Tiles over floorboards - condensation issues

[andymartin86]

Hello
I have a single story extension at the rear of my semi. The new floor is concrete and this meets with the original timber suspended floor from the 1930s.
The kitchen is the extension and the entire floor is tiled, these tiles extend partly onto the wooden floor, carpet then continuing on.
There is a problem with damp and condensation. The area of the wooden floor with the tiles above is wet through and dries as it moves to the carpeted area. The underside of the floorboards ar wet through and this is soaking into the joists. You can tell with the darkeness the moisture is travelling downwards from the floorboards.
When the extension was built the rear air bricks were blocked up so the only bricks are 3 at the side and 2 at the front. The problem is worst in the corner of the house closest to the outside. The wall is also very cold around this area. Is the cold floor (due to the tiles) causing condensation and then damp? Or is inadequate ventilation not removing the condensation which is then resulting in damp?
As i cant fit any rear air bricks would fitting more down the side help?

 

[vinn]

Pics would help, and a rough scanned plan of the property showing where the air bricks are?

On the face of it it sounds as though you have severe condensation in the sub-area due to lack of through ventilation.
How come "pipe vents" were not installed under the new concrete floor?

Any knee walls in the sub-area - are they honeycombed to allow the passage of air?

Is there a membrane below the concrete?
At DPC level was the break through detailed for damproofing?

It might help to move the tile back for the suspended floor.
Any signs of damp in the skirting or walls?

 

[andymartin86]

Thanks i will sort a photo or 2
Its a soil subfloor base with honeycomb sleeper walls. There were no pipes for airflow as the builder at the time said ventilation would be adequate however I still have his details to speak to him.
The walls arent damp but do get very cold in the corner and this leads to condensation which is giving the impression of damp and the plaster in areas is crumbling.
As its confined to the rear corner of the house could I maybe fit another air brick or 2? Ive already replaced the square hole type for the louvered plastic ones which have better airflow. Also we have cavity wall insulation, Im tempted to get this removed