Loft insulation

[bullethead123]

I currently have 100mm loft insulation just to the top of the joists. It looks very dark and dusty but does that matter? Can I not just roll out 200mm insulation at a right angle to the joists thus giving me the 12 inches of insulation which will score top marks on the EPC?
Also, which is the best brand of insulation to use?
Chris.

 

[Swwils]

Photo would help.

And rolling it accross is good practice since it will cover any joins in the layer below.

Use whatever is cheapest it's all the same candy floss rocks, it's almost always better to keep it simple and add more than some super-special high performance stuff.

 

[robinbanks]

It looks very dark and dusty but does that matter?

Turn it over, so the contaminated, heavier, dirty layer is no longer compressing it. If it's just light surface dust that isn't compressing it, you can leave it alone

Yes you can roll out 200mm top up at right angles. Ensure you get all the way to the edge, without cutting off all the ventilation to the roof space.
If you want better performance you can look at purchasing some seconds grade PIR/PUR boards for over the studs. PIR is typically twice as good as wool so can be half as thick, and a loft boarded out with 100mm PIR boards could easily be used for light storage. If using rigid board make sure the old wool isn't so compressed that air can get between it and the PIR board, otherwise there's nearly no point having the board. Though not as good as board thermally, wool's tendency to collapse/distort to fill voids means it performs well