Improving a Precast sill’s weatherproof & run-off

[Kilt]

Replacing rotten timber windows shortly and I’m looking to improve a (precast concrete) sill’s weather proofing and run-off.

The sill in question faces the worst weather we get and we live on a exposed hill in Scotland. (Alot of time, the water can’t escape as force of wind is so strong). 
The sill is not quite level (Jam to jam) so one side stays wetter far longer. Cant fix that without taking out the whole sill.

 

What would your suggestions be for improving sills weather proofing?

Attaching an over-sill, aluminium sill?

I don’t want to use lead, as there is another window and decking under this sill, so don’t want any staining. 

 

also can anyone point me towards some decent window sill make-up drawings? I’m going to ask window fitters to give me some time with opening, once old window is out, to do as much prep as possible,  installing anything needed, like some DPC of original missing or damaged.

 

any advice appreciated. 

[tonyshouse]

Cut in a water bar, vertical metal strip that is recesses into the sill and into the window.

 

what sill will the new window have? 
 

I have very nice European style folded ali sills with end caps 

[Declan52]

How big is the opening???

What's the outside skin , brick block or timber??

How much out of level is it???

A pic would help

[Kilt]

27 minutes ago, Declan52 said:

How big is the opening???

What's the outside skin , brick block or timber??

How much out of level is it???

A pic would help

Its 820mm jam/quoin to jam/quoin.

 

It’s not far out, still within vial marks, but it’s def a few degrees out, which means onside of mortar is still damp whilst rest of sill and mortar is dry. 
 

Outter skin is stone and lime mortar.

 

I think we’re getting water penetration under window or through the sill, so would like to beef it up, improve run-off and ensure more water drips clear of wall and lintel below. 
 

[Dave Jones]

this the one that was causing the one below with no cav try to leak ?

[Kilt]

7 minutes ago, Dave Jones said:

this the one that was causing the one below with no cav try to leak ?

Yep. 
 

but I recently fixed window all up and replaced burnt mastic under the window, with silicone; I don’t want to count-my-chickens yet, but very tentatively, leaks seemed to have stopped. 
 

I've a surveyour coming out in next few weeks, to help identify other issues, including this leak. 
 

but speaking to a few trades, harling is being recommended, rather than a cavity tray. 
but quotes of +£10k, it’s money I simply don’t have. 
So looking at other options for belt ‘n braces. (Cavity tray still an option). 

Edited November 13, 2020 by Kilt

[Kilt]

1 hour ago, tonyshouse said:

Cut in a water bar, vertical metal strip that is recesses into the sill and into the window.

Not sure I follow your thinking here.. got a link or a photo?

 

1 hour ago, tonyshouse said:

what sill will the new window have?

 

Exact windows and company still a TBC.

But they’re going to be upvc sliding sash, but depending on company depends on the sill

Edited November 13, 2020 by Kilt

[Dave Jones]

10k sounds a bit drastic.

 

Could you try a lead apron to force the water to the front of the cill below ? 

 

Cut a slot beneath the top window cill the full width of the cill below and much in lead that laps down over the front of the cill below. Then two more cuts and more lead over the top with side of the little window to catch run off from the edges. 

 

It's not going to look the prettiest but a decent lead man could dress it nicely and it would be no more than a days work. 

 

Have him use waterproofer in the muck to belt and braces.

 

 

[Declan52]

When they have the window out I would take the cill out and reform dpc at the back of it, chances are there isn't any. You will just need to cut out whatever stone pieces are above the edges and it should slide out with the mortar removed at the sides.

Can also redo the reveals if they are bad. Won't really know till the window is out.

[Kilt]

16 minutes ago, Dave Jones said:

10k sounds a bit drastic.

 

Could you try a lead apron to force the water to the front of the cill below ? 

 

Cut a slot beneath the top window cill the full width of the cill below and much in lead that laps down over the front of the cill below. Then two more cuts and more lead over the top with side of the little window to catch run off from the edges. 

 

It's not going to look the prettiest but a decent lead man could dress it nicely and it would be no more than a days work. 

 

Have him use waterproofer in the muck to belt and braces.

 

 

My major concerns with any lead flashing is the potential for the lead to stain window below. 
I agree, it’d be a great solution, but with the weather this gable gets, we’re going to get lead sulphate building up on the glass. That’s an utter sod to get off. 
My neighbour has a fully cloudy Velux due lead staining. 
 

Yeah +£10k seems ridiculous.. but it was full works of Hot lime, lime wash, steam cleaning of organic material etc. 
scafolding was a good 1/4 of price. 
 

it’s also been suggested to install a slate detail, maybe course of 3 in brick pattern to act as “a tray” and to create a further drip point.

[Dave Jones]

your right these are all compromises as the cill below wasn't fitted correctly.

 

I think id be inclined to take out the top window, acro it up,  and have a builder fit a tray to the lintel below then refit. 

 

 

[Kilt]

20 minutes ago, Dave Jones said:

your right these are all compromises as the cill below wasn't fitted correctly.

 

I think id be inclined to take out the top window, acro it up,  and have a builder fit a tray to the lintel below then refit. 

 

 

Yeah, this is my inclination too. 
 

I get where trade recommendations for harling are coming from, it’s traditional, and what would have been in place here, if it had been a dwelling at time of construction. But at that cost.. a tray is going to be cheaper and will achieve same result. 

We don’t have any damp issues else where.