Breathable roof underlay?

Phil4432

Good point about the breath ability decreasing with dirt over the years. 
The moisture in the roof is minimal and is to be expected, but definitely don't want to increase it.  Am trying to avoid re roof and keep the costs down.  If I can't get the membrane to work, I'll probably just leave the roof as is. 

TELLIT01

FreeBear said:

Chickereeeee said: I also considered the spray-on foam insulation you can have installed on the underside of the roof.

Spraying foam over the underside of a roof is possibly the worst thing you can do. Aside from the fire risk, the stuff traps moisture in the roof timbers which eventually leads to rot. When you come to replacing the roof, most of the tiles will get broken during removal so can not be reused. The foam gives of toxic fumes as it cures, and again if/when it burns.

There are also a growing number of mortgage companies refusing to lend on properties that have had spray foam put in. Surveyors are also wising up to the problem and are starting to down value their valuations.

It would seem that expanding foam insulation has come on a long way.  Which is now listing is as an acceptable option.  It is also commonly seen on programmes such as Grand Designs.  https://www.which.co.uk/reviews/insulation/article/spray-foam-insulation-ajTlp7t5K7lT