AI Software for Construction Scheduling: Programme Updates After Delays

Give ChatGPT or Claude your task list with durations and dependencies, plus the facts of the delay, and ask for re-sequencing options as changes to the logic, not new dates. Calculate the dates in your scheduling tool or a spreadsheet, check the critical path by hand, then have the assistant draft messages to each affected subcontractor.

That split exists because assistants are good at proposing alternatives and drafting notices, and unreliable at date arithmetic across weekends and overlapping delays. Take a rear extension planned at 69 working days that meets a late window delivery and two lost weather days. The assistant helps with options, wording and records, and cannot be trusted on dates or on how delays overlap; the walkthrough below marks the line.

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I'm assuming a firm of two to ten people with a programme in a spreadsheet or basic project software, one site manager (often the owner) and subcontractors for the trades you do not employ.

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The job: a rear extension, 69 working days, two things go wrong

Every figure in this example is invented. A four-person building firm is adding a single-storey kitchen-diner extension. Its programme runs 20 tasks over 69 working days, roughly 14 weeks on a five-day week. Durations are in working days, "After" lists the tasks that must finish first, and float is how many days a task can slip without moving the handover date. Where trade terms differ between regions, both are given, such as first fix (rough-in).

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The critical path, the chain of tasks with zero float, is everything except tasks 9 and 14. External works have 43 days of float, and the kitchen units have one. The firm has already used some of that float: the groundworker moved to another job after the slab, so external drainage and paving (task 9) has not started. On day 30 (Friday of week 6) two things are known. The window supplier emailed on day 24 to move delivery from day 33 to day 41, eight working days later. And rain on days 29 and 30 stopped roofing, so task 7 will finish on day 34 instead of day 32.

Write the delay down as facts before anyone opens a chatbot

Start with a record, because everything later depends on it and because a vague record is useless if the delay becomes a dispute. One entry per event, in plain facts:

Keep cause and effect separate. Whether a supplier delay or a weather day entitles you to more time or money depends on your contract, and some contracts require written notice within a short window. That is a question for your contract and a construction adviser, not for an assistant. Your job here is to capture the facts and the dates they became known.

Why delays of 8 and 2 days cost 8, not 10

A tempting error is to add the delays together. An assistant asked "the windows are 8 days late and the roof lost 2 days, what's the new finish?" may well answer day 79, which is 69 plus 10. The correct answer is day 77, because the two delays overlap.

Walk through it. With the weather days, the roof finishes on day 34, so the earliest the windows could be fitted is day 35. The supplier's new date is day 41, which is later. The windows start on day 41, and the roofer's two lost days no longer matter, because the roof now has six days of float. Run in isolation, the weather alone would cost two days (finish day 71) and the delivery alone eight (finish day 77). Together they cost eight.

Check it by adding up the chain. From day 41, the tasks that follow in sequence are windows (2), first fix (4), insulation and plasterboard (4), plastering (5), drying (5), second-fix carpentry (4), second-fix electrics and plumbing (3), decoration (5), flooring (2), snagging (2) and handover (1). That is 37 working days. Day 40 plus 37 is day 77. The critical path has moved: it now starts at the delivery date rather than at the roof.

You can do this check in about two minutes, and it catches the overlapping-delay mistake before it reaches a client. Everything below builds on it.

Let the spreadsheet do the dates and the assistant do the options

Date arithmetic belongs in software that does not guess. In Excel or Google Sheets, WORKDAY returns a date a set number of working days before or after a start date. Microsoft's description says working days exclude weekends and any dates you list as holidays, and WORKDAY.INTL handles a different weekend, for example if your crews work Saturdays. Put your holidays in a range and reference it, and the arithmetic is exact.

Use the assistant for the parts that need judgement and language: what could run earlier, what must not, and how to word the message to the electrician. That split keeps the failure modes apart. If the assistant invents a dependency, you catch it when you rebuild the programme. If it miscounts weekends, the spreadsheet never relied on it. The tutorial on AI scheduling for small builders covers the everyday version of this, and the table near the end of this one shows where each tool fits.

Asking for options: logic changes, not dates

Paste the programme as plain text and tell the assistant what you know. Notice what the prompt forbids: new dates. You want ideas about the order of work, which you then test.

