Loft Company, Builder or Shell Only: What Each Route Leaves You to Manage

The council's enforcement notice for a non-compliant loft goes to the owner. Section 36 of the Building Act 1984 lets a local authority require the owner to pull down or alter work that breaks the Building Regulations, for up to 10 years after the work is completed, and the owner then has 28 days to comply unless a court allows longer. Who drew the loft and who built it doesn't change the address on the envelope.

Use that as the lens for choosing how to buy a loft. The Manual to the Building Regulations, in paragraph A26, puts compliance on "those carrying out the work, for example, agents, designers, builders, installers and the building owner". Each route shares that list out differently, so compare them by what each one leaves with you.

Three ways to buy a loft conversion

A design-and-build loft company. One firm surveys the loft, draws it, gets the structural calculations, applies for building control and builds it. HomeOwners Alliance calls these firms "a one-stop shop for loft conversions". For a standard rooflight or dormer loft on a common house type, this is the sensible place to start.

A builder, with your own designer and engineer. You appoint an architect or architectural technologist to draw the loft and a structural engineer to size the steels and the floor, then put the drawings out to builders. The Manual to the Building Regulations says homeowners may want this help: design professionals "can produce coordinated drawings and other design information to reduce risks once you start to build."

Shell only, with your own trades. A contractor builds the structure and makes it weathertight. Everything after that is yours to buy, book and sequence. One public cost guide puts a shell at £21,000 – £40,500, against £34,500 – £75,000 for a whole dormer loft across the published guides. Those ranges don't compare like for like, because every company draws the edge of the shell somewhere different.

HomeOwners Alliance is blunt about the specialist firm: "the most expensive option but might be the most cost effective in the long run." Whatever one route saves in fees, another pays back in your time and in risk.

Who owns what on each route

Read the right-hand two columns first. They show what you take on as the price comes down.

Two things hold on every route. The completion certificate comes from the building control body, never from the company, and regulation 17 of the Building Regulations 2010 makes it "evidence (but not conclusive evidence)" that the work complies. And the party wall notice is the building owner's duty: section 3 of the Party Wall etc. Act 1996 requires it at least 2 months before the work begins. On a semi or a terrace a loft often triggers it, because section 2 covers cutting into a party structure and into a neighbour's wall to insert a flashing. One agreed surveyor costs £800 – £1,200 per neighbour on public figures. A company that serves the notice does so as your agent, so check it has gone, and when. Neighbours can also consent in writing instead.

What a loft company still leaves with you

Buying design-and-build doesn't buy you out of the job. It shrinks it to a handful of decisions only you can make, and most of them fall before you sign.

• Choosing and checking the company. More on that below.
• Reading and comparing the quotes. Exclusions, allowances, VAT and the deposit are covered in checking a loft conversion quote.
• Agreeing stage payments that follow finished work, as set out in contracts and payment schedules.
• Signing off the stair position and the layout before the drawings go to building control. The stair has to land somewhere on the floor below, and that's far cheaper to change on paper. Loft conversion stairs has the rules.
• Collecting the certificates and snagging. Hold back the final payment until you have the completion certificate and the electrical paperwork. Under Approved Document P paragraph 3.4, the registered installer or its registration body must give you a copy of the Building Regulations compliance certificate within 30 days of the work being finished.

The design is a trade-off. An architect quoted by Self-Build.co.uk says loft companies "tend to work according to a generic design for your type of property". On a standard rear dormer, a proven template is a strength. Where the planning constraints or the roof shape need thought, it's a weakness, and that's the point to look at the builder route.

Checking the company will finish the job

Complaints about loft firms going into liquidation with deposits paid and work half done turn up on forums and review sites. Reliable figures for how often it happens are hard to find. Treat it as a risk you can shrink before any money moves.

Search the company on Companies House, which is free. Look at whether its accounts are filed and how long it has traded under this name, then at what happened to the directors' earlier companies. If the company says your money is protected, in a client account, a deposit scheme or by insurance, ask who holds it and what it covers, and get that answer from the scheme or the insurer, not only the brochure. Ask who underwrites any guarantee. A trade-body logo proves nothing without evidence of membership. And read reviews on more than one platform.

The general vetting steps are in finding a builder, and the insurance a company should hold is in insurance and liability.

What the builder route adds

You become the person in the middle. The designer, the engineer, the building control body and the builder each answer for their own piece, and nobody is paid to check the joins except you.

You also pay for each piece separately. One public cost guide, with VAT added to its figures, puts architectural drawings for a loft at £1,800 – £4,800 and a structural engineer at £500 – £2,500. Another guide puts the building control fee at £800 – £1,350. All of it comes before the builder's price. Homebuilding & Renovating warns that on a job this size "the design fees are likely to be a high percentage of the overall costs." What that buys is a design steered to your house, which Self-Build.co.uk's architect argues pays off where planning constraints or overheating need designing around.

You don't always need a registered architect. One architectural practice says a technologist may be enough for a simple dormer or rooflight loft, while complex roofs, listed buildings and conservation areas need an architect or similar professional. Finding an architect and structural engineer cover both appointments.

Here's how a gap opens. Picture drawings that show a fire door on the new loft room and say nothing about the bedroom doors below. The builder prices what's drawn. The designer assumes the builder will raise the rest. But where the loft adds a storey above 4.5m, Approved Document B Volume 1 paragraph 2.21 asks for the full extent of the escape route to be addressed, with fire-resisting doors of at least E 20, upgrading existing doors where necessary. In that picture, building control raises it at the final inspection and you pay to put it right before the certificate is issued. Loft conversion fire safety sets out what the escape route needs.

