House extension architects in Liverpool

What does Liverpool expect of a rear extension?

The council's yardstick is section 5.3 of its Housing Design Guide, adopted on 2 June 2026 (Liverpool Housing Design Guide). It wants a new rear addition to match the height, depth and width of its neighbours' rear additions where those exist, and it treats a glazed conservatory in the same way as a brick extension. For terraced houses a single-storey scheme should normally be flat-roofed or fall towards the back boundary, with rooflights bringing light into the deep plan.

Two angles decide a lot of schemes. The 45 degree rule bars any building mass from the viewing arc of a neighbour's window or external door, measured from the window centre line in plan and in elevation. The 25 degree rule draws a line up from the middle of the lowest window opposite, and mass that crosses it is, in the council's words, likely to be rejected. A scheme that passes both is not automatically approved, because the guide says so itself.

Why does a side extension need more thought in Liverpool?

Section 5.4 says that infilling the gap between semis or adding a first-floor side extension over a garage is likely to significantly affect the rhythm of a street. First-floor side additions should step back at least 1 metre from the original front wall and drop below the ridge, and the guide asks for at least a metre of side access so that a pair does not read as a terrace. Openings should have a similar ratio of window to wall as the original house. The guide singles out the combination of a side and a rear extension as the case where a house is most likely to look overwhelmed.

Does your extension still count as permitted development here?

Sometimes. The council says many householder projects may not need permission if they stay within set limits, and that this route does not apply to flats or maisonettes (council permitted development page). Our article on whether an extension needs planning permission explains the national limits, and the Planning Portal's extensions pages summarise the England-wide limits and conditions. The council's hosted advice note quotes the 1995 Order, so use the current national rules for dimensions.

Conservation areas change the answer. Article 4 directions cover most of the 36 areas, and Liverpool lists roofs, chimneys, dormers and rooflights, windows and doors, cladding, gates and hard-standing as items that can need permission (Article 4 directions). The Historic Environment SPD, adopted on 16 December 2025, adds that extensions projecting forward of the front building line will be resisted, and that rear extensions are generally looked on more favourably (Historic Environment SPD). Check your street on the council's conservation area page.

What does Liverpool building control charge for an extension?

Building regulations apply to an extension whether or not it needs planning permission. For full-plans applications the council lists a plan charge and an inspection charge, both including VAT. A new floor area under 10 square metres is £234 plus £426. Between 10 and 40 square metres it is £300 plus £522, and over 40 square metres £390 plus £744. Building notice and regularisation charges are higher (council fees table). Charges assume up to ten site inspections, and anything beyond that can be billed at an hourly rate.

If the extension adjoins a neighbour's wall or involves excavation close to it, the Party Wall etc. Act 1996 may apply; the government's explanatory booklet sets out the notice process, and our page on party wall agreements summarises it.

What else do officers check inside and around the extension?

The general principles in section 5.1 of the guide go beyond massing. Every habitable room, kitchens included, needs a window or glazed door, and rooflights or obscured glazing cannot be the only opening because they give no view out. Sills should be low, with at least one window per habitable room no higher than 1,200 millimetres above the floor. Overlooking is handled by design, not by frosted glass: the guide says obscured glazing is not sufficient to prevent it, so a first-floor window facing a neighbour's garden needs a different answer.

The rooms left behind in the old house matter as well. The guide says an extension must not leave existing habitable rooms short of daylight or ventilation, and that access to utility infrastructure must not be harmed, so drains and service runs should be traced before the footprint is fixed. Extensions should generally not be visible from the public realm and should use materials, water and energy efficiently. A proposal that significantly improves access for someone with specialist needs is given special consideration, provided anything that departs from the guidance can be reversed.

How do Liverpool's house types change the brief?

The Valuation Office Agency records 20.7% of Council Tax homes as built from 1919 to 1939 and 30.9% before 1919 (VOA, 31 March 2026). Where a run of older terraces already has similar back additions, the guide's first rear-extension rule asks you to respect that pattern. On inter-war semis the side gap and set-back rules are likely to be the pressure points. Our national page on house extensions covers costs and stages that apply everywhere.

What can you ask the council before you commission drawings?

• A householder pre-application enquiry is £90, or £225 if you want an office or site meeting.
• The council assigns a dedicated planning officer to pre-application cases, according to its professionals page.
• Submit your sketch scheme with the 45 and 25 degree angles drawn on it, so the officer can respond to the real geometry.
• Decisions in the year to June 2026: 629 householder cases, 90.8% granted, 96.2% decided on time by our calculation from MHCLG counts.

What should you ask an architect before hiring one for a Liverpool extension?

1. Check the practice on the Architects Registration Board register at arb.org.uk.
2. Ask for an example that deals with a 45 degree constraint on a terrace or semi.
3. Ask whether the fee covers pre-application work, planning drawings and building regulations information.
4. Ask who coordinates structural design and party wall notices.

For the wider picture, see the Liverpool hub page, the Liverpool loft conversions page and Liverpool planning applications.