How do I put together a simple construction programme?
List the jobs in the order they happen, put a duration on each, link each job to the one it waits for, and find the longest chain, because that chain sets your finish date. Allow for lead times, holidays and weather, then update it every week and give a copy to every trade.
Break the job into activities
Start with a list of activities, in the order you would build them. For a small job, 15 to 25 is plenty. Each one should be a piece of work that one gang can do and that you can see finished, such as "foundations" or "first fix electrics", not "building work".
Add the things that are not trade work but still hold the job up: ordering materials, inspections, deliveries of long-lead items and client decisions.
Durations and dependencies
Put a duration on each activity, in days or weeks. Ask the trade who will do it, and use your own experience from similar jobs. Do not make it tight on the first draft.
Then link the activities. The simplest link is finish-to-start: the next job cannot start until the one before it has finished, such as brickwork cannot start until the foundation concrete is in. Some jobs can overlap, or run in parallel, such as first fix electrics and first fix plumbing. For a small job, finish-to-start with a few overlaps is enough.
The critical path in plain words
The critical path is the longest chain of linked jobs from start to finish. Every job on it has no spare time. If one of them slips a day, the finish date moves a day. Jobs not on that chain have some slack, and can slip a little without moving the finish.
This tells you where to put your effort. Keep chasing the jobs on the critical path, and do not let the slack jobs surprise you by eating their spare time.
Lead times, holidays and weather
Long-lead items are the ones that catch people out: windows, bifold doors, steelwork, special bricks, kitchens. Ask the supplier for the lead time in writing, and work back from the date you need the item on site. Put the order date on the programme as an activity of its own.
Allow for days when nothing happens. Check bank holidays for your area, any Christmas or summer closure your client or your trades work to, and any restricted access. For weather, allow some float on the outside work, such as groundworks, brickwork and roofing, rather than assuming dry weather throughout. It is usually better to put it into the early outside activities and the roof than to add a lump at the end.
A worked example: single-storey rear extension
This is a made-up programme for a small rear extension. The durations are illustrative, so use your own.
- Before week 1: order windows and bifold doors (lead time assumed to be six weeks, so confirm yours).
- Week 1: set up, protect the house, strip out and excavate.
- Week 2: foundation inspection, then pour.
- Week 3: brickwork to damp-proof course, and drainage.
- Week 4: floor, insulation and slab or screed.
- Weeks 5 to 6: walls to eaves, steel and lintels.
- Weeks 7 to 8: roof structure and covering.
- Week 9: windows and doors fitted, so the building is weathertight.
- Weeks 9 to 10: first fix electrics and plumbing.
- Weeks 10 to 11: insulation, plasterboard and plaster.
- Week 12: drying time. Check with the plasterer and the floor and paint suppliers.
- Weeks 12 to 14: second fix, kitchen and decoration.
- Week 15: final inspections, snagging and handover.
The critical path runs through foundations, walls, roof, windows, plaster, drying, second fix and handover. The windows are not on it as long as they are ordered early. Order them late and they become the critical path.
Update it weekly and share it
A programme that is not updated is only a wish list. Once a week, mark what is done, move the dates on anything late, and check whether the critical path has changed. Keep each version with its date, so you can show what changed and why, and put the reason in your site diary.
Share it. Give every trade a copy at the start, ask them to check their durations and tell you what they need before they start, and send the new version each week. A trade who can see where they fit can plan their own labour and deliveries, and is less likely to be told about a start date on the day.