There are many ways to design a parking ramp, but I am going to share a few rules of thumb that I use to get started. Be sure to always check the municipal code of the location of the project as they may have more stringent rules.
Rule of thumb
Width = 24’
The minimum width of a drive aisle with no parking on either side is 20’. I like to assume the worst case scenario and use 24’ wide which can accommodate curbs on either side to protect adjacent walls from cars or allow for a middle curb with a barrier gate.
Transition slope 8%, 16% 8%
The transition helps to blend the slope so the angle is not too sharp for the car to drive over. The first and last 10’ of the ramp should be 1/2 of the slope of the middle ramp. The ramp’s max slope is 20% when there are no adjacent parking stalls. I start the design with a more conservative number of 16% and increase if necessary. (A parking ramp within the garage that has adjacent parking stalls on it should have a slope of 6%)
Some municipal codes, like San Diego Municipal Code require the first 10’ of length from the property line to be 5% slope.
Elevation change of 6′ (72″)
Measure the distance between the two elevations. In this example I am going to use two elevations that are 6’ (72″) apart.
Rise over run: Use this simple slope formula to find the height of the transition slope and the length of the ramp.
A. Transitions. We know the SLOPE is 8% (.08) and the RUN is 10′ (120″) from our general rule of thumb assumptions above:
120” RUN x .08 SLOPE = 9.6” (~9 5/8”) RISE
The first transition RISE (9 5/8”) + the last transition RISE (9 5/8″) = 19 1/4” RISE
B. Ramp. The total RISE needed is 6′ (72″). First subtract the first and last transition ramp rise from the overall needed rise. Then, use the rise/run =slope formula to calculate the remaining length of the ramp needed.
72” TOTAL RISE– 19 1/4″ RISE= 52 3/4” RISE remaining
52.75” RISE/ .16 SLOPE= 329.68” (~27’ – 5”) RUN
Total RUN of ramp 10’ + 27’ – 5” + 10’ = 47’ – 5”
Total RISE of the ramp 9 5/8″ + 52 3/4″ + 9 5/8″ = 72″
Model Ramp in Revit
There are many ways to model ramps in Revit. I will show you one simple method I have used. I will start from the top of the ramp and work my way down.
Create a floor
A. Create a 10’ x 24’ floor
- Select slope arrow and draw it pointing down the ramp.
2. Select the slope arrow. In the properties, specify the level at the tail of arrow to be Level 1, Height of 0′-0″. Level at the Head of arrow to be Level 1, Height -0′ 9 5/8″
B. Create 24’ x 27’ – 5” next to the first ramp. Specify your levels Level 1 tail to be -9 5/8” head to be Level 0 9 5/8”
Specify your levels Level 1 tail to be -9 5/8” head to be Level 0 9 5/8”
C. Create 10’ x 24’ slab for the last transition.
Specify the tail to be 9 5/8″ above level P1 and the Arrow head to be 0″.
Use the spot slope tool to show your final slopes
You can tag the slopes in section:
and in plan view:
This post is a great reference to quickly calculate and model a ramp. It is helpful to have an idea of length when doing the initial space planning of a garage. Happy ramping. Leave comments below. Let me know how you typically space plan for ramps!