Homeowners Guide To Bungalow Extensions
Bungalow Extensions: Planning, Building Regs, Loft/Dormers, Structure, Accessibility & Costs — The Complete Guide
Bungalows are some of the most flexible homes to extend. With everything on one level and generous roof space, you can add a rear/side extension, wrap around the corners, vault ceilings, or convert the roof with dormers for extra bedrooms. Done well, a bungalow extension makes living simpler today and future-proofs for tomorrow. Done poorly, it can overheat, steal daylight from the centre of the plan, or trip over approvals. This guide is your step-by-step map from first sketch to completion.
First principles: what makes a great bungalow extension?
Plan depth & daylight: Bungalows often have deep central corridors; extensions can make the middle of the home dark. Prioritise rooflights, lightwells and borrowed-light internal glazing to keep the core bright.
Flow & zoning: Single-storey living shines when circulation is simple. Aim for an open kitchen-diner living space with quiet rooms grouped away from activity.
Roof logic: Bungalows carry character in their roofs. Decide early whether you’ll continue the existing pitch, hip-to-gable, or add dormers.
Future-proofing: Even if you don’t need it now, design for step-free thresholds, wide doors, and a level shower.
Buildability: Think access to the rear garden, temporary weathering during knock-throughs, and protection of finishes in the existing house.
Planning Permission vs Permitted Development (PD)
Many bungalow projects can proceed under householder permitted development if the design stays within national limits/conditions. That said, roof alterations and dormers have their own PD rules, and some areas restrict PD via Article 4 or conservation designations.
Single-storey rear/side extensions (typical bungalow cases)
Rear extensions: Often PD up to set depth and height limits. Materials should be similar to the existing house.
Side extensions: Single-storey side additions can be PD when within height limits and no forward encroachment. Wrap-arounds that alter the front elevation may require planning.
Height & eaves near boundaries: Keep an eye on eaves height and overall height when building close to a boundary.
Roof extensions, dormers & hip-to-gable
Dormer additions to the rear roof slope can be PD if within cubic volume limits, set back from the eaves, below the ridge height, and not fronting the highway.
Hip-to-gable conversions can be PD on many houses provided the total roof enlargement volume stays within PD limits and other conditions are met.
Raising the ridge (increasing overall roof height) is not PD — that needs planning permission.
Front dormers visible from the street typically require planning.
Designated land / Article 4: In conservation areas, AONBs, National Parks or streets with Article 4, PD may be removed or limited. Always check before you assume.
When you’ll likely need planning permission
Two-storey elements on a former bungalow (e.g., forming a chalet house with a raised ridge).
Front dormers or prominent changes to the principal elevation.
Large wrap-around mass that changes street character.
Sites with restrictive previous conditions (e.g., original consent requiring low roof profiles).
Practical strategy: If you’re comfortably inside PD, gather a neat plan/elevation set and consider a Lawful Development Certificate for certainty. If your brief nudges beyond PD (e.g., a bigger dormer, front roof change, or ridge lift), a householder application with a policy-aware design note is appropriate.
Neighbour amenity & streetscape — design to pass before you submit
Daylight/outlook tests: For side neighbours, run 45-degree (in plan) and any local vertical tests to avoid harmful loss of daylight to their windows.
Overlooking/privacy: Position new windows to protect privacy; use obscure glazing to bathrooms and consider high-sill or oriel windows where overlooking could occur.
Mass & rhythm on the street: Bungalows often sit in rhythmic groups; match eaves height, roof pitch, brick bond and window proportions so the extension reads as part of the original composition.
Building Regulations — what will be checked
Whether PD or planning, Building Regulations always apply to habitable extensions and roof conversions. Expect control over:
Part A (Structure): foundations sized to ground; beams/lintels for knock-throughs; roof strengthening for dormers; lateral restraint; padstones and bearings.
Part B (Fire): escape from new bedrooms in the roof (egress roof windows or protected stair depending on plan), cavity barriers, fire stopping, alarms, boundary fire separation for flank walls and eaves.
