Bay windows mullions

[mwf28]

Hi,
First Post for a long while, but still gained so much knowledge and help from all the members.
My question is about 1930s bay window mullions.
I five 160 cm high by roughly 60cm wide bay upvc windows fitted into sandstone mullions.
This is repeated on the first floor bedroom windows.
Their has been a lot building work just across the road,new housing estate.
I admit the street used to be very quite (semi rural) but since the construction work started the noise is very notable in the rooms with the bays to the point that it sounds like a window is open?
Since I noticed the increased sound levels I also became aware just how cold the areas around the bays are,you feel the change in temperature as you get closer to the windows.
I have had problems with mould under the sills on wall beneath.
I gather this is moisture and condisation hitting colder surface.
Next year I plan to insulate the bays with insulated plaster board removing original plaster under bays.
My question is how are the upvc window frames fitted to the mullions, I guess there must be wood behind the mullions to which the upvc frames are screwed. I am kinda guessing that the upvc fitters that fitted the windows might have not foamed around the frames or behind the mullions.
I hope to address this when I start work on the bays.
Many thanks.

 

[Notch7]

I am kinda guessing that the upvc fitters that fitted the windows might have not foamed around the frames or behind the mullions

Window fitters are the kings of foam

Unless they had none on board that day

 

[crank39]

If they were originally sliding sash windows then theres 2 ways how the replacement upvc windows could be fitted, either within the original sash 'box' frame, or a full rip out, the first way is quick, easy, cheaper and way way way less mess and damage to decor, the second is removing every last timber bit of the window back to brick, that includes about 100 years worth of dust, birds nests, wasps nests and any other type of nest, will involve a boat load of replastering, new windowboards, new reveal linings......but its the proper and only way in my book, fitting a new window within the old timber frame means painting is still required and it leaves voids within the boxes where the weights are which could let the cold and noise through, will need some pics from outside to see if they've been fitted within the box or if its a full rip out

 

[Notch7]

100 years worth of dust

The first time I did a box sash rip out I ended up looking like a coal miner.

 

[crank39]

The first time I did a box sash rip out I ended up looking like a coal miner.

And the customer said 'will there be much mess as i've just had an expensive cream carpet fitted'

 

[mwf28]

Thanks everyone,
@crank39
There are no original parts of wood frames left.
The original wood cill is visible under a upvc cill.
The windows were already fitted in the house when I brought it 11 years ago.

I am planning to redecorate the living room and front bedroom which have the bays next year, so not really bothered about any mess or how far I go with insulation.

On the inside of the mullions between the windows there is a upvc trim which is about 200mm wide running vertically top to bottom.
I really want to carefully remove it and see what's behind, any foam, fixings.
I will post some photos tomorrow.
Cheers.

 

[mwf28]

He's some photos,

 

[mwf28]

Another of the top bay.