The exclusive deep 55 mm GRP cill is a beautiful feature designed to achieve the authentic appearance of an original 3” timber cill. This feature, along with patented Timberweld ® butt jointed corner construction and integral mullion for multi-light windows, completes the package that offers ‘like for like’ matching to original timber sash windows in conservation areas.

Ray Rabett, Technical and Compliance Director says “One of the most common requests from customers about product improvement was “we need a deeper cill to mimic the old ex 3” timber cill”, Masterframe responded and this cill is now available as standard on the Vintage Collection.

Design was quite complex, requiring twelve revisions to get the cill perfect. The design criteria was that the cill had not only to replicate the old timber cill, but critically could not undermine the WER (BFRC window rating scheme), it had to remain an A rated product. The intention was to also improve the weather performance if at all possible. The final design has maintained a WER rating of “A” +2 result and increased the weather performance to 250pa.”

Ray continues “The increased strength brings a further advantage; the most common installation issue we get called to look at is where the cill has bowed upwards and the sashes are not closing properly. This occurs because the installer has not packed underneath the jambs as they should. This rigid GRP cill will overcome this problem, even if the installer does not pack the frame correctly. The strength of the deep cill is 12.289 n/mm2 which, compared to the reinforced standard cill at 0.769 n/mm2 is stronger by a magnitude of 16.8 times. “

Regular PVC-U Cill

Deep GRP Cill

The strength of the deep cill has yet another benefit; allowing large and unusual windows to be replicated more authentically, for instance where required in sea front hotels, renovated / converted former schools, industrial buildings and ecclesiastical buildings.

The GRP deep cill is indistinguishable from the other PVC-U sections because all are bond wrapped in the same Renolit foil to maintain the appearance of timber.

To read about all the other features that make Masterframe sash windows so traditional, consult the handy tick box guide