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Extensions and lofts

House extension drawings in London

House extension drawings are the plans, elevations and sections a council and building control need before you build out. We draw rear, side return, wraparound and double-storey extensions for London homes from £695 including VAT, and every set is checked by a second MCIAT chartered technologist before it goes in.

From £695 (VAT included)

  • MCIAT chartered
  • £2m PI insured
  • LABC Partnered
  • Fixed fees, VAT included

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    Architectural model of a four-storey London stucco townhouse in its terrace, with a portico, area railings, sash windows, a cornice and chimney stacks
    The house as it stands: four storeys over a lower ground floor.Existing Proposed worksAn illustrative model, built for this page.

    How we work on house extension drawings

    Nine steps from first call to approval.

    The same model cut through the middle: every floor, the stair, the chimney breasts, the new mansard, rear extension and basement in section
    Section through the model: every floor on one datum.

    1. Enquiry and constraints check

      We check the property against conservation areas, listed status, Article 4 directions, tree preservation orders, flood zone and planning history. We choose the right route and send a fixed quote.

    2. Measured survey

      We survey the house on one datum: rooms, levels, boundaries, drains, trees and the neighbours' windows that the 45° and 25° tests depend on.

    3. Design options

      We model the house in Revit and show you options in 3D and plan, with the planning strategy and the precedents in your street.

    4. Design frozen

      You choose an option in writing. Nothing changes after this without your say.

    5. Independent check

      A second chartered technologist checks every sheet against the council's validation checklist and the policy. A senior review signs it off before anything is submitted.

    6. Submission

      We prepare the forms, certificates, fee and documents and submit through the Planning Portal.

    7. Officer liaison

      We answer the planning officer and make any amendments within five working days, at no charge until approval.

    8. Building regulations

      Technical drawings are coordinated with the structural engineer's calculations, the drainage and the planning conditions.

    9. Approval and hand-over

      Building control approval, then a next-steps pack covering the commencement notice, party wall timing and CIL.

    Free redraws until approval. Every drawing set is checked independently, and the checker is never the person who drew it.

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    House extension under construction with scaffolding, new glazed doors and building materials

    Which type of house extension suits your home

    We draw four common extension shapes, and each has its own page, its own rules and its own price. A rear extension pushes the kitchen or living room into the garden. A side return extension fills the narrow passage beside a Victorian terrace. A wraparound extension combines the two. A double-storey extension adds a bedroom or bathroom above.

    The right choice usually comes from the plot rather than the wish list. Garden length, the neighbour's windows, the position of the drains and whether the house sits in a conservation area decide what is realistic before any design starts.

    Not sure which one fits? Send us the address. The free constraints check tells you which type is realistic and which route it takes.

    Brick house being extended, with a wide new opening supported over the ground floor

    What the drawings include

    A householder set shows the house as it stands and as it will be: existing and proposed floor plans, elevations and sections, plus a location plan and a block plan. Sheets carry a scale and a north point so the council can validate them without a query.

    Where the extension needs building regulations approval too, we continue into technical sheets: foundations, wall and roof build-ups, drainage runs and the openings. Our building regulations drawings are priced separately, and a combined package is available.

    Because the whole house is modelled in Revit, the plan, the section and the elevation come from one model and cannot disagree with each other.

    Permitted development or a planning application

    Many single-storey rear extensions can be built without a planning application. A Lawful Development Certificate puts that in writing, which buyers and solicitors like to see later. Larger rear extensions can go through prior approval, where the council only looks at the effect on neighbours.

    The limits bite quickly. Permitted development is withdrawn for side extensions in conservation areas, is not available to flats, and can be removed by an Article 4 direction. That is why our first step is a check of the address for conservation area, listing, Article 4, trees, flood zone and planning history.

    If your design goes beyond those limits, a householder application through planning drawings is the usual route.

    The rules that shape every extension

    Some rules apply whatever the shape. A householder application for an extension to a single dwelling carries a council fee of £548, paid to the council and separate from our fee.

    Energy rules apply to every extension. For new elements in an existing home, the limits are: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. Glazing is capped too: Windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension floor area plus the area of openings removed or covered.

    If your project touches the neighbour's wall or digs close to their foundations, the Party Wall Act applies: Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations. We can prepare the notices through party wall notices.

    Two exemptions help with cost and paperwork: Residential extensions and annexes can claim exemption (claim before commencement), and Householder applications are exempt from biodiversity net gain.

    What extension drawings cost

    Extension drawings start at £695 for a rear extension, VAT included, and the price is published before you commit. Side return, wraparound and double-storey extensions are priced from the same list on their own pages, so you can compare them honestly.

