Phase 2 · Pre-Construction · Task 12 of 12
Loft Conversion Stages and How Long Each One Takes
Every loft conversion stage in order, how long each one takes before and on site, where building control inspects, and what you must decide at each step.
Ask a loft company how long the job takes and the answer is often a number of weeks on site. That is the shorter half of the answer.
Those weeks start the day the scaffold goes up. Before that day, someone has to draw the loft, a structural engineer has to size the steels, the council has to decide at least one application, and a neighbour who shares a wall may be owed notice. Very little of that is labour. Much of it waits on someone else's clock. A Bristol loft builder, writing about its own jobs, describes projects quoted in weeks that end up measured in months, "for reasons that are mostly predictable".
The loft company runs the programme. Your part is smaller but it matters: know the order well enough to see it slipping, and have each decision made before the stage that depends on it.
These rules are for England. Wales and Scotland run their own planning and building control systems.
Do this first
Read checking a loft conversion quote first: the programme should come with the quote, and the stage payments should follow it. The first jobs on site are clearing and preparing the loft and loft floor joists and steels.
Before site: the stages that come before the scaffold
Design comes first. On a design-and-build job the company surveys the loft and draws it, and those drawings fix the layout and where the stair lands. Nothing else moves until you've signed them off.
Then the structural engineer sizes the steels and the new floor joists. Building control needs those calculations with a full plans application, and nobody can order steel without them. No statute governs either, so the pace is set by the designer's diary and by how fast you decide.
Once the design is fixed, the approvals and notices run side by side:
| Stage | How long | What sets the clock | Waiting on |
|---|---|---|---|
| Planning permission, if the loft isn't permitted development | 8 weeks | DMPO 2015 article 34(2)(b): from the day after a valid application is received, or longer if you agree in writing | The council |
| Lawful development certificate, if you want proof the loft is permitted development | 8 weeks | DMPO 2015 article 39(10): same start, same written extension | The council |
| Building control approval with full plans | 5 weeks | Building Regulations 2010 regulation 14A(6): from receipt, or longer if agreed in writing | Building control |
| Party wall notice, on a semi or terrace | At least 2 months before work to the wall | Party Wall etc. Act 1996 section 3(2)(a), then surveyors and an Award if the neighbour doesn't consent | Your neighbours |
| Bat emergence survey, if roost potential is found | Only in season, roughly May to August | Survey season, not a statute | The calendar |
| Steel delivery | 3-7 working days | Supplier lead time, counted after the engineer's specification | The supplier |
| Made-to-order stair | 4-10 weeks | Joiner's lead time, once the opening is fixed on the drawings | The joiner |
The longest of these waits sets your start date, and on a semi or terrace that can be the party wall. The notice period is a minimum. A neighbour who stays silent for 14 days is treated as dissenting, and then surveyors have to agree an Award before work to the wall can start. The government's explanatory booklet gives no time for that. It says only: "The surveyors draw up an Award, then work can start." With no official figure, any number a company gives you is its own estimate. Talk to the neighbours before the notice lands. Of all the waits in that table, theirs is the only one you can influence.
Don't serve it too early either. Under section 3, a notice lapses if work hasn't begun within 12 months.
The council periods are deadlines on paper. Both planning articles allow a longer period agreed in writing, and regulation 14A(7) says a missed building control deadline counts as neither approval nor rejection. Some loft guides quote a longer planning period than the one above. That longer limit is for major development, not a house.
