Construction schedule: creating a realistic Gantt chart

You know the main phases of a build, now you need to put them on a calendar. The Gantt chart is the ideal tool: it shows each task on a timeline, with its dependencies and durations. In self-build, a solid Gantt chart stops you ordering plasterboard before you have run the cables, or laying tiles before the screed has cured. Here is how to create one, which tools to use, and the pitfalls to avoid.

What is a Gantt chart?

A Gantt chart is a two-axis diagram:

• Vertical axis: the list of tasks to complete, grouped by phase.
• Horizontal axis: time (in weeks or months).
• Bars: each task is a bar whose length represents its duration.
• Arrows: dependencies between tasks (task B cannot start until task A is finished).

Tools for creating your Gantt chart

For a self-builder, Google Sheets is the best choice: free, accessible from anywhere (including the site on your phone), and shareable with your family or tradespeople.

Building your Gantt chart in 5 steps

Step 1: List all tasks

Take the 8 build phases and break each one down into concrete tasks:

Step 2: Estimate durations

For each task, estimate the duration in days or weeks. Here are reference figures for a 120 m² house:

Step 3: Identify dependencies

Some tasks cannot start until another is complete:

Step 4: Allow for curing times

This is the number one trap in a construction Gantt chart. Curing times are not compressible:

Step 5: Add contingency

A schedule without contingency is an unrealistic schedule. Allow for:

• 2 weeks of weather contingency between outdoor phases (foundations, structural works, roof).
• 1 week buffer between each major second fix phase.
• 1 month of global contingency at the end of the schedule.

Example Gantt: 120 m² house, partial self-build

Structural works and roof by professionals, second fix self-built full time:

Total duration: approximately 11 months (May 2026 to March 2027). With contingency, allow 13–14 months.

Classic scheduling mistakes

1. The “best case” schedule

Everyone plans in the best-case scenario: no rain, no supplier delays, no fatigue. In reality, you will lose at least 15–20% of time to unforeseen events. Plan for the average scenario, not the ideal one.

2. Forgetting lead times

Made-to-measure windows and doors take 6 to 8 weeks to manufacture. Ready-mix concrete needs 48 hours’ notice. Special materials (slate, bespoke timber) can take 4–6 weeks. Note lead times in your Gantt as separate tasks.

3. A rigid schedule

A schedule is not a document you create once and forget. Update it every week:

• Task complete → mark green
• Task delayed → push subsequent tasks
• Unexpected new task → add it in

4. Not sharing the schedule

If you are working with tradespeople (in partial self-build), share your Gantt with them. They need to know when you need them — and you need to know when they are available. A shared Google Sheet does the job.

The schedule and the budget: the connections

Your schedule and your budget are linked:

• Bridging loan interest: every extra month on site means more interest on the loan already drawn down.
• Renting in parallel: if you are renting while building, every month of delay is another month’s rent.
• Material price rises: a project that drags on is exposed to price increases. Buy materials as early as possible when prices are favourable.

Key takeaways

The Gantt chart is your co-pilot throughout the entire build. Create it before you start, update it every week, and use it to plan ahead for orders, tradespeople and curing times. A good schedule does not make the build faster — it makes delays visible and manageable.