Why two loft conversion quotes for the same job can be £35,000+ apart
The difference almost never comes from one builder being more expensive than another for the same work. It comes from one quote including things the other has quietly left out. Paul, Fluent’s construction consultant, reviews competing quotes with clients regularly, and the same handful of missing items come up again and again — tin hat scaffolding, fire doors, and the bathroom suite and finishes.
To show this isn’t theoretical, we pulled three real quotes submitted for the same hip-to-gable loft conversion in Windsor. The totals ranged from £75,782 to £112,663, excluding VAT — a gap of nearly £37,000 for the same job. Here’s the checklist, built partly from Paul’s own experience and partly from what these three real quotes actually did and didn’t include.
1. Is the tin hat scaffolding included, or shown as an optional extra?
A “tin hat” is a full scaffold roof over the whole structure, protecting the work from weather and letting your builder strip the roof safely in any conditions. Paul sees this constantly: a builder leaves the tin hat out of the base price, then presents it as an optional extra once you’re comparing numbers. In one of our three real quotes, the scaffolding line stated outright that the tin hat “is not included at this stage” and would “need to be discussed and confirmed separately” — a direct, real example of exactly this trick. Another of the three quotes included a full temporary roof scaffold as standard. Same job, two different starting positions.
2. Are fire doors shown as included, or as an optional extra?
Fire-rated doors are mandatory to pass Building Control on any habitable loft space, not optional. One of our three real quotes replaced every affected door with a proper FD30 fire door as standard. Another quote had a line item labelled “FD30 Door” — but the actual product specified underneath was a standard hollow door, not a fire-rated one. That’s the kind of mismatch between a line item’s name and its actual specification that’s easy to miss unless you read past the heading.
3. Does the quote state the exact number of windows or rooflights?
A proper quote states the exact number, size, and type of window or Velux rooflight included, priced as a firm cost. Of our three real quotes, one specified three named Velux windows with a firm supply-and-install price. Another also said “three” — but the actual cost of those windows was folded into a £4,000 provisional sum for “external glazing,” so the quantity was clear but the price wasn’t fixed. The third didn’t state a window count at all, just a vague provisional sum for “rear dormer, patio door” that varies depending on specification. Three real quotes, three different levels of clarity on the same three windows.
4. Is decoration priced for a plain mist coat, or your actual colour scheme?
Some quotes only price a mist coat, which is a plain white base coat, not a finished decorated room. Two of our three real quotes stated this explicitly in their own wording: one specified walls and ceilings painted “with mist coat only.” The other, more expensive quote specified “one mist coat and two full coats emulsion in white paint” — a full finish, not just prep. Worth noting: even the full-finish quote only commits to white. If you want colour, ask directly.
5. Does the quote actually include the bathroom suite, tiles, and floor finishes?
This is the one Paul flags as the biggest single gap he sees — and all three of our real quotes confirmed it. Every single one of them excluded the sanitaryware (toilet, basin, shower tray, taps), the wall and floor tiles, and the grout and adhesive, listing them as client-supplied. This held true even in the most expensive of the three quotes. Don’t assume a higher price means the suite is included — check every quote for this, because based on what we’ve seen, the default assumption should be that it isn’t.
6. Is the existing soil vent pipe (SVP) being replaced, or just connected into?
Paul flags this one from direct site experience: if the existing soil vent pipe is cast iron, quotes routinely assume it stays as-is and simply gets connected into, rather than replaced with new uPVC. Cast iron SVPs that are original to an older property are often past their working life, and replacing one mid-project is far cheaper than doing it as an afterthought once the new bathroom is plumbed in. None of our three real quotes mentioned the existing SVP at all — not to confirm reuse, and not to flag replacement. That silence is exactly the risk: ask your builder directly what condition the existing stack is in and whether it’s being replaced.
7. Are the existing roof tiles assumed to be reused, rather than replaced?
A related point from Paul: quotes will often assume the existing roof tiles get taken off, kept aside, and put back on rather than replaced — even when those tiles are years past a reasonable lifespan and prone to cracking during removal. In the three real quotes we reviewed, this wasn’t actually an issue: all three specified new matching tiles for every section of roof being altered. But it’s still worth checking on your own quote, because it’s an easy assumption for a builder to make silently, and reused old tiles that crack during the strip become an extra cost you didn’t budget for.
8. Are provisional sums clearly flagged as provisional?
A provisional sum is an estimate for something that can’t be priced exactly until work starts — most commonly, unknown ground or structural conditions once a wall or floor is opened up. All three of our real quotes actually did this part well: provisional and PC sums were clearly labelled as such throughout, on items like steelwork, floor beams, and glazing. That’s a good sign to look for. What’s not normal is a quote where provisional sums aren’t labelled at all, so they read like fixed prices until the final bill arrives and they’ve moved.
9. Does the quote separate structural work from decoration?
Steelwork, structural openings, and load-bearing changes should be priced separately from decoration and finishes. Two of our three real quotes broke structure and finishes into clearly separate sections with detailed sub-items. The third bundled scaffolding into a single £8,355 lump sum with no breakdown of what it actually included — which meant there was no way to tell from the quote alone whether a full tin hat was priced in or not.
10. Is Building Control or a private building inspector’s fee included?
Building Control sign-off is mandatory for a loft conversion, whether you use your local authority or a private building inspector. Tellingly, none of the three real quotes we reviewed included a Building Control fee anywhere in their cost breakdown. That doesn’t mean it’s forgotten — it likely means all three assume you’ll arrange and pay for it separately. Just make sure that’s actually the arrangement, and it isn’t assumed to be included by one side and excluded by the other.
11. Does the quote match what your architect actually designed?
Compare the quote line by line against your approved drawings, not just the room list. A builder quoting from a verbal description of “a loft conversion with two bedrooms and a shower room” will price differently — and often lower — than one quoting from your actual structural drawings, because they haven’t accounted for the specific steelwork, window positions, or roof type your design needs.
12. Is there a fixed price for scaffolding hire duration?
Scaffolding is usually priced for a set number of weeks. If your build overruns, some contracts charge extra hire per week, and that cost isn’t always disclosed upfront. Ask what happens to the scaffolding cost if the programme slips.