    If the council asks for changes, we redraw at no charge until approval. That is a commitment about our fees, not a promise about the council's decision.

    Need a structural engineer's beam sizes for the opening? Our structural calculations cover them, and we coordinate them with the drawings.

    How the work runs from enquiry to submission

    You send the address and a short brief. We check constraints, choose the route and send a fixed quote. A measured survey follows, taken from the house and garden on one datum, including the neighbours' windows that the daylight tests depend on.

    We model the house and show options in 3D and plan. You choose one in writing and the design is frozen. A second chartered technologist then checks every sheet against the council's validation list, and a senior review signs it off.

    Drawings are normally ready about a week after the survey. We submit through the Planning Portal, answer the officer and make amendments within five working days.

    Extension drawings by borough and council

    Each council applies the national rules through its own guidance, so a rear extension that suits one borough can need a lower roof or a shorter depth in the next. Our council pages give the local figures for conservation areas, Article 4 directions and recent householder decisions.

    Begin with the place where the house stands. See Camden's planning figures as an example of how a borough page reads, or browse every area under architectural drawings by council. Adding a room in the roof as well? See loft conversion drawings.

    The national rules in figures

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Householder: alterations/extensions to a single dwellinghouse, from 1 Apr 2026548 GBP—ribblevalley.gov.uk
    Approved Document L Vol 1 2021 incl. 2023 amendments, Table 4.2New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4—gov.uk
    Approved Document L Vol 1 2021, para 10.7(d)Windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension floor area plus the area of openings removed or covered—gov.uk
    Party Wall etc. Act 1996 s6(1), s6(2), s6(5)Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations—legislation.gov.uk
    CIL Regulations 2010 regs 42A-42BResidential extensions and annexes can claim exemption (claim before commencement)—legislation.gov.uk
    GOV.UK BNG exempt developments, 'Householder applications' (updated 6 Aug 2026)Householder applications are exempt from biodiversity net gain—gov.uk
    GPDO 2015 Sch 2 Pt 1 Class A, para A.1(f)(i)3 m (attached) / 4 m (detached) beyond the original rear wall, single storey—legislation.gov.uk
    Class A, para A.4(10)(c): development may begin if the LPA has not notified a decision within 42 days of receiving the information42 days—legislation.gov.uk

    A blank value means the figure has not been published, not that there are none. Check your own address with the council.

    Single-storey rear extension: the permitted development limitsDepth beyond the original rear wall: 3 m (attached) / 4 m (detached) beyond the original rear wall, single storey. Maximum height: 4 m. Within the zone near the boundary: Eaves no higher than 3 m where within 2 m of the curtilage boundary. Larger extension under prior approval: 6 m (attached) / 8 m (detached), single storey, height max 4 m; not on article 2(3) land or an SSSIABCD

    Single-storey rear extension: the permitted development limits

    The house in section with a rear extension; the dashed lines mark the zone near the boundary.

    A · Depth beyond the original rear wall
    3 m (attached) / 4 m (detached) beyond the original rear wall, single storey
    B · Maximum height
    4 m
    C · Within the zone near the boundary
    Eaves no higher than 3 m where within 2 m of the curtilage boundary
    D · Larger extension under prior approval
    6 m (attached) / 8 m (detached), single storey, height max 4 m; not on article 2(3) land or an SSSI

    What you receive

    Planning drawing sheet for a rear extension with plans, elevations and sections
    Sample drawing. Planning drawings for a rear extension: plans, elevations and sections on one sheet set.
    Finished white-rendered rear house extension with large glazed doors
    Every side considered
    Flick across the turntable to spin it.

    Where we prepare house extension drawings

    Types of extension

    London

    Questions

    What is the difference between a rear and a wraparound extension?

    A rear extension extends the back of the house into the garden. A wraparound extension adds that to a side infill, so the new room turns the corner. The rules are different, so each has its own page.

    How much do house extension drawings cost?

    They start at £695 including VAT for a rear extension. The council fee for a householder application, £548, is paid to the council separately.

    Do I need planning permission for an extension?

    Not always. Some single-storey rear extensions are permitted development and can be confirmed with a Lawful Development Certificate. Flats, conservation areas and Article 4 areas change that, so we check the address first.

    Will I need a party wall notice?

    Possibly. The rule is: Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations. Building up to or on the boundary has separate notice rules.

    Do householder extensions need biodiversity net gain?

    Householder applications are exempt from biodiversity net gain. We confirm the position for your project in the constraints check.

    Sources and dates

    City of London skyline glowing at dusk across the Thames under a dramatic orange sky

    Tell us about your property.

    We check the constraints, then send a fixed fee. Messages before 3pm get a reply the same working day.

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