The short answer
Insulated roof panels make sense when a commercial building needs a new, weathertight and warm roof in a single pass and the structure can carry them. A panel is a factory-made sandwich of two steel skins around insulation, fixed as one layer. Built-up sheets add the liner, the insulation and the outer sheet one at a time. The right choice depends on the building.
Both systems keep a unit dry and warm. They differ in speed, in how they cope with condensation and in what the existing roof can carry.
What a panel is and how it differs
An insulated composite panel is made in a factory. An outer steel skin, a core of insulation and an inner steel skin are bonded together, so the roof goes up as one layer and arrives as a finished, insulated sheet. The panels are lifted onto the purlins, the beams the roof rests on, and fixed down through the outer skin.
What is a built-up sheet system instead?
A built-up roof is assembled in layers on site. An inner liner sheet goes onto the purlins, then spacers or rails, then a layer of insulation, then the outer profiled sheet. Each layer is a separate task, so the system can be adapted to awkward shapes and varied insulation depths, and it can be repaired in sections later.
Panels suit simple, regular roofs where speed and a clean ceiling line matter. Built-up systems suit buildings where the roof shape, the loads or the insulation depth vary from bay to bay. Neither is better in the abstract, and a good roofer will tell you which one the building in front of them calls for, with the reasons laid out in plain words.
When panels earn their place
A panel is a good fit when the whole roof is coming off, the structure is sound and the building cannot stand open to the weather for long. Fewer layers means fewer trades on the roof and a shorter exposed period. The inner skin gives a smooth, easy-to-clean ceiling, which food, storage and workshop uses often want.
Do panels suit a re-roof over an existing roof?
Sometimes, but the old roof has to be checked first. A new panel roof laid over the old sheets is overcladding, and that raises questions about the load on the purlins and what lies beneath. Our page on roof overcladding covers it.
Where the existing roof is fibre cement of unknown age, the asbestos question comes before the panel choice. Building Regulations can apply to a new roof covering, and a covering that weighs 15 per cent or more above the one it replaces needs approval, which brings the frame under the deck into the decision too. Your building control body in Taunton is Somerset Building Control, and a call to them costs nothing before you commit.
Condensation and how it is controlled
Warm, damp air inside a building meets a cold surface and turns to water. In a roof that surface can be the underside of the outer sheet. Drips from condensation get blamed on the roof, and they can fall for months before anyone works out that the roof itself is sound. A moisture reading and a look at the weather on the days it drips usually separate the two causes.
Do insulated panels stop condensation?
They reduce it by keeping the inner skin warm, so damp air has no cold surface to settle on. The result depends on the joints. Performance rests on the sealed laps, the end seals and the junctions at the ridge, the rooflights and the eaves, because moist air finds any gap and condenses where it meets cold steel.
In a built-up roof, the liner and its seals do the same job. If your unit has a wet process, such as a kitchen, a wash bay or damp storage, tell the roofer at the start, because the amount of moisture in the air changes the design. A roof specified for a dry warehouse can drip in a food unit.
What decides the choice, and the price
There is no single right answer, and a roofer who offers one before seeing the building is guessing. We look at the structure, the condition of the purlins, the shape of the roof, how the building is used and how long it can stay open to the weather.
Why is there no price on this page?
Panel and built-up costs move with the area, the insulation depth, the access, the rooflights and the state of whatever lies beneath. A figure borrowed from another building would mislead you. What you receive after the survey is photographs of the building and one written total for the panel system that suits it, with the reasons laid out next to that total.
If the old roof is leaking while you decide, read about why unit roofs leak at the laps, and for a coating alternative see liquid coatings on commercial roofs. The overview of this work is on our commercial roofing page. To begin, send the building's dimensions and a few photos of the roof.
Choosing a roof system
Can panels go over my existing sheets?
Sometimes. The old roof and the purlins must be sound, the extra load must be acceptable, and any asbestos cement must be dealt with first. A survey decides it. Where the building is old, we check the structure from inside before recommending overcladding or a full strip.
Will a panel roof make the building quieter in rain?
Insulation in the core tends to soften the drumming of rain on steel, and an inner skin helps further. How much quieter depends on the panel and the building, so if noise matters to your business, mention it as soon as you book the visit, and the options can be talked through then, including an acoustic layer where the building calls for one.
The full picture: Commercial roofing in Taunton ยท More short answers