Red Brick, AAC, Fly Ash or Concrete Block: Which Wall Material Suits Your House?

For most new houses in India, which are built as a reinforced concrete (RCC) frame with walls filled in between, any of the four common wall materials can work. The choice comes down to heat, water and local supply. As guidance: AAC blocks insulate best by a wide margin, fly ash-lime bricks are the closest swap for red brick (and the law pushes you towards them near a thermal power plant), burnt clay bricks remain the material for exposed brickwork and traditional load-bearing walls, and concrete blocks suit compound walls and fast, dry construction.

Below, each is compared on what its Bureau of Indian Standards (BIS) code requires, Bureau of Energy Efficiency (BEE) thermal values and CPWD rates.

The short answer, by situation

• RCC frame house, hot climate, you want cooler rooms: AAC block infill walls, rendered outside. Its thermal conductivity is a fraction of brick's (see the table).
• RCC frame house, you want brick-like behaviour at a lower rate: fly ash-lime bricks to IS 12894. They are laid like clay bricks, in the same sizes.
• Exposed brick walls, or a traditional load-bearing house your engineer has designed: burnt clay bricks to IS 1077, in a class your engineer specifies.
• Compound walls, service blocks, quick partitions: solid or hollow concrete blocks to IS 2185 (Part 1).

This is guidance, not a rule: your architect and structural engineer should fix the material and class for your site.

What the Indian Standards require of each material

Burnt clay bricks (IS 1077)

IS 1077:1992 classifies common burnt clay bricks by average compressive strength, from class 3.5 up to class 35 N/mm². The familiar 230 × 110 × 70 mm brick is allowed alongside the modular 190 × 90 × 90 mm. After a 24-hour soak, water absorption may not exceed 20% by weight up to class 12.5 and 15% for higher classes. Efflorescence (the white salt bloom) may be no worse than "moderate" up to class 12.5 and "slight" above it. The code sets no density limit; BEE lists solid burnt clay bricks between 1,440 and 1,920 kg/m³.

One caution: BIS published IS 1077:2025 in November 2025. We could not open that paid edition, so these figures are from 1992; ask which edition your supplier's test certificate cites.

Fly ash-lime bricks (IS 12894)

IS 12894:2002 covers bricks made mostly of fly ash and lime, which react to form a calcium silicate binder. Classes run from 3.5 to 30 N/mm² (wet strength), in clay brick sizes. Water absorption limits are the same as IS 1077 (20% up to class 12.5, 15% above), and average drying shrinkage may not exceed 0.15%. BEE lists fly ash brick at 1,650 kg/m³ with a thermal conductivity of 0.856 W/m·K, almost the same as a mid-density clay brick. We read the 2002 text with its 2011 amendment; ask the supplier for any later one.

AAC blocks (IS 2185 Part 3)

IS 2185 (Part 3):1984 covers autoclaved aerated concrete blocks with oven-dry density up to 1,000 kg/m³, in five density bands from 451 kg/m³. Minimum compressive strength depends on the band: from 2.0 N/mm² (Grade 1) or 1.5 N/mm² (Grade 2) in the lightest band, up to 7.0 and 6.0 N/mm² in the densest. Each band has a maximum thermal conductivity (0.21 to 0.42 W/m·K) and drying shrinkage is capped, but the code sets no water absorption limit. Its foreword says AAC is used for load-bearing and non-load-bearing walls, and for external walls "when protected from weather by rendering". BIS still lists the 1984 edition as current, with one amendment that we could not open.

Concrete blocks (IS 2185 Part 1)

IS 2185 (Part 1):2005 covers hollow and solid blocks made with normal-weight aggregate. Hollow Grade A blocks (density at least 1,500 kg/m³) come in strengths from 3.5 to 15 N/mm²; Grade B (1,100 to 1,500 kg/m³) in 3.5 and 5.0; solid Grade C blocks (at least 1,800 kg/m³) in 4.0 and 5.0. Water absorption may not exceed 10% by mass. It requires blocks to be cured and then dried for 4 weeks before use (7 days after low-pressure steam curing). BEE lists solid concrete block at 1.40 to 1.41 W/m·K, the highest of the four.

