Elevated Wooden Driveway?

[Adam Roby]

Friend of mine is asking if it is possible to build an elevated wooden parking spot.  His question is related to a his lot that has a 6' drop from the road, and another drop after 20' or so, and therefore it would be difficult to build that up in a ramp with earth or rocks.  Question sounds silly and probably not something recommended, but I was wondering if anyone has ever attempted something similar?

My guess would be for a single vehicle, I guess it would have to be 3' wider on each side to allow to get in and out of the vehicle, and maybe 12'-16' long (he has a Jeep).  Standard Jeep weighs what, 4000 lbs?  Add 5 passengers, 1000 lbs more... plus gear and safety margin, 6000-6500 lbs capacity?

Just doing calculations for weight alone is one thing, but I imaging driving on a wooden pad suspended in the air, then you hit the brakes, that must put a lot of lateral force on the structure... post and beam would probably fall apart. 

Anyways, I told him I would check with you guys to see if this has any chance of working or not. 

[John Raabe]

Look to forest service roads and bridges for (probably overbuilt) ideas.

Using timber beams and 2x6 or thicker decking boards would probably work. You will want a stable foundation and good bracing bolted to beams and the piers/posts. I think I'd add more width than you suggest. Ideally you should be able to walk around the vehicle when the doors are open.

[Don_P]

In wood it needs to be high quality treated, and it would be a good idea to put a roof over it... the roof over a covered bridge wasn't to keep the river dry  . Sure you can do it, locally a 3 bay commercial garage attached to a Dodge dealership is a wood floor over a basement. I've worked in wood floored mill buildings that had far more weight on each floor than a car. I'd build it in masonry of some sort though.

[MushCreek]

I'd also follow the same rules as an elevated deck- if it's over 30" above grade, you need guardrails to keep people from falling off when not in the vehicle. I wouldn't build it any less than 20' long, and I'd probably go 24'. He may have the parking lot longer than he has the Jeep, and it's more comfortable to have some stopping room, too. To last a reasonable amount of time, you'd want massive timbers. It's surprising how strong wood is, though. My drywallers stacked 4400 lbs. of drywall in an area supported by two I-Joists. I couldn't measure any sag or movement, but it scared the heck outta me. Being outside, a parking structure is going to deteriorate and weaken with age, so it needs to be over-built.

[Adam Roby]

I am also tempted to tell him to build it using some PT lumber as a retaining wall perimeter, and then fill it with rocks or soil.  That way it should never fall, so long as the PT does not rot out. 

[cbrian]

Sounds expensive. Ever hear of the giant concrete Lego blocks? They are stack-able, and gravity holds them in place. You see them in commercial retaining walls that are over 20' tall. I used them for my driveway retaining wall, and paid 90$ a piece for them. They are cheap, but require some serious machinery to move. I would think fill dirt and these blocks would be way cheaper than the hardware and PT Beams required for what you are talking about.

[Adam Roby]

What are the dimensions of those?  They appear to be around 4' long, 2' tall and 2' deep.
Would probably need around 40 of them for the 3 sides (minimum) so $3500 for the retaining wall. 
Something to consider...  this was for a friend of mine.  He bought the property but wound up getting a bit more land so now he has better access.
This option will probably be put on hold and possibly canceled all together.  I hadn't seen these Lego type blocks before, pretty cool.

[cbrian]

You guessed it perfectly, they are 2' x 2' x 4' and weight about 3000 lbs. The concrete plant I get them from offer several sizes, this one is the biggest. They are cheap because they use left over concrete to make them. As long as you do not mortar the joints a drainage system is not required, and they work based on gravity alone, they are a real life/money saver.

I was thinking a p/t wood driveway would be cool. Maybe embed some railroad ties spiked into my road base. Have the ties come 2 or 3 inches above grade and place them 3' on center, then spike either some 2x or 4x treated lumber across it to form the driving surface. Would probably have to put some deck paint with sand mixed in it so it doesn't get slick. Would sound cool as your tires road over it  But my wife will probably want asphalt