Once you have decided on a conservation rooflight, a quieter question follows. Should the frame be steel or aluminium? From the garden, on a dark slate roof, the two can be hard to tell apart. Look closer, and live with the choice for decades, and the differences begin to show.
Neither metal is simply better. Each has things it does well, and one will usually suit your house a little more than the other. This guide sets them side by side so that the decision rests on the building rather than the brochure.
How each frame is made
Steel frames are made from solid bar and section, cut, welded and finished with care. The weld lines are ground back, and the frame is usually treated and painted before it leaves the workshop. The process is closer to a blacksmith's craft than a production line, and it allows very fine sections.
Aluminium frames are made from extruded profiles, formed in a die and cut to length. The process is repeatable and precise, and the profiles can include a thermal break, a strip of insulating material between the inner and outer faces of the frame. The result is a clean, consistent frame at a more modest price.
Appearance up close
Steel gives the finest, most authentic look. A traditional steel rooflight has the slim, slightly irregular lines of the cast iron lights it echoes, and the frame can be as narrow as the glass will allow. Many owners of older houses choose steel for that reason alone.
Aluminium looks crisper and more uniform. The edges are sharper and the sections a little wider, though good makers have narrowed them a great deal. On a roof of slate or pantile, seen from the ground, most people would struggle to say which metal they are looking at.
How they age
Steel is a living material. It can rust if its coating is damaged, so it relies on a good galvanised or painted finish and, over a long period, on repainting. A well finished steel frame lasts a very long time, and it takes on a soft, lived in look as it weathers.
Aluminium does not rust. Its powder coated finish is hard and holds colour well, and it asks little of the owner. Left alone, it stays much as it was on the day it was fitted, which some people see as a strength and some see as a lack of character.
- Steel: authentic, needs its finish kept sound, ages with the roof.
- Aluminium: consistent, very low maintenance, stays as installed.
Thermal performance
This is where aluminium usually has the advantage. Metal conducts heat, and a steel frame with no break carries cold from the outside to the inside more readily than a thermally broken aluminium one. Condensation can form on a cold frame, especially in a bathroom or a bedroom.
Makers of steel rooflights deal with this in different ways, using thermal breaks of their own and efficient glass. Part L (2021) asks for 2.2 W/m²K for rooflights in existing homes, and a good frame of either metal can reach it. Our guide on whether conservation rooflights are energy efficient goes into the detail.
| Frame sections | Steel is the slimmer; aluminium has caught up |
|---|---|
| Finish | Steel is painted or galvanised; aluminium is powder coated |
| Upkeep | Steel may need its finish renewed; aluminium rarely does |
| Heat loss through the frame | Aluminium with a thermal break usually does better |
| Price | Steel is generally the higher line |
Strength and span
Steel is stronger for its thickness, so a slim steel frame can carry a wide pane of glass with little visible support. That is a real benefit on a large rooflight, and it is part of why steel is chosen for generous openings in period roofs.
Aluminium sections need to be a little deeper to span the same distance, and wide rooflights often gain a central bar. A bar is not a fault; it can echo the glazing bars of the windows below. For help with how wide to go, see what size conservation rooflight do I need.
Weight and handling
Steel frames are heavier. On a roof it matters in two ways. The structure round the opening has to carry the load, and getting the unit up to the roof and into place needs more hands. Both are handled at the survey and in the day plan, and neither is a problem when planned for.
Aluminium is lighter and easier to lift, which can make access simpler on a steep or awkward slope. It is a small point, but where a roof is hard to reach, it counts.
The listed building and conservation area angle
Where consent is needed, the council may have a view. Some conservation officers favour steel on the oldest buildings because it is closer to what was there originally. Many accept aluminium on later or more modest roofs, provided the frame is slim and sits flush.
If the house is listed, ask the council early; rooflights for listed buildings explains the route. If it is in a protected area, rooflights in conservation areas covers what applies.
What each does to the price
Steel is generally the more expensive choice, because of the hand made process and the finish. Aluminium is generally the lower line. The gap changes with size, bar pattern and finish, so the survey is where a figure is worked out for your roof. Our conservation rooflight cost guide shows where each element sits on a quote.
