I'm pretty sure the air gap is the key component;
without an air cavity, heat or cold will conduct through your roof.
I believe around here for tight ceilings (eg: narrow scissor trusses) spray foam is used - but it doesn't vridge the bottom chord to the top chord...
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1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.
1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
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