Spray Foam in attics

Recent attic I inspected had all the insulation removed and the rafters were encapsulated with open cell spray foam.

If the attic or crawl space has an opening that can be entered then the spray foam needs to have an ignition barrier. This barrier can be 1/4 plywood over the foam insulation.
In a typical attic with hatch access this would allow for the 2x4 rafters to be filled giving 4 inches of insulation between the roof decking and the ignition barrier.
Open cell Spray foam has an Rvalue of 3.7 per inch giving your newly sprayed attic a 14.8 Rvalue.

Depending on what climate zone map or insulation requirements you look at. Attic insulation in zone 4-6 should be Rvalue 30-55.
Required thickness needed to achieve this would be at a minimum:

Open Cell @ 8 inches thick
Closed Cell @ 4.5 inches thick

the minimum Rvalue requirements for an attic that can be entered can not be achieved by spray foam alone.
would you then recommend additional insulation (blown in, Batts, ect…)

So you’re asking… what are you asking?

Open cell huh? Is it sprayed directly on the sheathing, a hot roof? You would use closed-cell foam in that application so no air or moisture could pass through.

Is there any air exchange system in the home?

I have questions…

In what I have read so far.

either open cell or closed cell can be used in this application

No added system for air exchange in the home.
House was built in 1892.

question was in the last few lines

in this scenario there was estimated 5" spray foam, to meet the minimum Rvalue guidelines there should be 8"

Would you recommend additional spray foam added to increase Rvalue, or would it be acceptable for the new home owner to add more insulation with a blown cellulose or fiberglass batts in the joists?

I would go with blown in or batt insulation over the spray foam. I recently saw this done by a contractor, a house had serious attic condensation problems (too many potlights and other penetrations), so the contractor hired to fix it used a two inch layer of closed cell spray foam foam in the attic to form a continuous vapor barrier, loose fiberglass to be placed on top. I saw this as it was being done, so no info yet on how well it will work, but from what I could see I think it will work just fine.

From what I’ve read just the other day, both applications can be used, however, Jeff is right, recent studies (from roofs now coming of age) have shown open cell foam has in all climates frequently resulted in wet roof decking. I suspect in time that application will no longer be recommended. Open cell is cheaper and I suspect many are going to regret that.