logo

Kind Cost per sq.metre Light transmission
K ( U ) =
Watts per sq. M. per degree difference
Thickness
Weight
per sq. M
Hence running cost
(assume £600 for glass + bubble plastic)
Capital cost of glazing - for 24ft long, 17ft wide house, on a dwarf wall.
Hort. Glass £4 per 2x2 piece.Assume 33% discount for quantity ,then = £7.25 p.sq.M. Assume 95%
5.5 for glass
maybe 4.2 for glass with bubble plastic lining
5mm ? 6.6kg £600 £520
twinwall
polycarb
£13 82% 3.2 10mm 1.7kg £450
£900
S factor=2.5
triple-walled
polycarb.
£19 78% 2.4 16mm 2.7kg £385
£1350
S=3.85
5-walled
polycarb
£25 68% 1.6 25mm 3.4kg £228
£1775
S=3.37

Note: polycarb is guaranteed for 10 years, but will at some time after that need replacing due to crazing and yellowing from UV.
The S factor, is the time taken to recover the extra cost .(i.e. extra cost in glazing divided by annual savings).
If it is less than 10 years - ( it always is) then it is economically efficient.

Also note that the extra cost of the 25mm over the 16mm is recovered faster - the sharply improved K factor is responsible as compared to the smaller increase in cost.

Geoff Hands, 2001

Culture
Culture