Attic conversion insulation choice

logistic

I've a choice of pir board between rafters or spray foam. Which would you choose and why?

TimHorton

https://www.boards.ie/discussion/2058283925/attic-conversion-insulation-choice

What is going on over the top , More insulation or just plasterboard - If its Just plasterboard it will leave the rafters creating cold bridges all over the place .Most on here will tell you stay away from spray foam , Also what depth are your rafters? You will need to leave 50mm air gap ! so your PIR depth will be affected ,

logistic

https://www.boards.ie/discussion/comment/120231410#Comment_120231410

Should have provided more information. Air gap will be a given.

Options are

(1) Strengthen rafters to 6x2, spray foam open cell, 38mm K18 Kooltherm warmboard

or

(2) Double up all roof timbers, 60mm Kingspan insulation and foil tape all joints, 25mm insulated board

dazza181

Which did you go with in the end?

logistic

https://www.boards.ie/discussion/comment/122713153#Comment_122713153

Went with the spray foam and 38mm warmboard. 50mm gap was left for airflow.

Madd002

https://www.boards.ie/discussion/comment/122715057#Comment_122715057

Have foam done 4yrs, amazing how much heat stays in the house.

dazza181

Converting upstairs in dormer and don't know what insulation to go with. A lot saying stay away from spray foam with concerns over rot. You'd obviously recommend it?