“How long will it take?” is the second question every client asks, after what it costs. The standard answer — that it depends on the size and complexity — is true, and completely unhelpful if you are trying to plan around it.
So here is the useful version: not a number, but the sequence, which parts overlap, which part is almost always the bottleneck, and the things that actually move the date.
The sequence, in order
A tensile structure is not built in one continuous run of work on your site. It is made in a workshop and assembled at your site, and those are two different timelines that meet near the end.
- Site survey. Measurements, levels, where the columns can go, what is under the ground, how a vehicle reaches the spot. This is also where the awkward constraints surface — the gate swing, the existing drain, the tree nobody mentioned.
- Form-finding and design. The membrane geometry is developed first, because the shape is structural. Only once the surface is settled can the steel be designed around it.
- Structural engineering. Frame, cables and foundations sized for the span and for the site's design wind pressure. See why a tensile roof is held down for why the foundations are the serious part.
- Drawings and approval. Fabrication and installation drawings go to you or your consultant. Nothing is cut until they come back signed.
- Workshop fabrication. Steel cut, welded, drilled and hot-dip galvanised; membrane patterned and welded into panels.
- Foundations on site. Excavation, reinforcement, casting, curing.
- Erection. The frame is stood and aligned.
- Tensioning and handover. The membrane is lifted, tensioned to its design pre-stress, and the documentation pack is handed over.
The part that saves the most time
Look at that list again and notice that stages five and six do not follow each other. They happen at the same time.
While the steel is being fabricated and galvanised in the workshop, the footings are being excavated and cast at your site. Neither is waiting for the other. By the time the steel arrives, the concrete has had most of the curing time it needs.
The workshop and the site run as two parallel clocks. Only at erection do they meet.
This is the practical reason a tensile structure is so much less disruptive than a conventional roof of the same area. The phase that actually interferes with your car park, your courtyard or your drive is short, because almost everything arrives finished. It is also why sections of a site can be fenced, worked and handed back one at a time rather than closing the whole area for the duration.
The part that usually takes longest
It is rarely manufacturing. It is approval.
Between the design being ready and the first piece of steel being cut sits a loop: drawings out, comments back, revisions, drawings out again. Each lap is small on its own. Three or four of them, with a few days' wait at each end, quietly becomes the longest single stage of the project — and none of that time is visible as work happening.
Where a housing society, an RWA or a local authority also has to approve the structure, that runs on its own calendar entirely, and it is worth starting before the design is finished rather than after.
The single most effective thing a client can do for the programme is to nominate one person who can actually sign off drawings. Approval by committee, in sequence, is where weeks go.
The part nobody can compress
Concrete gains strength over time. A footing cannot take the load of a frame — let alone the pull of a tensioned membrane working against it — until it has cured sufficiently.
There is no way to buy that time back. It is a property of the material. Any programme that appears to skip it has either cast the footings earlier than you think, or is about to put load into concrete that is not ready, which is a problem that shows up later and is expensive to fix.
What actually moves the date
In rough order of how often it happens:
- Changes after drawings are frozen. A change to the span, the height or the column positions after fabrication has started means re-cutting steel and, often, re-patterning the membrane. This is the expensive kind of delay.
- The site not being ready. Material stacked where the footings go, no power, no water, a locked gate, a vehicle that cannot reach the spot. Every one of these turns a working day into a wasted one.
- What is found in the ground. A cable, a water line, a septic run, or soil that is worse than assumed. The survey reduces this risk; it does not eliminate it.
- Heavy rain during the foundation phase. Excavation and concreting suffer; workshop fabrication does not. Where the date is flexible, it is worth planning the site phase around the worst weeks.
- Approvals running in parallel with fabrication. Tempting, and it works right up until the approval comes back with a condition that changes the structure.
So what should a quotation tell you?
Not a single number with nothing behind it. A programme, broken into the stages above, with the dependencies named — what has to be signed, by when, for the rest to hold. That is what makes it something you can plan against, and something both sides can be held to.
If a quotation gives you one figure for “completion” and no stages, the question to ask is which of those stages it assumes you will complete instantly. Ten questions to ask before you sign covers the rest of what should be in there.