Hollow clay blocks

Perforated clay blocks fall under IS 3952; we could not open its 2013 edition, so we quote none of its figures. BEE lists a "resource efficient (hollow) brick" at 1,520 kg/m³ and 0.631 W/m·K, which puts it between solid brick and AAC for heat.

Exposed brick, like the screen on this Nagpur house design, is where clay brick is hardest to replace. With the face bare, water absorption and efflorescence matter more, so as guidance ask for a higher class and its test results.

Heat: what the thermal numbers mean for a wall

Thermal conductivity is how easily heat passes through a material. The BEE residential code, Eco-Niwas Samhita, gives a method to turn it into a wall U-value (lower is better). Using that method and its published values, with 12 mm plaster inside and 15 mm outside, we get these illustrative figures:

• 230 mm clay brick (1,760 kg/m³): about 2.1 W/m²·K
• 230 mm fly ash-lime brick: about 2.1 W/m²·K
• 200 mm solid concrete block: about 2.85 W/m²·K
• 200 mm AAC block: about 0.77 W/m²·K

So an AAC wall lets through roughly a third of the heat of a similar brick wall. Eco-Niwas Samhita 2018 caps the envelope's heat gain (its RETV) at 15 W/m² for composite, hot-dry, warm-humid and temperate climates (BEE issued a 2024 edition since). Your architect can run the full calculation, including windows and shading. Our sustainable building cost and benefit guide covers where else the energy savings come from.

The fly ash rule near thermal power plants

The Ministry of Environment, Forest and Climate Change's ash utilisation notification (S.O. 5481(E), 31 December 2021) was amended on 1 January 2024 by S.O. 05(E). Its paragraph B(8) now reads that all building construction projects of Central, State and local authorities, government undertakings and agencies, "and all private agencies", located within 300 km of a coal or lignite thermal power plant shall use ash bricks, tiles, sintered ash aggregate or other ash-based products. The condition is that they are offered at no more than the CPWD or state PWD Schedule of Rates price. Local authorities are also told to provide for ash-based products in their bye-laws.

Ask your architect whether your plot is within that radius and what your bye-laws now say. In practice that usually means fly ash-lime bricks; AAC may also contain fly ash, which IS 2185 (Part 3) allows.

What it costs: CPWD rates

Compare walls per cubic metre or per square metre of finished wall, not per piece: blocks are larger, use less mortar and may need thinner plaster. For item-rate contracts, DSR descriptions make a useful template (see turnkey, item-rate and labour-rate contracts). For the whole house, use the MOA home cost calculator and our state-wise cost breakdown for the whole house.

How to check what you are buying

1. Ask which standard and class. The quote should name the IS code and a class or grade, such as A(7.0) for a concrete block.
2. Check the markings. Concrete blocks must carry the maker's identity and grade; AAC lots must show maker, grade, density and month of manufacture.
3. Verify the ISI mark. If the product carries the BIS Standard Mark, enter its CM/L licence number in the BIS Care app to see the licensee's details.
4. Ask for a recent test certificate for compressive strength and water absorption, dated and for your lot. Both block codes also let the buyer order independent tests on samples taken at delivery.
5. Do not lay green concrete blocks. Ask how long they were dried; IS 2185 (Part 1) requires 4 weeks after normal curing.

Mistakes to avoid

• Leaving AAC or concrete block walls unrendered on a rainy face. The AAC code expects external walls to be protected by rendering.
• Choosing the strength class by price. For load-bearing walls the class is a structural decision for your engineer.
• Mixing materials in one wall without detailing the joint. Different materials shrink and move differently, and cracks often appear at the junction (guidance).

