Solid external walls – a modern solution
UK homes built before the 20th century would typically use solid brick external walls. While durable, brick is porous and solid brick walls can draw moisture into the interior of the building.
It was largely for this reason that cavity wall construction was introduced during the 20th century and over time the cavities were increasingly filled with insulation to improve the thermal performance of exterior walls.
However, modern solid wall constructions can produce the thermal performance required under current building regulations and have often been used as the basis for high-performance constructions such as Passivhaus designs.
The aircrete advantage
Aircrete’s unique closed cell structure – where the body of the material is filled with air pockets – means that it does not absorb moisture like brick. In fact it is entirely moisture resistant so an untreated aircrete solid wall would meet the requirements of Building Regulations Approved document C.
To meet the requirements of Building Regulations Approved Document L, a solid aircrete wall would need to include insulation – either externally or internally. The wall structure should also include a durable, permanent external finish such as render, brick slips or other cladding – all of which can be applied with or without external wall insulation.
When internal insulation is used it is common to use a render finish on the exterior surface of the wall. When this is the preferred choice, adequate surface preparation of the aircrete material must be completed before the render is applied.
More information on the application of render can be found here
H+H products for solid wall construction
Celcon Blocks of 200mm width or greater can be used for solid wall construction and standard mortar, Thin-Joint or H+H Vertical Wall Panels are all appropriate.
H+H has produced a series of U-Value calculations to illustrate the thermal performance achievable with different insulation materials and these demonstrate that a U-Value as low as 0.11 W/m2K is possible. Standard junction details, including CAD files, for solid wall construction are also available as downloads.
Solid wall construction has been favoured in some of the high-performance projects with which H+H has been involved.
As long ago as 2008 the Barratt Green House (a demonstration project accessible at the Building Research Establishment Innovation Park) used storey-high panels of H+H aircrete externally insulated with 180mm foam and finished with render. The construction gave a U-Value for the external walls of 0.11 W/m2K.
The objective of this project was to demonstrate how Level 6 of the (now obsolete) Code for Sustainable Homes – effectively zero carbon in use – could be achieved.
Another demonstration project, this time a social housing development in the Isle of Wight, used a solid wall construction with Thin-Joint blocks for Passivhaus certified performance. In this instance the blockwork walls of the houses were insulated externally using 230mm of phenolic insulation finished with an acrylic render. This solution provides a U-Value of just 0.08W/m2K.
In order to achieve the Passivhaus certification the homes had to pass a rigorous airtightness test, which is why the Thin-Joint system was specified. With just a 2-3mm mortar joint, Thin-Joint walls are extremely airtight: when tested, these units achieved an airtightness level of less than 0.6 air changes per hour at 50 Pascals.