Do conservation rooflights and skylights have glazing bars?
Most ranges offer a bar and most also offer the unit without one. The bar reproduces the division of a nineteenth century cast iron rooflight, where the available glass sizes needed supporting. On a modern unit it is decorative rather than structural, and whether it is needed depends on who can see the slope.
What the bar is reproducing
A structural necessity of the original that no longer exists.
Victorian cast iron rooflights were glazed in panes of the size the industry could make, and a bar across the light carried the joint between them.
Modern sealed units come in one piece, so the bar carries nothing. It is there because the original had one.
How it is formed
Two ways, and they look different at close range.
An applied bar is fixed to the face of the glass, on one or both sides. A structural bar divides the unit into two sealed units with a genuine member between them.
The second is more convincing and costs more. Which a range offers is worth establishing, because from a pavement they are indistinguishable and from a room they are not.
Horizontal or vertical
Both exist and the choice follows the unit’s proportions.
A bar generally runs across the shorter dimension, dividing the light into two roughly square panes. On a tall narrow unit that is horizontal; on a wide one it can be vertical.
Matching what is already on a building, where an original survives nearby, is the safest guide.
When an officer wants one
On a visible slope in a designated area, frequently.
The bar is the most recognisable signal that a unit is a conservation type rather than a slim modern one, and it is what an officer is looking for on a roof in public view.
On a concealed slope it is generally not required and the question does not arise.
What it costs in light
A real amount on a small unit, and it is worth being concrete.
These units are modest to begin with, and a bar across the middle removes a strip of glass and adds a shadow. On the smallest sizes that is a noticeable share of the light.
Which is a reason to prefer the unbarred version wherever it is acceptable.
What it does to the view
Divides it, and in some rooms that matters.
Where somebody will lie or sit looking up through a unit, a bar across the middle of the sky is more intrusive than it sounds on paper.
In a bedroom or a study it is worth thinking about; in a hallway it is not.
Two units, and matching the bars
A composition point on a pair. Where two units go on one slope, the bars should align with each other and, ideally, with the head of the windows below. Two bars at different heights read as an accident.
Cleaning around one
A minor practical consequence of an applied bar.
An applied external bar gives dirt an edge to collect against, which on a slope under trees means a line of accumulated debris.
It rinses off and it is worth knowing about before choosing between an applied and a structural bar.
Condensation and an applied bar
Occasionally raised and rarely a problem. An internally applied bar is a slightly different surface temperature from the glass around it, so on a very humid morning a faint line can show. It is a room humidity issue rather than a fault.
On a modern house
Optional and frequently omitted. Nothing requires a bar outside a designation, and on a 1990s house the reference is decorative rather than historical.
What a conservation unit does on a modern roof generally is on can a conservation rooflight go on a modern house.
Whether it can be added later
An applied bar sometimes, a structural one no.
Where a range offers an applied bar as an accessory, it can be added to a unit already fitted. A structural bar is part of the glazing and is decided at order.
Which is worth knowing where an application outcome is uncertain.
More than one bar
Available on larger units and rarely the right answer on a domestic roof.
Original cast iron lights of any size carried several bars, so on a large unit a single bar can look under-divided to an eye that knows the type.
On the modest sizes these units come in, one bar is generally right and two make a small light look busy.
Finish of the bar
Matched to the frame in almost every case.
A bar in the same dark finish as the frame reads as part of the unit. One in a contrasting colour reads as an applied strip, which is exactly what an officer is hoping not to see.
It is a default rather than a decision on most ranges, and it is worth confirming on order.
What to do if unsure
Ask the officer before ordering rather than guessing.
A short pre-application question about whether a bar is expected on a particular slope costs nothing and avoids ordering a made to size unit twice.
What we specify on a designated roof
We specify a bar where a slope is visible in a designated area and recommend against one where it is not, because it costs light and view for an appearance nobody is assessing.
The product overall is described on what is a conservation rooflight.
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