Insulation is not a strategy
Adding resistance to a wall is a decision about one term in a balance. In several Indian climates it is not the term that matters.
Insulation has become shorthand for environmental seriousness. It is measurable, specifiable, and easy to point at in a drawing. It is also, in a large part of the country, not the first thing a building needs.
Resistance answers conduction. Most of India's envelope problem is not conduction.
In a hot dry climate the dominant term is direct solar gain on surfaces and through glass. A wall with twice the resistance and no shade in front of it is still receiving the same enormous incident load; it simply takes marginally longer to pass it on. Shade removes the load rather than delaying it.
In a warm humid climate the dominant term is moisture, and the resource that insulation would normally protect — a cool interior charged overnight — barely exists, because the diurnal swing is small. Worse, an assembly detailed to hold heat out is frequently detailed to hold moisture in.
None of this is an argument against insulation. It is an argument for order. Establish which term dominates in this climate, on this orientation, for this use, and then decide what the envelope is made of.
- 01Hot & dry — shade first, then mass, then resistance.
- 02Warm & humid — shed and dry first, then air movement, then modest resistance.
- 03Composite — sequence for the worse season, then check the other has not been made unliveable.
- 04Cold — resistance and airtightness genuinely do lead.
The failure mode we see most often is not an under-insulated building. It is a well-insulated building that never had its solar loads or its drying paths resolved, and which therefore performs no better than the one it replaced.