From BOQ to Gantt: Build Your Schedule in One Afternoon

Why does the BOQ already contain your schedule?

Most Thai contractors win a job with a BOQ — a breakdown of every work item and its cost. That document tells you the what of your schedule: the trades, the materials, the quantities. The Gantt planning view in SiteBoard adds the when. Instead of building a schedule from scratch, you are translating a document you already have into a timeline. The gap most contractors leave is not knowing how to make that translation quickly. This guide walks the whole process for a typical residential project — from a freshly signed BOQ to a live Gantt your foremen can update from the site by the end of day one.

How do you group BOQ line items into Gantt phases?

A Thai residential BOQ typically has fifty to two hundred line items across ten to fifteen trades. You do not need a Gantt task for every line item. Instead, group related work into five to eight phases that match how the site actually runs: site preparation, foundations, structure (columns, beams, slabs), envelope (walls, roof, windows, doors), MEP rough-in (electrical, plumbing, air conditioning), finishing (plaster, tiles, paint, joinery), MEP trim-out, and handover. Each phase becomes a parent task in SiteBoard; the key sub-tasks within each become the children. A 160-line BOQ typically collapses into twenty-five to thirty-five Gantt tasks — enough detail to catch slippage, simple enough for a foreman to follow.

How do you convert BOQ quantities into task durations?

For each task, ask one question: at the planned crew size and pace, how many working days will this take? BOQ quantities give you the starting point. Bricklaying runs at roughly fifteen square metres per crew per day, so three hundred square metres of masonry takes about twenty working days with one crew. Concrete work is poured in floor-by-floor cycles; plastering follows after a curing wait. Thai residential contractors typically add a ten to fifteen percent buffer to the calculated duration for site-specific friction: access restrictions, material delivery timing, and trade coordination gaps. If you have built a similar project before, your past timeline is your best reference — adjust from that rather than calculating from first principles every time.

What dependencies should you set from day one?

Dependencies are the most valuable part of a Gantt that a BOQ alone cannot tell you. They come from the physics of construction: you cannot pour a slab until the reinforcement inspection passes, you cannot plaster until the MEP rough-in is complete, you cannot lay floor tiles until the screed has cured for the required number of days. Mark these in SiteBoard as finish-to-start links between tasks. When the foundation runs two extra days, every task that depends on it shifts automatically — you do not have to manually recalculate the entire schedule. For a first-time Gantt builder, marking the five or six critical dependencies in the structure and finishing phases is enough to make the schedule genuinely useful; you can add finer links over time.

A worked example: a three-bedroom house in Samut Prakan

A residential contractor in Samut Prakan won a three-bedroom single-storey house on a 64 m² plot with a BOQ of 2.4 million baht and a contractual finish of 180 working days. They opened SiteBoard and created eight phases: site preparation (3 days), foundations (14 days), structure (22 days), envelope (25 days), MEP rough-in (18 days), finishing (35 days), MEP trim-out (10 days), and handover (8 days). Adding weekends, long weekends, and a ten-day buffer brought the total to 168 working days — leaving twelve days of float before the deadline. They linked the critical dependencies, shared the Gantt through the owner sharing link on day one, and used that same plan as the reference for every foreman update and every owner question for the next seven months.

How should Gantt milestones align with BOQ payment stages?

Many Thai construction contracts tie payment stages to physical milestones: thirty percent on completion of structure, fifty percent on roof and envelope, eighty percent when rough-in is done, ninety-five percent on finishing complete. Mark each of these as a milestone diamond on your Gantt in SiteBoard. When the foreman's on-site progress updates show the tasks feeding that milestone reaching one hundred percent, both you and the owner can see the payment condition has been met. The owner sharing link shows the milestone approaching in real time, which means the owner rarely needs to call asking about the payment trigger — they can already see it on the shared Gantt.

What level of detail is right for a small contractor?

The most common mistake is making the Gantt either too coarse (five tasks for a six-month build) or too granular (one task per BOQ line item). The right level is whatever makes a meaningful delay visible: if a task slips, would you change a decision — which crew to accelerate, what to tell the owner, whether to order materials early? For most residential and small commercial projects that means twenty to forty tasks. If you cannot keep on-site progress updates current at that level, scale back. A coarser Gantt that is actively maintained beats a detailed one that goes stale in week two every time.

Should you share the Gantt with the owner from day one?

Yes, for most projects. Sharing the initial plan through the owner sharing link on day one sets a professional tone and reduces the number of "what is happening on site?" calls throughout the build. The owner sees the planned timeline, the tasks being updated, and the milestones approaching. They do not see the BOQ cost breakdown, the subcontractor names, or your margin — only the physical progress the plan describes. Contractors who share from day one typically find owners more patient when tasks slip and quicker to approve payment triggers, because they can see the conditions being met on the Gantt in real time.

FAQ: What if the BOQ is revised after contract signing?

BOQ revisions are normal in Thai construction. When a revision adds or removes work, update the affected Gantt tasks at the same time you agree the variation with the owner. Add a new task for new work, extend the duration if quantities grew, or remove the task if work was descoped. A Gantt kept in sync with the current agreed scope means the owner sharing link always reflects the actual contract — not the original one. A Gantt that still shows the original plan six weeks after a major variation is a dispute waiting to happen, so treat every agreed variation as a two-minute Gantt update before moving on.

FAQ: How do I keep the Gantt useful as the project runs?

The single most important habit is ensuring foremen submit on-site progress updates daily or every two days. Without current task percentages, the Gantt becomes a wall calendar — it shows the original plan but not where you actually are. Establish the update habit in week one: show each foreman how to slide the percentage and attach a photo for their assigned tasks. It takes ten seconds per task. When a task runs over, extend its bar rather than leaving it red and ignoring it — an honest Gantt that shows slippage is always more useful than a green one that pretends everything is on track. Review the whole plan weekly and flag any task ten or more days behind to the owner before they ask.