Anyone with experience please share your thoughts on the following:

 

We’re using SIP walls trust for our mild southern California climate.

 

1. Is it better to spray on foam (roof or inside ceiling) or use fiberglass inside the truss, drop down ceilings?

 

2. HGTV Pro stated that the majority of houses are not property vented giving way to mold and wood rot. What is the calculation for roof vent soffits and eves?

 

3. A side by side comparison stated Gorilla wrap was much strong and had improved longevity vs. Tyvek

 

4. One SIP builder stated a/c can be reduced 50% in SIPs vs stick  another stated 30% ?

Thanks Buddies!  

John in the OC

1. SIP roof is best but costs more then sticks/trusses. Air infiltration is a bigger problem then R value so you are better off with the spray foam but at a cost. Spray foam is much more expensive so spray a couple inches of foam and then fill with fiberglass to increase the r value.

2 You can use vented soffit everywhere but isn't usually applied to gables. If you use a ridge vent, you can run it along all your ridges.

3 Wraps are expensive and they seem to have issues. Check with your building dept. because they may require a specific type. I use felt paper because it is inexpensive and has shown to work for years.

4 Getting calcs done for your build is best. Windows/exposure/climate/sq ft of walls/height/roof/thermal masses, etc. all play a role.