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What changes the price when an extension meets a loft?
In Cheshire, an extension and a loft done together are priced as one structure with two sets of rules: the extension limits, and the roof-enlargement limits. This page prints no combined pound total, and it explains where those rules meet and how to split a quote so the join is not missing.
Last reviewed:One contract, two rule books
An extension loft conversion, in the way people ask for it in Cheshire, means building out and building into the roof on the same house, often so a new stair serves both. The price is not the sum of a generic extension and a generic loft, because the roofs have to meet and the structure is shared. No pound total for that combined job is printed here.
Crewe, Nantwich and Sandbach are the first places this is written for. Builders usually lead. Roofers may cover the tiling where the new roof cuts into the old one. Say, in the post, which firm you expect to coordinate.
Anyone in the UK can post or register.
Where the roof rules step aside
Class B on the Planning Portal is the enlargement of a house by an addition or alteration to its roof. Among the construction conditions, the original eaves are maintained or reinstated, any enlargement is set back at least 20cm from those eaves so far as practicable, and the enlargement does not overhang the outer face of the original wall [S1].
The exception to write on the drawing is this: none of those three points apply to the relevant parts of an enlargement that joins the original roof to the roof of a side or rear extension [S1]. That is not a free pass for the whole loft. Volume of enlargement, counting earlier enlargement, must stay within 40 cubic metres for a terraced house or 50 cubic metres otherwise [S1]. The work must not exceed the height of the existing roof [S1]. On the principal elevation facing a highway, it must not extend beyond the existing roof slope [S1]. Materials must look similar to the house [S1]. Side windows must be obscure-glazed, and opening parts must be 1.7 metres above the floor of the room [S1].
The house itself has to qualify. It is not a flat, it has not already gained storeys under permitted development, it was not changed to be used as a house from a previous non-residential use under those rights, it was not built as a new dwellinghouse under those rights, and it is not on Article 2(3) land [S1]. Article 2(3) land includes conservation areas, National Parks, the Broads, World Heritage Sites and areas of outstanding natural beauty [S1].
Read the loft planning page for the roof half. The exception is easy to over-read. It covers the relevant parts of the join, not every dormer on the house.
The extension half is still an extension
The ground-floor or two-storey box is assessed under the extension rules. A single-storey rear extension cannot go more than four metres past the original rear wall on a detached house, or three metres on any other house, unless the prior-approval route for eight metres or six metres is open and is actually used [S2]. Work of more than one storey must not go more than three metres past that rear wall, and must not come within seven metres of a boundary opposite the rear wall [S2]. Side extensions under permitted development are single storey, no more than four metres high, and no more than half the width of the original house. Anything of more than one storey on the side needs a householder application [S2].
Only half the land around the original house can be covered by extensions and other buildings [S2]. The original house is as first built, or as it stood on 1 July 1948 [S2]. Floor space over 100 square metres can attract a Community Infrastructure Levy charge [S2]. A loft plus an extension can cross that floor-space line even when each half looks modest. Ask the designer to add the areas up from the drawings rather than from memory.
The extension planning page is the pair to the loft page. Use both.
Building regulations on each half
Turning the loft into a liveable space requires building regulations approval, according to the Planning Portal. The purposes it gives as examples are a new floor strong enough for the load, a roof whose stability is not put at risk, a safe fire escape, stairs that are safely designed, and reasonable sound insulation to the rooms below [S3]. It says that in most homes the ceiling joists were not designed to carry a significant weight [S3]. Contact building control, and find out whether the Party Wall etc. Act 1996 applies [S3].
The extension is covered because the Building Regulations 2010 deal with the construction and extension of buildings [S4]. Planning permission, if you need it, is a separate yes or no. GOV.UK says you might need both [S4]. Citizens Advice describes an extension as work that is not handled only through a competent person scheme, so the building control application comes first, usually with a fee, and sometimes with a further inspection payment [S5].
GOV.UK: building regulations approval. QuoteZila is not affiliated with this organisation. GOV.UK: find your local council for building control. QuoteZila is not affiliated with this organisation.
Do not ask a friend to "just open the ceiling" to see the joists if that means standing on a ceiling that was not built as a floor. The Planning Portal's warning about load is the reason to leave the opening-up to the firm that will be responsible for temporary support [S3].
Party wall and the neighbour's roof
Cutting into a party wall, or making one taller, is on GOV.UK's list of work the Act can cover. So is excavation near and below a neighbour's foundation [S8]. A combined scheme can do both: a deeper footing for the extension, and a roof cut on a shared wall for the loft.
The Act is not planning permission and it is not building regulations approval [S8]. Adjoining owners receive a party wall notice in the form the Act requires [S8]. Details are on the party wall guidance. If the houses are detached and the extension is well off the boundary, say that on the drawing so the quote does not include a surveyor you do not need. If they are semis, do the opposite: make the shared wall obvious.
Splitting the quote so the join is visible
Citizens Advice wants the quote to separate each part of the work and each material, and to say how long the price stays open and whether VAT is included [S5]. Try to collect that in writing from at least three traders [S5]. An estimate is only a rough guess [S5]. Be cautious if a price is a lot lower than other quotes: it might mean the trader does not have the right skills or experience, or is not being honest, and it could also mean they are not quoting for exactly the same work [S5].
| Slice of the job | Belongs in the quote because | Easy to lose |
|---|---|---|
| Extension shell | Walls, roof, openings and the projection past the rear wall [S2] | Priced as a box with no insulation standard |
| Loft volume | 40 or 50 cubic metres, depending on whether the house is terraced [S1] | A dormer drawn larger than the cap |
| The join | The three eaves conditions do not apply to the relevant parts of a roof that ties into an extension roof [S1] | Steel at the junction left as "extra if required" |
| Loft floor | Existing joists may not be fit for a room [S3] | Boards only, with no new structure |
| Stair | Needed for a liveable loft and checked under building regulations [S3] | Rises through a room nobody priced to lose |
| Fire and sound | Both are named purposes of the loft regulations [S3] | Doors and insulation appear after plastering |
| Party wall | Footings and the shared wall may be Act work [S8] | Surveyor omitted |
| VAT | Standard rate 20% on most existing-house work [S6] | One firm net, one firm gross |
The deposit guidance from Citizens Advice is to avoid paying the whole sum first, and if some money has to go early, not to agree more than 25%, with a receipt [S5]. Buying materials yourself is the option they offer so you still own them [S5]. VAT registration kicks in above £90,000 of taxable turnover in a rolling 12 months [S7].