External resource
Party Wall etc. Act 1996: explanatory booklet
The government's plain-English guide to party wall notices, notice periods, surveyors, Awards and appeals.
gov.uk
Who's waiting on whom
Most loft delays aren't the company being slow. They're the company waiting on a council, a neighbour, a supplier or you.
| Stage | The loft company | You |
|---|---|---|
| Design | Surveys, draws and revises | Fix the layout and where the stair lands before you sign the drawings off |
| Calculations and approvals | Commissions the engineer and makes the applications, if the quote includes them | Ask for a copy of every decision notice and the council's inspection plan |
| Party wall | May serve the notices as your agent | Speak to the neighbours first. The Act puts the duty to serve on you as building owner |
| Bat survey | May arrange it | Agree in writing what happens to the start date if the assessment finds roost potential |
| First fix | Runs the electrician and plumber | Choose the ensuite sanitaryware and fix socket, switch and light positions before cables go in |
| Second fix | Fits what you've chosen | Have doors, flooring and finishes chosen and ordered before second fix starts |
| Completion | Gives the completion notice and collects the installers' certificates | Hold the last payment until the completion certificate and electrical certificate are in your hands |
Decisions are where homeowners lose weeks without noticing. The Bristol firm lists "Waiting on decisions" and "Design changes once the roof is open" among its causes of delay, and in a 2023 Mumsnet thread several posters said they'd had to decide on the spot where windows, sockets and lights should go. No source gives a deadline in weeks for each choice. You don't need one. Decide before the stage that depends on it, and put the answer in writing.
On site, in order
The sources agree on the broad order. Homebuilding & Renovating, the Federation of Master Builders and a builder's week-by-week dormer plan all put structure first and the finishing trades last, and where they give the detail, first fix comes before plaster. They differ on the week each stage lands, so track progress by the order rather than the week numbers.
The inspection points below are where building control usually wants to see work before it's covered. Your council decides the actual list: regulation 16(3) lets it name, in writing, the stages it intends to inspect. What building control inspects on a loft explains each visit and what happens if one is missed.
Scaffold, start notice and preparation
Building control gets its start notice at least 2 days before work begins (regulation 16(1)). The scaffold goes up and the loft is cleared, mostly from outside. Clearing and preparing the loft covers what has to come out.
Steels and the new floor
The new structure goes in before the old roof is touched. The Federation of Master Builders puts it plainly: "This new structure must be put in place before any of the old trusses are cut." Inspection point: the steels, their bearings and the new joists, before the floor deck goes down (Approved Document A, requirement A1).
Roof opened and dormer or gable built
The exposed stretch. The roof comes off where the dormer or new gable goes, and the house below relies on a temporary covering until the new roof is on. Inspection point at some councils: the new roof timbers, before the felt and battens.
Watertight
Felt, battens, roof covering, windows and roof windows. After this the weather risk drops away.
First fix electrics and plumbing
Cables and pipes, including the ensuite's waste, go in before anything is boarded. Your socket and light positions and the ensuite layout are fixed from here on. If the ensuite connects to the drains, expect a drainage inspection.
Insulation
Approved Document L Volume 1 paragraph 11.6 treats the newly heated loft as a change of energy status. Inspection point: the insulation, before plasterboard covers it.
Stair opening and stair
The sources put this somewhere in the middle of the job. What they agree on is the window: after the roof is watertight, before plaster. For anyone living below, it's the dustiest stage of the lot.
Plasterboard and plaster
Some councils add a pre-plaster check, and Ealing's example inspection plan includes one. Don't let the boards go up until every earlier stage has passed.
Second fix, fire doors and alarms
Sockets, sanitaryware, doors and skirting. Approved Document B Volume 1 expects a fire detection and alarm system once a new habitable room is provided above or below the ground storey (paragraph 1.8). Where the new storey is above 4.5m, it also expects fire-resisting doors along the escape route, upgrading existing doors where necessary (paragraph 2.21b).
Decoration, snagging and completion
The completion notice goes to building control no more than 5 days after the work is finished (regulation 16(4)). Once satisfied, a council must issue the completion certificate within 8 weeks of receiving that notice (regulation 17(2)). A private approver issues a final certificate instead. Snagging is where many jobs grow their tail.
