Building Materials for a House in Kerala: Laterite, Brick, AAC and Monsoon Detailing

For most houses in Kerala, build the walls in laterite or burnt clay brick (AAC or concrete block where budget or speed decides), put a steep, deeply overhanging tiled roof over them, lift the floor on a proper plinth with a damp-proof course, and finish with plaster and paint made for damp. The reason is the rain: about 3,000 mm a year in Kochi and Kozhikode, most of it between May and October. Below: what the climate and ground ask for, how each material answers, and what PWD Kerala's own schedule says it costs.

What Kerala's climate and ground ask of a house

Rain, heat and humidity

India Meteorological Department climatological tables for 1981 to 2010 give Kochi an average of 3,015 mm of rain a year over 124 rainy days, with 700 mm in June alone. Kozhikode averages 3,054 mm and Thiruvananthapuram, the driest of the three, 1,761 mm. Mean daily highs sit between 29 and 34 °C and lows between 22 and 26 °C: warm and humid rather than very hot.

The Bureau of Energy Efficiency's Eco-Niwas Samhita 2018 lists Kochi and Thiruvananthapuram as warm-humid. For that zone it asks for openable windows of at least 16.66% of floor area (a figure adapted from the National Building Code 2016) and a roof U-value no higher than 1.2 W/m²K. The code covers plots of 500 m² and above, but both are sensible targets for any house here.

Soil and slope

Kerala's ground falls into three belts. A study funded by the Kerala State Disaster Management Authority describes them for Kozhikode district: lowland below 7.6 m above sea level, midland from 7.6 to 76 m and highland above, with alluvial soil along the coast and valleys and reddish, well-drained lateritic soil across the midlands. It also records slope failures in the Western Ghats, so a highland plot needs a geotechnical check, and a coastal or backwater plot needs a soil test before the foundation is fixed.

Seismic zone

Kerala lies in Zone III, the moderate zone, of IS 1893 (Part 1):2016; the National Center for Seismology's report on the 2020 Idukki tremors cites that code and zone. BIS issued a revised map in November 2025 but withdrew it in March 2026 and reverted to the 2016 standard, as ETV Bharat reported. Whatever the wall material, follow the bands and corner reinforcement your engineer specifies.

Walls: laterite, brick, AAC or blocks

Laterite, Kerala's own stone

Laterite is cut from the midland ground itself, and the standard for it, IS 3620:1979, lists Kerala among the states where it occurs. It notes that fresh laterite is soft and hardens on exposure, so blocks should preferably be seasoned for about three months, kept out of the rain, before they go into a wall. For masonry it asks for a compressive strength of at least 3.5 N/mm² and water absorption of no more than 12% by mass. Ask to see seasoned stock, reject crumbly blocks, and keep exposed laterite under generous eaves.

Burnt clay brick

Brick is the other long-standing answer. IS 1077:1992 grades common burnt clay bricks by compressive strength and limits water absorption to 20% by weight for bricks up to class 12.5. Ask the kiln for a test certificate. Exposed brick stays good only under deep eaves; on a wall facing the south-west monsoon, plaster is safer.

AAC and concrete blocks

Autoclaved aerated concrete (AAC) blocks are light, large and quick to lay. IS 2185 (Part 3):1984 covers AAC blocks up to a density of 1,000 kg/m³, and PWD Kerala's items specify Grade I blocks laid with polymer adhesive and RCC bands at sill and lintel. Solid and hollow concrete blocks to IS 2185 (Part 1) are the cheapest walls in the PWD schedule. Interlocking and stabilised earth blocks save mortar on small buildings; ask which standard they are tested to and get your engineer to approve the system. With any block, judge the product by its BIS licence and a recent test certificate, and plaster it well outside.

Roofs: slope, tiles and deep eaves

A steep roof with deep overhangs does two jobs in Kerala: it throws rain clear of the walls and shades them. The traditional covering is the Mangalore-pattern clay tile. IS 654:1992 notes these interlocking tiles are made on a large scale in southern India, grades them as Class AA and Class A, and caps water absorption at 18% and 20% respectively. Tiles over a sloping RCC slab give a second line of defence against leaks; tiles on a treated timber or steel frame are lighter. Either way, check the tile class and the fixings.

Flat RCC roofs work only if they are laid to fall and properly waterproofed. Private Residente 1, a Cochin house by THOMAS+ASSOCIATES, takes the pitched, tiled route with wide eaves.

Foundations, plinth and termites

Firm midland ground often suits rubble or laterite masonry foundations for low-rise houses; coastal sand, filled paddy land or soft clay may need a raft or piles. Land checks come first, and our permit guides for Kochi and Thiruvananthapuram explain them.

