11:04AM | 05/17/04
Member Since: 05/16/04
2 lifetime posts
Hello All:

I need to insulated the roof of my 104 year old house in QC. The rafters are 2x6, 24 on center.

How do I do this best?

I know I need at least 1" for ventilation, that leaves me with 5" for insulation. Is it possible and smart to use rigid insulation between the rafters? Should I add to the rafters with framing from the inside?

How does one get an R-value of at least 30 when one only has 6" rafters?

Thank you for all tips or hints.



12:32PM | 05/17/04
Member Since: 04/03/04
30 lifetime posts
Find a wholsaler of EPS foam near you and you can have it cut to whatever dimensions you'd like. If you use 2# EPS, 6" will give an R value of 30.


03:17AM | 05/18/04
Member Since: 05/16/04
2 lifetime posts
Thank you for the response. Of course, I have a follow-up questions:

From what I just looked up on the internet, EPS foam can have a maximum R-value of 4 point something. So if I leave 1" for ventilation (Is that enough?), 5" of insulation will give me a R-value of a little over 22. Am I looking at the wrong material? Do I not need to ventilate my roof?Can you be more detailed? And how do I attach the panels in the bays. Toe nail each?

How about the variations in rafter spacing? Fill the holes with spray-in foam?

Thank you.



05:19AM | 05/18/04
Member Since: 04/03/04
30 lifetime posts
That's one of the nice features of EPS. You can measure all of the spaces that you need to fill between the rafters, and have the EPS cut to fit perfectly. You can put it up with construction adhesive and a calk gun. You can use the minimal expanding foam in a can to fill any small voids or seams as well. The "R" values change depending on the density of the foam you use, ie: 1#, 2# etc. Regarding ventalation, check with a local roofer in your area as per your climate etc. Here's a link for EPS suppliers in the USA.


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