Hi does anyone have any idea why there’s a gap underneath my back door sill? There’s no mortar it’s just been left open, is it a movement gap or something? 
Could I fill this with expanding foam and silicone? 
thanks 

Edited May 4, 20224 yr by Alwayslearning22

Mortar for me 

8 minutes ago, tonyshouse said:

Mortar for me 

+1 pushed well in to support the door sill.

would do both, low expansion foam to the back with mortar to the front. have you given the spiders notice to quit as they'll need time to find a new home?

I wouldn’t but you can, we will never know 

One side expansion foam and the other half mortar.

 

Then report back to the forum after a thorough test! 

 

Thank you for the replies. I read somewhere that timber frames need Differential movement joints at door openings and window openings.

( i also have gaps underneath one of my window sills) 

Is this actually a done thing? 

Yes but it shouldn’t be, windows often on packers should get sealant on the outside as a minimum 

 

door sills should not be unsupported