The short answer
Not every lantern needs one. A tie bar is a slim horizontal bar that spans the inside of a larger roof lantern and holds the two sides together, resisting the outward push of the sloped frame. Smaller lanterns often stand without it, and some makers build a stiffer frame so the bar can be left out. Your lantern maker decides, from the span.
What the bar is actually holding
A lantern is a pitched roof in miniature, and like any pitched roof its sloping sides push outwards as well as down.
Each side of a lantern leans in towards the ridge. The weight of the glass and any snow presses down on those sloping sides, and part of that load turns into a sideways push at the foot of each slope, where the lantern meets its base frame. Left alone, a wide enough frame would try to spread, as a pair of rafters does when nothing ties their feet together.
A tie bar is the tie. It runs from one side of the lantern to the other, usually at the level of the base frame or a little above it, and it carries that sideways push as a pull along its length. Because it works in tension, it can be very slim, which is why the bars you see are thin rods or flat sections and not heavy beams.
In a small lantern the push is small and the frame itself is stiff enough to take it. As the span grows, the push grows with it, and somewhere along the way a designer has to choose between a tie, a deeper frame or a steel section hidden in the kerb. That choice is where the different designs on the market come from.
Three ways to resist the spread
There is more than one answer to the same problem, and each one changes what you see from below.
| Approach | How it works | Look from below |
|---|---|---|
| Visible tie bar | A bar crosses the lantern as a tension tie | A thin line across the glass |
| Stiffer frame | Deeper aluminium sections resist the spread | Chunkier bars, nothing across |
| Steel in the kerb | The base carries the push, hidden below | Clean glass, a deeper upstand |
The bar is the most efficient of the three, in the sense that it uses the least material. The other two move the work into the frame or the kerb, and so need more metal or more depth there. None of them is better in every case. They are trade-offs, and the right one depends on how large the lantern is and how you want the room to look.
Which approach a particular lantern uses is part of the manufacturer's design, not something we adjust on site. Our answer on whether a lantern can be made to measure explains how a made-to-order unit is engineered for its own span.
How a tie bar changes the room
From inside, a tie bar is the only part of the lantern that crosses open air, so it is noticed.
A thin bar near the base catches the eye less than one set higher up. Placed low, it reads as part of the frame. Some people like it, because it gives the lantern a crafted, architectural feel and breaks up a large expanse of glass. Others find it cuts across the ceiling and would rather have clear glass.
The bar also affects what you can hang from the lantern. A pendant light or a blind track may fit neatly to a tie bar, or may have to work around it. The page on lighting and blinds around a roof lantern covers how to plan for that, and the question of fittings inside the glass is answered in our page on putting lights inside a roof lantern.
If you want clear glass from below, say so before the lantern is ordered. A design without a visible tie can usually be supplied, but it will use a different frame or a different kerb, and that has to be planned into the roof.
Where size tips the decision
The bigger the span, the more the question matters, and the earlier in the design it should be settled.
A lantern over a small utility room is unlikely to raise the issue. A lantern over a wide kitchen, where the span is larger, is where a maker will start to specify a tie or a heavier frame. Snow adds to the load the frame carries, so the snow design of the lantern is part of the same thinking. Our answer on whether a roof lantern is strong enough for snow covers it.
The size of the lantern also decides how many glazing bars it has, and bars and ties work together in the frame. Our guide to glazing bars and how many you need and the roof lantern size guide set out how the pieces scale. If the opening is large, the trimming round it matters too, as our page on whether a lantern needs a steel beam explains.
What we put in writing before the order
The lantern is specified in full on paper, so nothing about the frame comes as a surprise on delivery day.
At the survey we measure the opening and look at the room. If your lantern is one where the maker's design calls for a tie, we tell you where it will sit and how it will look from below. If you would prefer clear glass, we ask the maker which frame or kerb arrangement does that for your span, and the answer goes on the quote. The glazing build, the seals and the upstand are recorded in the quiet spec that comes with every quote, so the written description matches what arrives.
A tie bar has a small acoustic side to it as well. A bar that is tightly fitted and firmly seated does not rattle, while a loose one can tick in wind. That is one of the things checked when the lantern is fitted, along with the gaskets and the bars. The wider picture of rain and sound is in our answer on lanterns in heavy rain.
Questions about tie bars
Can a tie bar be removed after the lantern is fitted?
No, it should not be taken out. If it is part of the design, it is carrying a load. Clear glass has to be designed in from the beginning, not altered later.
Does a tie bar make a lantern less watertight?
No. It sits inside the lantern, below the glass and the weathering, so it plays no part in keeping water out.
Are tie bars only for big lanterns?
They are mostly a feature of larger spans, where the outward push is greater. A small lantern is unlikely to need one.
Do all makers use them?
No. Some rely on a stiffer frame or steel in the kerb instead. See the aluminium roof lanterns page for how frames differ.
If you are weighing a lantern with a tie against clear glass, get a quote and we will set out the options for your span. The full service is on our roof lantern installation page.