Hi All

Currently in the process of fitting aluminium windows to a timberframe self-build. I'm using various butyl-type sealing tapes to waterproof the cill plate and surrounds (as per manufactures details - pro clima and ampacol). However, I can't find any information as to whether to fix the cill to the cill plate. For the smaller windows, jamb fixings have been more than sufficient, however I'm wondering whether simply resting the cill on packers and cill plate is sufficient for larger (longer than 1600mm) windows as recommended by manufacturers. Although the butyl tape should in theory self seal around any screw penetration, it seems a shame to puncture an otherwise waterproof layer.

If anybody has any experience, it would be appreciated, thanks.

What windows did you use? Window sills are generally fitted to the bottom of the window. They'd either have a precast sill that the windows sit on top of, or a section underneath recessed, where the window sill is fixed to. Every system is different in how they do things but, usually that is the standard method. Do you have a picture to show what it is you are trying to do?

Edited 3 hours ago3 hr by craig

Hi Craig. Thanks for your reply. We chose a product from a local supplier which I believe is manufactured by Smart Systems/Architectural Aluminium. I've fixed the supplied 225mm cills to the frames and have installed the first window sitting on top of the cill plate (which has been waterproofed using tape as per the Back to Earth guidance - image attached).

I'm happy that the smaller windows will be fine simply sitting on the wooden cill plate, but was curious as to whether bigger windows need to have the cill mechanical fixed to whatever substrate it is sitting on.