Upstairs bedrooms hitting 88 degrees by 3pm even when the thermostat downstairs reads 74

The static pressure number is the one I'd want before spending anything beyond the insulation. A lot of contractors skip straight to equipment because it's billable, but if the return path upstairs is blocked or undersized, adding a mini-split treats the symptom and the duct problem stays. A manometer reading across the air handler tells you whether the system is moving the air it's rated for, and if it isn't, rebalancing registers and cutting a proper return grille into an upstairs hallway can close four or five degrees of that gap for a few hundred dollars rather than a few thousand.

The insulation is still the right first move and I wouldn't argue with the sequencing in your post. The thing I'd add is that blown cellulose and open-cell spray behave differently in a vented versus unvented attic assembly, and a 1988 build almost certainly has a vented attic, which means open-cell spray against the roof deck without closing the vents creates a moisture problem in humid climates. Blown cellulose over the attic floor to R-49 is the lower-risk call there.

What's the climate zone, and do you know whether the existing return system has any upstairs return at all?

This is a genuinely useful breakdown for any landlord dealing with a late-eighties two-story, and the logic holds up well.

One thing I'd add for context: the cost framing at the end is the part worth sitting with. Three months of lost rent on a house renting for, say, $1,500 a month is $4,500. The insulation and airflow work described here comes in under $3,000 in most cases. That math is the reason experienced landlords treat comfort complaints as maintenance calls rather than tenant complaints. A tenant who leaves in August over a livable-heat issue is expensive in ways that go beyond the vacancy: cleaning, showing, screening, and potentially a gap before the next lease starts.

I'd be careful about one framing in the original post. The mini-split "raises the rental ask on the next turn" is a reasonable possibility in some markets, but it is not a guarantee. Whether a second cooling source commands higher rent depends on what comparable houses in that specific neighborhood are offering. In some markets it matters; in others tenants do not price it. Worth checking local comps before counting that upside.

On the HVAC question at the end: the return air situation is genuinely the first thing to confirm. A room with no return duct will pressurize and stop accepting conditioned air almost entirely. That is a quick diagnostic before spending anything.

For anyone reading this who owns a single-family rental and is newer to the landlord side, the strategy guide for SFR has a section on operating costs and what affects cash flow. Worth a read alongside threads like this one.

What climate zone is the property in? That changes which fix has the most impact first.

Spray foam at the attic hatch is the leak everyone misses first.

The piece of this that sits in SFR underwriting rather than just maintenance is the deferred capital expense exposure. When a tenant sends a written complaint using the word "uninhabitable" and the property is a 1988 single-zone house in a climate zone where summer highs run over 95 regularly, you are no longer in routine repair territory. Several states treat the failure to maintain habitable temperatures as a breach of the implied warranty of habitability, and a landlord who has documented complaints and has not acted has a much weaker position if the tenant withholds rent or a housing authority gets involved. The insulation and airflow fixes described above are the right moves mechanically, but the sequencing matters for liability too: do the attic insulation first because it is the cheapest work, it is permanent capital improvement rather than a repair expense, and it shows a documented response to a documented complaint.

The related strategy that shifts the picture here is the capital expense reserve model you should be running at underwriting. A 1988 house with original single-zone HVAC has a system that is past or near end of useful life regardless of whether it is currently running. If you underwrote this property assuming minimal capex because the HVAC "works," the insulation job and a mini-split together might run three to four thousand dollars, and a full system replacement in the next three to five years could be another six to ten. That is a basis problem more than a maintenance problem. What did you underwrite for annual capex reserve on this property, and did you stress that number against the age of the mechanical systems?

What climate zone, because R-38 stops the bleeding in 4C but barely matters in 2B Phoenix heat.