I found the following information about building a wheelchair ramp at
The question posed was a little different from yours but the answer
gives some general guidelines that I think could answer your question.
Also they suggest the following:
Before you begin construction, I recommend you check with your local
building department on this issue for your state's accessibility
regulations. I also recommend that you contact the U.S. Department of
Justice, Office on the Americans With Disabilities Act
(1-800-514-0301) to obtain a copy of the ADA (Americans with
Disabilities) Handbook or ask for Federal Register, Part III (28 CFR,
Part 36, Vol. 56, No. 144, Order No. 1513-91) which gives ramp design
specifications and dimensions.
I have found a version of the 28 CFR Part 36 at the American with
Disabilities Act web site
http://www.usdoj.gov/crt/ada/adastd94.pdf if you want to take a look
at it in pdf format.
Here are the general requirements:
General Ramp Requirements
Single-family residences have no ramp width dimensional requirements
but I recommend a minimum 36" clear (consider 48" clear).
Level landings are needed at both the top and the bottom of the ramp.
In addition, a 60" long landing is needed after every 30" elevation
change. Landings need to be at least the same width as the ramp. If
the ramp changes direction at a landing, the minimum landing size is
60" x 60".
Guardrails need to be mounted along both sides of the ramp, and
handrails are to be mounted to the inside.
The top of the handrail (gripping surface) must be between 34" and 38"
off the ramp surface. Consider installing a second handrail about 20"
off the ramp surface.
A handrail needs a clear space of 1 1/2" from it and the surface to
which it is mounted.
Use 2" x 6" decking boards and install the short way (the width of the
ramp, 36" or 48") to provide better traction for wheelchair tires, and
install a non-slip surface.
The maximum slope of a ramp in new construction is 1:12, but a slope
of 1:16 or 1:20 may be easier for a wheelchair user to navigate. A
slope of 1:12 means that for every 12" length of ramp, the ramp will
The transition at the point where a concrete walk or drive meets the
ramp should be smooth and level with the landing. The landing should
be at least as wide as the ramp, and the length should be a minimum of
60" (72" according to the UBCUniform Building Code).
0n an exterior door (door swings to the interior) and/or slider, the
landing immediately outside should be level and clear of any
obstacles. Depending on how a wheelchair approaches the door, the
landing requires a maneuvering clearance in front and/or to the side
of the entrance. The entrance itself requires a minimum net opening
(width) of 32" for the wheelchair to pass through. This 32" net
measurement starts from the doorstop to the door face when the door is
in a 90° open position or, the case of a slider, when the door is
fully opened. A wheelchair can approach a door or slider straight on,
from the hinge and/or slider side, or from the latch side. Each of
these approaches requires a minimum landing size:
Straight-on approaches: Both door and slider require a minimum 32"
width net opening by a minimum 42" in depth (measuring out from the
Hinge and/or slide side approach: Both doors require a 54" (minimum)
width with the measurement starting from the latch side and measuring
back toward the hinge and/or slide side and have a depth of 42"
Latch side approach: Both doors require a minimum 32" width net
opening plus 24", with the measurement starting from the hinge and/or
slide side and measuring back toward the latch side, and have a depth
of 42" minimum.
Keep in mind the barrier of the threshold for the exterior slider
should not exceed 3/4" in height. For all other types of doors, it
should not exceed 1/2" in height.
Door hardware should have a shape that is easy to grasp with one hand
and does not require tight grasping and pinching or twisting of the
wrist to operate. Use a U-shaped, lever-operated, or push-type handle.
The operating hardware shall be exposed and usable from both sides on
a slider when the door is fully open, and mount the hardware no higher
than 48" above the finished floor.
When installing a handrail, there should be a clear space of 1 1/2"
between the wall and the handrail. The diameter or width of the
gripping surface should be between 1 1/4" and 1 1/2". If you prefer to
design the handrail so it is located in a recessed area, the recess
should be a maximum of 3" deep with 1 1/2" between the handrail and
the adjacent wall. The recess should extend 18" above the handrail.
To answer your question, I will assume that your porch, steps,
guardrails, and handrails are made of wood and that your steps are 36"
(or less) in width for the purpose of helping you design your ramp for
a permanent base.
First, I recommend removing the steps and sections of the guardrail(s)
on either side of the steps (up on the porch) so when you complete the
ramp and install the handrails, the distance between the two will be a
Depending on how the main post was installed, you may have to remove
some of the porch decking material in order to remove and reinstall
the posts down into the porch framework. If you have a crawl space,
then you can work from the underside.
Seal the complete framework before installing the decking material.
This includes the underside of the ramp joists where it lands on
concrete (assumed) or lift the framework off the concrete with a PVC
spacer. This way you can replace the very first decking board on the
ramp if need be. Be sure to fasten the decking boards with decking
screws instead of nails in order to make this step easier.
Once the ramp has been completed, consider using decorative
latticework on either side of the ramp to finish it off.
I also found some useful information specific to building a ramp in
cold icy climates. I found this at Abledata Informed Consumer's Guide
to Accessible Housing http://www.abledata.com/text2/icg_hous.htm
For curb-height obstacles and small steps, several manufacturers offer
a variety of wheelchair ramps, frequently made of aluminum or
fiberglass, designed for temporary, semi-permanent, and permanent
applications. For longer, steeper inclines, it may be necessary to
construct a wooden or concrete ramp. Ramps should be at least 36
inches wide and have a maximum incline of 1:12 (12
inches of length for every 1 inch in rise). Exterior ramps in climates
where ice and snow are common should have a more gradual incline,
preferably 1:20. In those instances where the ramp has a rise of more
than 30 inches, a landing platform should be constructed half way up.
Additional safety requirements include handrails on both sides and a
non-slip surface. ... "
Let me know if this is enough information, I will be happy to help you
further if needed