Lintel Failure Below Window and Water Penetrating

[Cestrian]

I have a 1900 terrace house. Windows are UPVC replacements (before I bought the house). The windows don't appear to be supporting the brick work and ledges below creating downward movement.Water also seems to be getting in as the plaster inside is damp and crumbling too.

I am about to approach builders, but before I do I'd like a rough idea at the scale of the work involved and costings - just so I know what I am dealing with and to avoid being ripped off.

Thanks

[welsh brickie]

the sandstone sill need repair, But the water ingress is from the window having been poorly fitted, the silicone has not been applied correctly and the rubber seals will have failed, I would replace the window and have the sill repaired while the window is removed