Purchase some Pronavit Smoke Bombs Pal ! (3 for £10) Place one in your loft (Read instructions) And light It !(Best on a calmish day with a slight breeze)stand outside your loft and watch how the Smoke behaves ! IE-Where it is exiting your loft the most and how quickly ! If your not happy then you can adjust/tinker with your ventilation abit ! Also good for clearing any lice/mite and other creepys out yer loft !!