Powder coated oversills covering weep vents..

[ray316]

Just had new windows fitted and now having exterior wall insulation so they are fitting powder coated oversills , the oversills are 5 mm thick and my weep vent is a slot along the bottom to exisiting sill.
So the oversills will go into the slot and cover the weep vent.

I suggested leaving the oversills out just enough not to block the vent , they are saying it would fill with water when it rains..
They said they slide the oversills into the vent slot and silicone up..

So is it alright to cover and silicone like they suggest.
Or my idea of leaving a 10mm gap so the weep vent is not covered..

Could I have problems if the vent is covered..
I never had weep vents with my single glazed wooden windows..

 

[crank39]

You are asking for trouble if you block the drainage slots, if you leave it forward as you suggest then water could be allowed to run to each end and possibly find its way down the side of the existing cill, this could result in damp appearing inside on the plaster reveals

You old timber windows did not need weep vents or drainage slots because they were single glazed, dg units in timber windows don't really work as it is difficult to get an efficient drainage system under the glass and invisible slots to let water out, it can be done but its not perfect. PVC sections are hollow and have been designed to flow water away from the underside of the glass, dg units do not like water, if the pvc channel holds water and touches the dg unit then its on borrowed time.......probably months

You could ask the installer of the cills to drill 'face drain slots' in the front of the window and cover with a 'face drain cap' but ideally the window needs to be removed to have the concealed drainage slots sealed up, these would be the ones the new cills would interfere with

 

[ray316]

You are asking for trouble if you block the drainage slots, if you leave it forward as you suggest then water could be allowed to run to each end and possibly find its way down the side of the existing cill, this could result in damp appearing inside on the plaster reveals

You old timber windows did not need weep vents or drainage slots because they were single glazed, dg units in timber windows don't really work as it is difficult to get an efficient drainage system under the glass and invisible slots to let water out, it can be done but its not perfect. PVC sections are hollow and have been designed to flow water away from the underside of the glass, dg units do not like water, if the pvc channel holds water and touches the dg unit then its on borrowed time.......probably months

You could ask the installer of the cills to drill 'face drain slots' in the front of the window and cover with a 'face drain cap' but ideally the window needs to be removed to have the concealed drainage slots sealed up, these would be the ones the new cills would interfere with

Thanks for some info.
So I'm in abit of a dilemma , any other suggestions as I don't know what to do for the best.
You say ideally the window needs to be removed to have the concealed slots up.. Would that be like sealing it from outer sill, as the vents would be blocked up.
Can I ask what does the weep vents do, how can condensation get in the frame from inside your house if the frame and window has seals.

I would also like to ask ,
Is it a big job to put weep vent onto the dg frame above the oversills if l have these sealed up to the dg slot vent.

 

[Gazman16]

In the early days of double glazing they didn't have drainage or ventilation around the units, It was soon learnt that DGU's wouldn't last long like that.

Basically it dosent matter how good the seals are or how good the compression is between the glass and those seals, Both rain water and water vapor will find a way in and it needs a way to get out or your units will mist up in short order.

Retro fitting drainage to the front of the frames is easy but as mentioned its sealing up the old holes underneath thats the tricky bit.
Without taking the frames out to seal the holes theres no way to be sure they are fully sealed and even then how long will the silicone seal last.

I'm supprized no-one has come up with a good solution to this yet as it keeps coming up.

I know you can get 2 or 3mm thick over cills that may in theory do the job but I haven't tried them personally.