V cold room, draughty behind dry lining.

[flyboy777]

My house is 9 years old of std cavity construction.
I have a problem in 2 rooms at one end of the house, one above the other.
Whilst they warm up when the heating is on, rads get hot etc, the temp plummets as soon as the heating is off.
The rooms are dry lined with the board dot and dabbed to the breeze blocks.
The walls touch freezing cold so I have cut a small hole in the dry lining and there is a very strong cold draught blowing out, having removed a light fitting there is also a draught blowing in the ceiling space of the gnd floor room (floor space of room above), this on a day with no external wind.
The loft above the 1st floor room is well insulated but I have noticed it is draughty up there on a windy day but assumed that is normal due to the soffit ventilation.
The windows appear to be properly fitted and sealed from external inspection.
Any ideas as to why the rooms get cold so quickly.

I have romoved the internal window board from the only window, the cavity is insulated but there is a 3 inch gap between the inner breeze blocks and the underside of the window board and about a 1 inch gap between the window frame and the cavity.
There is a lot of air circulating in the cavity despite the insulation and this can bleed under the window board and behind the dry lining.
Is this the problem or are all windows fitted like this?
The hole I cut in the dry lining on an adjacant wall is still blowing out cold air despite there now being a much bigger exit for it where I removed the window board.

Thanks

 

[centricx]

having a related problem but not dot and dab, I do know that the dot and dab should be sealed at the top with a solid bead all the way across so that the vertical cavity void is more or less airtight. Many dot and dab installations do not do this, which leads to the problems. Can be solved by either access from outside or inside, drilling holes every 30 cm or so and filling with expanding foam.