I need to transition from a porch raised 3" to an existing ramp

Question

We had to raise the floor of an outdoor but enclosed porch 3" to match the home's interior floor height. The porch leads to a wheelchair ramp.

An attempt was made to create a ramp to a ramp. This causes no problems with the manual wheelchair, but the electric wheelchair wants to tip forward on it. The back wheels of the electric wheelchair actually leave the ground while going down the mini-ramp. The electric wheelchair has no problems with the mini-ramp created on the opposite side. That mini-ramp is both steeper and shorter, but leads to a flat floor, not a ramp.

I realize the mini-ramp probably needs to be longer, possibly doubled. What is there is a series of piled wedges. I don't know how to measure to create a flat ramp since I am going into a ramp.

Here is a photo of what was done. How can we do a better job of it?

Answer 1

Measure the problem

The problem isn't the angle of the ramp, it's the pitch of the chair. Measure it. Even though the short ramp is steep, the chair's pitch remains OK because the lower wheel is on level floor beyond the bottom of the ramp before the upper wheel reaches the top of the ramp. Not so with the troublesome ramp - probably both wheels get onto that transition at the same time, the pitch of the chair matches the pitch of the transition ramp, the chair's center of gravity gets too near the front wheel, and it starts to topple forward.

With the chair unoccupied, and/or with whatever assistance is needed to keep things safe, position the chair straddling the "opposite side" ramp where the chair is stable. Put on your mathematician hat and visualize a triangle connecting the points where the upper and lower wheel contact the floors and one third point in space. Using a carpenter's level and a measuring tape, figure out the rise and the run of the chair's pitch/slope in this position. Do the same with the chair positioned in the unstable place on the ramp-to-ramp. (image from Monterey Institute algebra course)

The run is the same in both conditions because the chair's size (wheelbase) is the same. The rise changes -- for the particular wheelchair you have, the rise on the "opposite side" ramp is acceptable but the rise on the ramp-to-ramp is too much.

Now that you are armed with numbers and a method you can start estimating how much change is needed on the ramp-to-ramp to make it safe. You'll be able to confidently answer questions like "if we change X, will that be enough?" or "how much longer does the transition ramp need to taper?" before you start cutting materials.

Fix the problem

The ideal thing is to have no ramp-to-ramp transition at all. In the photo I see three posts interrupting the handrail, making four sections of ramp. Is it possible to raise the high end of the ramp and place shims beneath all or even just some of those posts? It might even be sufficient to raise only the top end of the first section of ramp and leave all the rest alone.

If adjusting the existing ramp isn't an option, a much longer taper on the transition ramp is second best.

Dodge the problem?

One thing you could try is maneuvering the chair through this spot facing the other direction. The center of gravity may not be centered between the wheels; the chair may be able to tolerate a little steeper pitch facing one way than it can facing the other way.

Operators of earth-moving equipment are familiar with this problem and solution. I virtually always load my skid-steer loader into a transport trailer by backing it up the ramps. The engine is at the back of the machine; if I climb the ramps leading with the rear/engine end it's stable. If I climb the ramp facing forward, ie leading with the empty bucket, it feels like it's very close to rolling backward onto its back.

Answer 2

You have a couple of Code violations: 1) your short ramp is too steep, 2) a landing is required between the two ramps, 3) exterior landing is more than 1 1/2” below top of existing threshold.

1. Ramps cannot exceed 1:8 slope. So, if the height difference for the short ramp is 3”, then it needs to be a minimum of 24” long. (3” x 8 = 24”) Your ramp appears to be about 18” (when I compared it to the 6” boards on the long ramp). (See ICC R311.6.1)

2. You need a landing between the two ramps. “A ramp is required at the top and bottom of all ramps.” (See R311.6.2.1)

3. A landing is required at all exterior doors. (See R311.4.3.1) The interior finished floor is more than 1 1/2” below the top of the threshold for the door on the left in the first picture. Maximum difference by code is 1 1/2”. (See R311.4.3)

You can ignore these requirements and just cross you fingers and hope it all works out, but when you invite the neighbors to your next birthday party, don’t serve beer… or make sure you have a good attorney. These are the things attorneys love.

I’d start by changing the small ramp (making it longer) then add a landing, then add a new ramp on top of your existing long ramp. Seems silly, but you’ll sleep at nights.

Answer 3

Eliminate ramp to ramp transition: Just change the slope of the top of the ramp. Remove the ramp floor boards starting at the top and extending 8 feet along. Sister new 8-foot-long joists to the existing ones at a slightly higher slope that begin at the same level at the bottom but will meet the new floor level at the top. Replace the floor boards.

For added safety, tape or paint a stripe at the transition between the two slopes, and also cut the hand rails at that point and change their slope too so they will always be the same height from the deck.

Answer 4

The mini transition-ramp is currently too short compared to the distance between the front and rear wheels of the wheel chair in question.

This means that the front wheel starts to travel down the long ramp (on the right), past the mini transition ramp, before the rear wheel enters the mini-ramp.

Since the long ramp is sloped, the front wheel drops further before the rear wheel enters the mini ramp and starts to drop. As a result, the wheelchair tilts forward with a steeper angle than the long ramp. This is like placing the chair on the ramp, facing down hill, and then lifting its rear wheels by a bit.

The problem does not exist at the other mini ramp on the left side because the landing there is not sloped. When the front wheels enter the flat landing and the rear wheel is still on the raised platform, the wheelchair will keep its tilt based on the wheel base and not the length of the mini-ramp.

Measure the distance between the front and rear wheels and build a new mini-ramp that is at least that long, as in the picture below.

This is what one of the comments means with the recommendation to make the 3" steep ramp longer. How much longer? It should be at least as long as the wheel base.