You are helping a small building firm re-plan a rear extension after delays. The programme is below as CSV: id, task, working days, tasks that must finish first. Today is working day 30.
Facts: (1) the roof (task 7) now finishes on day 34, not day 32, because of two lost weather days; (2) the windows (task 8) cannot be fitted before day 41 because the supplier moved delivery. Everything else is unchanged.
Do four things.
1. Do NOT give new dates. List options for shortening the delay as changes to the logic or durations: tasks that could run earlier, in parallel, or with extra crews.
2. For each option, name the tasks affected, what must be true for it to work (temporary protection, access, a subcontractor's availability) and what could go wrong.
3. Flag any option that would break a real-world dependency, such as work being covered up before inspection, or finishes going on before the building is weathertight.
4. List your assumptions and anything you need to ask me.

id,task,days,after
1,Site set-up and protection,2,
2,Demolish old rear wall and strip out,3,1
3,Excavate and pour foundations,5,2
4,Foundation inspection,1,3
5,Blockwork to slab level and ground slab,6,4
6,Walls to eaves,8,5
7,Roof structure and covering,7,6
8,Windows and glazed doors fitted,2,7
9,External drainage and paving,6,5
10,First fix electrics and plumbing,4,8
11,Insulation and plasterboard,4,10
12,Plastering,5,11
13,Plaster drying,5,12
14,Kitchen units fitted,3,13
15,Second fix carpentry,4,13
16,Second fix electrics and plumbing,3,14;15
17,Decoration,5,16
18,Flooring,2,17
19,Snagging and clean,2,18;9
20,Handover,1,19

A typical reply, summarised below with the checks a site manager would add, is a mix of good ideas and one or two that should be thrown out. The "real effect" column comes from recalculating each option, not from the assistant.

This is where the assistant adds value. Options two and five came from a model that does not know your specification or the physics of drying, so it proposed them anyway. Option one, which a stressed site manager might not think of on day 30, is a genuine find. Section 3 of the prompt (flag broken dependencies) catches some of the bad ideas but not all, which is why the real-effect column is yours to fill in.

Checking the critical path by hand in ten minutes

You do not need project software to verify a small programme. The method has two passes.

1. Forward pass. A task's start is the latest finish among the tasks before it, plus one working day (and never before any fixed date, such as a delivery). Its finish is its start plus its days minus one. Work down the list in order.
2. Backward pass. From the final finish, work back up. A task's latest finish is the earliest latest-start among the tasks after it, minus one. Float is the latest start minus the earliest start. Zero float means critical.
3. Chain check. Add the durations along the critical chain, starting from the first fixed date. Day before the fixed date plus the chain total must equal the finish.

Apply this to the two options worth pricing. With first fix moved ahead of the windows (option one), the chain from day 41 is windows 2, plasterboard 4, plastering 5, drying 5, carpentry 4, second fix 3, decoration 5, flooring 2, snagging 2 and handover 1: 33 days, so 40 plus 33 gives day 73, four days late. Add the second plasterer and plastering drops from 5 days to 3, so the chain is 31 days and the finish is day 71, two days late. Float shifts as well: first fix now has four days of float, because it can slide anywhere before plasterboard starts on day 43.

These are the new dates for the work that changes, with the old ones beside them (week and weekday on a five-day week):

Notice the coincidence: first fix keeps its original dates, because the two weather days lost on the roof happen to equal the two days of window fitting that first fix no longer waits for. A site manager could easily miss that without a calculation, and an assistant that "shifts everything by eight days" would get it wrong.

Pricing the options before choosing one

Days saved is not the same as money saved. Give each option a cost and compare it with what each day of lateness costs you. These figures are invented, so replace them with your own.

The $400 a day stands for the costs of running the job while it overruns: hire, supervision, temporary facilities and any penalty or loss the client has told you about. If you cannot put a figure on it, you cannot rank the options. Ask each subcontractor for their price, not the assistant. The second plasterer is a marginal call at these numbers: it makes $160 only if the extra plasterer is actually available.

Who to tell, what to say, and when

Tell people the day you know, even if the answer is still uncertain. A sub who hears on day 30 has weeks to rearrange; one who hears on day 40 has days. Use the revised table above and write one message per person, with only the dates that concern them.

Draft a short, polite message to the plasterer about a programme change. Facts: plastering was due Wk 9 Wed to Wk 10 Tue with one plasterer. It is now due Wk 10 Tue to Thu, and I need two plasterers for those three days. The reason is a late window delivery, not anything on their side. Ask them to confirm by Friday 5pm whether they can supply a second plasterer for those days, and to say the earliest alternative if not. Use [first name] and [your name]. Do not promise payment terms or blame anyone.

Before and after, so you can see what the draft is replacing. Before: "Hi, a few delays so things will slip a bit, I'll let you know." After: "Hi [first name], the windows are now due Monday of week 9, not Wednesday of week 7. Plastering was week 9 Wed to week 10 Tue with one plasterer. It is now week 10 Tue to Thu, and I need two plasterers for those three days. Can you confirm by Friday 5pm? If you can't supply a second plasterer, tell me your earliest alternative start. [your name]". The second version gives the old date, the new date, what changes and a deadline for the reply.

Have the assistant draft each one, then read the dates against your recalculated programme before sending. For customer-facing wording on delays, five customer messages to draft and check gives more templates, and the tutorial on chasing subcontractors and progress updates covers follow-up when a reply does not come.

