Which is the most cost-effective, pumped cavity wall insulation or drylining?
Both methods have their advantages. Pumped cavity wall insulation involves minimal disruption as the insulation beads can be injected directly into the cavity from inside or outside the building. There is also little or no waste of materials with this system and is generally a very cost effective means of upgrading the insulation of an existing cavity wall.
The width of the cavity is the limiting factor as this determines the thickness of insulation that can be installed and therefore the thermal performance of the wall. Dry lining is also an effective means of insulating an existing external wall, whether solid or cavity construction. Various systems, methods and insulation materials are available.
These generally involve a layer of insulation, possibly fixed to the wall on battens, adhesive ‘dot and dab’ fixed or fitted within a stud wall construction. A board is fixed to the room side of the build-up which can then be plastered in the case of plasterboard or in the case of a cement fibre board, the joints taped and filled, and finished to the client’s specification.
There is no real limiting factor in terms of maximising the insulation, but bear in mind the reduction of floor area within the room; thinner insulation products are an advantage here. There is more work involved in this approach, but significant savings can be made on heating costs over time.
Externally applied insulation is also an option, with a number of similar systems on the market, these effectively wrap the outside of the house in an insulated envelope. Systems involve a mechanically fixed layer of rigid insulation with a covering mesh, to which render is then applied. Overhangs of roofs and window sills are important factors to consider here. Ideally, insulating the window and door reveals should be considered as these can be areas for ‘thermal bridging’, however this may not always be practical. In considering which system(s) to use, I would advise that the U-value of the newly insulated wall should be calculated, and costings of the work established to enable a comparison to be made. A Building Energy Assessor may be able to assist in producing a payback calculation. In all of these cases a Building Control application is required. Insulation products should be fitted with workmanship and attention to detail paramount, and in accordance with manufacturer’s instructions, BBA certificates and the Building Regulations Technical Booklets; for further guidance contact your local Building Control office.
David Millar, Building Control Officer at Ards and North Down Borough Council
Building Control ROI
To comply with the Building Control regulations, you need to either opt in, whereby an assigned designer and assigned certifier are appointed, or opt out of having a professional oversee the design and construction of your home in a statutory capacity.
You must notify your local authority if you’re opting in or out when you apply for your commencement notice, online, on the Building Control Management System. The Department of Housing’s Building Control office informed SelfBuild you can only switch from opt in to opt out before construction has started. If you’ve broken ground already you can’t go back unfortunately.