Inspections fall into the same gap. In a 2016 DIYnot thread, a homeowner who had drawn their own dormer conversion found the builder had never told building control, so no stage inspections took place. At the final visit the inspector asked for the roof and floor to be opened up to check the insulation, joists and steels. Replies put the owner first in line for arranging inspections and the designer "next port of call in the blame game".

Close the gaps in writing before anyone starts: whose building control application it is, who books each inspection, who specifies the doors on the floors below, and which electrician certifies the work.

CDM 2015 asks a quieter version of the same question. Under regulation 7, a domestic client's duties pass to the contractor where there's only one, so on a loft where the builder is the only contractor they sit with the builder. If you want your architect to take them on instead, regulation 7(1)(c) needs a written agreement.

7-15%

of the build cost is what firms selling independent project management commonly quote. It buys someone whose job is the joins between designer, engineer, builder and building control. It's an optional extra, priced by the firms that sell it.

What shell only adds

This is the route where you take on the second half of the loft company's job.

Start with the word. "Shell" has no standard meaning. Published pages agree on a minimum: the structure, the new floor, the roof or dormer, weatherproofing and the windows. After that they disagree. One company builds the stair but leaves the handrail and spindles to the buyer. Another counts insulation inside its shell, while a third treats it as fit-out. One cost article says the building control sign-off in a shell price is a structural interim one, not the completion certificate. Two shell quotes can describe different jobs.

Get these seven answers in writing before you sign:

1. Insulation: in the shell or out, and who calls the inspector before it's covered.
2. Plasterboard: fitted, or left to your plasterer.
3. First-fix electrics and plumbing: in or out.
4. The stair: fitted complete, or without the handrail and balustrade.
5. Whose building control application covers the finishing work, and who books each stage.
6. The Part P route, and who certifies the electrics.
7. What sign-off the shell price buys: a structural stage, or the completion certificate.

Inspection timing is where shell buyers get caught. Councils set their own inspection stages under regulation 16 of the Building Regulations 2010. One council's published list includes a pre-plaster stage, where the inspector checks beams, timbers, insulation and electrical work before plastering. Miss it and that council says it will require you to open up or remove part of the work, adding: "This can be expensive." The Manual to the Building Regulations is plain that the visits aren't a safety net: "you cannot rely on this as the only method of ensuring that the work complies with the Building Regulations." What building control inspects on a loft lists the stages to plan around.

The electrics need a named owner too. A new circuit or a consumer unit replacement is notifiable under regulation 12(6A) of the Building Regulations, and the duty to notify sits with the person intending to carry out the work. Approved Document P paragraph 3.1 allows three ways to certify it: a registered competent person, a registered third-party certifier, or the building control body. Use an electrician registered with a competent person scheme and they self-certify. Otherwise someone has to appoint a third-party certifier or notify building control before the electrical work begins. Any ensuite plumbing and extract fan run through your trades as well.

CDM changes shape here. Hiring a plasterer, an electrician and a plumber after the shell contractor leaves the project with more than one contractor, and regulation 7(1)(b) puts a domestic client's duties on the principal contractor where there is more than one. If you appoint none, regulation 7(2) makes the contractor in control of the construction phase the principal contractor. That is an inference from regulation 7, not an HSE statement about shell-only jobs, but the practical step follows: agree in writing which contractor takes the role before the second trade arrives.

This is the reader the Access Pass is written for. The later phases of this tree set out the trade booking order, when to call the inspector, and Part P sign-off, step by step.

Living at home while the loft goes in

Loft companies and builder directories say most households stay put, and they have an interest in saying so. The first stretch is scaffolding and external access, with little happening inside, because the loft is reached from outside until the stair goes in.

Disruption rises when the stair opening is cut. Expect dust and noise on the landing, and ask for dust protection along the route the trades use and temporary guarding wherever the opening leaves a drop. Companies also describe short, pre-agreed shut-offs of water and power when the new electrics and plumbing are connected. Get those dates in advance, and plan around anyone at home who works nights or whose health is affected by dust and noise.

Once the roof is opened, the house relies on temporary protection until the loft is weathertight. One builder directory's own guidance says tarpaulins "are temporary precautions, not substitutes for proper weatherproofing." Ask what the company will do if a storm is forecast, and who pays if water gets in.

Companies describe the shut-offs as short but give no hours, and none states how many days the roof stays open. Companies call these stretches short and leave it there. Ask for them on the written programme, and use loft conversion stages to see where each falls in the order of work.

Which route suits whom

A loft company suits you if the loft is a standard type on a common house and you want one contract and one phone number. Put your effort into checking the company and reading the quote.

A builder with your own designer suits you if the house is listed or in a conservation area, the roof is awkward, or you want a design made for the house. Be ready to run the coordination, or pay a project manager to.

Shell only suits you if you've managed trades before and you'll be around for the inspections. Line up a registered electrician and a plasterer before the shell contractor finishes. It's the wrong choice for a first project with a fixed move-in date.

Whichever route you take, you'll end up comparing quotes. Rate My Quote checks the general building lines in a quote against typical UK costs, and the first full breakdown is free once you're signed in.

These rules cover England. Wales has its own Approved Documents and Scotland works through building warrants, so check the local equivalents outside England.

External resource

HSE: domestic clients under CDM 2015

Who takes on a homeowner's client duties, and how to hand them to your architect with a written agreement.

hse.gov.uk

External resource

GOV.UK: building regulations approval

Choosing a building control body, using a competent person scheme, and why you need the certificates when you sell.

gov.uk