Drainage and Ventilation

Leaving aside the meeting rails for a while (this window is for the first floor so security is not so critical). Time to finish of the main sash pieces

The double glazed units will have a 5mm air all round. The bottom rails need venting to allow any moisture in the air gap to get out also any water that gets past the glazing seals needs to be drained away to the outside.


So first drill some holes. I've used 9mm at approx 150 centres. Easy job in the top sash meeting rail but I had to drill in two steps through the bottom sash rail as the stroke on my pillar drill would go the full depth. I also counter sunk the external face to aid painting.

Then with a batten clamped to rails making up for the rebate I routed from the first hole to the last with a round ended bit.

The resulting groove stops any water from the outer face reaching the inner bead. It looks like:-