Accommodations are free
A reasonable accommodation is a change in rules, policies or services. 24 CFR 100.204 requires them; its own example is refusing a blind applicant's seeing-eye dog under a no-pets rule. HUD Notice FHEO-2020-01 adds that providers cannot charge a fee or deposit for service or assistance animals, though the tenant stays liable for damage the animal causes.
The trap is equal treatment: a neutral no-pets policy must still yield to a necessary accommodation. Where the disability is obvious, no verification may be demanded, and providers may never require notarized statements or specific forms. Other tenants' allergies are not a permitted condition.
Modifications are at the tenant's expense
A reasonable modification is a physical change, such as widening a doorway, under 42 U.S.C. § 3604(f)(3)(A) and 24 CFR 100.203. The tenant pays; refusing because the change is structural is itself a violation.
The landlord may condition permission on restoring the interior, wear and tear excepted, and may require a reasonable amount, not exceeding the cost of restoration, paid over a reasonable period into an interest-bearing escrow account whose interest accrues to the tenant. The trap is calling that money an additional security deposit: it goes into escrow, and no extra deposit may be charged. Only a Section 504 recipient of federal assistance pays.
The leasing office is an ADA space
ADA Title III covers a property's public accommodations, and a leasing office falls in the sales or rental establishment and office categories. The ADA does not govern the dwelling units — the Fair Housing Act does — but it reaches the office, where staff may ask only two questions: whether the animal is required because of a disability, and what work or task it is trained to perform. They may not probe the disability, demand a physician's confirmation, ask for certification or registration papers, or ask for a demonstration.
The one lawful refusal
42 U.S.C. § 3604(f)(9) is the only ground: nothing requires a dwelling to be made available to a person whose tenancy would be a direct threat to the health or safety of others or cause substantial damage to others' property.
Neighbors' discomfort is never a defense. Where a disability is not obvious, the provider may request verification, not refuse. The accessible design rules for dwellings first occupied after March 13, 1991 govern construction, not applicants.