What Insulation Material

[nealD]

We have a 340 Yr old grade 2 listed former thatched cottage. The thatch was removed 35 years ago and a extended truss roof with tiles added. The distance between the original wattle & dawb is 400-500mm and has no insulation. The energy efficiency rating is a G and we would like to insulate the space as its freezing in winter and hot in warmer temperatures - what material would be suitable please?

 

[malcolm]

The roof looks like it is lined with bitumen felt. Very often they didn't include eaves ventilation with that system. Whatever insulation you add it would be a good idea to add eaves ventilation. You want a wind blowing through there and the whole eaves need to be ventilated both sides and not just a couple of little vents. Full length eaves vents at least 1 inch tall will probably do the job. Otherwise the problem you are going to have is the underside of the felt will be cold and any air getting past the insulation will condense on the roof lining and pour back down the walls. The cold roof lining will suck water out of the house to make it's rain.

After that is done you've got some nice straight surfaces and a lot of space. I would go for 100mm Celotex under (not between) the rafters. Seal all the edges of the Celotex with the silver tape to try to stop any air getting past.

 

[nealD]

Thanks - there is a 20mm gap along the entire length of the roof line and the walls (front & back of the property). The wind whistles through this gap and I wondered if this would be sufficient ventilation. Guess, I'll need to get a specialist installer to check it out!