Retrofitting Historic Buildings - Westminster City Council

Heat loss through the floor amounts to around 15% for theaverage house. Simple draught-proofing of gaps between floorand skirting and between floorboards with sealant can beundertaken relatively easily and at low cost (around £20).Suspended timber floors on the ground floor, typical for manyolder properties can be insulated to improve thermal comfort.This will be quite straightforward if there is a cellar or crawlspacebelow, but without this, floorboards can be lifted and insulationinserted underneath, supported by netting. This should be to thedepth of the joist only and should not block air bricks. Careneeds to be taken when lifting boards to minimise damage.Avoid blocking airbricks when draughtproofing or wheninsulating, and take care to maintain cross ventilation beneathsuspended timber floors to avoid rotting floor timbers. Considerthe potential loss of historic fabric (floorboards/skirting/doorsurrounds/doors) that may occur if insulation increases floorheight.Advantages: Underfloor insulation can save around £50 per yearon energy bills and improve thermal comfort, with draughtproofing saving around £15 per year.Disadvantages: This will be fairly disruptive as it will requirerooms to be emptied, and floorboards to be lifted, which risksdamaging the floor. For this reason it is sensible to takeadvantage of any opportunity to insulate, for example if existingrotten floorboards are being replaced.Risks: Incorrectly installed insulation which blocks air bricks andreduces air circulation beneath a floor may result in damp andcondensation problems. The risks inherent in lifting floorboardsmay be too great in a listed building where one of the featuresfor which it is listed is a particularly attractive floor. Some historicbuildings may also contain historic pugging, which is a coarsemortar between joists and beneath floor boards to deadensound.Costs: Generally although the capital cost of insulation is nothigh, there is significant disruption and cost in having floorslifted. The cost of lifting floorboards properly can be around£25/m 2 while the cost of the insulation itself is only around £5/m 2Floorinsulation(suspendedtimber)UnitCost(lower)Cost(Upper)Cost(average)Subsidies(refer toESTwebsite forlatest info 16Unlisted 80m 2 £875 £917 £896 50-100%building 17When to do this: Floor insulation is disruptive therefore it is bestdone as part of a whole house refurbishment, or whenfloorboards are being lifted or replaced, for example to install oraccess heating pipes below. When it is carried out ensure thatgaps are sealed such as under skirting boards and where waterand gas pipes are located to minimise draughts.19