If you have a conditioned attic, the problem is not heat moving from the conditioned space below the ceiling, but inadequate insulation and/or air sealing under the roof deck or in the previously open soffits.

Here is a link that might be useful: Insights on conditioned attics

So, here's the inside of the exact same space pictured. Are you saying that somehow I'm getting heat transfer from the attic space through the space between the top plates and the roof deck? That doesn't seem very likely...

The soffits ARE still vented (even though there is nowhere for the air to go once it's IN the soffit. Would that part alone explain the patterns in my first picture and if so, do I need to worry about that area or is it simply going to be more directly impacted by ambient air temps than the upper deck with foam behind it?

your overhang extends beyond the
top plates at the soffit/eaves area.

seal is from roof to top plates to attic floor.

soffit area is not insulated and is
vented.

from your pic it looks like a decent seal
although areas like the joist bay
with the iron pipe may not have
the seal the other bays have.
hard to tell from picture.
I like to see the spray continue on down
to the floor of the attic like in other joist
bays.

if the seal at the eaves was the issue
then the frost pattern would be different.
as it is it lines up with walls.

just my .o2

Making sawdust is my thing, but I'll take a stab at this.

The overhang of the roof looks to be well isolated from the attic by the foam insulation. I suspect the lack of frost at the eaves is due to heat loss through the walls rising up between the sheathing and brick and into the soffit.

There's very little foam on the bottom of the rafters. I believe the striping effect in the frost above the attic proper is due to heat loss through the rafters themselves.

"There's very little foam on the bottom of the rafters. I believe the striping effect in the frost above the attic proper is due to heat loss through the rafters themselves."

didn't see that until I enlarged the photo of the roof.
in my climate we over fill the rafter bays with foam,
so that faces of rafters are covered.

at a generous R-7 per inch...4" is only R-28
what is recommended for your area OP?
what is your location?

although foam companies like to say lesser
amounts perform as R-whatever, it is the
actual R-value that matters. not sales talk.

best of luck

I suspect the heat loss out of the wall and behind the brick is the culprit. I think the house was made before wrapping was common. Only so much I can do there without opening up the walls. The depth is a little lower than I would like, but it is closed cell so it's not as much of a factor. The rafters not being sprayed and the total depth was a cost issue. I'm in Atlanta, so I think it should be okay, I suspect most of the value was in the air sealing. I've noticed a significant difference in air and heat/cooling loss already.

The little stripe on the one rafters is where there was a sistered pair and it had spread about 1/8". The foam guys didn't shoot that little crack, so a can of single-part and my gun should fix that.

The brick is a thermal mass, that by itself can be the source of enough warmth to keep the cornice above dewpoint through the hours that dew (or frost) would form. The rafter thermal bridging is a separate issue.
Casey

Thanks, Casey. I'll have to see if the pattern differs much on cold days on the north side of the structure (with no chance to raise the brick temps much above ambient). Totally agree that the vertical lines are simple thermal bridging from the attic space.

Dan

what does your installer say about it all???

or was this DIY?

ken

at a generous R-7 per inch...4" is only R-28
what is recommended for your area

The ceiling/roof insulation is well below both the IECC 2012 minimum of R38 for the OP's climate zone and the Georgia Code minimum of R30 as per IECC 2009.

A thicker application of the spf would have yielded better results.

If the soffits aren't venting up thru he attic, how is the attic ventilated? It looks like you spray foamed them closed.

Yes, because the OP converted his vented attic to an unvented, also known as a conditioned attic.

Yes, it's a "conditioned attic", which is why the soffit penetrations (above top-plates) have been foamed shut. They're actually backed with with some of the original fiberglass batting to give the outside surface of the foam something to cure against.

I'm in CL3, so recommended ceiling R-value is 30 or 38 depending on which version of the IECC specs you use. Unfortunately, I fell pray to the "foam performs better than permeable insulation, so even 3-4 inches performs better than the most of your neighbors" argument, so strictly speaking, the R-value requirements were likely not met. In fairness, I probably have around R-25 once all is said and done and any inefficiencies are accounted for. I'd love to go back 6 months and pay a little more for the extra pass (1-2 inches) to bring it up to the rafter surface and all the rafters, but I didn't. Thankfully, the argument that the biggest benefit is the near perfect air sealing is still true and I will get the lion's share of the benefits even if it's slightly below the recommended thickness. If I ever have my other roof elevation sprayed (over the garage, still a "vented attic"), then I may have the contractor "skim" another inch on top of the existing job. The cost of getting them out there to set up the job is most of the cost. $/foot goes down somewhat as the job gets bigger, so it'll only make financial sense to add foam if there's other work being done.

Thanks for all the comments!

Dan