House extension or loft conversion in Manchester: How to choose, with the planning limits in plain numbers

By the team at Ivanov Renovation & Construction Group, family builders in Manchester. Updated October 2026.

Extension or loft conversion: side by side

Start with the big picture. This table puts the two options next to each other.

Still not sure? The sections below take each row in turn. Or send us a few photos and we will tell you what your house can take.

Start with the room you are missing

The best choice is the one that fixes your daily problem. Be honest about what that is.

• Cooking in a narrow kitchen while the family eats in another room? A rear or side house extension gives you one open space, and we can fit the new kitchen as part of the same job.
• Children sharing a room, or working from the sofa? A loft conversion adds a quiet room at the top of the house without touching the garden.
• A queue for the bathroom every morning? Either option can carry a new bathroom: a shower room downstairs or an en-suite in the loft.
• Need both? Plan them together, even if you build them a year apart. The stairs, drains and steelwork can then be designed once.

Can your loft be converted? The 2.2 metre test

You can check this yourself in five minutes with a tape measure.

1. Go into the loft and stand under the ridge, the highest line of the roof.
2. Measure straight down from the underside of the ridge timber to the top of the ceiling joists.
3. Write the number down. The Planning Portal's loft guide gives 2.2 metres as the minimum height for a conversion.

Less than that does not always mean no. A dormer adds height across part of the room. It does mean the design matters more, so ask before you rule it out.

Look at the roof timbers too

Older roofs are usually built from separate rafters and purlins, which leaves the middle of the loft open. Homes built after the 1960s are more likely to have roof trusses, the W-shaped frames that fill the space. A trussed roof can still be converted, but it needs extra structural support, and that adds work.

The four main types of loft conversion

• Roof window: windows set into the existing slope. The least building work, if the loft is already tall enough.
• Dormer: a box built out from the slope. The most popular choice, because it adds both height and floor space.
• Hip to gable: the sloping side of the roof is built up into a straight wall. Common on semi-detached houses with hipped roofs.
• Mansard: one side of the roof is rebuilt almost upright. The biggest change, and the most structural work.

Is there room for an extension? Five things to check outside

• The garden you will have left. An extension that swallows the whole yard rarely feels like a win.
• Drains and manhole covers. A drain under the new floor can often be built over or moved, but it has to be planned and approved.
• Access. Every brick and bag of sand has to reach the back of the house. A terrace with no side passage is still possible, but it takes more labour.
• The boundary. Building right up to it, or digging close to next door's wall, brings in the Party Wall Act.
• What is already there. An old lean-to or outhouse counts towards how far you can extend.

Planning permission: the limits in plain numbers

Many extensions and loft conversions do not need a planning application. They are covered by national rules called permitted development. Here are the main limits for houses in England, as published by the Planning Portal and checked in October 2026.

Single-storey rear extensions

• Depth: up to 3 metres beyond the original back wall on a terraced or semi-detached house, or 4 metres on a detached house.
• Larger: up to 6 metres, or 8 metres on a detached house, if you first go through a step called prior approval, where the council consults your neighbours.
• Height: no more than 4 metres. Within 2 metres of a boundary, the eaves can be no higher than 3 metres.
• Materials: similar in appearance to the existing house.

Side extensions

• Single storey only, and no more than 4 metres high.
• No wider than half the width of the original house.

Every extension

• Extensions and outbuildings together must not cover more than half the land around the original house.
• Nothing can be built forward of the front of the house.
• No balconies, verandas or raised platforms.

The full list is on the Planning Portal extensions page.

Loft conversions

• Added roof space: up to 40 cubic metres on a terraced house, or 50 cubic metres on a detached or semi-detached house. Earlier roof extensions count towards the total.
• Nothing higher than the existing roof.
• No dormer on the roof slope that faces the road.
• Side windows in obscured glass.
• Dormers set back at least 20 centimetres from the eaves, where practical.
• Materials similar in appearance to the existing house.

The full list is on the Planning Portal loft conversion page.

When these rules do not apply

• Flats and maisonettes do not have these rights. You need a planning application.
• Conservation areas: a loft conversion that changes the roof needs a planning application, and so does a side extension. Manchester has many, from Ancoats in the city centre to parts of Didsbury and Chorlton.
• Listed buildings need consent for almost any change.
• Some streets and newer estates have had the rights removed. The council or your deeds will tell you.

Each council decides for its own area: Manchester, Bury, Bolton, Salford, Oldham, Wigan and the rest. Find your local council on GOV.UK and ask its planning team before you commit. If you want the answer in writing, you can apply for a lawful development certificate.

