Question re driveway grade...

[Dottore]

A year or so ago we purchased a flat off a plan in Germany which is now nearing completion.

On pre-inspection yesterday, I noticed that the driveway to the underground garage is incredibly steep. I asked about this, and the builder claimed that although the building code require a maximum 15 degree grade for driveways in private houses, there are no such maximums for condominiums. The grade of the driveway in question is 21 degrees.

I have had various discussions with authorities yesterday, and it appears we are SOL on the grade. There really is no maximum prescribed by code, and all the plans were approved by the local regulatory authority. I am seriously pissed about this — but the topography of the site is such that there is no other obvious place to put the driveway.

Everyone involved has assured me that I will still get a Porsche in and out without bottoming out. I am unable to test this because of the scaffolding etc. that is still in place.

My question is simply what is the norm for these grades elsewhere? Does anyone have any experience with a grade as high as 21 degrees? (It is heated, so snow should not be the issue.)

Obscure question I know, but any thoughts will be much appreciated.

[Neilk]

So is the approach angle 21 degrees kind of like a "V" or does it gradually max out at 21 degrees?

If the former, then it might be problematic, but thought I would ask first, not really contributing anything here...

Oh, one last thing... it's 2012... do they realize you are talking about a Carrera and not a Cayenne?

[Porsche-O-Phile]

21 degrees is very steep indeed. Who approved the drawings on behalf of the owner - was it you or an agent or what? If you bought it just "off plans" without visiting the site or having a site plan drawn up then you probably shot yourself in the foot.

I thought in Germany everything had to involve an architect - did this? If so, I'd start with them. Any architect should have known that this was going to be an issue looking at the site constraints and layout of the building.

[GH85Carrera]

I would give that a grade of D- or F.

[MFAFF]

As NeilK says... The issue is the angle at the top and the bottom of the ramp (actually the rate of change of angle)

At the top the risk is grounding the middle of the car as the front goes over the angle first...
At the bottom then the risk is grounding the front end first and then scraping the rear.
Those angles will determine whether or not you can use the ramp not the absolute angle of the ramp.

If it goes from flat to ramp in a single go then 21 degrees going to be a problem on a Carrera...

(I've designed, built a ramp at 22 degrees and then had to drive my Clients' Carrera on it... however the approach and departure angles were well controlled to avoid bottoming out..)

[tevake]

Is the issue really the transition from the slope to the flats at the top and bottom? If they are able to stretch out the transition so you don't bottom out or drag the nose or tail then it should work out. Or are you concerned about traction in wet/ snowy conditions on the steep section?
Aggravating none the less. Hope this works out to your satisfaction.

Cheers Richard

[genrex]

There are two 21-degree angles to be concerned about -- the angle at the top of the driveway, where you could get "high centered" and damage the middle of the car's underside -- and the angle at the bottom of the driveway, where you could damage the front of the car, or the rear of the car (or both).

If you "try" to see if the car will clear, it will be very difficult or impossible to avoid serious damage if the answer is no.

Perhaps pictures of the driveway might be helpful...

_

[vash]

Originally Posted by Dottore

Everyone involved has assured me that I will still get a Porsche in and out without bottoming out. I am unable to test this because of the scaffolding etc. that is still in place.

.

the make-believe lawyer in me wonders, "did you specify which model of Porsche?"

they may or may not be lying.

[Dottore]

The cement for the driveway has not been poured yet. The contractor is currently doing the landscaping prior to pouring cement. I gather the average grade will be 21 degrees measured from garage entrance to street level. It may well be that they intend to solve the problem by making the transition pieces a lesser grade...but that would mean that the main part of the driveway would have to have a grade even exceeding 21 degrees.

I have spoken to the architect, who claims that his hands were tied by the topography, and since the municipality approved his plans, he feels he cannot be faulted.

Given the absence of applicable regulations I think I may well be screwed on this...and this doesn't sit well with me.

I will post some pics after the next site visit.

[Dottore]

Originally Posted by MFAFF

As NeilK says... The issue is the angle at the top and the bottom of the ramp (actually the rate of change of angle)


(I've designed, built a ramp at 22 degrees and then had to drive my Clients' Carrera on it... however the approach and departure angles were well controlled to avoid bottoming out..)

Well this gives me some comfort. I will take this up with the contractor tomorrow.

Thanks for the input.

[Dottore]

Originally Posted by Neilk

Oh, one last thing... it's 2012... do they realize you are talking about a Carrera and not a Cayenne?

Ha, ha! Good point.

You can be damn sure I'm driving the Carrera to the next site meeting.

[icemann427]

Just a few mods will do the trick. lol

[Bill Douglas]

I was thinking the same Icemann. Plus the poor car will get death on the cold engine hauling itself up the incline.

[red-beard]

Dot, can you put up the wheelbase of the Porsche and the clearance?

[red-beard]

Dot, not to get too technical on you, but you are saying grade and degrees. These are not the same. Is it a 21 degree angle slope or a 21% grade slope?

To understand, a 45 degree angle is 100% grade slope, you are going up the same amount as forward.

[RWebb]

the ramp breakover angle for a 1980s stock 911 is ~13o

good luck with this - maybe you can add a contract provision post hoc?

or give him a cease work order and pay liquidated damages?

[ckissick]

Originally Posted by red-beard

Dot, not to get too technical on you, but you are saying grade and degrees. These are not the same. Is it a 21 degree angle slope or a 21% grade slope?

To understand, a 45 degree angle is 100% grade slope, you are going up the same amount as forward.

Yes, you must mean 21 percent. 21 degrees is equivalent to 38%, and it can't possibly be that steep. I mean, that would be ridiculously steep. It better not be that steep. If it is, you are SOL.

I design driveways, and 20% is the max allowed. I've seen 25%, and that's pretty darn steep. 25% requires grooves in the concrete for traction. 38%? Wow. Did I mention that's ridiculously steep? The steepest hill in San Francisco is Filbert Street, at 31.5%.

How long is the driveway? Can you measure the vertical change across the horizontal distance? Percent slope is vertical divided by horizontal.

[onlycafe]

there is this option.

Million Dollar Rooms 106 Subterranean Garage - YouTube

[on2wheels52]

I'm just curious re "It (the driveway) is heated, so snow should not be the issue."
Is that a feature I could retrofit to mine?
Jim

[porwolf]

I think a regular 911 cannot negitiate anything bigger than a 16 degree angle. That is the way it looks from a blueprint that I found somewhere. The black lines are the original blueprint markings. The red markings are mine that I drew over the blueprint in my Visio CAD program.