Can I nail the lead flashing under UPVC windows?

[datarebal]

A cavity tray will serve zero purpose beneath that window.

The Window should be sat in a tray. To not do it is shoddy and amateurish.
It picks up any water from around the window and under the cill including off the cill ends.
just as one might fit in a Dormer window.. well some do....

There are plenty of examples on this site where people have spent £1000s trying to find the leak.. before realizing its lack of trays

 

[datarebal]

A cavity tray can't be used below the window

of course a tray can and it should

 

[noseall]

The Window should be sat in a tray

Nonsense. It's sat in a masonry aperture.

 

[datarebal]

You obviously have limited knowledge .. maybe stick to Lego

 

[catlad]

A lot will depend on the direction of the prevailing wind as to whether enough damp gets through to be an issue, in this instance with limited amount of masonry and a decent sized soffit it may be ok. Painting the brickwork with stormdry as you finish off the extension should help.

 

[SpecialK]

Thanks for the advice.
The soffit above overhangs 600mm so the windows very rarely get wet. The bricks are odd too...they may be concrete...not sure if this makes a difference?
I will give it a coat of stormdry - it looks like a good product!

The flashing is in - I used lead straps nailed with the tiles to hold the lead in place. I wedged some Packers between the sill and folded lead and sealed with leadmate. I will redo all the silicone around the windows too.

Fingers crossed it won't leak. The conservatory that used to be there just had flashband poorly stuck to the wall and stayed dry. Fingers crossed !

A lot will depend on the direction of the prevailing wind as to whether enough damp gets through to be an issue, in this instance with limited amount of masonry and a decent sized soffit it may be ok. Painting the brickwork with stormdry as you finish off the extension should help.