Perlite concrete and green building ratings: IGBC, GRIHA, LEED and what the certifier actually asks for

No material earns a green building credit on its own. Not insulation, not glazing, not flooring. Credits are earned by the building's measured performance and by the documentation you submit for it. Any supplier who tells you his product carries points is selling you something that does not exist.

What a material can do is make a credit reachable, and give the consultant the evidence to claim it. This page sets out exactly where insulating perlite concrete fits in that, and, just as usefully, where it does not.

The systems you are likely working to

In India the voluntary ratings in common use are IGBC, run by the Confederation of Indian Industry; GRIHA, from TERI and the Ministry of New and Renewable Energy; LEED, from the US Green Building Council; and EDGE, from the IFC, on a growing number of projects.

Underneath those sits the regulatory floor, which is not a rating at all. For commercial buildings that is the Energy Conservation Building Code, with its ECBC, ECBC+ and SuperECBC tiers, each tightening the maximum roof assembly U-factor further. For residential buildings it is the Eco-Niwas Samhita, which sets a maximum roof thermal transmittance of 1.2 W per square metre per Kelvin across all climate zones.

The thresholds that apply to your project depend on its climate zone, its occupancy type and which tier you are targeting, and the code tables are revised periodically. Work to the current table for your project rather than to a number quoted on anybody's marketing page, this one included.

Where insulating concrete actually counts

In every one of these systems the heaviest weighted credits are the energy ones, and the roof is part of the thermal envelope those credits measure. GRIHA assesses envelope heat gain; IGBC and LEED work through minimum energy performance and envelope criteria, by prescriptive route or by whole-building simulation.

Whichever route your consultant takes, the input is the same: the thermal transmittance of the roof assembly. That is built up from the resistance of each layer in it, and the insulating screed is one of those layers.

The calculation, and what our material contributes

Thermal resistance of a layer is its thickness divided by its thermal conductivity. Our measured conductivities, tested to ASTM C518-21 at a mean temperature of 0 degrees Celsius, are 0.0865 W/m.K for the 400 grade, 0.1025 for 500, 0.1150 for 600, 0.1254 for 700, 0.1952 for 900 and 0.3447 for 1200.

Worked out for the 400 grade, the layer resistance you can put into the assembly calculation is:

• 50 mm: 0.58 square metre Kelvin per watt

• 75 mm: 0.87

• 100 mm: 1.16

• 125 mm: 1.45

• 150 mm: 1.73

Your consultant adds the slab, the finishes and the internal and external surface film resistances to those figures, inverts the total, and compares the result against the threshold the project has to meet. The screed is one line in that sum, not the whole answer.

The point worth noticing is that the same screed is also forming the fall and taking the finish. You are getting envelope performance out of a layer the roof needed anyway, rather than adding a separate board on top of a separate screed.

What the certifier will ask you to submit

• The thermal conductivity of the material, from a test to a recognised standard, at the density being used

• The assembly calculation showing how the layers combine to the U-value claimed

• Drawings and specifications showing the build-up as constructed

• For material credits, product declarations such as an EPD, or a third-party product certification

We hold ASTM C518-21 thermal conductivity test reports for the grades listed above and will provide them for the grade you are specifying. Ask for the report at your density. If a figure has been interpolated between tested grades rather than measured at that density, we will say so.

What we cannot claim, and will not

This is the part most suppliers leave out, so here it is plainly.

• We do not hold GreenPro certification. IGBC leans on product declarations and third-party labels for materials credits, and without that label we cannot support those particular credits

• We have not published an Environmental Product Declaration, so embodied carbon and recycled content credits are not ones we can document

• Our non-combustibility position rests on published Perlite Institute data for the mineral, not on fire testing of our own material. If your project needs a product-specific fire test, that has to be commissioned

• Energy credits are earned by the building, not by the screed. We contribute a number to the envelope calculation and nothing more

If a competitor's literature claims points for the product itself, ask to see the credit clause it is claimed under. The question usually settles the matter.

Working with your consultant

Send us the roof build-up and the target U-value or heat gain figure your consultant is working to, and we will return the grade and thickness that get you there, the layer resistance to drop into the calculation, and the test report behind it.

Write to info@theperlite.in or call +91 98600 63626.

Kelite, a product by Keltech Energies. Specified, engineered and executed by Perlite India.