On an elevation, zinc and aluminium roofing can look fairly similar. Once the project moves into the detail, the differences become much more important.
The finish, roof build up, panel arrangement, junctions and fabricated components all need to suit the system being installed. On an extension, there is the added challenge of connecting the new roof back into an existing building.
At C&S Roofing, we install both zinc roofing and aluminium roofing. Neither is the automatic choice for every extension. Before the specification is settled, these are some of the details we look at with contractors.
Start With the Finish the Project Actually Needs
One of the clearest differences between zinc and aluminium is how the finished roof will look and how that appearance changes over time.
Zinc is often chosen for its natural character. Its surface develops a patina as it weathers, so the appearance gradually changes rather than remaining exactly as it looked on the day it was installed.
Aluminium roofing systems are available in a range of coated colours and finishes. That can be particularly useful where the roof needs to coordinate with window frames, cladding, aluminium cappings or other external metalwork.
So the specification needs to go further than simply saying “metal roofing”.
For zinc, the product and finish need to be confirmed. For aluminium, the particular system, colour and finish need to be agreed. If several suppliers are providing visible metalwork, it is worth looking at actual samples together rather than assuming similarly named colours will be identical.
The Roof Build Up Can Affect the Decision
The visible metal is only one part of the roof. Pitch, substrate, insulation, ventilation, separation layers and moisture control all need to suit the chosen roofing system and the manufacturer’s requirements.
Zinc, for example, can be used with different roof constructions, including ventilated and non ventilated systems, but those build ups are not interchangeable. The correct substrate, underside protection and ventilation strategy need to be established for the specified system.
Aluminium standing seam systems have their own requirements for the supporting substrate, separation layer, clips and detailing.
That is why we would rather review the proposed roof build up while the drawings can still be adjusted. Changing it after the structure has been formed is a much more difficult conversation.
Look Closely at Where the Extension Meets the House
The main roof area is often relatively straightforward. The junction with the existing building can require far more thought.
An extension roof may meet masonry, an existing pitched roof, parapets or different wall finishes. Rooflights, outlets and changes in level can add more detail into a relatively small area.
Before installation, there should be clear answers to questions such as:
- Where will the water run, and where will it discharge?
- How will the new metal roof meet the existing wall or roof?
- How are rooflights, edges and changes in level being finished?
- Which contractor is responsible for each flashing, capping and adjoining component?
- At what stage can final measurements be taken?
A clean elevation does not answer those questions. They need to be resolved in the roof details and scope of works.
Panel Layout Matters Too
Metal roofing should not be treated simply as a finish applied once the roof structure is complete.
Panel widths and lengths, seam positions, roof geometry and penetrations can all affect how the finished roof is laid out.
Longer panels can also influence fabrication, transport, handling and access.
On one of our aluminium roofing projects in Maynooth, we formed seven metre panels in the factory. The panel layout and fabrication therefore had to be considered together. It was not something that could be decided once the material arrived on site.
That kind of planning becomes particularly important on extensions where access may be restricted or the new roof sits below existing windows, balconies or other completed areas.
Exposure Needs to Be Part of the Specification
The location of the building also matters.
A roof in a sheltered urban setting does not face exactly the same conditions as one in a coastal or highly exposed location. Wind exposure, rainfall and the surrounding environment can influence the system specification, fixings, detailing and finish.
The answer is not simply that zinc suits one type of location and aluminium another. The proposed material needs to be checked against the particular system, manufacturer guidance and conditions on that project.
Compare the Whole Roofing Package, Not Just the Roof Covering
Price comparisons can become misleading if the quotations do not cover the same scope.
One contractor may be pricing the main standing seam covering, while another quotation also includes cappings, flashings, roof edges, outlets or other fabricated components.
Roof geometry, access, finish, panel layout and the amount of bespoke fabrication can all affect the final cost.
Our in house fabrication workshop allows us to produce items such as cappings, flashings and roof edge profiles alongside the roofing work. Where these form part of the same package, measurements, finishes and installation requirements can be reviewed together rather than treated as separate items later in the programme.
Where a project also needs made to measure aluminium details, our custom aluminium fabrication service covers items such as flashings, cappings, trims and other roofline components.
So, Zinc or Aluminium?
There is no single answer for every extension.
If the design calls for a natural metal finish that will change as it weathers, zinc may suit the project well.
If a particular coated colour is important, especially where the roof needs to coordinate with windows or other external metalwork, an aluminium system may be more appropriate.
But appearance is only part of the decision.
The roof pitch, build up, exposure, panel layout, junctions, fabrication requirements and overall roofing scope all need to be considered before the material is confirmed.
If you have drawings for an extension or refurbishment where zinc or aluminium roofing is being considered, send them to us while the details are still open. We can review the roof build up, junctions and wider roofing package before the specification is finalised.
