zones, wider cavities are required to prevent moisture penetration. Facing materials also play a vital role. Mixed finishes, such as a combination of render and facing brickwork, can perform well in high-exposure areas, provided joints are flush and detailing is carefully executed. Recessed joints and flush sills or copings are generally only suitable for sheltered or moderate zones where the risk of wind-driven rain is low. Architects and specifiers should also consider how small changes in detailing can dramatically influence performance. Effective water management through correctly designed sills, drips, and overhangs can prevent saturation and prolong the life of the wall system. The choice of render system, too, should match the exposure classification, with higher-performance formulations specified for more exposed façades. Partial or full-fill cavities? Approved Document C provides guidance on the maximum exposure zones suitable for different masonry cavity wall constructions. Both partial-fill and full-fill systems can be viable across the UK’s exposure range, but the choice depends on the balance of thermal performance, buildability, and moisture resistance. In more severe exposure zones, wider cavities are required – and this is where the choice of insulation becomes especially important. A 150mm full-fill cavity insulated with glass mineral wool provides an effective solution for both thermal and moisture performance. It meets the updated U-value requirements of Approved Document L (Conservation of fuel and power) while maintaining compliance with moisture resistance requirements under Document C. Full-fill mineral wool insulation has several practical advantages
over partial-fill systems. Its flexible composition allows it to accommodate irregularities in the masonry substrate and ensure
a continuous fit. The fibres knit together at joints to minimise air gaps, reducing the risk of thermal bridging and moisture ingress. Compared with rigid boards, which require precise cutting and taping to maintain integrity, mineral wool is faster to install correctly and more forgiving on site. A 150mm cavity wall can be used to achieve compliance in every exposure zone with a variety of external wall finishes including facing masonry, render and cladding. A consistent cavity width across a project also simplifies detailing and procurement, while ensuring every elevation can meet or exceed the performance standards required for its exposure rating. Designing for the future climate Climate projections suggest the UK will continue to experience wetter winters and more intense rainfall events in the decades ahead. This reinforces the need for architects and specifiers to prioritise robust, moisture-resilient wall designs now. Designing to the upper limits of exposure, rather than to the average, ensures buildings can cope with future conditions as well as current ones.
By understanding and applying the principles of exposure zoning, architects can make informed decisions that balance performance, sustainability, and durability. Specifying full-fill 150mm glass mineral wool cavities offers a practical, compliant, and future- proof approach – one that allows buildings to weather whatever the UK climate delivers.
JW248
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
