FHA does not have a specific MPR for no stairs, but, does address topography and drainage. I would likely quote these sections of the 4000.1.
iii. Determination of Defective Conditions
Definition
Defective Conditions refer to defective construction, evidence of continuing settlement, excessive dampness, leakage, decay, termites, environmental hazards or other conditions affecting the health and safety of occupants, collateral security or structural soundness of the dwelling.
Standard
The Appraiser must identify readily observable defective conditions.
Defective Conditions Requiring Repair
The Appraiser must identify defective conditions that are curable and will make the Property comply with HUD’s MPR or MPS when cured, and provide an estimated cost to cure.
iv. Site Conditions
Onsite Hazards and Nuisances
Topography
The Appraiser must notify the Mortgagee of the deficiency of MPR or MPS if the surface and subsurface water is not diverted from the dwelling to ensure positive drainage away from the foundation.
Grading and Drainage
The Appraiser must check for readily observable evidence of grading and drainage problems. Proper drainage control measures may include gutters and downspouts or appropriate grading or landscaping to divert the flow of water away from the foundation.
The Appraiser must make the appraisal subject to repair if the grading does not provide positive drainage away from the improvements.