Where AI gets a construction programme wrong

• Adding overlapping delays. The 79-versus-77 error above. Prevent it by always asking which tasks are on the critical path after the change, then verifying with the chain check.
• Weekend and holiday arithmetic. Calendar days and working days get mixed. Keep dates out of the prompt and use WORKDAY afterwards.
• Dropping real-world dependencies. Inspections before cover-up, curing and drying times, deliveries, access and a sub's other commitments are not in your CSV unless you put them there. A typical bad suggestion is to run the foundation inspection alongside the blockwork to save a day. That breaks the order, because the inspection exists to look at work before it is covered.
• Invented durations and lead times. If you ask it to estimate how long a task takes, treat the answer as a guess and replace it with your own jobs' history or the sub's quote.
• Overconfidence. A tidy table of new dates looks authoritative. It is only as sound as the logic in your CSV, and the assistant cannot see a dependency you forgot.

The early-warning habit helps here. If you review weekly which tasks have zero float and what deliveries are due in the next three weeks, the delay learned on day 24 could have been a conversation with the supplier on day 18. The tutorial on weekly early-warning flags builds that routine.

Records that protect you when a delay becomes a dispute

Keep four things for every delay: the delay record above, the evidence (emails, photos with time stamps, diary pages), the recalculated programme before and after, and every notice you sent with its date. Use the assistant to tidy the log into a consistent format if you like, with the instruction not to add anything you did not provide.

It cannot tell you who is liable or whether you must give formal notice. Contracts differ on notice periods, excusable delay and what counts as a cause, and the safe move is to read the clause the day a delay appears, and to ask your lawyer or contract adviser if it is unclear. Do not rely on an assistant's reading of your contract for a decision that costs money.

Where this fits in the software you already use

For a one-crew extension, the first three rows are enough. The home-builder angle, with selections and sub chasing, is in the tutorial on build schedules, delays and sub chasing for home builders.

A ten-minute routine for the next delay

1. Write the delay record: date known, cause, tasks affected, evidence.
2. Update the programme by hand or in your tool. Rebuild the dates with WORKDAY.
3. Ask which tasks are now critical, and verify with the chain check.
4. Ask the assistant for options as logic changes, with dependency warnings, and recalculate every option you like.
5. Price the options against your daily cost of lateness.
6. Draft one message per affected person, check every date, send them yourself, and save copies with the record.

If your weather days are frequent, for roofing and groundworks especially, the roofing weather-delay checklist has a reschedule routine and message wording you can adapt.

Questions about AI and construction schedules

Can ChatGPT or Claude calculate a new finish date reliably?

Not on its own. Assistants slip on weekends, holidays and overlapping delays, and may add two delays that actually overlap. Use them for options and wording, calculate dates with a scheduling tool or Excel's WORKDAY function, and confirm the finish by adding up the durations along the critical path.

How do I handle weather days and a late delivery together?

Treat each as its own event with its own record, then test whether they overlap on the critical path. If the delivery date is later than the earliest date the weather-hit task allows, the delivery governs and the weather days cost nothing extra. How your contract treats each cause is a separate question for the contract.

Should an assistant send messages to subcontractors for me?

No. Let it draft, then check the dates against your recalculated programme and send the message yourself. Wrong dates sent in your name cost more than the minutes saved, and subs reply to a person, not to a draft. Keep every message with the delay record.

Is an enterprise AI scheduler worth it for a small contractor?

Usually not for small jobs. ALICE, for example, describes itself as generative construction scheduling for owners, contractors and consultants on capital projects, says on its pricing page that it is used on projects worth at least $75M, and sells by custom quote with no published price. A spreadsheet with dependencies, plus an assistant for options, covers a one-crew job.

What if the assistant's dates disagree with my software?

Your software wins, provided its dependencies are right. Find where the two diverge: usually a missing dependency, a calendar that includes weekends, or an overlap the assistant added up. Fix the cause, then recalculate. Never paste an assistant's dates straight into a programme you send to a client.

Further reads

• AI Tool for Construction Planning: Pre-Start Checklist and Long-Lead Items — Order long-lead items early so the delay never starts
• How Small Builders Use AI to Price Variations and Change Orders — Pricing the variation when a delay changes the work
• AI Tools for Construction Project Management: RFIs, Logs, Reports — One eight-week fit-out followed through its daily logs, RFIs and weekly client reports: which tools do each job, what they cost and what you must still check.
• AI for Electrical Project Management: Diaries, RFIs, Snag Lists — Voice note to site diary, an RFI log that gets chased, and snag lists others can close: a working setup for a small electrical contractor, with prompts.
• Best AI for Building Companies: Quotes, Programmes and Site Admin — Tool types for a small building company, sorted by quotes, programmes and site paperwork, with one rear extension priced, programmed and documented.
• AI Tools and AI Development: The Complete 2026 Guide — the AI hub, including every tutorial in the AI-for-business series.

Sources: Microsoft Support (WORKDAY function), ALICE Technologies website (product description and pricing page), OpenAI and Anthropic pricing pages. Programme figures are illustrative and were calculated with a forward and backward pass.