Tendering and estimating, 2 November 2026
AI tendering for roofing and cladding contractors
AI tendering for roofing and cladding contractors means software reads the tender pack, measures the roof and wall areas and lists what the spec demands. It flags fixings, details, access and any design duty you'd be taking on. Most money is lost in what a single m² rate leaves out. You still price the details, the wind and weather risk, and any design you take on.
What happens between the pack arriving and the price going out?
Most of the work is reading, and less of it is measuring than people expect. Here is one package followed through: a terrace of six new houses, concrete interlocking tiles at 35°, priced for a main contractor.
- The pack lands.
An enquiry letter, a roof plan, two sections, a 14-page specification, the preliminaries and a bill with one roofing item: "Interlocking concrete tiles on battens and underlay, 35° pitch: 475 m²". Return date in ten working days.
- Read the spec before the drawings.
The tile clause names the tile and colour, a breathable underlay, and "fixings to manufacturer's wind uplift calculation". The preliminaries say "scaffold by main contractor". Two questions already: who runs the fixing calculation, and is the scaffold built for roofing.
- Measure the roof, not the plan.
The roof plan shows 54 m by 7.2 m. That is plan area. Tiles go on the slope, so the area has to be converted (see the next section).
- Count the details.
Eaves both sides, a ridge the full length, a verge at each end, two soil vent pipe slates, and a lead flashing where the end house steps down. Each is priced per metre or per item.
- Send the questions.
One email to the main contractor's estimator: fixing calculation, scaffold spec and loading bay, who supplies the vent terminals, programme dates.
- Price it.
Field area from your gang's real output and the tile coverage, details as separate lines, then overheads and margin. If you haven't worked out your overheads per man-day, do that first.
- Qualify and send.
State what the price includes, what it assumes and what is excluded. A list of tender qualifications and exclusions saves rewriting them each time.
AI does steps 2 to 4 in minutes: it reads every page, pulls the clauses that matter to a roofer, and measures from the PDF. Step 5 and the rates in step 6 are yours. To see how far you can trust the measuring, test AI on a tender you have already priced.
Why doesn't the bill's m² figure match the roof?
The bill gives one area, and the roof needs a lot more than an area. Laps, cut tiles at verges and hips, breakages, and every metre of eaves, ridge and abutment sit outside a plain m² figure. A roofer who prices the field area well and then forgets the details loses money on every job.
Six-house terrace: from plan area to what you price
Duo-pitch roof, 54 m long, 7.2 m plan depth, 35° pitch.
| Plan area54 m × 7.2 m | 388.8 m² |
| Slope factor at 35°1 ÷ cos 35° | 1.221 |
| Slope area388.8 × 1.221 | 474.7 m² |
| Tiles at an illustrative 9.8 per m²474.7 × 9.8 | 4,652 |
| Allowance for verge cuts and breakages, 5%4,652 × 1.05 | 4,885 tiles |
| Eaves2 × 54 m | 108 m |
| Ridge54 m | 54 m |
| Verges2 ends × 2 slopes × 4.39 m rafter | 17.6 m |
| Shortfall if you had priced plan area474.7 − 388.8 | 85.9 m² |
Here the bill area matches the slope area. Plenty don't. Bills are sometimes measured on plan, sometimes to the wrong pitch, sometimes with the details folded in. Measure it yourself, or have AI measure it and check one slope by hand. Our guide to pricing a roofing job covers the rates side.
I didn't even understand how to price in overheads.
He had been pricing commercial roofing at around £60 a square metre when the work was going for nearer £36.50. A rate that far out usually means the build-up is missing: no true output per day, no overhead per man-day, and details priced by feel. Once the rate is built from those parts, you can see which line is out.
Who works out the fixings, and who provides the scaffold?
Usually someone else, and the tender should say who. If the spec says fixings are to a manufacturer's or engineer's wind uplift calculation and nobody has run it, you are pricing an unknown number of clips, nails or fasteners. Ask for the calculation, or price a stated fixing pattern and qualify that changes are a variation. Our guide to wind uplift and fixings explains what the calculation changes.
Scaffold is the other open question. "Scaffold by main contractor" doesn't tell you whether it has a working platform at the eaves, a loading bay for pallets of tiles, or how long it stays up.
If any part of the roof is fragile, such as fibre-cement sheets or rooflights, HSE expects you to plan the work to keep people off it or to use stagings, guard rails and nets slung close beneath the roof. That kit costs money and time. Price it, or name who provides it.
How much weather and programme risk should a roofing price carry?
Enough to cover the days you lose, and no more than the contract makes you carry. Read the programme and the contract terms together. A main contractor programme that gives the terrace 15 working days for roofing assumes dry weather and a scaffold handed over on time.
Three things to check. First, whether the subcontract passes down damages for delay, and at what rate per day. Second, whether you must keep the building watertight overnight with temporary sheeting, which is labour every evening. Third, what happens when the scaffold is late: an idle gang standing by costs you the same as a working one. A line in your qualifications ("programme assumes continuous working once the scaffold is handed over complete") moves that risk back to the party who controls it.
Who carries design and fire risk on cladding and curtain walling?
On many facade packages, you do. Cladding and curtain walling are often let as a performance specification: the architect sets the look and the targets, and the specialist designs the system, the brackets, the fixings and the movement joints to meet them. That is design responsibility, with design liability attached, and it should be priced and insured as such.
Fire rules come next. In England, regulation 7(2) of the Building Regulations means only materials classed A1 or A2-s1, d0 can become part of the external wall of a relevant building, broadly one with a storey 18 metres or more above ground that includes flats, an institution or residential rooms. GOV.UK's guidance says window frames and conventional curtain wall mullions, transoms and glazing are exempt, as are membranes, seals, gaskets, fixings and sealants. Spandrel panels and other opaque insulated curtain wall panels are not exempt, and internal plasterboard and sheathing boards count as part of the external wall.
