Open cavity after removing window sill

[landsh99]

Interior window sill was removed recently and now I'm left with an open cavity underneath the window frame.

The cavity is filled with blown in mineral wool insulation, but there's a small gap just below where the sill would normally sit.

Should I top up that gap with loose insulation refill? Does it have to be mineral wool, or is another material acceptable?

Do I need to fully close off the cavity before fitting the new window sill? Since the window was newly fitted, I cannot use a cavity closer. What's the proper way to close it up?

I'd appreciate any advice on best practices here.

Thanks!

 

[jj4091]

I just used the cills on all my windows

 

[foxhole]

You could use Celotex insulation board , or rock wool, or expanding foam ( protect frames if you foam as it can mark them ).

 

[noseall]

Interior window sill was removed recently and now I'm left with an open cavity underneath the window frame.

The cavity is filled with blown in mineral wool insulation, but there's a small gap just below where the sill would normally sit.

Should I top up that gap with loose insulation refill? Does it have to be mineral wool, or is another material acceptable?

Do I need to fully close off the cavity before fitting the new window sill? Since the window was newly fitted, I cannot use a cavity closer. What's the proper way to close it up?

I'd appreciate any advice on best practices here.

Thanks!

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