Metal Building Insulation: Stopping Radiant Heat and Condensation
Steel roof and wall panels soak up the sun and radiate that heat straight into the building. In cooler months the opposite happens: warm, moist inside air meets cold steel and condenses, and the roof starts to drip. A reflective liner deals with both problems.
Why a reflective liner works
- Reflects radiant heat: the metallized face turns back heat radiating from hot panels. It needs an air space next to it; a 3/4 in (19 mm) gap is the basis for the R-values we publish.
- Helps control condensation: bubble liners are low-perm films. Installed with overlapped, taped seams, they slow warm, moist air on its way to cold steel, which is the usual cause of dripping roofs.
- Finishes the interior: the white face of foil/white products gives a bright, clean surface, so no extra ceiling is needed.
Which IIP product goes where
| Part of the building | Product | Why |
|---|---|---|
| Roof, over or under purlins | Double Bubble Foil/White or Foil/Foil | White face down for a finished ceiling |
| Walls, on the girts | Double Bubble Foil/White | Wide rolls mean fewer vertical seams |
| Highest R-value walls and roofs | Superbubble 1 in (25 mm) | R-37 wall and R-48 roof systems |
| Budget or light-duty buildings | Single Bubble Foil/White | Lighter, lower cost per roll |
| Seams and edges | IIP seam tapes, 2 to 4 in (51 to 102 mm) | White tape on white faces, aluminum on foil |
The numbers
Double Bubble Foil/White gives R-17.2 (RSI 3.03) as a system with heat flowing down (ASTM STP1116 method). Double Bubble Foil/Foil gives R-7.95 heat flow down and R-5.42 horizontal with at least a 3/4 in (19 mm) enclosed air space. Both are Class A / Class 1 under ASTM E84.
How to install
- Measure the roof and wall areas and choose a roll width that suits your purlin or girt spacing. Widths run from 4 to 8 ft (1.22 to 2.44 m), on 125 ft (38.1 m) rolls.
- New buildings: run the liner across the purlins and girts before the panels go on. Existing buildings: fix it to the inside of the framing.
- Keep an air space of at least 3/4 in (19 mm) on the reflective side, using the framing, spacers or furring.
- Overlap sheets by at least 2 in (51 mm) and seal every seam with IIP tape so the liner is a continuous vapor retarder.
- Seal edges and penetrations, then install the panels or interior trim.
Ventilation and sealing gaps at the eaves and ridge still matter for condensation. Always follow local codes and the product data sheet.
Questions we get asked
Can I add a liner to an existing building?
Yes. Fix it to the inside of the purlins and girts, keep the air space on the reflective side and tape every seam.
Will it stop my roof from dripping?
A liner with overlapped, taped seams acts as a vapor retarder, the main defense against condensation on steel. Ventilation and sealing gaps at the eaves and ridge still matter.
Pricing a metal building? Send the roof and wall square footage and your ship-to ZIP through our quote form. More detail on our metal building insulation page.