What are the pros/cons of going this route?

I have no idea about the expense of doing this, but I'm curious about its value versus regular fiberglass rolled insulation.

an unvented attic (foam on roofline) will keep
mechanicals and ducts in semi conditioned area.
this will also make attic to living space air infiltration
less of an issue.

check out buildingscience.com for your location
and educate yourself with unbiased information rather
than mfg's websites that are selling products.
your state's dept of energy will also have climate specific
info for you.

there is another thread on this site that covers this info
in greater detail.

best of luck.

The power of pink! How else to explain that molten glass became the
standard and everything else "also ran." There are many more effective alternatives.

If you live in a cold area and have to heat with oil or propane than you definitely want to spend all you can on insulation. But spray foam is rarely the most cost effective answer - thicker walls, triple pane windows, rigid foam.

I am still not sold on foaming the rafters even. Put the air handler and ducts somewhere else and then conventionally insulate.

By putting down a layer of foam you get its infiltration protection, and the layer only needs to be thick enough to make sure the dew point is in the foam.

The remainder of the cavity is filled with fiberglass to increase the R-value at lower cost.

guess I understand, but don't agree.
even the foam company I recommend knows that they
won't get a foam the walls job from me. the payback is
just too high. and it is something that with the foam sheathing to the exterior is unnecessary, with the proper air sealing details.

its all I can do lately to keep up with the many
many folks who think they can spray foam and totally
encapsulate the attic. seems like a new company pops
up every week!
I'm almost to the point of getting a can of red paint to mark the places where foam isn't needed, and a can of black paint to mark the places where foam is needed.
(and that is BAD)
too many foam insulators don't understand what the
thermal boundry in the attic is. they want to foam
the roofline of porches and patios that have ventilated vinyl ceilings when they should be installing felt paper
to make a wall to seal off these areas.

its bad enough when I go into the attic after the foam job
with my blower door and mark with red paint the areas they have to come back to seal.

sue, I ran these numbers 8 years ago and came up with an average of 25 year payback for foam insulation in walls
and roof.
by putting the foam sheathing on the exterior of the walls and making them air tight (for a fraction of the cost) and foam insulating the roofline the payback is
about half.

in a perfect world...ductwork and mechanicals wouldn't be in the attic. doesn't often happen itrw.
so then if the hvac companies would actually mastic seal the leakage sites, and the builders would not leave thermal bypasses from attic to living space..plumbers and electricians would seal the holes they make we could probably do all right with conventional insulation.
unfortunately..this isn't how it is in the real world.

it is a sad fact that the homeowner has to pay for these
unsealed areas every month with higher utility bills.
foam does make a lot of these problems less of an issue
but again it is at the homeowner's expense.

just my experience, and it has taken me some time to get to this point. even if you get trades people to seal like they should on one job..come the next house you start all over again.

I think that performance based contracting is the way to go
but finding like minded trades people is a rare thing.

best of luck OP

All in all, six of one- half a dozen of the other.

Glad we did what we did- stepping into a house this cozy in the dead of winter is amazing...but to each their own.

The latest from Dr. Lsitburek on spf.

A number to work in. Oil is now 4 times the cost of NG on the wholesale market on a btu basis. Propane is close to oil and tracks it in price. Heat pump with cheap electric is just a little better than NG.

As someone said, you can seal a house just fine with other techniques. I foamed penetrations and around windows and my blower door was 50% below energy star specs. There was a cat door thrown in that, relatively inexpensive windows, and a large wood french door that just doesn't seal perfectly.

you mentioned "regular fiberglass rolled insulation."

someone responded by mentioning that the pink panther keeping company with the pink product seems to have made people go for it as the unconscious choice.

there are two big subjects here.

One is technical: sealing the house = airtight = less heat loss, because less outdoor air seeps in.

The other big subject is how it came to be that the average bear began to think of "pink" as the Go -To product. It is a lousy product in many installations. It doesn't stop air from moving through it (even with a backing). Air moves every day as barometric pressure changes, and as normal activities inside the house produce humidity and warmth.

That is NOT the movement that is the problem.

Infiltration (movement of conditioned air) in and out through gaps, cracks, etc. is the problem.

Fiberglass, cellulose and other fill type insulation are NOT effective at stopping infiltration.
Their purpose is to hold air still, but they cannot function against the slightest thermal driven movement.

Sprayed foam (even the stuff in the little can), caulk, etc. are the infiltration tools, and should be used before you even stat using blown or rolled insulation of any type.

We're considering it for our soon to be constructed home.