Make the parent window controls accessible to the user which has a iframe element of border height and width being 100%

Make the parent window controls accessible to the user which has a iframe
element of border height and width being 100%

I have an iframe of height and width 100% i.e occupies entire height and
width of the main page. But the main page is an aspx page already, with
its own controls. On page load, this iframe occupies the entire page ,
hence lying above the main page controls, making them inaccessible. Now,
what i need is that this main page controls must be accessible. What do i
do for that. Can this be done using Uframes?? Please note that. the iframe
src links to an url which is basically a chat application, hence, there
can be as many chat windows which open in this frame based on the user,
hence the height and width of the iframe cannot be fixed. Please help me
out in finding a solution for this issue.