Seven Metres on Two Posts: What the Steel in the Gutter Makes Possible

Stand under a seven-metre veranda with a post at each end and nothing in between, and the first thing you notice is what is not there. No upright in the middle of the view, no support in the walking line, no vertical dividing the garden in two. It is the single most requested thing in this trade and the one people are most often told is not possible.

It is possible, on specific models, and the reason sits inside the gutter where nobody looks. This is what the steel reinforcement actually does, why it is what makes a wide clear span achievable, and how to tell whether the structure you are being offered can genuinely do it.

Why the Front Beam Is the Constraint

On a lean-to veranda the gutter along the front edge is the main structural beam. Every roof beam lands on it, and it carries all of that horizontally to the posts. The posts hold up the gutter; the gutter holds up the roof.

So the distance between posts is the span of that beam, and span is brutal. Bending rises with the square of it, and deflection — how much the beam sags — rises with the fourth power. Go from a four-metre bay to a seven-metre one and you have not increased the demand by three-quarters. You have roughly tripled the bending and multiplied the sag by nearly ten.

That is why standard systems cap post spacing at four metres, and why the answer to "can we lose the middle post" is usually no. Not because anything would break, but because the beam would visibly droop, and a drooping gutter puts glazed edges out of square in their pockets and stops draining to its outlet.

What the Steel Is Doing

Aluminium is about a third as stiff as steel for the same shape, and stiffness is exactly what resists sag. You can compensate with more aluminium, which means a deeper, heavier, considerably uglier front profile — or you can put a relatively small piece of steel where the bending stress is highest and let it do the work.

That is the design. On glass-capable models the gutter carries a steel strip — twenty by one hundred millimetres on the systems we supply — slid into a channel in the profile before the structure goes up, with the gutter flat on trestles and lubricated so it does not jam. From underneath you see a slim aluminium gutter. Structurally you have a composite section behaving like something far deeper.

On the standard models that reinforcement is what makes four metres achievable at a domestic scale. On the wide-span models it is scaled up, and that is what buys you the long clear bay.

Why Glass Models Need It More

The reinforcement is not the same demand on every roof, because the covering weighs wildly different amounts.

Sixteen-millimetre multiwall polycarbonate weighs somewhere in the region of two and a half to three kilograms per square metre. The laminated safety glass used on these roofs weighs around twenty-two — roughly eight times as much. A five by three metre roof is therefore carrying about forty-five kilograms of covering in polycarbonate and over three hundred in glass, and all of it arrives at the front edge through the beams.

Which is why a glass roof and a polycarbonate roof of the same dimensions are not the same structural problem, and why a frame built for sheet cannot simply be re-roofed in glass later. The gutter has to have somewhere for the steel to go.

Seven Metres on Two Posts

The wide-span models exist for one reason: to put a clear opening between two posts where a standard system would need three or four.

The Giallo, the Luxa and the Pigato all reach around seven metres, and they get there with a heavier front member and additional reinforcement rather than by being asked to work harder than a standard profile safely can. It is a different product rather than an option box, because the section, the reinforcement and the calculation all change together.

What that means in a garden is specific and worth spelling out. A seven-metre rear elevation covered with posts only at the corners. A set of bifold doors that can be thrown fully open with nothing standing in the opening. A dining table that sits where you want it rather than where the post allows. And a view down the garden that is not bisected.

The Trade-Offs, Honestly

Three, and none of them is a reason not to do it — only reasons to go in with the right expectations.

Cost. A wide-span model is a heavier system throughout and it is priced accordingly. If the clear opening is genuinely the point of the project, it is worth paying for. If a post moved half a metre would have solved the objection, it is worth checking that first with a cane in the ground.

Depth. Span and projection compete for the same capacity. Every extra metre of depth means each roof beam collects more area and delivers a bigger load into the front gutter, so the deepest projection in a range is rarely available at the widest span. Ask for the figures at your width and your depth together rather than reading the two maximums off a page and assuming you can have both.

Weight and handling. A seven-metre reinforced gutter with a steel strip inside it is a substantial thing to lift, and the assembly manuals recommend material lifts for the larger systems for good reason. It is not a two-people-and-optimism job, and access to the site matters more than it does on a smaller structure.

How to Check What You Are Being Offered

Four questions separate a specified structure from a priced one.

What is the maximum span between posts on this model, at my projection? The answer should be a number tied to a configuration, not a general reassurance.

Is the gutter reinforced, and with what? On a glass-capable model the answer should be a steel section of a stated size.

What are the published load figures for this width and depth? On the systems we supply those come with a stated basis — a fifty-year reference period, consequence class CC1, a deflection limit of one two-hundredth of the span, calculated to EN 1990, at a maximum height. A figure without its basis cannot be compared with anything.

And what happens at the foundations? A post carrying half of a seven-metre span is taking a serious share of the roof, permanently, plus whatever the wind does to it. A properly founded concrete base under each one is the specification rather than an upgrade — the whole point of a long span is that there are fewer supports, which means each one matters more.

Whether It Is Worth It

The test we would apply is what the clear span is actually for.

If it is an opening you walk through, or a set of doors you want fully open, or a view that a post would sit squarely in the middle of, the wide-span model is buying you the reason you built the thing and it is worth the money.

If a post is merely inelegant, mark it out with a cane and sit where you will sit for ten minutes before deciding. A surprising number of clear-span requests turn out to be objections to a post in one particular position rather than to a post existing at all — and moving one is free while it is still a drawing.