joists need replacing

[gaztfa1]

Hi all.
I will soon be taking on the job of stoping the floor 'bouncing' when jumped on in the kitchen next to the exterior wall. Obviously having never done this before I have taken up a few floor boards in a select place to see what exactly the problem is. I found that the joists are resting on a dpc on a 1ft high brick wall, now heres the question.
From the 3 joists that are exposed two are stable and one is not. It seems that between the joist and the dpc/brick, there is a wedge of some sort, wood I think, The unstable joist has no wedge and therefore when stood on goes down untill supported by the brick, and then returns when you remove your foot. The space between the joist and dpc is about 15mm. Can I resolve the problem by wedging slate in the gap or will I have to replace the joist up to the first internal wall support, also replacing the dpc. Obviously this problem has occured so I should therefore look into proventing any future problems of the same sort. But is it a damp problem or something else? the joists don't seem to be soden or breaking up like I would think damp wood looks.

Thanks for reading, Please if you have any ideas, I appreciate any suggestions.

 

[MANDATE]

I can't see why you can't fill the gap with slate, if its had wood packing it may have worked loose after shrinking, Wood may not be the ideal material but it is easy to cut/shape to suit and will probablely last a long time. I would also consider jacking/wedging the joist upwards while you fit the slate.
Replacing a joist is not that simple and you wouldn't replace the whole joist, what is usually done is to saw some off the end and bolt another short joist along side.
Mind you having said that I've never done one, but I have wedged the joists below the washing machine upwards to reduce vibration.

 

[gaztfa1]

you've confirmed my suspisions, thanks.
You see this problem extneds along the entire back wall, so, I'm thinking that theres been some kind of house movement and these wedges have fallen out, It's just that I did'nt expect to find that the joist would be wedged up, I thought that they would just rest on the brick.
Thanks again.

 

[masona]

If you want to use wood, why not glue it ?