The risk for specifiers comes when applying modern, vapour-closed logic to a vapour-open structure – or vice versa. Cement renders, impermeable insulation and non-breathable coatings applied to solid masonry can trap moisture within the wall, leading to condensation, mould growth, timber decay and accelerated deterioration of the fabric. Over-insulating a breathable wall without addressing the ventilation strategy can produce exactly the same issues. None of this is new information, but it remains one of the most common specification errors on retrofit projects. The lesson for new-build is equally
relevant. Vapour-open materials such as lime, hemp-lime, wood fibre and clay offer genuine hygrothermal buffering that many modern high-performance builds now deliberately reintroduce, precisely because they manage moisture risk more effectively than fully sealed systems. Natural insulation materials Materials, such as wood fibre board, hemp, sheep’s wool, cellulose and lime-clay-cork plasters, offer thermal performance, while retaining vapour permeability, which allows them to be used on solid wall construction without the moisture-trapping risk associated with closed-cell or foil-faced insulation systems. For specifiers, the practical advantage
is risk reduction as well as enhancing sustainability credentials. Breathable natural insulation materials are more forgiving of workmanship variance, less likely to create localised condensation at thermal bridges and are better suited to buildings with irregular geometry or unpredictable moisture pathways – a category that includes most retrofit stock and increasingly
is a design ambition for new low-energy buildings too. Embodied carbon – the calculation that changes the retrofit-versus- demolish decision Carl Elefante’s well-known observation that “the greenest building is the one that already exists” is now backed by increasingly robust carbon accounting. Retained masonry, timber and lime structures already carry significant embodied carbon from extraction, manufacture and construction. Refurbishment, rather than demolition and rebuild, can reduce embodied carbon by an estimated 50–75% compared with new build. The retrofit risk landscape Anyone involved with carrying out thermal upgrades to traditional buildings is effectively managing two opposing risks: Inaction – Leaving a traditional building poorly insulated leads to high energy and running costs, increasing carbon emissions and leaves occupants exposed to fuel poverty and cold/damp-related health risks. Occupants face higher energy bills, increased fuel poverty and health risks from cold and damp conditions. Poor thermal performance also accelerates material decay through condensation, mould and freeze-thaw cycling – inaction does not preserve historic fabric, it degrades it. Inappropriate specification or mismatched
renovation of buildings with non- breathable materials leads to thermal bridging from poorly detailed upgrades and increased airtightness without a corresponding ventilation strategy. This can lead to more damage than the problem they were meant to solve, and can also risk heritage compliance issues and loss of architectural character.
What this looks like in practice When it comes to existing buildings, there is a very real need to diagnose the issues correctly and understand how the existing building manages moisture, heat and movement before selecting materials. It is also important to match material
behaviour to structure. Contractor David Benn (DMB Building) describes moving away from standard-fix approaches. He says: “Building Better, for me, starts long before materials are specified. It starts with understanding the building. I’ll be honest, I didn’t always think like that. Like most builders, I started out using the usual fixes. Damp? Inject it. Cold wall? Board it. I didn’t really understand how traditional buildings behave or how easy it is to make things worse with the wrong materials. That changed when I started working more closely with breathable materials and approaches designed for traditional buildings.” Applying the same thinking to new-build The relevance of the principles of traditional building to new construction and renovations is clear. Traditional buildings are not a heritage
category to be managed separately from sustainable construction – they are a proven template for it. For architects and other building professionals, the principles used to create traditional, sustainable buildings is leading to them being reintroduced into contemporary low-energy and Passive House design. Building Better is about understanding and learning from our predecessors and carefully choosing compatible materials and utilising them to enhance comfort, wellbeing and the energy efficiency of our buildings.
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