Insulation under a bay window

MaudeLebowski

Looking for a bit of advice if anyone can offer it. We live in a tenement flat with a bay window in the living room; it’s double glazed (only in the last year) but it’s so cold near the window. I think the culprit is a lack of insulation in the panels underneath as the windows themselves don’t seem to be draughty.
Does anyone know if adding insulation would be a DIY type of job? Any idea what’s involved at all?

FreeBear

Is this a top floor flat ?
If so, insulating the ceiling/roof will help a lot - If you can access the area from the loft space, it would be fairly easy to get some insulation down.

As for the walls, can you lift the window boards and see how the wall is constructed ?
If it solid brick/stone, then I'd suggest insulating using the "warm batten" method with a suitable air gap, but you'd need to give some thought on finish around the wood trim either side of the bay.
If it is just studwork with an external brick/stone facing, rip off the plaster, and fill the void with Celotx/Kingspan boards (leave an air gap between the brick & insulation). Cover with plasterboard, and skim.

Total cost if you do the work yourself, no more than £150-200. But do bear in mind that even with double glazing, the air near the windows will always feel cold. Thick curtains will make a huge difference.