External insulation has become big news with the impending Green Deal due to start with a soft launch in October this year. Ecomerchant has developed a vapour open external walling insulation system (in partnership with Lime Green, render manufacturers and Steico, insulation manufacturers).
External envelope - Protect render system
The system, known as Ecomerchant Protect, is suitable for use in masonry, timber frame and cross-laminated timber construction, for new build or refurbishment. The Ecomerchant Protect system has been used in the UK on new build passive house projects right through to listed buildings and commercial refurbishment projects.
The system includes wood fibre insulation boards, designed for external applications and a UK engineered and blended two-coat lime render. The Pre Bond (base coat render) is applied in two 5mm passes with a glass fibre (GRP) mesh pressed onto the first pass which is then covered in the second pass to give strength. The second and final coat is then applied once the first coat has dried. The second coat is also 5mm, so the overall render thickness is 15mm, whereas many other mineral and acrylic systems are 10mm or less. The render is hydraulic lime based with additives to improve workability and adhesion and is currently going through a BBA certification process.
The top-coat is pre-coloured giving a through colour, so should the finish get scratched, the colour remains intact. The top-coat also acts as a finish coat not requiring painting, thereby reducing long term maintenance. The system includes a range of base rails and profiles for corners, window reveals expansion joints and a like. The product range includes specific fixings for different substrates, with recessed heads to reduce cold bridging and nylon plugs.
The insulation boards are manufactured with a tongue and groove edge profile and impregnated in paraffin wax to give weather resistance. The boards are supplied with different densities, of 265 kg/m3 and 230 kg/m3 which results in thermal conductivity of 0.048 W/m2k and 0.046 W/m2k respectively. To put these figures into context, when applying 40mm of 265 kg/m3 wood fibre on a new 140mm timber frame the typical U value will be 0.24, well inside the 0.30 recommended minimum, whereas 120mm of 230 kg/m3 wood fibre applied to a 215mm masonry wall will achieve 0.29 and therefore comply with current Building Regulations for refurbishment.
Detailing external insulation systems requires careful consideration especially around DPC level, reveals and intersections with other materials. The wood fibre board isn’t recommended below DPC due to the potential for excess moisture, so moisture resistant boards such as Foamglas should be used and a slightly harder basecoat, known as Pre Bond Q. This combination is able to cope with greater moisture levels but is impervious so should only be used below DPC.
Getting details right around windows is equally as important and ideally the window or door unit should be mounted directly behind the fibre board with a flexible material such as Compriband inserted between the elements and covered by an edge bead.
The render system is going through a BBA assessment process and the system will become suitable for use as a Green Deal product, with particular reference to pre 1919 properties, where breathability is going to be important, although post 1919 properties should also be assessed for breathability as there are many concerns about trapping moisture within walls when applying impervious insulation systems. The health issues associated with dampness in buildings must be considered when selecting an External Wall Insulation as the dew point moves and the risks of hair line cracking of renders, when buildings move, which allow moisture ingress but restricts evaporation can lead to excess moisture build up over time.
Another interesting fact often quoted is that wood fibre boards are flammable and therefore shouldn’t be used, however fibre boards are often used in fire doors, as there is very little air contained within the board so combustion is restricted.
View Ecomerchant Protect system