If the building is a higher-risk building, the Building Safety Regulator is the building control authority, and work must not start until the application is approved. Changes to the approved documents go through change control, and a major change stops work on that part until the regulator approves it. A product substitution you would make without a second thought on a low-rise job can become a programme delay here.
Expect the combustibles ban on the external wall and, for buildings with two or more homes, regulator approval before work and change control on substitutions. Price evidence, product data and approval time, and qualify that substitutions need approval.
A tall building without residential use may sit outside the ban, but Approved Document B still applies. Ask for the fire strategy before you price.
The ban and the higher-risk regime don't apply on height, but Approved Document B guidance on external walls does. Confirm the fire strategy and the product classifications.
Scotland, Wales and Northern Ireland set their own building rules for external walls. Ask the designer which standard applies and price to it.
Two bids for the same roof, compared line by line
The cheapest headline rate often hides the most. Here are two bids for the same 320 m² warm flat roof, single-ply membrane, mechanically fastened, on a single-storey extension.
| Line | Bid A | Bid B | What the difference means |
|---|---|---|---|
| Field area, 320 m² | £18,560 | £16,640 | A prices £58 a m², B £52 |
| Perimeter upstands and trims, 74 m | included | £1,776 | A says it's in the rate; nobody can check |
| Rainwater outlets, 3 | included | £480 | Same |
| Rooflight upstands, 2 | excluded | £620 | A leaves a gap the main contractor must fill |
| Extra fixings at corners and edges, 96 m² | to be confirmed | £336 | A will claim this later once the calculation is run |
| Edge protection | by others | by main contractor's scaffold, as tender docs | Both qualify it; B ties it to the pack |
| Total as tendered | £18,560 | £19,852 | A looks £1,292 cheaper |
| Gaps priced at B's rates | £956 | £0 | Rooflight upstands £620 plus fixings £336 |
| Like-for-like total | £19,516 | £19,852 | The real gap is £336 |
Rates are illustrative. A main contractor who reads only the totals picks A and later meets £956 of extras. One who reads the lines sees that B has priced the roof and A has priced a rate. If you are Bid B, a short covering note that points to the excluded items in the other bids ("our price includes rooflight upstands and the fixing allowance") does more than cutting your margin.
AI is good at this comparison, because it is reading and matching. Put both bids or your price against the bill, and it will flag every line that is "included", "excluded" or "TBC".
Where does each roofing and cladding trade go wrong?
Each trade loses money in a different place. These are the ones we see most.
AI tendering for pitched roofers
Pitched roofers most often price plan area or a bill area without checking the pitch, then add details by feel. AI helps by measuring each slope, counting eaves, verges, ridges, hips and valleys, and flagging a fixing spec that depends on a calculation. It can't see the existing roof timbers or decide how long your gang takes on a cut-up roof.
AI tendering for flat roofers
Flat roofers tend to lose money on upstands, outlets, rooflights and edge details hidden inside one m² rate, and on fixing density in the wind zones. AI reads the system clause and measures perimeter and penetrations as separate lines. It can't judge the deck you'll find when the old covering comes off, so qualify the deck condition.
AI tendering for cladding contractors
Cladding contractors most often miss that a performance specification makes them the designer, and that substitutions on tall residential buildings need evidence and approval. AI pulls the design duties, the product classifications asked for and the building height from the pack. The design, the fire classification evidence and the sign-off stay with you and the designer.
AI tendering for curtain walling contractors
Curtain walling firms get caught by spandrel and insulated panels, which aren't exempt from the combustibles ban like mullions, transoms and glazing are. AI can schedule every panel type from the elevations and check each against the spec. It can't confirm a product's test evidence or the structural design of brackets. See also AI tendering for fire protection and fire-critical work and the full guide to AI tendering by trade.
Where Nexley fits
Nexley is the AI back office for UK trade firms: five AI assistants run your tenders, quotes, buying, scheduling and invoicing. It connects to the tools you already work in, you run it all from WhatsApp, and you approve everything.
For roofing and cladding tenders, Nexley reads the whole pack, measures slopes and details from the drawings, builds your price from your own m² rates and day costs, and drafts the questions and qualifications. You get the draft on WhatsApp and approve or change it before anything goes to the main contractor. More on how it works for roofing firms.
Common questions
What is AI tendering for roofing and cladding contractors?
It's using AI to read a roofing or facade tender pack, measure the areas and details from the drawings, pull out the spec clauses that affect price, and draft a priced return with qualifications. The roofer still sets the rates, checks the measure and decides the risk.
Can AI price a roofing tender on its own?
No. It can measure and apply rates you give it, but it doesn't know your gang's output, the state of the deck, or how a site's access and weather will affect the programme. Treat its price as a draft you check line by line.
Does the combustibles ban apply to roofs?
The ban in regulation 7(2) covers external walls and specified attachments of relevant buildings in England. Roof coverings follow other parts of Approved Document B. If a roof and a facade meet, as with a mansard or a parapet, ask the designer how they have treated it.
How should I price scaffold that the main contractor provides?
Price your own access needs on top: loading out, any extra lift or bay, edge protection on flat roofs if it isn't in the scaffold, and standing time if it's late. Then qualify the scaffold spec and handover date you have assumed.
Sources
- HSE: Roof work
- HSE: Fragile surfaces
- GOV.UK: Building (Amendment) Regulations 2018, frequently asked questions
- GOV.UK: Building control approval for higher-risk buildings
- GOV.UK: Approved Document B, frequently asked questions
Every rule, rate and date above was checked against these sources on the date shown at the top.
Topic: Tendering and estimating
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