Single skin vs double skin roofing: sheet, built-up roof or PUF panel

What do single skin and double skin mean?

Single skin

One layer of profiled metal sheet (GI, galvalume or colour-coated) screwed to the purlins. It keeps rain out but does almost nothing for heat, noise or condensation.

Double skin, built-up

An inner liner sheet, spacers or sub-purlins, a layer of insulation such as glass wool or rockwool, and an outer weather sheet, all assembled on site.

Double skin, sandwich panel

Two steel skins bonded to a rigid PUF (or PIR) core in the factory, delivered as one panel and fixed in one operation. In India this is often what people mean by a “double tin” or “double sheet” PUF roof.

How do the three roofs compare?

Is a built-up double skin roof as good as a PUF panel?

It can be, on paper. With enough mineral wool between the sheets, a built-up roof can match or beat a PUF panel’s U-value, and mineral wool cores bring better fire performance. Built-up roofs are common on very large industrial buildings and where the fire specification rules out foam cores.

The catch is site quality. The insulation has to be laid without gaps, kept dry during installation and protected by a sealed liner, or it slumps and loses performance. A factory sandwich panel arrives with the insulation already bonded in place, goes up faster, and gives the same result on every sheet. For most small and medium sheds, cabins and cold rooms, panels are simpler.

When is a single skin sheet enough?

• Single skin is enough for open-sided sheds, vehicle parking, canopies and storage of goods that do not mind heat or a little condensation.
• Choose a PUF sandwich panel for warehouses, factories, workshops, site offices and homes, where people work under the roof or stock is sensitive to heat or drips.
• Consider a built-up roof on very large spans where the fire specification asks for mineral wool, or a PIR or rockwool panel as the factory-made alternative.

Upgrading a single skin shed is usually done by replacing the sheets with roof panels on the same frame, after checking purlin spacing against the maker’s span table. The PUF panel vs tin shed guide covers that decision in more detail.

What to specify when you order a double skin PUF roof

1. Core thickness: 30–50 mm is typical for ambient sheds; thicker for air-conditioned or very hot buildings.
2. Skin thickness and coating for each face, for example 0.5 mm PPGL outside and 0.4 mm inside: see PPGI vs PPGL.
3. Colour of each face, and whether the inner face is exposed as the ceiling.
4. Panel lengths for each slope, the roof pitch and the purlin spacing.
5. Ridge, eave and gable lengths for flashings, which are made as per your requirement.
6. Any skylights, ventilators or roof penetrations, so the panels and flashings around them can be planned before cutting.

Rates for each roof thickness and sheet are on the roof panel price pages. Transport is extra and quoted for your pincode. If you are replacing an old single skin roof, send a photo of the existing frame and the purlin spacing with your enquiry; it makes the first quote far more accurate.