How long each type of loft takes on site
These are reported ranges, and the sources behind them disagree:
| Loft type | Reported weeks on site | What the type involves |
|---|---|---|
| Rooflight | 4-8 weeks | Roof shape unchanged; floor, steels and roof windows |
| Dormer | 5-12 weeks | A box built out from the roof slope |
| Hip-to-gable | 7-14 weeks | The sloping hipped end rebuilt as a vertical gable wall |
| Mansard | 8-14 weeks | The roof slope rebuilt almost vertical |
The short end of each range is Which?. The long end is the Bristol firm reporting its own projects, and Homebuilding & Renovating, quoting architects, puts hip-to-gable and mansard lofts higher still. Nobody has published an independent study of how long loft conversions take. None of these figures is an average, and averaging them would invent a precision that doesn't exist. Even Which? says the answer "depends on the trader you're using and the type of loft conversion".
Homeowners' own reports show the same spread. In the 2023 Mumsnet thread, reported durations ran from about 6 weeks to about four months, and one 8-week quote became "more like 12", with snagging and gaps between stages taking the blame.
Plan on the top of your type's range. Ask the company for its programme week by week, and do what the Federation of Master Builders advises: "make sure you have an agreed project deadline in writing, with an agreed contingency plan for any delays".
Where loft projects slip
Steel ordered before the specification
Steel isn't a long-lead item on a loft. The lead time in the before-site table is short. What goes wrong is the order of events.
Warning
Don't let anyone order steel until the structural engineer's specification is issued. One steel supplier calls ordering too early "the most common cause of problems in loft conversion steelwork", and adds: "No exception to this rule is worth the risk of having to return steel and reorder."
The same goes for revised calculations. If building control queries the design and the engineer changes it, any steel already cut to the old sizes is wrong.
The open roof
This is the stage that turns a slow job into a damaged house. The Federation of Master Builders warns that "winter weather can slow things down", and Homebuilding & Renovating notes that older homes "may hide issues like rotten beams, weakened joists, or dampness within the roof structure", which surface once the roof is open.
In a 2022 MoneySavingExpert thread, rain came through a poor temporary covering on a bungalow loft and damaged the ceilings below, and the argument that followed turned on an additional-works clause in the contract. Replies were clear that the roof should have been kept watertight. In a 2015 Mumsnet thread, a downpour during the outside work sent water into the first floor and the builders came out overnight to fix it.
No source says how long a loft roof is typically open. So ask before you sign: which weeks is it planned to be open, and who pays for weather damage, under which clause? If you're renovating other floors too, take the advice from that 2022 thread and work from the top down.
Bat surveys
A preliminary roost assessment can happen in any month. The follow-up emergence surveys can't, because they only run in the survey season. If the assessment finds roost potential in autumn or winter, the start can wait until the next season. Is your loft suitable covers when a survey is needed and who arranges it.
Party wall disputes
Which? warns that party wall matters "can be a lengthy and costly process if they're not happy with the plans". Serve on time, and allow for the surveyors and the Award on top of the notice period; no official source says how long that takes.
The gap between shell and finish
On a shell-only job a contractor builds the structure and you bring in the finishing trades. Building control doesn't stop at the shell: replies in a 2014 MoneySavingExpert thread pointed out that no completion certificate can be issued until the finishing work is done. If your electrician, plumber, plasterer and joiner aren't booked before the shell is finished, the loft sits empty while you find them. Book them while the roof is still going on, and agree in writing who calls building control for the pre-plaster and completion visits.
Living at home through the stages
Many people stay. In the 2015 Mumsnet thread, posters described the scaffold weeks as hardly intrusive and the knock-through for the stair as the dustiest part. Most posters in the 2023 thread found the work less disruptive than they'd expected. Plan around the stair opening and the plastering, the two stages that come inside the house. Loft company, builder or shell only covers dust protection and the short shut-offs of water and power.
Once you know the stages, tie the money to them. Contracts and payment schedules shows how to set each payment against a stage that's finished and, where it applies, inspected.
External resource
Planning Portal: lawful development certificates
How to apply for a certificate confirming a permitted development loft is lawful, what it costs and how long the council has to decide.
planningportal.co.uk
General guidance for homeowners in England (and Wales where we say so), not professional advice. Every site is different: check anything that affects your build with a qualified professional, your local council or building control. Terms
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