From 2005 we have been replacing timber, aluminium and steel framed windows with our PVC-U windows for our customers. During these window replacements it is quite often found that timber building frames under the original aluminium windows were rotten.
This happens because (1) Some aluminium windows leak. (2) The timber building frames underneath were not treated and protected.
Aluminium windows are mechanically joined at corners. Water can get into the building structure through some of the joints when they become loose because of the building structure changing and/or temperatures changing over time.
The new building code requires timber building frames to be protected by sill tapes and detail tapes at corners before installing windows. This is necessary because of the reality that some aluminum windows leak through the joints at corners.
A big difference between aluminium windows and PVC-U windows is that PVC-U windows are fusion welded at corners. There is no gap for any water getting into the building structure.
In our opinion because PVC-U window corners are watertight it is not necessary to apply the high cost sill tapes and detail tapes for installing PVC-U windows into timber structured building.
Current Homerit Window Installation System requires sill tapes and detail tapes same as aluminium windows to meet building code requirements. We hope such requirements will be be reviewed.