Why mock PVC sash & case "boxed around" original frame?

[boilerhater]

Hi - was hoping someone could help me understand what's going on with my UPVC replacement bay window. (I'm not looking to get anything changed, but want to understand why it's the way it is.)

Basically I had 1980s PVC replaced with mock sash & case PVC windows a couple of years ago when I bought the place. It's an 1890s tenement in Edinburgh. The original wood windows had been torn out decades ago so I didn't feel guilty - and I'm happy with the aesthetics of the mock ones anyway.

My question is just regarding the frame... The original boxframe has been left in situ, so both of the PVC installers "boxed around" it internally as the attached pic shows.

Why was it necessary to "build inwards" like this? Are there weights inside this new box column or is it empty? If I'd understood my options originally I would have paid extra to tear out the boxframe, because the new addition is ugly & stops my original shutters closing correctly (not a major issue as I have curtains). From what I understand it'd be very messy doing that now because the boxframes are structural.

Too late for me to fix it, but I want to understand why the contractor took this path & learn from my mistake basically

 

[Notch7]

Upvc installers will tend to do the easiest option.

Retajning the box frame meant not disturbing the structural support.

I expect it could be altered and it may not be that involved, but there is no way to tell from the image.

 

[ronniecabers]

I agree with Notch , they were left as its structural more than likely. Whats above that bay window ? Another bay? tiled roof?

It may be quite involved to change it now though , as its very possible the load bearing baypoles will not fill that entire ' gap ' between the frames , so the frames would need to be wider than the existing frames so that the baypoles are screwed to the frames and the correct covers can be used

 

[boilerhater]

Hi Notch & Ronnie - thanks for your replies! Yep there's four more storeys of bay windows above mine (see pic) so I'm sure they must be load bearing.

If so and if the baypoles would require wider frames, that basically means I'd have to replace the windows right? (As they'd need wider stiles?) Or could new jambs be installed to fit the windows? Definitely wouldn't get new windows as they're fine & the columns aren't that bad really.

Just can't help but wonder if I could have avoided that boxing somehow. Even with the original boxframe in there I'm surprised the columns needed to protrude so much. (Do they support the PVC somehow?)

Cheers again