Roof Overlay - looking to add insulation

[look 171]

I think its the cheapest solution. Another very important thing is to get rid of the stagnate hot air neat the highest paint of the roof. it helps a lot.

[look 171]

This may help, a little.

[JavaBrewer]

Originally Posted by look 171

I would try 3" to get a lil' more R value in there. It will help a lot. The spray foam is DIY but messy. Rigid foam can be cut with a knife, but we use a table saw. If you don't have one, use a fine tooth hand saw. It cuts easily. Are you painting the ship-lap or tongue and groove to match the beam? You have T-111 plywood on top of those beams now, why not save yourself a lot of work and install T-111 on there, paint to match it white or what ever color you (I should say your wife) like and be done with it. Yea hold it with 1/4 round. If you want to go with 3" foam, then you can extend the beam and fake it by making a U shape piece and nail it on the side of the beam and eliminate the 1/4 round all together. Its all DIY and requires a table saw, glue and some nails. Paint to match. You know how to get hold of me. I am always available

Update. I pressure washed and scrubbed the roof in prep for 10 gallons of elastomeric white paint. Before this my inside ceiling temps closely matched outside temps (100F+). Now my inside temps are maxing out at 88F - so that is decent progress. Next step is to install the rigid foam between the beams inside the home.

I found a 2" product at HD (Rmax Thermasheath-3 2 in. x 4 ft. x 8 ft. R-13.1 Polyisocyanurate Rigid Foam Insulation Board) and calculate I will need 8 sheets to complete the inside coverage (again wedged in between the support beams). This product has a foil coating for reflective property.

Question 1, does the foam need to make contact with the inside ceiling or would it be better to leave a 1" space for more heat isolation?

Question 2, I have read that this product needs to be protected from fire as it causes dangerous gas when exposed to flame. So is my idea of covering with ship lap a no go and I should be looking to enclose the insulation with sheetrock instead? If so would 1/2" be sufficient or do I need to go with 5/8"? That would be a bummer. Or should I use a different rigid foam product?

Thanks!

[dad911]

Fire rating of wood is better than you would think. How do you demonstrate the fire resistance of exposed wood members using char methods in lieu of gypsum? - WoodWorks

As I recall a 2x4 has a 60 minute rating, as used for firestops.

Typically there is an air-gap above bat insulation in cathedral ceilings, not insulation sprayed foam. That is to prevent condensation issues. I would do a bay as a test, then check it in a few months before you do it all.