Building a Windowsill

[MisterFish]

I am attempting to make a windowsill for a bedroom.

In order for the sill to look right it needs to emerge from underneath the existing window. We currently have the plaster off and are going to replace it with insulated board and skim.

The window is sited in an original Victorian stone window surround. There is a small void under the window which is "backed" by the stone of the ornate external sill. The stonework is substantial and in good condition.

Images are: https://www.diynot.com/diy/media/img_2490.106432/

and: https://www.diynot.com/diy/media/img_2491.106433/

I have, I think, two choices for attaching the window.

1. To attach the sill timber to a piece of 3" x 2" angle iron with bolts and woodscrews and then to attach the angle iron to the stone with rawlbolts.

2. To attack the sill to a length of 3" x 2" timber with bolts and/or woodscrews and then attach the timber to the stone with screws and plugs.

Another Image: https://www.diynot.com/diy/media/img_2492.106434/

The first is heavier and, if it works, more secure. My worry is that the rawlbolts might crack or split the stone. The second is lighter and less invasive to the stone but has a downside of being substantially less stable when, for instance, a momentarily unsupervised child decides to use the sill as a chair or climbing frame.

What would you guys do?

 

[JohnD]

a windowsill

i think you mean a windowboard, which is a sort of shelf placed inside the reveal on many houses when the windowframe is set on the outside face of the wall.

you say yours is a Victorian stone house, and looking at the pictures, it appears your windowframe is set on the inside face of the wall, recessed from the outside.

such houses did not have windowboards. They had/have stone sills projecting outside. A piece of wooden trim is more usual inside.

Do you really need/want a shelf under the window?

 

[MisterFish]

Do you really need/want a shelf under the window?

Yes.

Dot and dab, insulated board and skim change all that. By about 100mm.

Back to the actual question?

 

[Deleted member 174758]

I'd go for a treated 3 x 2 (or even 4 x 2) softwood with a layer of DPM between the timber and the stonework, but fitted edge on. This will require extra long screws (something like 6.0 x 130 to 6.0 x 150 for 3 x 2) into brown (7mm) plugs. Properly fixed this should hold quite a bit of weight. Victorian houses often have an additional moulding below the window board called a shoe moulding. This was fitted partly for aesthetic reasons and partly to improve strength. Maybe worth considering