Part C (Moisture): DPC/DPM continuity; cavity trays; detailing at abutments; roof ventilation or warm-roof strategy to avoid condensation.
Part E (Sound): party elements (if semi/terraced), and acoustics between rooms/floors (helpful even where not strictly tested).
Part F (Ventilation): background/purge ventilation; extract to wet rooms; whole-dwelling rates as envelopes tighten.
Part H (Drainage): connections, rodding access; no internalised manholes; rainwater sizing.
Part K (Stairs & guarding): if adding a stair to a new loft storey — correct geometry, headroom, guarding and handrails.
Part L (Energy): U-values for walls/roof/floor, glazing performance, thermal bridge control, and SAP/area-weighted compliance.
Part M (Access): reasonable provision — door widths, thresholds, accessible WC where feasible.
Part P (Electrics): notifiable works, certification at completion.
Structure & knock-throughs — beams, vaulted ceilings and roof strengthening
Bungalows regularly use fink-truss roofs that rely on the internal web for stiffness. Removing webs for a vaulted ceiling or loft space means re-engineering the roof:
Vaulted ceilings: replace lost triangulation with a ridge beam or rafter ties designed to take thrust; check rafter size, span, and deflection limits.
Dormers: trim around dormer openings with trimmer rafters and doublers; carry loads with beams to bearings on new or existing walls.
Hip-to-gable: extend the ridge and replace the hipped end with a gable; tie new gable into the cavity with appropriate wall ties and lateral restraints.
Knock-throughs to create open-plan spaces: size RSJs/UBs, ensure adequate bearings on padstones, and plan temporary works (needles and props) so the existing roof/walls remain stable.
Lateral stability: when internal walls come out, reinstate shear panels, straps and ties to keep the building wind-stable.
Foundations for bungalows — trench, deepened, piles or raft?
Bungalows can have shallow original foundations. New loads from extensions, gables, or dormer supports may require something more substantial:
Standard trench-fill/strip: straightforward on competent ground away from trees; concrete below frost and down to suitable bearing.
Deepened trench near trees or shrinkable clay: expect more depth, concrete and spoil; consider piled foundations with ground beams or a reinforced raft if trenches become excessive or unstable.
Raft slab: a shallow, engineer-designed solution that spreads loads and simplifies thermal detailing — useful for variable ground or where deeper trenches are undesirable.
Build-over/near sewers: check for rear garden sewers; plan for protective details and consents; keep manholes outside the footprint.
Set finished floor levels early so thresholds remain step-free and external paving falls away from the building to manage water.
Roof options — extend, vault or lift?
Continue the existing pitch over a rear extension to keep form simple and sympathetic.
Cat-slide/lean-to roofs can reduce mass near boundaries and work well for kitchen-diner extensions.
Flat roofs (done as warm roofs) offer slim build-ups, neat parapets, and easy rooflight placement for centre-of-plan daylight.
Vaulted ceilings add volume without touching the ridge height — great over living spaces.
Dormers unlock usable floor area in the roof; keep proportions tight, set back from eaves, and match materials for a calm elevation.
Ridge lifts to create a full chalet level require planning permission and careful streetscape handling.
Walls, floors & junctions — warm, airtight, condensation-safe
External walls: modern cavity wall with full-fill insulation or partial-fill + insulated lining; or timber frame/SIPs for speed.
Thermal bridges: treat steel penetrations, thresholds, and floor-wall junctions with thermal breaks/insulation continuity; use insulated cavity closers.
Air-tightness: membranes and tapes at ceilings, around windows/doors, and along steelwork; seal service penetrations.
Floors: insulate over existing slabs (DPM + insulation + screed/board) or use suspended timber with a robust moisture strategy where slabs are poor.
Moisture management: cavity trays at abutments and over openings; weeps; breathable build-ups where moisture risk exists.
Accessibility & future-proofing — make single-storey living shine
Bungalows are ideal for age-in-place design. Even modest tweaks have outsized benefits:
Step-free access: plan flush thresholds to garden and main entrance; coordinate door sills with external levels and drainage.
