Home DIY

I have done many professionally. I wouldn't describe what you have said needs doing as reconditioning per se.

In order to replace a cord you need to

Remove the beading on one side of the inside
Pull out the lower sash and remove the cords from the sides of the sash
remove parting beading
If the problem is the upper sash then remove the cords from that too
remove covers to the sash boxes which are usually hidden under a few layers of paint
now you have access to the weights you can replace the cords
nail new cords to upper sash
replace parting bead
nail new cords to lower sash
replace bull nose beading

That's a simple guide to the process. If you need a source for parting bead or bull nose or you decide to add some draught proofing you can browse a lot of options at Mighton or Reddiseals.

If you want to paint the exterior while they are out of the frames you can shutter the windows with 12mm ply strengthened with some pine on the back. Then prep and paint them with something like Zinnsers Cover Stain followed All-Coat. Other exterior paint systems are available but this one dries quickly.

I'm skimming over a lot of processes which I would carry out as 'prep'. But often I am stripping the frames to the wood, removing the glass and replacing with 6.3mm acoustic glass. Draught proofing all round and replacing weights to accommodate the heavier glass.