Cost should not be the only deciding factor. A frame that suits the house and lasts as intended is worth more than a saving that you look at every day.
Glass and bars in each frame
The glass is much the same whichever metal you choose. Sealed double glazed units with a coated face and a gas filled gap are standard, and we specify a laminated inner pane because it stays together if it is ever broken overhead. That is a choice we make, not a requirement of Part K.
What changes is the bar. A steel frame can carry a wider pane before it needs a central bar, and the bar itself is thin. An aluminium frame of the same width often wants a bar sooner. Neither is a flaw. Many period roofs had a central bar, and on a slate slope it can look as though it was always there.
Think about the view from inside too. A bar divides the sky into two panes, which some people find restful and others find fussy. Looking at samples of each at the survey is the easiest way to decide how it feels.
Opening versions
Both metals can be made as opening rooflights, though the mechanism and the sizes available vary. An opening version adds hinges, a stay or an electric motor, and the frame has to carry them without growing thick. Where ventilation matters, as in a bathroom or a small attic room, it is worth checking what each maker offers. Our page on whether a conservation rooflight can open goes into the options.
An opening rooflight is also a place where the thermal break matters more, because a moving part has seals that need to meet cleanly all round. Ask to see the closing action on a sample, and look for an even gap on every side.
Sound and condensation in daily use
Rain on a roof sounds different through glass than through slate, and a rooflight is one of the places you will hear it. The frame has little effect on that. The glass build does, and a laminated inner pane tends to soften the noise. It is worth knowing before you fit a rooflight over a bedroom.
Condensation is more to do with the frame. A cold frame in a warm, damp room collects moisture on its inner face, and it can run down onto the reveal. In a bathroom, a thermally broken aluminium frame, a well insulated reveal and a fan that works properly together keep this in check. In a dry living space, it rarely arises with either metal.
Lead times and the quote
Steel frames are made to order and take longer to arrive. Aluminium frames from a standard range are often quicker, though a made to measure one will take its turn in the factory too. We build the wait into the plan, so the date for the fit is fixed only once the frame is confirmed.
On the written quote, each choice has its own line: the frame, the glazing, the finish, the opening mechanism if there is one, the roofing work, the structure, the reveal and the building control fee. That makes it plain where steel and aluminium diverge in price for your roof. Our conservation rooflight cost guide explains each of those lines.
Colour, finish and how they sit on the roof
Both metals come in a limited set of finishes for this kind of rooflight, and most are dark, matt and quiet. A deep grey or near black frame disappears against slate and sits comfortably against clay tile. A lighter colour can look right on a pale stone roof, though it will draw the eye more than the dark one.
Steel is often painted by hand or sprayed in the workshop, and the finish can be matched to a colour of your choice. Aluminium is powder coated in the factory, which gives an even surface and a wide choice of colours. If a council has asked for a specific colour, say so before the order is placed, because the frame cannot be changed once it is made.
Look at the finish in daylight, next to a spare slate or tile if you can. A colour that looks right on a swatch indoors can read very differently in the open, under a grey Yorkshire sky.
Living with your choice
A rooflight is fitted once, and you will look at it for a long time. The best way to choose is to imagine the room in ten winters and in ten summers. Will a steel frame still be what you want when it has darkened slightly and been repainted once? Will an aluminium frame still look right when everything else in the house has changed round it?
There is no wrong answer, only a right one for your roof. We would rather talk it through at the survey, with samples in hand and the roof in view, than guess from a photograph. What is a conservation rooflight is a good place to start if you are new to the idea.
Choosing between them
Steel suits an old building where authenticity matters, where a wide span is wanted or where the council has asked for it. Aluminium suits a later house, a bathroom or bedroom where condensation is a worry, or any roof where a low maintenance finish is the priority.
A short way to decide
- Is the building listed, or its roof very old? Lean towards steel.
- Is the room a bathroom or a bedroom? Aluminium's thermal break helps.
- Do you want the slimmest possible frame? Steel.
- Do you want the lowest upkeep? Aluminium.
Whichever you choose, the fit is the same. We cover the floors, screen the area, keep the roof weathertight at the end of every day, and photograph the hidden work for you. Book a free survey with the form below, or return to our conservation rooflights page.