Cost effective U-value targets for ground floor renovation works

Ground floor constructions Renovation of a solid or suspended floor involving the replacement of screed or a timber floor deck. Solid floor – replace screed with an insulated floor deck to maintain existing floor level. Suspended timber floor – fit insulation between floor joists prior to replacement of floor deck. The cost effectiveness of floor insulation is complicated by the impact of the size and shape of the floor (perimeter/area ratio). In many cases existing un-insulated floor U-values are already relatively low when compared with wall and roof U-values. Where the existing floor U-value is greater than 0.70 W/m²·K, then the addition of insulation is likely to be cost effective. Analysis shows that the cost benefit curve for the thickness of added insulation is very flat, and so a target U-value of 0.25 W/m²·K is appropriate subject to other technical constraints (adjoining floor levels, etc.)