Above the foundation, build a plinth high enough to clear flood and splash water on your site, with a damp-proof course on top. Termites are a real risk in warm, wet ground: IS 6313 (Part 2) sets out pre-construction chemical treatment of the soil under and around the building. It is cheap at foundation stage and hard to add later.

Plaster, finishes and floors

Walls here stay damp for months, and humid air grows mould and algae. Use drip moulds over openings, sunshades and eaves, and exterior paint made for damp and fungus, applied only once the plaster has dried. For floors, vitrified tiles are the default and terracotta or oxide the traditional choices; the plinth and damp-proof course matter more than the tile.

Timber in a humid climate

PWD Kerala's own schedule prices door and window frames in Anjili or jack wood, Pincoda and Vengai, which shows the timbers in local use. Use seasoned, treated timber, keep it away from wet masonry, and consider steel for hidden roof members termites could reach.

The Laurie Baker tradition

COSTFORD, the Centre of Science and Technology for Rural Development, was founded in Thrissur in 1985 by C. Achutha Menon, K.N. Raj, the architect Laurie Baker and T.R. Chandra Dutt. Its material and technology notes describe rat-trap bond brickwork, which it says uses 25% fewer bricks, filler slabs that it says cost 30 to 35% less than conventional concrete roofs, brick jali walls and arches that avoid lintels. These are COSTFORD's own figures; the techniques need a skilled mason.

What these materials cost: PWD Kerala's schedule

Per cubic metre, laterite, brick, block and AAC walls sit within about ₹1,300 of each other, so durability and detailing should decide more than price. The cost index is what an engineer applies to DSR-based rates for a local estimate. For current prices, get written quotes from two or three local suppliers. For the whole-house budget, see our Kochi construction cost breakdown or MOA's home cost calculator.

Mistakes to avoid

• Fresh laterite straight into the wall. Let it season and harden first.
• Short eaves on exposed brick or laterite. Soaked walls stain, grow algae and let damp through.
• A flat roof with no fall and cheap waterproofing.
• A low plinth on a low plot. Raise the floor above the worst water your site has seen.
• Skipping anti-termite treatment at foundation stage.
• Buying blocks or tiles without a BIS mark and a dated test certificate.
• Painting before the plaster dries, which traps moisture and lifts the paint.

FAQ

Which brick is best for house construction in Kerala?

There is no single best. Laterite and burnt clay brick are proven in Kerala's rain; AAC and concrete blocks are quicker and, in PWD's schedule, slightly cheaper per cubic metre. Check the BIS test certificate and protect the wall with eaves and plaster.

Is laterite better than brick for a Kerala house?

Both work. Laterite is local to the midlands and needs seasoning and careful selection; brick is more uniform. In PWD Kerala's 2021-base schedule, laterite masonry is about ₹800 per cum dearer than class 7.5 brick, before the district cost index.

Is AAC block good in Kerala's climate?

Yes, if it is BIS-licensed, laid with the right adhesive and RCC bands, and plastered well outside. Like any wall, it fails when it is left wet.

What roof is best for heavy rain in Kerala?

A pitched roof with deep eaves: Mangalore clay tiles over a sloping RCC slab or a treated frame. A flat RCC roof can work, but it needs a proper fall and waterproofing.

Choosing materials for your own plot? An architect who knows your district can match them to your site, budget and the monsoon. Find an architect on MOA, or browse studios in Ernakulam and Thiruvananthapuram.

Sources

• India Meteorological Department: climatological tables 1981 to 2010 for Kochi, Kozhikode and Thiruvananthapuram (accessed 17 Oct 2026)
• Bureau of Energy Efficiency: Eco-Niwas Samhita 2018, Part I, Building Envelope (accessed 17 Oct 2026)
• Kerala State Disaster Management Authority: Landslide Susceptibility Assessment and Preparedness Strategies, Thiruvambady, Kozhikode (Christ College, Irinjalakuda, 2019) (accessed 17 Oct 2026)
• National Center for Seismology: report on micro-earthquakes in Idukki district (Sept 2020) (accessed 17 Oct 2026)
• ETV Bharat: A bold policy reversed, the withdrawal of India's 2025 seismic code (11 Mar 2026) (accessed 17 Oct 2026)
• Bureau of Indian Standards, via Public.Resource.Org: IS 3620:1979 Laterite stone block for masonry, IS 1077:1992 Common burnt clay building bricks, IS 2185 (Part 3):1984 Autoclaved cellular concrete blocks, IS 654:1992 Clay roofing tiles, Mangalore pattern and IS 6313 (Part 2):2001 Anti-termite measures, pre-constructional chemical treatment (accessed 17 Oct 2026)
• COSTFORD: About COSTFORD and Material and technology (accessed 17 Oct 2026)
• Public Works Department, Kerala: PRICE portal, data book (DAR civil, DSR 2021 base, revision 40), approved market rates and civil cost index (accessed 17 Oct 2026)