Wider doors & routes: aim for minimum 838 mm leafs (or pocket doors) to key rooms; maintain turning circles in kitchens/bathrooms.
Accessible bathroom: design a level-access shower, sensible grab-bar reinforcement in walls, and thermostatic controls.
Lighting & switches: generous, even lighting; switch/socket heights usable for all ages.
Acoustics: mineral wool in partitions near bedrooms; soft closures; decouple noisy utility areas.
If adding a loft storey: choose a stair with compliant rise/going, continuous handrails, and consider a future platform lift position.
Energy & comfort — build the low-running-cost home you feel
Extending is the moment to upgrade the whole-house fabric:
Insulation: exceed minimum U-values where cost-effective; detail for thermal continuity.
Airtightness + ventilation: a clear air-barrier line and either trickle/purge with good practice, or MEV/MVHR if you’re tightening significantly.
Glazing: use solar-control for large south/west panes; combine with external shading or deep reveals; plan cross-ventilation.
Heating: UFH in new slabs is efficient and comfortable; check boiler/heat pump capacity after adding rooms.
Hot water: extra bathrooms need capacity; right-size cylinder or combi outputs.
Renewables: extensions are a neat moment to add solar PV (and pre-wire for battery), EV charger infrastructure, and heat-pump readiness (emitters, cylinder space).
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Loft & dormer design — bedrooms that feel like real rooms
Headroom: aim for 2.2 m+ over a decent floor area; shape dormers to achieve comfortable standing zones at the window.
Stairs: position centrally if possible to minimise landings and roof structure conflicts; maintain headroom at the top landing.
Escape: provide egress roof windows to new bedrooms or create a protected stair route to a final exit depending on layout.
Structure: dormers need trimmed openings, beams, and careful load paths to walls or new posts with proper bearings.
Thermal & moisture: insulate at rafter level with a defined ventilation path or design a warm roof; control interstitial condensation with a continuous VCL.
Services & drainage — plan routes, avoid surprises
Rainwater: rear/side downpipes often sit where the extension goes; reroute and size gutters and soakaways; avoid internal rainwater runs.
Foul drainage: keep runs short and graded; provide rodding points; relocate manholes outside the footprint.
Electrics: new circuits are notifiable; plan sockets, data points, and layered lighting.
Ventilation: extract rates for new bathrooms/utility rooms; keep duct runs short/straight; avoid terminating in roof voids.
Kitchens: duct cooker hoods to outside; design make-up air in tight envelopes.
Meters/boilers: gas/electric meters on side walls may need moving; boilers/flues must retain clearances.
Party Wall etc. Act 1996 — when it bites for bungalows
You’ll likely need to serve notice if you:
Excavate within 3 m of a neighbour’s building and deeper than their foundations (or within 6 m for certain deeper cases).
Build a new wall at the boundary (line of junction).
Cut into or raise a party wall (e.g., for steelwork, flashings, or hip-to-gable works).
Include clear sections and foundation details with notices. If neighbours dissent, surveyors will agree an Award; build the programme to allow for it.
Costs, timelines & procurement
Indicative programme
Survey, concept & planning/LDC: 3–8 weeks (add ~8 weeks for planning decision if required).
Technical design & Building Control: 2–6 weeks.
Build on site:
Single-storey rear/side extension: 8–16+ weeks.
Loft/dormer conversion: 6–12+ weeks (concurrently or sequentially with the extension).
Ridge lift/chalet conversion: 12–20+ weeks depending on structure and finishes.
Key cost drivers
Foundation type (deep trench vs piles/raft), extent of steelwork, roof form (vault/dormers), glazing quantity/spec, services relocations, brick/roof tile matching, and internal fit-out spec (kitchens, bathrooms).
Procurement
Traditional tender with drawings/specs to comparable builders, or a design-and-build route with clear employer’s requirements.
Fix scope with schedules (windows/doors, finishes, sanitaryware) to control variations.
Party Wall etc. Act 1996 — Don’t Leave It Late
Two storeys usually mean deeper foundations and work near shared walls:
Excavation notices: within 3 m (and deeper than neighbour’s foundation), or within 6 m where your deeper foundations fall within specific angles to theirs.
