Exterior Oak window sill replacement - spacers??

[Beanwood]

I am restaining a friend's external oak windows. They are a few years overdue, and several of the external sills have rot in them.
When I say 'sill', they are sill shaped, but are actually a bit like a glazing bar, sat over the bottom frame, and under the vertical glazing bars.
I have made new ones out of oak to match the existing profile... but I've made them 2mm thicker, as the old ones were all mounted on top of a 2mm spacer.
I thought maybe it was a mistake, but on removing sills 2 & 3 they also have 2mm spacers under them. I'm now wondering if this is standard practice, and this is some cunning way to allow air space under the sill for evaporation, and reduce the risk of rot (Which has't worked...)
Can anyone shed any light please.

Many thanks.

 

[Beanwood]

It may actually be called a 'Stool', not a Sill

 

[Doug71]

It sounds like you are actually replacing the bottom glazing bead.

There are 2 ways of glazing windows, fully sealed or drained/vented. The theory is if they are drained/vented any moisture that gets in or condensation that forms can get out, it is supposed to make the glazing units last longer before they breakdown.

I would say it's best to replace them on packers again if that is how they were done originally although I have glazed loads of windows the sealed way without problem.

 

[Ollie78]

I think Doug is right. Pictures would help though.

Ollie

 

[Beanwood]

It sounds like you are actually replacing the bottom glazing bead.

There are 2 ways of glazing windows, fully sealed or drained/vented. The theory is if they are drained/vented any moisture that gets in or condensation that forms can get out, it is supposed to make the glazing units last longer before they breakdown.

I would say it's best to replace them on packers again if that is how they were done originally although I have glazed loads of windows the sealed way without problem.

Thanks- some kind of venting is what I suspected.

 

[Beanwood]

Pictures slightly out of sequence - the second shows one of the there frames for reference.
I was thinking to put some wood hardener on the remaining rotten frame and fill with epoxy or similar as it won't be seen.