Modular Pergolas

One question comes up more often than almost any other, usually near the end of a conversation and usually a little apologetically: can I add to it later? People ask because gardens change. A structure that suits a family with young children is not the one they want when the trampoline goes and a dining table appears, and very few homeowners are willing to commit to the full length of a terrace in one go. A modular pergola is the industry's answer to that question, and it is a genuinely different way of building rather than a marketing distinction.

At Roma Verandas the modular question tends to decide itself once someone explains how the two approaches differ structurally. This guide sets out what modularity actually means in an aluminium system, how bays share posts and loads, how louvred roof modules behave across multiple bays, who the approach genuinely suits, and where a single purpose-made structure remains the better answer.

What Modular Actually Means

A modular pergola is built from repeating bays. Each bay is a rectangle of four beams and the posts that hold them up, sized within the system's own range rather than made to a one-off dimension — typically something in the region of three to four metres in each direction, in fixed steps rather than any figure you care to name. Bays bolt to one another along a shared line, so a run of three bays is not one long structure with intermediate supports added; it is three complete frames sharing their posts and their beams.

That distinction matters because it changes what can happen afterwards. In a purpose-made structure the beams are cut for that opening and the whole assembly is a single item; extending it means an addition that has to be spliced to something not designed to be spliced. In a modular system, the joint between bays is a standard detail that the manufacturer intends you to use, so a fourth bay is added the same way the third was. Systems built on this logic, such as the Deponti Bosco modular veranda, are designed around interlinking from the outset rather than accommodating it grudgingly.

The Post That Does Two Jobs

The structural interest sits in the shared post. Where two bays meet, one post carries the end of a beam from each side, which means it takes roughly twice the vertical load of an end post and its foundation has to be sized accordingly. It also has to present fixing faces in two directions at the same height, so modular systems generally use a slightly heavier post section, often around a hundred and twenty millimetres square, with a head detail that accepts beams on more than one face.

Drainage follows the same logic. Most louvred and glass-roofed pergolas drain into hollow perimeter beams and then down inside a post, and a shared post could in principle be asked to take the water from two roofs. In practice good systems avoid that by draining each bay outward to its own corner, which keeps outlet sizing sensible and means a blockage in one bay does not back up into the next. It is worth knowing because it explains why downpipe positions in a modular run are not always where you would intuitively put them.

The last consequence of standardisation is profile size. Beams in a modular system are sized for the largest module the manufacturer offers, so a small bay carries a beam heavier than it strictly needs. The structure is not over-engineered in any harmful sense, but the profiles look slightly more substantial than a bespoke structure of the same size would. Some people prefer that appearance; others notice it immediately.

Louvred Roof Modules and Zoning

Modularity becomes most useful with a louvred roof, because each bay is naturally its own set of blades with its own motor. A motorised louvred pergola of this kind lets blades rotate through a wide arc, from fully closed and weathertight to almost vertical, and where there are several bays each can be controlled independently. In practice that means shade over the dining bay while the seating bay stays open, or the windward bay closed down in a squall while the sheltered one is left alone.

There is a practical caveat. Blades run in one direction only, so the orientation of a bay is fixed by the direction the louvres are set to span, and in an L-shaped run the two arms will have blades running at right angles to one another. That is not a fault, but it does read as two structures joined rather than one continuous roof, and it is better seen on a drawing than discovered on installation day. Rain also has to be considered bay by bay: closed louvres shed water into that bay's own gutter, so each module needs a working outlet, not just the end one.

Who Modularity Genuinely Suits

The clearest case is phased spending. A single bay over the back doors now, a second bay next year reaching towards the garden — the first foundation set, the first frame up, the extension a known quantity rather than a hope. The second clear case is an awkward garden. Terraces that wrap around a corner of the house, L-shaped patios and gardens that narrow towards the boundary are difficult to cover with one rectangle, and easy to cover with two or three bays stepping round.

Freestanding modular structures open up a third case, which is a covered area that has nothing to do with the house at all. A structure like the Ribolla freestanding pergola takes no fixing into a wall, so bays can be sited over a dining area in the middle of a lawn, alongside a pool, or against a boundary where the house is simply too far away to help. Hospitality and commercial customers use the same properties for different reasons: a terrace can be covered a section at a time as budget allows, replacement parts are standard rather than bespoke, and a damaged bay can be repaired without dismantling the run.

Finally there is the customer who expects to move. A bolted modular structure can in principle be taken down and re-erected, which a welded or purpose-cut one cannot. Be realistic about what that is worth: the foundations stay behind, dismantling and re-erecting is skilled work, and gaskets and fixings are usually renewed. It is a real option rather than a free one.

What You Give Up

The main cost of modularity is posts. A wide-span purpose-made veranda can cross six or seven metres on two posts and leave a completely clear view; the same width in modules puts a post every three or four metres. If the whole point of the structure is an uninterrupted outlook across the garden, that is a significant loss, and no amount of good detailing disguises a post in the middle of a view.

The second is dimensional fit. Modules come in steps, so a terrace of five and a half metres is covered by two bays totalling six, or two totalling five, and the leftover has to go somewhere. A bespoke structure is simply made at five and a half. The third is a slower problem: if a later bay is added two or three years on, the powder coating will have come from a different batch, and even a well-controlled finish like a matt RAL 7016 can vary very slightly between batches. Where the junction falls on a post the eye rarely picks it up, but on adjacent beam faces in full sun it sometimes does. It is also worth asking whether the system you are buying is likely to still be in production when you want the extra bay, because a discontinued profile makes the whole argument for modularity academic.

Deciding Which Kind of Structure You Want

The honest position is that modularity is worth paying for only if you will actually use it. If the plan is one structure of a settled size over a settled area, a purpose-made pergola will usually give a cleaner result with fewer posts and a better fit to the space, and the flexibility you are not using is not free. If, on the other hand, there is a real prospect of a second phase, an awkward shape to negotiate, or a commercial terrace that has to grow, modularity earns its keep and then some.

What is worth avoiding is deciding this by instinct. The two approaches produce structures that look broadly similar in a photograph and behave quite differently over ten years, and the deciding factors — post positions, module steps against your actual terrace dimensions, drainage outlets, blade direction — are all things best resolved on a survey drawing. If you are weighing up whether to build once or build in stages, that is exactly the conversation to have before anything is ordered.