replace box sash windowsill !

16 Oct 2006
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United Kingdom
i need to replace a window sill on a box sash style window as the existing one is rotten, i have two concerns really,

firstly how to get the existing one out with as little damage to it's surroundings as possible,
is the 'box section' which sits on top of the sill generally fixed to it? how to best detach it ? is it generally possible to pull the old sill out from the window opening into the room to remove it?

secondly, if the bottom of the box frame uprights have also been affected with rot is it practical to cut out a section from the bottom and fit in a new piece?

any advice would be gratefully received
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14 - this is a common job to do. Remove the bottom staff bead (the inner most bead fixed to the wooden sill) with a chisel (do this on the outside edge so as not to bruise the visible side of the bead); this is likely the be held by 3 nails ... tip= run a Stanley knife around the paint at the joins so as to minimise paint damage to rest of frame. Then remove one vertical staff bead (you might have to remove the other one later maybe but don't bother yet). You will re-use these beads.

With a handsaw make a vertical cut in the centre of the sill all the way through, tip= angle the saw left to right (or right to left) as this will ease removal and stop the two cut faces from binding. If really rotten the sill should pull away, if not then make vertical cuts at each side. Chop all rotten timber away from below boxed frame - these would have been jointed into the sill. Your aim here is to remove the sill but leave the frame hanging intact. Square off the base of the box frame removing any tenons.

Your next problem is obtaining the correct size of sill ... but everything is now metric and your old stuff would have been imperial (and so bigger). Take a bit of the old stuff to a timber yard for best match - you will not get an exact match 'cos of the metric/imperial clash. You will have to pack/laminate additional timber maybe to lift the sill to touch the frame.

You next problemis securing the frame to the sill (in the absence of the joints) ... easy done. Fashion a couple of timber blocks which you drop down the insides of the box frame, via the pockets. These can be glued/screwed to the sill - a bit awkward 'cos you're working in the pocket. Then you secure the frame to these blocks with screws. Check that the sashes don't bind then re-assemble the window elements - parting bead, staft beads, etc.
thankyou very much symptoms,
good clear info, when you don't know exactly what happens in the bit that's not visible it's good to hear a word from experience,
especially the sill size difference, that saves a lot of unnecessary legwork.
it's appreciated !

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