Best fixing point for window blind?

[dogfonos]

Would appreciate advise on fixing blinds into a window reveal in a recently built extension...

I'd like to fix a blind (roller or Venetian) into a window reveal but am unsure as to where to attach fixing brackets. To maximise the usable internal window cill area - even with the blind down - I want to mount the blind as close to the window as possible, window handles permitting. But to which surface can I fix the brackets?

An insulated cavity wall lintel (plastered over) sits at the top of the window reveal and each side of the reveal has insulated cavity closures, again plastered over. These areas sound hollow when tapped so I'm wary that they may not make secure bracket fixing points. From memory, I think the side cavity closures were made of plastic and the lintel of thin steel. The window reveal size is approx. W=120cm, H=100cm.

The windows are DG aluminium framed and may provide the only secure fixing point but I'm reluctant to start drilling/screwing into the frames. Also, if I use the top edge of the window frame to fix brackets, I suspect that most blinds will sit too close to the window and foul the casement handles when down.

Any help gratefully received.

 

[foxhole]

Fit to frames, you normally only required one screw per side as its easy to secure well to ali, [will mean less holes in the frame], I fitted mine tight to frame and the roller mechanism sits as tight as possible but still easily passes the handles as it sits out far enough to avoid the handle.