rotten wood in porch

[Dipy]

Hi, I lifted a cracked tile in my porch , there is rotten wood behind where the stone step is.

I noticed gaps round the stone step outside, could this be the cause ?

 

I couldnt feel any draught under the wooden floor for ventilation, but there are airbricks a few feet away round the corner on the next wall

Edited March 2, 2020 by Dipy