Line of junction/new wall on boundary: notifiable.
Works to a party wall: cutting in steel, raising, or inserting flashings.
Serve the right notices on time, attach drawings and sections, and be ready with foundation details. If neighbours dissent, surveyors agree an Award; build your programme with that in mind.
Common pitfalls (and how to dodge them)
Dark centre: deep plan without rooflights; solution: rooflights, sun pipes, internal glazing to share light.
Overheating: huge west-facing glazing without shading; add solar-control glass, external shading, and cross-vent routes.
Undersized structure: removing walls without proper beams/padstones/temporary works; get calcs and a sequencing plan.
Dormer boxiness: oversized dormers dominating the roof; keep set-backs, align with windows below, and respect the ridge/eaves lines.
Moisture at junctions: missing DPC/cavity trays at abutments, leading to damp patches; detail trays/weep holes.
Internalised manholes: discovered late under the new kitchen island; survey drains and relocate externally early.
Boundary fire rules ignored: flank windows too close to boundary; check unprotected openings limits during design.
Accessibility as an afterthought: threshold steps, narrow doors; set levels and spec door widths at concept stage.
Party Wall left late: notices served when the digger arrives; start the process during technical design.
Step-by-step workflow we recommend
Feasibility & constraints — PD vs planning, Article 4, conservation, trees, sewers, neighbour tests; note eaves heights and street rhythm.
Measured survey — plans/sections/elevations; roof form, truss type, slab level, drains, meters.
Concept options — rear/side massing, vault vs flat, dormer shapes; test daylight (45/25-degree), privacy, and roof logic.
Planning/LDC — choose the right route; prepare tidy elevations and a short, policy-aware note.
Structure — beams, ridge beams, dormer trimming, hip-to-gable ties; foundation strategy (trench, piles/raft).
Technical design — U-values, membranes/VCL, junction details; roof ventilation or warm roof; drainage/services layouts; boundary fire compliance.
Party Wall & build-over — serve notices/apply early with clear sections.
Tender & contract — drawings/specs/schedules; programme with milestones and inspection points.
Build & inspections — photograph membranes, insulation, steel bearings; maintain a revision log.
Completion — snag, Building Control completion, and an O&M pack (as-builts, certs, warranties).
FAQs
Can I extend to the rear and add a dormer under PD at the same time?
Often yes, provided each element individually and collectively complies with PD limits and conditions, and your property still has PD rights. Keep careful track of cubic volume for roof enlargements.
Do I need planning to raise the ridge?
Yes. Increasing overall roof height requires planning permission and streetscape justification.
Is a front dormer PD?
Typically no — a front dormer usually needs planning. Rear dormers are more commonly PD if within limits and set back from the eaves.
Will Building Regulations force me to upgrade the whole bungalow?
You must make the new work compliant and avoid making the existing worse. Some improvements to the existing fabric/services may be triggered for overall performance.
Can I keep the space single-storey but vault the ceiling?
Yes. Provide a ridge beam/engineered ties and design ventilation/insulation properly. Vaults can transform perceived space without adding a storey.
Can I achieve step-free garden access with big sliders?
Yes — coordinate finished floor level, threshold systems and external falls early; include drainage to protect the sill.
Next Steps
Share your address, brief (rooms you want, roof ideas, vault vs dormers) and any past plans. We’ll confirm PD vs planning, run neighbour tests, set structure/foundation strategy, and produce planning + Building Regs drawings with the right roof and junction details — so your bungalow feels brighter, flows better, and performs like a modern home.
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Building 13, Thames Enterprise Centre, Princess Margaret Road, East Tilbury, Essex, RM18 8RH
- Phone: 0800 494 7023
- Hours: Mon-Fri 8:30AM - 5:30PM
Get In Touch
Building 13, Thames Enterprise Centre, Princess Margaret Road, East Tilbury, Essex, RM18 8RH
- Phone: 0800 494 7023
- Hours: Mon-Fri 8:30AM - 5:30PM