We thought we were being clever. Feed the project details into an AI tool, get a clean schedule out the other end, hand it to the contractor. It worked beautifully, right up until it didn't.
The renovation was a mid-terraced house, nothing exotic. New kitchen, bathroom, some replastering, new flooring throughout. We had used AI to help with the planning side before, including using a chatbot to map out a kitchen reno, and that had gone reasonably well. So we pushed it further this time and asked the tool to generate a full week-by-week schedule, with task dependencies, supplier lead times, and a projected finish date.
What came back looked convincing. Detailed, logical, well-formatted. We should have questioned it more carefully before we sent it on.
The bank holiday problem
The schedule treated every Monday the same. It had no awareness of Irish bank holidays, which means it cheerfully scheduled material deliveries, contractor attendance, and inspection sign-offs on days that simply do not exist as working days for most suppliers and trades here.
June bank holiday, August bank holiday, the October bank holiday that always seems to catch people off guard. All of them invisible to the tool. By the third week of the project, things were already a day behind because a delivery had been booked for a Monday that turned out to be a public holiday. Small thing on its own. Compounded over a twelve-week build, it started to matter.
The fix is simple in hindsight. You have to tell the AI explicitly which dates are non-working days in Ireland and ask it to avoid scheduling anything on those dates. It will not know this unless you tell it.
Irish supplier lead times are not the same as everywhere else
The AI built its timeline on what seemed like reasonable assumptions about how long things take to arrive. Tiles, two to three days. Sanitaryware, three to five days. Kitchen units, roughly a week.
That is roughly true if you are ordering from a large UK or European supplier with a warehouse close to your door. It is not always true here. Some Irish builders' providers have to order in from the continent. Certain tile ranges that look like they are in stock are actually held in a depot across the water. We had one bathroom suite take nearly three weeks to arrive because the supplier was waiting on a container.
The AI had no way to know any of that. It was working from general assumptions, probably trained on content from markets with better-stocked supply chains. Before you feed a materials list into any scheduling tool, ring your suppliers and get actual lead times. Then put those numbers into the prompt yourself. Do not let the tool guess.
Weather does not appear in Gantt charts
External work was scheduled across October and November. Pointing, a small section of roof repair, some external insulation boarding. The AI laid these out in a perfectly orderly sequence with zero buffer days.
Anyone who has lived in Ireland for more than a week knows where this is going. We lost about eight working days to rain, wind, and one genuinely miserable fortnight that felt like it should have had a name. None of that had been accounted for.
For any external work scheduled between September and March, we would now add a blanket contingency of at least fifteen to twenty percent on top of the AI's estimate and probably more for anything that requires scaffolding to be up for an extended period.
What we would do differently
AI is genuinely useful for getting a project structure down on paper fast. It will catch dependencies you might have missed and give you something to react to, which is often easier than starting from a blank page. But it needs to be fed real, local information to produce a schedule that actually holds up.
Build your own list of Irish bank holidays for the year. Get lead times in writing from your actual suppliers before you start. Add weather buffers to any external work. Then give all of that to the tool along with your project brief, rather than expecting it to know.
Treat the output as a draft that needs a human pass, not a finished document. That one shift in how you use it makes a real difference.