Bidfident for extension builders
Estimating software for extensions
An extension is a small house joined to an old one. With Bidfident you price footings and foundations by the cubic metre, timber frame, roof and cladding by the square metre, and windows by number, with a lorry-mounted crane charged only for the hours it spends lifting trusses. Groundworks and plumbing quotes sit side by side, and building control fees and weekly supervision are carried as prelims.
Enter your email and Bidfident sends you a sign-in link. New companies start with a starter rate library. Who runs Bidfident, and what it keeps about you.
Sound familiar?
Supervision priced for the first programme
The extension was meant to take 14 weeks, then the foundations slip and it takes 16. In a spreadsheet the weekly costs stay at 14. In Bidfident weekly and monthly prelims follow the job duration.
The crane charged for the gang's hours
The lorry-mounted crane is on site for a morning, but the spreadsheet charges it for every hour the carpenters work. In Bidfident a line's plant can have its own hours per unit, so it's charged for the hours it runs.
Groundworks and mechanical quotes on scraps of paper
One groundworker rang, another emailed, and the plumbing and heating quote is in a text. In Bidfident each package's quotes sit side by side, the lowest is flagged, and you carry the one you pick.
How Bidfident fits your work
A crane for the hours it runs
Give the truss line its lorry-mounted crane with its own hours per unit, and the crane is charged for those hours. Leave it blank and it runs for the gang's hours.
Prelims that follow the programme
Supervision by the week, building control fees as a lump sum, hire by the month. Change the job duration and every linked weekly or monthly item follows it.
Foundations to roof, in division order
Group the sheet by division: concrete, timber frame, roofing and cladding, then windows and doors, each with its subtotal. Name your own divisions where the standard ones don't fit.
Groundworks and mechanical quotes side by side
Enter each quote for the dig and backfill, and for plumbing and heating. The lowest is flagged and carried unless you pick another.
The decking as an option
Price the covered decking as a line, then switch it off. It stays on the estimate, struck through, with what it comes to shown beside the totals.
Cubic metres beside square metres
Concrete in m³, timber frame and cladding in m², windows by number, each line in its own unit with a material price and waste percentage. Totals add up as you go.
Worked example: a two-storey rear extension, built to weathertight
A made-up job, priced in Bidfident: 26 lines of your own work, 4 subcontract packages and 5 preliminaries items over a 14-week programme. The 6 lines this page talks about are listed one by one, and the rest are added up in one row. It's the same job you can open as an example project in Bidfident, so every figure below matches it.
To open this job in Bidfident: sign in and set up your company in the UK, then on the Projects screen, under Example project, pick "Refurbishment and housebuilders" and "Extensions" and press Add example project.
| Item | Amount |
|---|---|
Strip foundations, concrete poured, 38 m3
| £8,711.50 |
Timber frame walls, 140 x 38 studs at 400 mm centres, 153 m2
| £9,648.18 |
Trussed rafters, lifted in and sheathed, 67 m2
| £4,463.88 |
uPVC windows, double glazed, 9 nr
| £6,660.00 |
uPVC weatherboard cladding with breather membrane, 130 m2
| £5,967.00 |
Option 1: covered timber decking, 3.6 x 4.8 m, 18 m2
| £5,265.00 |
21 more lines of your own work
| £21,217.88 |
| Item | Amount |
|---|---|
Groundworks, dig and backfill
| £4,800.00 |
Plumbing and heating
| £9,100.00 |
Electrical installation
| £5,400.00 |
Roof tiling and leadwork, allowance
| £6,200.00 |
| Item | Amount |
|---|---|
Site supervision, lead carpenter
| £6,300.00 |
Welfare unit and Heras fencing hire
| £743.08 |
Building control fees
| £1,250.00 |
Structural engineer's calculations and setting out
| £900.00 |
Skips, exchanged
| £1,650.00 |
| Item | Amount |
|---|---|
Own work
| £56,668.44 |
| Excluded lines, not counted | £5,265.00 |
| Subcontractors | £25,500.00 |
Preliminaries
| £10,843.08 |
Direct cost
| £93,011.52 |
Contingency
| £6,510.81 |
Overheads and profit
| £14,928.35 |
| Subtotal before the bond | £114,450.68 |
Bond
| £0.00 |
Insurance
| £572.25 |
Tender total
| £115,022.93 |
VAT, for reference
| £23,004.59 |
See it in Bidfident
Coming soon Ask your estimate anything. Claude first, ChatGPT to follow. See how it will work
Questions
Can I price concrete in cubic metres and the frame in square metres on one estimate?
Yes. Each line has its own unit, as free text. Bidfident doesn't convert between units, so price each line in the unit its rate is in.
Can the crane be charged for fewer hours than the gang?
Yes. Give the line's plant its own hours per unit. Leave it blank and it runs for the gang's hours.
Do prelims update if the programme runs longer?
Yes. Link a weekly or monthly prelims item to the job duration and it follows it. Part weeks work too, such as 14.5.
Can I carry building control fees as one amount?
Yes. Add them as a lump sum on the Overhead tab, and they're carried as they are.
Can I price decking the client hasn't decided on?
Yes. Price it, then switch the line off. It stays on the sheet, struck through, and isn't in the tender total until you switch it back on.
Does it read the wall and roof areas from my extension drawings?
No. Measure the timber frame, roof and cladding areas yourself and type them in, or copy and paste them into the sheet from a spreadsheet, such as your bill of quantities.
Does Bidfident work with Claude or ChatGPT?
Not yet, but it's coming. You'll be able to connect Bidfident to your own Claude or ChatGPT account and ask about your estimates in plain English. The answers will come from Bidfident's own figures, so they match the estimate. It will use the account you already have: Claude first, ChatGPT to follow.
Price your next extension in Bidfident
Enter your email and Bidfident sends you a sign-in link. New companies start with a starter rate library. Who runs Bidfident, and what it keeps about you.