AI tendering for window and door installers

Price a window and door tender unit by unit from the window schedule, then add making good, disposal, access and sign-off as separate lines. Agree first whether drawing sizes or your survey sizes get manufactured, and check every unit meets the thermal and safety glazing rules. In England, replacement windows in homes need a U-value of 1.4 W/m²K or better.

What makes window and door tenders hard to price?

The schedule looks complete, but the risk is in the gaps. A refurbishment pack might list 40 window types by reference, with sizes taken from old drawings, glass specs in a separate document and building regulations sign-off left vague.

The problems that come up on most window and door packages:

• Survey versus drawing dimensions. Old buildings are rarely the size the drawings say, and a window made to the wrong size is a remake.
• Thermal performance. U-values or Window Energy Ratings that the specified product may or may not meet.
• Safety glazing. Glass in critical locations, such as low-level panes and glazing in and beside doors, must meet the impact rules.
• Lead times. Factory lead times mean the order date, not the start date, drives your programme.
• Making good. Internal reveals, plaster, sills and decoration after removal of the old frames.
• Sign-off. Who notifies building control or issues the competent person certificate.

How do you price a 48-unit window refurbishment?

Price each unit from the schedule, then add the work around the frames. Show the cost of getting sizes wrong so you can see why the survey matters.

Five wrong windows out of 42 costs £2,525 plus the delay of a second factory slot, and that's before any liquidated damages. A survey visit before ordering is cheaper, so price it and make the order depend on it.

Do the drawings or your survey set the sizes?

On new build, usually the drawings, with openings built to them. On refurbishment, almost always your survey. Get the answer in writing before you price, because it decides who pays for a remake.

What do the rules say about windows and doors?

Replacement windows and doors are controlled building work. In England, the installer either notifies building control or is registered with a competent person scheme and self-certifies.

The 2026 edition of Approved Document L keeps the 1.4 limit for windows in existing homes and adds that a replacement must be no worse than the one it replaces. For tenders that run past March 2027, check which edition applies under the transitional arrangements.

The gov.uk list of authorised schemes for replacement windows, doors, roof windows and rooflights, updated 17 September 2026, names Blue Flame Certification, CERTASS, Certsure, FENSA, NAPIT and ASSURE. For buildings other than dwellings, those schemes don't cover load-bearing structural glass, glazed curtain walling or revolving doors, so building control is needed for those.

These figures are for England. Wales, Scotland and Northern Ireland set their own energy and safety standards, so check the local building regulations for any job there. On fire doors, escape windows or buildings over 18 m, get the fire strategy from the designer before you price; that's a fire engineer's call, not yours.

What should a window tender clarify?

Sizes, lead times, making good and sign-off. Each one moves cost between you and the main contractor, and each is easy to state in one line.

Tender: project, windows and external doors
Our price: £amount excluding VAT, dated date

Survey and sizes
1. Priced from window schedule reference, revision and elevations drawing numbers. Final sizes will be taken from our site survey before manufacture.
2. Remakes caused by openings that differ from the survey or the drawings by more than x mm are a variation.

Lead times and programme
3. Manufacture lead time number weeks from signed-off survey and order. Programme dates assume order by date.
4. Price based on number visits and continuous working. Additional visits charged at £rate.

Performance
5. Windows priced to U-value 1.4 W/m²K / Window Energy Rating Band B. Doors to value.
6. Safety glazing to Approved Document K in critical locations shown on the schedule. Additional locations identified on site will be valued as a variation.

Making good
7. Included: making good internal reveals to a plastered finish ready for decoration. Excluded: decoration, external render or brick repairs, and work to existing lintels.
8. Asbestos in existing panels, sealants or sills excluded. Survey to be provided before we start.

Sign-off
9. Building regulations: compliance certificates issued through our competent person scheme, scheme name, for work it covers. Any building control fees for work outside the scheme by others.

Payment
10. Deposit of x% on order for manufactured items. Monthly applications thereafter.

The general lines on access, attendances and payment are in the tender qualifications and exclusions template. A deposit on order matters more in this trade than most, because you pay the factory weeks before you fit.

What can AI do on a window tender, and what can't it?

AI is strong on the schedule work that eats evenings. It can't stand at an opening with a tape.

What AI does well on a window and door tender:

• Builds and checks the schedule. Counts by type, size, opening and glass from the schedule and elevations, and flags units on the elevations missing from the schedule. See can AI do a take-off from drawings.
• Checks performance against the spec. A U-value, a security standard or a glass spec that the specified product's data sheet doesn't meet.
• Flags safety glazing where elevations show low-level panes or glazing beside doors with no safety glass noted.
• Finds the deadlines in the prelims: order dates, phasing, liquidated damages.
• Drafts clarifications from your standard list with this job's references.

What still needs the installer:

• The survey. Opening sizes, out-of-square frames, rotten sub-sills and lintels.
• Buildability. Whether a unit fits through the stair, whether a mullion lands on a structural member.
• Lead time risk. What your factory can promise this month.
• The price and the decision to bid.

How do you win more window tenders?

Bid where your product range and factory slots match the job, and make your submission easy to compare.

• Price the specified product, and offer alternatives separately with their U-values.
• Show the survey stage in your programme; it reassures clients who've been burned by remakes.
• State your competent person scheme and what certificates the client receives.
• Read the pack first with the 10-minute tender read and drop jobs where sign-off or sizes are unworkable.

Fit-out firms can see how Nexley supports their trade on the fit-out trade page.

Common questions