Building regulations: needed for both

Planning permission is about how the building looks and where it sits. Building regulations are about whether it is safe and warm. Almost every extension needs approval, and every loft conversion does.

For a loft, the Planning Portal lists five things the regulations make sure of:

• The new floor is strong enough.
• The structure, including the existing roof, stays stable.
• There is a safe escape from fire.
• The stairs to the new floor are safely designed.
• There is reasonable sound insulation between the loft and the rooms below.

For an extension, the checks cover the foundations, structure, insulation, drainage, ventilation and electrics.

An inspector visits at set stages. At the end you receive a completion certificate. Keep it safe, because you will be asked for it when you sell. GOV.UK explains how building regulations approval works.

Your neighbours and the Party Wall Act

Most Manchester houses share at least one wall. If your project touches that wall or goes near it, the law asks you to tell your neighbour in writing first.

• Work on a shared wall, such as resting loft beams in it: notice at least two months before you start.
• A new wall at the boundary, or digging within 3 metres of next door's building and deeper than its foundations: notice at least one month before.
• Your neighbour has 14 days to reply. If they do not agree, a surveyor settles the details.

A friendly chat before the letter arrives makes all of this easier. The rules are set out in the GOV.UK guide to party walls.

Which Manchester houses suit which?

Victorian and Edwardian terraces

Terraces in Bolton, Oldham, Salford, Liverpool and inner Manchester, from Levenshulme to Moston, often have a narrow kitchen at the back with a yard beside it. Filling that side return gives a proper kitchen-diner. The roofs are usually steep and built the traditional way, so a dormer loft conversion often works well too.

1930s and post-war semis

Semis in Prestwich, Whitefield, Radcliffe and Bury tend to have longer gardens and hipped roofs. A rear extension across the back is the classic answer. For the loft, a hip-to-gable conversion with a rear dormer turns a cramped roof into a full bedroom.

Newer estate houses

Homes on newer estates in Warrington and Wigan often have space at the side, or a garage to build over. Their lofts are usually trussed, so the loft is the harder route. Check the deeds as well, because some estates restrict extensions.

What moves the cost

Neither option has a fixed price, and a figure given without seeing the house is a guess. These are the things that move it.

• Extension: the size, the ground and foundations, the type of roof, how much glass you choose, and whether the old back wall comes out.
• Loft: the type of conversion, the steelwork, the stairs, the number of windows and whether you add a bathroom.
• Both: the finish inside. Plastering, flooring and decorating are part of the real cost, so make sure they are in the quote.

Ask for a written quote for each option on your own house. Ours is free, and it covers the job from the first brick to the final coat of paint.

Life at home while the work is done

A loft conversion is the quieter guest. Most of the early work happens on the scaffold and inside the roof. The stairs go in near the end, and that is when the dust reaches the landing. Most families stay at home throughout.

An extension is built outside first, so the early weeks are calm indoors. The busy part comes when the back wall is opened and the kitchen is out of use. Good planning keeps that period short. Ask your builder how you will cook and wash up while it lasts.

A ten-minute checklist before you call a builder

• ✅Write down the one room you are missing.
• ✅Measure the loft under the ridge.
• ✅Measure the garden from the back wall to the fence.
• ✅Note where the drains and manhole covers are.
• ✅Find out if your home is in a conservation area.
• ✅Take four photos: the back of the house, the side, the loft and the landing.
• ✅Send them to us with your postcode.

That is all we need for a first, honest answer. We build extensions and convert lofts across Manchester, Bury, Bolton and the North West, and the same team finishes the inside. Planning more than one room? Read our guide on how to plan a house renovation.

Common questions

• Is a loft conversion cheaper than an extension?

  It depends on the house. A simple roof window conversion in a tall loft is usually less building work than an extension of the same floor area. A dormer or hip-to-gable conversion with a bathroom can come close to a small extension. The only fair comparison is a quote for each on your own home.

• Do I need planning permission for a rear extension in Manchester?

  Often not. A single-storey rear extension up to 3 metres deep, or 4 metres on a detached house, usually falls under permitted development if it meets the height and other limits. Flats, listed buildings and conservation areas are different. Your council's planning team gives the final answer.

• How do I know if my loft is tall enough to convert?

  Measure from the top of the ceiling joists to the underside of the ridge at the highest point. Around 2.2 metres or more is the usual starting point. With less, a dormer may still make it work.

• Do I need to tell my neighbours?

  If the work touches a shared wall, sits at the boundary or involves digging near their foundations, yes. The Party Wall Act asks for written notice one or two months before work starts, depending on the work.

• Can we stay at home during the work?

  In most cases, yes. A loft conversion happens mostly above you. With an extension, the hardest days are when the back wall is opened and the kitchen is out of use.