How to thermally insulate an existing roof
The right order of layers and why each one matters. Built for roofs that are already installed, without rebuilding.
On an existing roof, the biggest comfort jump for the lowest spend usually comes from adding a ceiling where there isn't one and applying a reflective coating, then reinforcing with a radiant barrier and insulation. Each layer attacks a different link in the heat chain.
The layers, in order
Reflective finish
Reduces solar absorption at the source. Big effect for low cost See.
Ceiling and air gap
Slows the roof's radiation toward people.
Radiant barrier
Reflects the remaining radiant heat: 8 to 12% less cooling needed See.
Insulation
Resistance to conduction. Choose the material based on fire, moisture and thickness See.
Ventilating the air gap
Lets hot air escape and avoids trapping moisture.
Your roof could be the point letting in the most heat.
A diagnosis determines exactly which layers your roof needs, without overselling. Gallardía assesses and installs.
◆ Sources for this page
Every important claim links to its evidence. Tap to see the source, its context and its limits: DOE PNNL Insulators. Full bibliography in the evidence library.