How much to insulate?
Q. I'm considering buying a two-storey solid-wall property, of around
160m2, in need of renovation. One of the big jobs would be to improve
the insulation. I understand from the Energy Saving Trust's website
that external insulation has the potential to reduce yearly bills by as
much as £400, while internal could save me up to £380. However,
there's no guidance on what it would cost to install either type,
so I can't figure out payback times. Can you help?
A. In the case of external insulation with a rendered finish, the
insulation is mechanically fixed to the outer face of the wall,
followed by a breathable membrane and vertically-arranged battens.
Stainless steel expanded lathing is then affixed to receive the render,
which may be decorated or left with its natural finish.
Appropriate types of insulation include Celotex (www.celotex.co.uk)
TB3000 and GA3000, as well as several options from Sto
(www.sto.co.uk). The cost of installing such a system would be around
£90-£100 per m2 (materials only cost approximately £25-£35 per m2).
External cladding, which works on similar principles to a rendered
system, is another option. It's also mechanically fixed to the
external face of a wall, followed by the breather membrane and
vertical or horizontal battens of metal or timber. A timber, PVCu or
tile finish can then be applied. This is likely to cost around
£75-£120 per m2, or £40-£70 per m2 for materials only.
Within each of the above systems you can expect considerable price
difference, due to the quality, finish, and materials available. The
prices above exclude works to openings, adjustment of doors and
windows, roof junctions, flashing and the like. You should also allow
for the possible removal and refitting of rainwater and soil pipes.
For internal insulation, laminated insulated plasterboard (70mm
thick) is fixed to metal studs with further infill insulation (25mm
thick) between the studs. It's a little cheaper at £40-£60 per m2
installed, or £20-£30 per m2 for materials only.
Peter Judd, www.vbjohnson.co.uk
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