We have caulked all the windows and seals this summer. I will go back and check the caulking to ensure it is air tight.
We did completely clean the weep holes and confirmed them by running a flex tie through each opening in the window until I could get it out of a weep hole. I will go back today and dry then apply some silicone spray to the seals. I was wondering about that as an option. I just don't see why the window has excess room at the bottom of the window. It is not the same on the sides. We can see the window flex towards the outer seal and it seems to be enough to completely come free from the inside seal if only by a MM or less. The sides of the window to not move at all. On the opposite side the bottom part of the window moves less and there is no movement on the sides.
