We specified this plaster not because
it looks beautiful —
though it does.

When we specified a natural lime plaster for a client's home office in North London, the decision was not primarily about how it would look. It was about how the room would feel to be in — specifically, how the air would feel to breathe.

Lime plaster is hygroscopic. It absorbs moisture when humidity rises and releases it when humidity falls, buffering the internal environment and keeping relative humidity in the range — 40% to 60% — that the WELL Building Standard identifies as optimal for human health. At the same time, it does not off-gas. Unlike many conventional wall finishes, it does not introduce volatile organic compounds into the air. The result is a room that feels, in a way that is difficult to articulate but immediately apparent, different from a room finished in standard paint on plasterboard.

The aesthetics — and it is beautiful — were the bonus, not the reason.

What VOCs are and why they matter

Volatile organic compounds are chemicals that evaporate at room temperature and enter the air as gases. They are emitted by an enormous range of building materials and finishes: solvent-based paints, synthetic adhesives, vinyl flooring, MDF board, laminate surfaces, foam insulation, carpet backing, and many types of sealant and grout. They are also present in furniture, particularly flat-pack products manufactured with formaldehyde-based adhesives.

The health effects of VOC exposure are well documented. Short-term exposure causes headaches, nausea, eye, nose and throat irritation, and dizziness — symptoms that are routinely attributed to stress, tiredness or the onset of illness rather than to the environment itself. Long-term exposure to certain VOCs, including formaldehyde and benzene, is associated with liver and kidney damage and increased cancer risk.

The problem is not that these materials exist. It is that the specification process in most residential and commercial projects treats them as invisible — as if the only criteria for a material choice were cost, appearance and availability. The air quality implications are not considered because they are not required to be, and because nobody in the supply chain is accountable for them.

The WELL approach to materials

The WELL Building Standard addresses this through its Materials concept, which requires that products used in a building meet defined thresholds for VOC content and emission rates. This applies not just to paints and coatings but to adhesives, sealants, flooring systems, composite wood products and insulation.

In practice, this means specifying products that have been tested and certified — typically against standards such as GREENGUARD Gold, Cradle to Cradle or the DECLARE label — and maintaining documentation through the project that tracks what went into the building and what it emits.

This is not exotic or difficult. The products exist, they are increasingly price-competitive with conventional alternatives, and the specification process is straightforward for an architect who knows what to look for. What is different is the intention behind the decision. You are not choosing a paint colour. You are choosing what your client breathes in for the next twenty years.

Natural materials — a selective guide

Lime plaster and limewash

As described above: hygroscopic, zero VOC, breathable, and durable. More expensive to apply than conventional plaster, requires a specialist, and demands a different approach to fixing and finishing. Worth it in almost every context where air quality matters — which is every context.

Solid timber and engineered timber

Solid timber off-gases very little. Engineered timber products — plywoods, CLT, glulam — vary significantly depending on the adhesives used. Specify formaldehyde-free or ultra-low formaldehyde products. The cost difference from standard products is modest; the air quality difference is not.

Natural stone

Inherently zero VOC, thermally massive, and durable to a timescale that makes most other materials look temporary. The environmental cost is in extraction and transport; specify locally quarried where possible.

Natural textiles — wool, linen, cotton

Conventional synthetic carpets and upholstery fabrics emit VOCs and, in the case of carpets, accumulate particulate matter. Natural fibre alternatives are both better for air quality and, in most cases, significantly more durable.

Low-VOC and zero-VOC paints

The easiest substitution and increasingly the industry standard. The performance gap between low-VOC and conventional paints has effectively closed. There is no longer a credible reason to specify high-VOC interior coatings.

The question to ask at every specification stage

When we review a material schedule — whether for a new build, a refurbishment or an interior design project — we ask a single question of every product: what does it emit, and for how long? If the manufacturer cannot answer that question with a test certificate, the product does not make it onto the schedule.

This is not perfectionism. It is accountability. The person who will live or work in the finished space deserves to know that every decision made about it considered their health, not just how it would look in the photographs.

Indomo is a RIBA Chartered architecture and interior design practice. As a WELL Accredited Professional, Mara Bravo specifies materials across all projects with documented attention to air quality, VOC emission and long-term health impact. If you are planning a project and want to understand the material implications, we start with a conversation.