Basement Conversion Drawings in Feltham TW13
Fixed-fee, MCIAT-chartered basement conversion drawings for Feltham (TW13) homeowners — London Borough of Hounslow validation and local constraints handled from the start.
Feltham is an outer-west Hounslow suburb built largely between the wars and in the post-war decades, so the bulk of our work here is family-driven: single-storey rear extensions, side-return infills and loft conversions on 1930s semis and estate housing. Wide plots on roads such as Southern Avenue and Ashmead Road usually leave comfortable room to extend under permitted development while keeping the front elevation intact.
Where a plot sits near the St Dunstan's or Hanworth Park conservation areas, or on the lower ground close to the River Crane, we design to Hounslow Council's expectations from the outset — matching brick and roof lines, respecting the depth and height limits, and building in flood-resilient drainage detail so the application clears validation without an avoidable refusal.
Planning in Feltham (TW13): what to know before you apply
There is no published householder Article 4 direction in Feltham, so most rear and loft projects proceed under permitted development. Watch the St Dunstan's, Hanworth Park and Feltham Town Centre conservation areas, and the flood constraint on plots near the River Crane, where PD rights and extension depths are more tightly read.
Typical Feltham housing stock
Feltham is dominated by 1930s bay-fronted semis and post-war council-built estates, with generous rear gardens on roads like Southern Avenue and Glebelands Road. Plots are wide enough for single-storey rear extensions, side infills and hip-to-gable loft conversions without needing to touch the front elevation.
Streets we regularly draw for in Feltham
Southern Avenue · Glebelands Road · Ashmead Road · Browells Lane
What TW13 is actually built of
Measured from 396 classified residential buildings in TW13, not from a description of the area.
Feltham TW13 housing mix
Residential building form across the TW13 postcode district, from 396 classified buildings.
| Attached on more than one side | 41% |
|---|---|
| Attached on one side | 54% |
| Detached | 5% |
| Median building footprint | 54 m² |
| Addresses per buildingAbove about 2 means flats and maisonettes dominate | 1.56 |
| Buildings classified | 396 |
Source: Ordnance Survey National Geographic Database (derived statistics). Contains OS data © Crown copyright and database right 2026. Contains Royal Mail data © Royal Mail copyright and database right 2026. Extracted 2026-08-17.
Basement Conversion Drawings for Feltham (TW13) homes: the package and the process
A basement package is led by its section. It has to show the existing structure, the proposed floor level, retained or underpinned walls, the tanking system, and how the finished room achieves head height without undermining what sits above. Structural design and architectural design are drawn together because here they are the same decision.
Habitable basement rooms also need light, ventilation and escape. The drawings set out lightwells and their guarding, mechanical ventilation where natural is not achievable, and an escape route that Building Control will accept — usually a protected stair, sometimes an external route out of the lightwell.
What sits below the house decides the route. An existing cellar under a Victorian terrace is a conversion with a known volume, while a house with no cellar is a dig-out with underpinning, structural design and a very different drawing set — and the two are rarely interchangeable.
Do I need planning permission for a basement conversion in London?
An internal conversion of an existing cellar — new floor, insulation, a habitable layout — often does not need planning permission, because the works sit entirely within the existing structure and do not change its external appearance. Digging out a new basement, lowering an existing floor to gain headroom, or enlarging the footprint under a garden usually does, particularly where excavation extends beyond the existing building line. Any external alteration needed to serve the basement — a front light well, a sunken external staircase, or altering the pavement or front garden — is also likely to need planning permission in its own right, even when the basement works themselves would not. In a conservation area, a front light well tends to draw closer scrutiny than the same feature elsewhere, since it changes the street-facing elevation and the pavement it sits within — one more reason we assess the whole scheme, not just the room below ground, before recommending a route.
Cellar conversion or new dig-out — which route fits your property?
The two starting points lead to very different drawing sets. A cellar conversion works with a void that already exists: the drawings focus on damp-proofing, insulation, headroom, natural or borrowed light, means of escape and a compliant layout, coordinated with building regulations rather than planning.
A new dig-out or floor-lowering project starts from a structural decision — how the existing foundations will be underpinned to allow excavation beneath them — and the drawings and structural calculations are produced together from the outset, since the sequence of underpinning, temporary works and waterproofing has to be engineered before a builder can safely start.
What structural design does underpinning a basement need?
Lowering a floor or digging a new basement beneath an existing house means underpinning its foundations in sequenced sections, so the building above stays supported throughout. We produce the structural drawings and calculations for the underpinning sequence, any new steel beams or retaining walls, and the interaction with neighbouring foundations, in-house as part of the same package — so your structural engineer sign-off and your architectural drawings are never out of step with each other.
The sequencing matters as much as the sizing: underpinning is dug and cast in short, alternating sections so the existing wall is never left unsupported over any significant length, and the drawings set out the order those sections are worked in alongside the retaining and waterproofing detail. Getting that sequence wrong is one of the most common causes of cracking and delay on a basement project, which is why we treat it as a design decision rather than something left for the contractor to work out on site.
| Route | Typical scope | Planning position | Fee from |
|---|---|---|---|
| Existing cellar conversion | Fit-out of an existing void, no excavation | Usually building regulations only | £2,400 |
| Floor lowering / partial dig-out | Increases headroom within the existing footprint | Often needs planning permission | £3,200 |
| New-build basement or light well extension | New basement area beyond the existing footprint | Full planning plus Party Wall Act | £3,850 |
Basement Conversion Drawings in Feltham TW13 — FAQs
How much do basement conversion drawings cost in London?+
Does a basement conversion need planning permission?+
Will I need a party wall agreement for a basement conversion?+
Are structural calculations included in a basement conversion package?+
Do I need an architect for a basement conversion?+
Do I need planning permission for an extension in Hounslow?+
What extra control applies in Bedford Park?+
Does Heathrow or the river affect my Hounslow project?+
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