Insulationheat, noise and condensation

Where the heat actually comes from

Almost all of the heat load in a steel shed arrives through the roof as radiant heat from the sun, not through the walls. That is why a shed with insulated walls and a bare roof still cooks, and why the cheapest effective upgrade is always roof insulation plus a way for hot air to escape at the ridge.

The second source is trapped air. Hot air stratifies under the roof sheets and stays there unless you give it an exit at the high point and a low intake to replace it. Insulation slows heat getting in; ventilation removes the heat that is already there. You need both.

Roof insulation is installed as the sheeting goes on — the foil-cell sheet is rolled out over the purlins and the roof sheets fix through it. That means it is genuinely difficult and expensive to add later, because retro-fitting means lifting the roof or working underneath it.

Insulation options compared

All of these sit under the roof sheeting and are installed as the roof goes on. Choosing at quote stage costs a fraction of adding it later, because the roof has to come off to do it properly.

We only use reflective cellular foil systems — bubble core and closed-cell foam core products laminated between aluminium foil facings. They cost more than wool blanket. They are the right product for a steel building in this climate.

Insulated panels are for our patios

Insulated panel, also called sandwich panel, is a different roofing system rather than an under-sheet shed insulation. We use insulated panels in different thicknesses starting at 50 mm for patios and outdoor living areas where a cooler, quieter roof and a clean finished underside are important.

Spartan Sheds does not build cold rooms. If you are comparing roofing for an insulated patio, see our patios and awnings range or ask us which panel thickness suits the span and comfort level you want.

The condensation problem

On a clear night, a steel roof radiates heat to the sky and drops below the dew point of the air inside the shed. Moisture condenses on the underside of the sheeting and drips. People blame a leaking roof; it is almost never a leak.

A reflective foil-cell product keeps the underside of the sheeting above dew point and gives the moisture somewhere to go, which is why we recommend it even on open structures like carports where nobody cares about heat but everybody cares about drips landing on a car.

• Reduces radiant heat gain through the roof
• Deadens rain noise on steel sheeting
• Controls condensation dripping onto vehicles and stored goods
• Works alongside roof ventilation rather than instead of it

Why we do not use wool or fibreglass

Plenty of sheds are still insulated with fibreglass or polyester wool blanket. It is cheaper, and in a steel shed it is the wrong product. Wool blanket needs wire mesh strung underneath to stop it sagging — that wire is there to hold the blanket up, not for safety — and the blanket holds moisture. Once it takes up water from a condensation event or a wind-driven shower during construction, it stays damp against your steel and slumps out of shape.

The reflective cellular products we use — GIBS Reflecta-Shed Plus™ and Plus V2™, Fletcher Sisalation® Bubble Cell and Foam Cell Shed Liner — are a sealed foil laminate over a bubble or closed-cell foam core. They hold their own shape, so no support wire is needed, nothing absorbs moisture, nothing sags, and the finish overhead is clean and bright instead of dusty wool.

Reflecta-Shed Plus V2™ is also wire-free. Reflecta All-In-One™ is the separate GIBS product with encapsulated roofing wire and fall-arrest functionality. Where that system is required, it combines the wire and insulation in one purpose-made product.

They cost more than wool blanket. We quote them anyway, because they are the product that suits a steel shed in this climate and they still look right in ten years.

Insulation and ventilation are a pair

Insulation slows heat getting in. Ventilation moves out the heat that is already there. Do one without the other and the result is disappointing — an insulated shed with no ventilation still builds up hot, still air through the day.

The combination we recommend most often for a Bundaberg workshop is roof insulation plus ridge or roof ventilators, with windows or wall vents low down to let cooler air in as the hot air leaves.

• Ridge or roof ventilators — the most effective option, exhausting hot air at the highest point of the building
• Whirlybirds — wind-driven turbine vents, low cost and effective in a breeze, less so on a still day
• Powered ventilators — for workshops, welding bays and anywhere with fumes or heavy machinery
• Wall vents or louvres low on the walls — the intake air that makes any roof vent actually work
• Roller doors and PA doors positioned to give cross-flow when they are open

COLORBOND® colour and heat

Roof colour genuinely matters here. Lighter COLORBOND® roof colours reflect substantially more solar heat than dark ones, and every COLORBOND® colour except Night Sky® is available with Thermatech® solar reflectance technology, which lowers roof surface temperature without changing the colour you chose.

If the shed is going to be a workshop and you have freedom on colour, a lighter roof in Surfmist®, Shale Grey™, Dune® or Classic Cream™ will run cooler than Monument® or Basalt®. If the roof has to match a dark house roof, put the money into insulation and ventilation instead.

What we would specify for a Bundaberg workshop

• Reflective cellular foil to the roof — GIBS Reflecta-Shed Plus™, or Plus V2™ if you work in there regularly
• Two roof ventilators or whirlybirds, sized to the roof area
• Wall vents low on the two long walls for intake
• Foil-cell insulation to the western wall
• A lighter roof colour where the look allows it
• Wall height 3.0m or more so hot air sits above head height