Heat insulation: which type is worth it and where it works best

About 70% of the heat entering a Thai house comes through the roof; the rest through west-facing walls and glass. So the first money for a cooler house should always go "under the roof and above the ceiling"

The 4 main types of insulation

• Fiberglass — Foil-faced rolls laid on the ceiling: the standard, best value per baht. Thicker is better (higher R-value); 3–6 inch rolls are popular and easy to fit in new or old houses
• Reflective foil sheets — Fixed under the roof purlins to reflect radiant heat before it enters the roof space; cheap, and it does a different job from fiberglass — using both together is best: reflective foil as the first layer, fiberglass on the ceiling as the second
• Spray PU foam — Sprayed directly under the roof sheets; excellent heat protection and reduces rain noise (a perfect match for metal sheet). More expensive; use skilled installers because uneven spraying is wasted money
• PE foam — Thin foam factory-bonded under metal sheets; basic heat protection, better than nothing, but don't expect as much as PU or thick fiberglass

Order of value (for a small budget)

Step 1: Fiberglass 3 inches or thicker on the ceiling throughout — the clearest result for the money Step 2: Ventilate the roof space (gable vents or turbine ventilators) so hot air has a way out Step 3: Shade west-facing walls — trees, slats or wall insulation Step 4: Film or awnings on sun-facing glass

Common misconceptions

High ceilings make a room "feel" airy but don't block heat without insulation · heat-reflective house paint really helps but is a supplement, not a substitute for insulation · lightweight blocks do insulate better than clay bricks, but walls take only ~30% of the heat — don't pour the budget into walls and leave the roof bare

Houses that complete steps 1–2 usually lower afternoon indoor temperatures by 3–5 degrees, which translates directly into lower AC bills every month — paying back in 2–4 years for houses that run AC regularly