Changing sash windows

[mimos4]

We've moved into a very draughty Edwardian house, and are looking into getting the windows double glazed. Two companies have quoted, with one saying we only need to replace the windows, and another saying the entire box needs to be replaced. There is of course a difference in price.

Does anyone have advice? Does the box really need to be replaced? One company said our boxes were in good condition, and they didn't expect any problems with fitting new sashes into them.

Thank you!

I ordered double-glazed sash windows for our Edwardian house a few weeks ago. We were told we needed to change the frames as well due to building regs (the existing frames were too narrow).

When you say frame, do you mean the wooden frame around the glass panes, or the box around the frame? I completely understand the former needs changing, but one company is saying the entire thing has to go (and not for regulatory reasons).

I have an early Victorian flat w Sash windows, and just got an extra layer of glass put in on the inside. It's two panes that meet in the middle in front of the middle join of the sash. Weirdly you hardly notice it and it works very well. Pretty much everyone in my block has this - it's a cheaper option than replacing the whole window, never mind the box as well.

Have had a few sash windows remade with double glazing (window by window over several years as it’s so flipping ££££). It’s always just been the sashes themselves that have been replaced - occasionally the outside sill where it’s rotted away. And our house was thoroughly neglected!

The box bit is literally a box where the sash weights hang, with a basic wheel at the top for the cord to roll through - you should be able to tell if that’s in ok working order, although the sash cord itself may have snapped. You’ll have to pay for extra lead to compensate for the extra weight of the double glazing.

Secondary glazing ie a pane stuck on the inside is a good option but means you can’t throw the windows open…which is the nice bit about sashes in the first place.

@mimos4 The box around the frame. I trust the tradesperson we’re using, having used him before, so I went with it. We’re expecting building regs inspections later this year as we’re renovating, I’m not sure if we’d have gotten away without otherwise.

Thanks all. We might try it without replacing the whole box for one window and see how we get on. It's really expensive as PP pointed out!