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Hi all
I've got some really old windows/window frames that are an eye sore, full of games and have holes (from previous owner - presumably from different fittings and locks). I'd like to replace them but am not sure what to expect to see underneath the frame. Are these sitting over a void in the brick work or just sitting on top of brick? I'm wanting to understand what materials I'll need to replace these windows myself I.e. order them made to measure and handle the install myself. Just want to be prepared before getting into the removal part. Any thoughts and tips for what to look out for when ordering windows are greatly appreciated.
Cheers
Rich 
Welcome to the Bunnings Workshop community @chi4short. It's terrific to have you join us, and many thanks for your question about windows.
Replacing aluminium windows isn’t usually considered a simple DIY job. In trade practice, you normally measure the maximum size that will fit within the existing opening, then expect that once the old windows are removed, some adjustments will almost always be necessary to make the new ones fit properly. The challenge is that until the old frames are off, it’s hard to know exactly what’s behind them.
From your description and photos, it’s unclear whether the existing frame sits on top of the brick or if the sill continues underneath it. Often, aluminium frames are slotted into the opening, with shims underneath to level them. The frame is then screwed into the surrounding timber or masonry, and the window sill is installed so it butts neatly against the frame. What’s exposed now may only be part of the actual window frame, so there’s a chance more is hidden under the trim.
The safest way to get accurate measurements for ordering replacements is to start carefully removing the interior trim and the window sill. That will give you a full picture of the frame depth, reveal any shims, and show how the frame sits in the wall. Once you have that, you can measure the opening properly and order your made-to-measure windows with confidence.
Even if you’re handy, expect surprises, such as uneven openings, hidden rot, or masonry irregularities, as they are quite common. If you haven’t done window installs before, having a tradesperson on call or at least consulting one during removal can save headaches.
Please let me know if you have any questions.
Mitchell
