Thermal insulation under a tile roof

Ron Arad, civil engineer
Arad Bedek Bayit

Introduction
You bought a private house with a tile roof, plus a nice attic you could turn into half a room or storage space.
But the heat in that attic, and even in the rooms below it, is unbearable in summer.

Running the air conditioner all day is expensive, and it still doesn't solve the problem at night in houses where nobody wants the AC running around the clock.
Thermal insulation can solve that, or at least cut it down significantly.

It's one of the things worth checking in a home inspection, whether you're buying a new house or a resale one: is there thermal insulation under the tile roof?

What the standard requires

Israeli Standard 1045, which covers thermal insulation, isn't clear-cut here. Where a tile roof sits over a light ceiling, such as plasterboard, rather than a concrete one, the standard is unambiguous: insulation is required.

The gray area is a flat concrete ceiling under the tile roof, where there's no explicit requirement.
In our experience inspecting thousands of apartments across the country, insulation always helps and always lowers the temperature in the top-floor rooms, and even more so in the attic.

Types of insulation

Several types exist. The most common is rock wool coated in aluminum foil on both sides, supplied in "blankets" that attach to the roof structure and to each other, forming an insulating layer under the tile roof. That layer significantly cuts the heat that reaches the attic and, from there, the floor below.

What insulation does in winter

The same insulation is also valuable in winter, when it keeps cold from getting in through the roof and protects the top floor. Poor insulation can also cause condensation problems in winter: vapor building up inside the house meets surfaces near the ceiling that are too cold, condenses, and creates moisture, which then attracts the spores that grow into mold. Good insulation, as described above, prevents or significantly reduces that condensation problem too.

Summary

We recommend a home inspection that checks for construction defects in the structure, and, for this topic specifically, pays attention to thermal insulation. Many home inspection engineers who check a building for defects skip the insulation question wherever there's a concrete ceiling under the tile roof, since it isn't formally a construction defect there.

Our experience tells us otherwise: it's worth telling a resale-house buyer, during the inspection they've ordered, that insulating the roof is worthwhile regardless, simply because it improves quality of life in both summer and winter.