If building a cold roof, maintain a ventilated void and avoid blocking airflow at the eaves and ridge. Check U-values against current Part L requirements.
Condensation control to BS 5250
Fit a well sealed vapour control layer on the warm side of insulation. Keep service penetrations neat and airtight. Provide eaves or high-level ventilation where the design demands it and choose a breathable membrane compatible with the build-up.
Cladding, windows and finishes
Tile hung or slate hung cheeks blend neatly with many Arundel roofs and offer proven performance. Lead or zinc cladding suits more contemporary schemes. Select robust window units with proper flashings, head drips and cills that project to shed water clear of the face. Integrate matching gutters, outlets and bird guards and keep access in mind for future maintenance.
Fire safety and boundaries
Close to a boundary, check Part B for fire resistance and external surface classification. Choose non-combustible or limited combustibility finishes where required and ensure cavity barriers are continuous at junctions.
Build sequencing and weather
Time the opening of the roof to a settled forecast and have materials ready. Temporary coverings, tidy sequencing and prompt installation of flashings reduce water risk and protect interiors.
Work with local specialists
A trusted local team will coordinate design, permissions and installation so details align from day one. If you are planning a dormer in or around the town, speak with Roofing Arundel for guidance, compliant specifications and careful workmanship tailored to Arundel’s homes and weather.
Aftercare
Schedule a quick annual check to clear debris, confirm fixings are sound and inspect flashings and seals. Small adjustments keep your dormer dry, efficient and looking the part for years to come.