Filling Cavity Gaps?

[JackJunior001]

Looking for some advice,

I just pulled all old windowsills off around my house and been greeted with them all looking like this, however, there all in good condition and so is the damp proof course.

I’m just wondering if i can use kingspan to fill these cavity gaps and make it easier to fit the new windowsills or will it cause a bridge for damp to come through onto the internal walls?

Thanks for your replies 😁

[Clare Snyder]

Best practice among professional windoe installers is to shim and screw the new windows into position, square, true, and plumb, then fill the gaps with low expansion polyurethane foam expressly designed for the application.