Minimum length for a shed ramp 8“ high using 2x12” PT?

Question

I've built a shed which sits on a frame built of 2x4's and those in turn sit on 4x4 runners, and the whole structure sits on a concrete patio.

The top of the shed floor sits approximately 8" above the patio.

I am using 12" aluminum ramp kit top and bottoms (pic below). The most weight that will be used on the ramp is a riding mower (Cub Cadet XT1 42" - approx 500 lbs) plus rider (say 300 lbs).

I plan to use 2x12 PT lumber to create the ramp and add non-skid traction strips to the lumber for traction.

I have a decent amount of clearance in front of the shed (approx 12') but the ramp still has to be short enough to allow the mower to be aligned properly for climbing the ramp, so the question is - what's the minimum length the ramp can be to ensure a safe trip up the ramp?

These are the ramp kit pieces I'll be using.

Answer 1

5° is standard (ADA) which is 1:12. So at 8" height you would have an 8' ramp. If this is too long to line up the mower, shorten/steepen it as little as is necessary for you to use it. How steep is too steep is impossible to know without understanding all the circumstances.

Find a solid sloped surface somewhere nearby and test drive the mower up and down, to get a feel for how steep is driveable and safe on your mower.

Answer 2

I had a very similar situation at my previous home. As far as I'm concerned, safety isn't much of an issue. It's mostly you going in and out, and not very often. The real concern is bottoming clearance for your mower. It's akin to asking what a tolerable slope is on a trailer ramp.

Do a little experimentation to find out what slope your mower allows with the deck down. Build to that (with a little buffer) and apply a non-slip surface and be happy.

P.s. I'm not sure how you intend to use 2x12s, but I'd run 3-4 2x8 stringers and lay 5/4 decking across them, essentially like a backyard deck. This assumes a length in the 4-6 ft. range.

You'll want to taper the stringers out at the bottom, but consider burying part of the height in the soil (on flat lumber bases) to retain rigidity. I did that recently for a handicap ramp.