Tell the buildings insurer you are opening both the back wall and the roof. Citizens Advice says the policy may cost more for the duration and after completion, and the insurer will probably want the trader's insurance details [S5].
Nantwich, the Weaver, and one set of photos
Nantwich stands on the River Weaver. Crewe is the railway town to the east. Sandbach is on the Trent and Mersey Canal. None of those facts designs the junction between a new extension roof and an old hip or gable.
What the three firms need is the same pack: each elevation, the landing, the loft hatch, the rear boundary distance, and a note of any extension already on the house. A previous owner's rear addition counts toward the original-house test [S2]. If you do not know whether one exists, say that, and let the designer check rather than pricing a blank history.
Jobs you might post
These are examples, not taken from real job posts.
- Rear extension and a loft dormer joined into one roof, on a semi-detached house in Nantwich, stair from the new extension.
- Loft conversion only where a single-storey extension is already built in Crewe, using the Planning Portal join exception if the designer confirms it applies.
- Structural drawings for the roof junction and the new loft floor, before a build price, for a house in Sandbach.
- Building control application covering both the extension and the liveable loft, plus the build, as one contract with separated lines.
QuoteZila is free for customers and local businesses [QZ1].
A job can be sent to up to five matched local businesses [QZ2].
Posting a job is not open yet
Questions when both are done together
Does QuoteZila check the businesses?
No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.
Do the eaves rules still apply where a loft joins an extension roof?
The Planning Portal says three construction conditions normally apply to a roof enlargement: keep or reinstate the original eaves, set the enlargement back at least 20cm from those eaves, and do not overhang the outer face of the original wall. It then says none of those three points apply to the relevant parts of an enlargement that joins the original roof to the roof of a side or rear extension. The volume cap and the ban on exceeding the existing roof height are separate limits on the same page.
Does the extension half of the job follow loft rules?
No. The extension is still an extension. Rear single-storey limits, side limits and the rules for more than one storey are on the Planning Portal's extension page, including the three-metre projection for work of more than one storey. Joining the roofs does not switch the ground-floor box into Class B. Ask the designer to mark which lines are the extension and which lines are the roof enlargement.
Will building control treat this as one job or two?
Both parts are building work. The Planning Portal says approval is required to turn a loft into a liveable space, and it lists floor strength, roof stability, fire escape, stairs and sound insulation among the purposes. GOV.UK says the Building Regulations 2010 cover the construction and extension of buildings, and that planning permission is a different decision you might also need. Ask the building control body whether they want one application covering both halves.
What should the quote say about the join?
Name the steel or trimmer where the new extension roof meets the old rafters, who designs it, and whether the loft floor is included. The Planning Portal says that in most homes the existing loft joists were not designed for a significant load. A bedroom over a new rear extension is a liveable space, so boarding alone is not the specification. Citizens Advice says each part of the work and each material should be separated on a written quote.
How is VAT usually shown?
GOV.UK puts the standard rate at 20% for most builder's work on houses and flats. Doing a loft and an extension on a house you already live in is not described there as building a new house. The registration threshold is taxable turnover over £90,000 in the last 12 months. Citizens Advice says the quote should tell you whether VAT is in the total.
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Related pages
- Flat Pack Houses: Separate the Quote Lines. A flat pack house in Cheshire is still a new building. Separate the kit from planning, building regulations, the foundations and the services on the plot.
- Flat Roof Extension Cost: What Changes It. What changes the cost of a flat roof extension in Cheshire: size, foundations, roof covering, glazing, planning limits and building control. No price printed.
Sources
- QZ1: QuoteZila product fact. QuoteZila pricing line.
- QZ2: QuoteZila product fact. QuoteZila matching cap.
- S1: Planning permission: loft conversion, Planning Portal. Accessed 2026-10-26. https://www.planningportal.co.uk/permission/common-projects/loft-conversion/planning-permission
- S2: Planning permission: extensions, Planning Portal. Accessed 2026-10-26. https://www.planningportal.co.uk/permission/common-projects/extensions/planning-permission
- S3: Loft conversion building regulations, Planning Portal. Accessed 2026-10-26. https://www.planningportal.co.uk/permission/common-projects/loft-conversion/is-building-regulations-approval-needed-for-a-loft-conversion
- S4: Building regulations approval, GOV.UK. Accessed 2026-10-26. https://www.gov.uk/building-regulations-approval
- S5: Before you get work done on your home, Citizens Advice. Accessed 2026-10-26. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/
- S6: VAT for builders, GOV.UK. Accessed 2026-10-26. https://www.gov.uk/vat-builders
- S7: Register for VAT, GOV.UK. Accessed 2026-10-26. https://www.gov.uk/register-for-vat
- S8: Party Wall etc. Act 1996 guidance, GOV.UK. Accessed 2026-10-26. https://www.gov.uk/guidance/party-wall-etc-act-1996-guidance