For how these choices fit into a green rating, see IGBC, GRIHA, LEED and the code you have to follow anyway.

FAQ

Which brick is best for house construction in India?

There is no single best. In an RCC frame house, AAC gives the coolest walls and fly ash-lime bricks are the closest swap for red brick; burnt clay bricks suit exposed and load-bearing work. Buy any of them against its BIS standard and class.

Is AAC block better than red brick?

For heat, yes: BEE lists AAC at 0.184 W/m·K against 0.62 to 0.98 for solid clay brick. AAC is also far lighter. Clay brick comes in higher strength classes and can be left exposed; AAC needs rendering outside.

Are fly ash bricks good for house construction?

Fly ash-lime bricks made to IS 12894 meet the same water absorption limits as clay bricks and come in classes up to 30 N/mm². Within 300 km of a coal or lignite power plant, government projects and private agencies are required to use ash-based products when they are offered at Schedule of Rates prices.

Is a concrete block stronger than a red brick?

Not by definition. Clay brick classes go up to 35 N/mm²; concrete blocks under IS 2185 (Part 1) go up to 15 N/mm² (hollow) and 5.0 N/mm² (solid). What matters is the specified class and your lot's test certificate.

What is the CPWD rate for AAC block masonry?

DSR 2023 item 6.47 (150 to 300 mm AAC blocks with adhesive mortar) is ₹8,333.65 per cum at Delhi prices, with RCC bands paid separately. It is indicative; check your state PWD Schedule of Rates for local rates.

Choosing walls for your plot and climate? An architect can weigh heat, rain, structure and local supply together. Find an architect on MOA.

Sources

• Bureau of Indian Standards: IS 1077:1992 Common burnt clay building bricks, Specification, with Amendment 1 (2008), via Public.Resource.Org (accessed 16 Oct 2026)
• Standards Ireland shop: IS 1077:2025 listing, published 13 November 2025 (accessed 16 Oct 2026)
• Bureau of Indian Standards: IS 12894:2002 Pulverized fuel ash-lime bricks, Specification, via Public.Resource.Org (accessed 16 Oct 2026)
• Bureau of Indian Standards: IS 2185 (Part 3):1984 Autoclaved cellular (aerated) concrete blocks, via Public.Resource.Org (accessed 16 Oct 2026)
• Bureau of Indian Standards: Know Your Standards: IS 2185 (Part 3):1984 record (accessed 16 Oct 2026)
• Bureau of Indian Standards: IS 2185 (Part 1):2005 Hollow and solid concrete blocks, via Public.Resource.Org (accessed 16 Oct 2026)
• Bureau of Energy Efficiency: Eco-Niwas Samhita 2018, Part I: Building Envelope, Tables 6 and 7 and paragraph 3.4 (accessed 16 Oct 2026)
• Bureau of Energy Efficiency: Eco-Niwas Samhita 2024 (accessed 16 Oct 2026)
• Ministry of Environment, Forest and Climate Change: S.O. 05(E), 1 January 2024, amendment to the ash utilisation notification S.O. 5481(E) (accessed 16 Oct 2026)
• Ministry of Environment, Forest and Climate Change: S.O. 6169(E), 30 December 2022, amendment to the ash utilisation notification (accessed 16 Oct 2026)
• Central Public Works Department: Delhi Schedule of Rates 2023, Vol. 1, sub-head 6.0 Masonry Work and basic rates, as hosted by the Railway Board (accessed 16 Oct 2026)
• Central Public Works Department: Delhi Schedule of Rates 2023, Vol. 2, sub-head 26.0 New Technologies and Materials (accessed 16 Oct 2026)
• Ministry of Railways, Railway Board: Adoption of CPWD Delhi Schedules of Rates 2023, letter of 3 July 2025 (accessed 16 Oct 2026)
• Bureau of Indian Standards: BIS Care app (accessed 16 Oct 2026)