Original stone cills give a property that added bit of aesthetic quality. However, their primary downfall tends to be a poor level of thermal insulation.
The Residence 9 window installation you see includes our Bedrock Cill, designed to replicate stone but in a thermally efficient clad polystyrene; hard to believe how closely it resembles the real thing isn’t it!
Traditional stone can create a thermal bridge resulting in significant heat and condensation. The Bedrock Cill bears a similar authenticity in terms of its appearance but comes with modern features and benefits.
So always consider upgrading your cills when you install R9