Dad has agreed to a threshold ramp. Good. Keep the agreement narrow.
You are not redesigning the house. You are fixing one change in level at one doorway. The trap is treating the ramp as a loose object that only needs to fit under the door. It also has to stay put, drain, preserve the doorway, and leave enough room to open and lock every door in the opening.
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A ramp that fits the step but defeats the storm door is not installed. It is merely nearby.
Start with the route Dad actually uses
Meet the installer at the door, not at the kitchen table. Ask Dad to identify the entrance he uses when he leaves, where he puts a hand, and whether he approaches straight on or from the side. Check both directions. Coming home with a bag in one hand is a different job from walking out empty-handed.
Trace the route from the driveway or walk to the interior floor. Include cracked pavement, loose mats, a storm-door closer, a narrow landing, the threshold, and the first place inside where Dad turns. The ramp cannot repair those other conditions, but the installer should not hide them by measuring only the height of the step.
If Dad uses a cane, walker, cart, or wheelchair, measure and test with that actual item. Do not substitute a showroom measurement or somebody's guess about what he may use later.
Measure the opening with every door in place
Have the installer record the vertical rise, the available run, the clear width, the landing depth, and the direction each door swings. Measure the threshold at several points. Old St. Louis houses have a way of making “level” a term of optimism.
Open the main door and storm door fully while the proposed ramp area is marked. Check whether a door bottom, sweep, closer arm, latch, or weather seal enters that space. Then stand where Dad must stand to unlock and pull the door. A technically clear opening can still leave him backing down a slope while holding a door.
The U.S. Access Board treats changes in level, slopes, stable surfaces, and door maneuvering clearances as separate parts of an accessible route. Its guidance also calls for level landings at ramp runs and warns that door operation must be considered at the landing. Those federal standards may not govern a private single-family house, but they are useful questions for exposing a bad layout before money changes hands. The underlying references are collected on the Sources page.
Set the legal line before installation
Dad can approve work on his house if he understands the choice and is making it himself. A spare key, family relationship, or power of attorney document does not automatically give you permission to authorize every alteration. If you are signing, establish whether you are signing for yourself, as Dad's agent under usable authority, or merely helping him communicate with the contractor.
Then identify the authority for the property's exact address. St. Louis City, St. Louis County, and the municipalities inside the county do not share one permit counter. Ask the enforcing office whether this particular installation requires a building permit, zoning review, historic review, or right-of-way approval. Ask who is responsible for applying and who schedules inspection.
In St. Louis City, structural changes and new construction generally require building authorization, and work extending into the public right-of-way has its own approval path. Historic and flood-area rules can add another review. A loose threshold device may be treated differently from a ramp anchored to a porch or walk. Do not let “portable” become the installer's homemade exemption. Cite the exact address and describe how the unit will be attached when you ask. See the City Building Division permit criteria and public improvement guidance listed in Sources.
Put the installation method in writing
The work order should identify the doorway and state whether the unit is modular, fabricated, or built in place. It should name the ramp material, finished width, attachment method, edge treatment, surface treatment, and what happens at the upper and lower transitions.
Require the installer to state where fasteners will go. Fastening through a threshold, masonry joint, siding, waterproofing layer, or porch surface can create a second repair. Ask what is behind each fastening point, how water will be kept out, and what remains if the ramp is removed.
The work order should also assign responsibility for moving and reinstalling door sweeps, weather stripping, closers, mats, trim, and railings. “Install ramp” is not enough if the installer plans to leave the door rubbing and call that a separate trade.
If excavation, concrete, or anchors are involved, ask who checks for buried utilities and who repairs disturbed pavement, soil, landscaping, or masonry. If the design needs footings or structural attachment, ask who prepared that design and whether the permit office requires drawings.
Protect the exit while the work is open
Before work begins, agree on the construction sequence. Dad needs to know which entrance will be unavailable, for how long, and which usable exit remains. Do not allow tools, packaging, cords, or removed railings to block the backup route.
Keep the keys and lock plan in view. An installer may need the door open for fitting, but that does not mean the house stays unlocked while the crew leaves for materials. Name the person who will open the house, remain reachable, and secure it at the end of each visit.
If the ramp cannot be made usable in one visit, require a safe temporary condition in writing. That may mean restoring the original step and rail until the next visit, not leaning an unfinished ramp against the house.
Watch the points that disappear after fastening
Before final attachment, photograph the threshold, substrate, proposed fastener locations, and drainage path. Confirm that the ramp bears on the surfaces named in the work order and does not rock when loaded from different corners.
Look at the upper transition from inside and outside. A lip left between the ramp and threshold is still a change in level. At the lower end, check whether the ramp meets firm pavement or ends in grass, gravel, a broken joint, or a puddle.
Pour a modest amount of water where rain normally reaches the opening, if conditions allow it without creating a hazard. Watch where it travels. The Access Board's ramp guidance calls for firm, stable, slip-resistant surfaces and landings designed to avoid water accumulation. Again, that is a useful installation benchmark, not a claim that the federal rule automatically controls Dad's house. See Sources.
Test the completed doorway before Dad uses it
Remove tools and scraps first. Then operate the main door, storm door, screen, deadbolt, latch, and closer through their full travel. Check that the doors do not scrape the ramp and that a closer does not pull someone off balance before the latch can be reached.
Test the route with Dad's actual mobility device while Dad watches from a safe position. Move up, down, through the doorway, and back out. Turn where he normally turns. Stop at the place where he must reach the handle or lock. If the device catches, the ramp shifts, or the user must stand sideways on the slope to operate the door, the installer still has work to do.
Check both edges and every transition by sight and touch. Confirm that anchors are tight, exposed hardware is finished, sharp edges are covered, and drainage openings have not been sealed. Verify that handrails or guards included in the work order are secure and do not reduce the promised clear width.
Do not conduct a ceremonial first crossing with Dad merely to prove the purchase was wise. The installer can demonstrate the route without making Dad the test weight.
Take the handoff, not just the receipt
Collect the final work order, permit and inspection record if required, product instructions, warranty terms, and photographs of concealed attachment points. Get the installer's written instructions for cleaning, snow and ice treatment, fastener checks, and removal.
Ask what movement is normal and what requires a service call. Assign one person to inspect the ramp after severe weather, ground movement, or work on the doorway. Put that person's name in Dad's house file. Ownership is less glamorous than installation, which is why loose ramps tend to have plenty of one and not enough of the other.
If the installer will not document the method, permit responsibility, door test, drainage check, and final handoff, pause the job. For more St. Louis contacts and jurisdiction starting points, use Local Help in St. Louis.
Your next move: stand at Dad's chosen doorway with a tape measure, his usual mobility device, and both doors fully open. Photograph the complete route and write down the rise, available run, clear width, landing depth, door swings, and exact property jurisdiction before calling an installer.