ADA recommended flatter slope percentages.

[Jean Tessmer-HI]

Under the ADA 2010 - 405.2 and 402.3 are recommendation for lower slopes for ramps and cross slopes.
Recommendations: Providing the least possible slope below the 1:12 (8.33%) maximum offers better usability for a wider range of users. Specifying a running
slope of 7.5% maximum and a cross slope of 1.5% maximum for exterior ramps will accommodate most irregularities or variances due to construction methods
or materials according to a study sponsored by the Board (“Dimensional Tolerances in Construction and for Surface Accessibility” by David Kent Ballast.)

I am posting this to remind designers that without the tolerances stated above the ramps and cross slopes will generally fail especially when the designers land lock the slope and don't allow at least an additional 15% added ramp length to accommodate the known variables listed above. As designers you are not safe just saying 1:12 (8.33%) because the recommendation above is saying that you need to give more than 1/120 inch tolerance so the contractor has a prayer of building the ramp to meet compliance. I personally recommend 7.25% for the 8.33%, 4% for the 5% slope, and 1.3% for the cross slope. These are final forms layout using flat work techniques for very experienced concrete contractors. I hope this helps. Concrete contractors may also want to check the plans before they bid ADA work to make sure the tolerances will allow the ramps or sloped surfaces to be buildable to construction industry standards with a slight tweak in technics. Thanks to all the hardworking men and women working to construct, provide and support individuals with disabilities with functional usable of sites and facilities. Remember 1/8 of an inch = 1 percent slope.

 

[Yikes]

When clearances have been really tight and we had no other choice, we've been designing as steep at 1.8% for "flat", 4.8% for "walkways", and 8.1% for "ramps". We do these only in concrete, not asphalt.

LA Housing Department and their Neutral Accessibility Consultant tested about a dozen digital smart levels. Stabila has been the most accurate, claiming 0.1% tolerance on their 2' long smart level, and it needs no calibration. These levels cost about $300 each. Most other manufacturers have up to a 0.3% tolerance, but they cost less than $100.

As a result of this testing, it is LAHD's / NAC's protocol that if the plans as designed meet code, they will accept as-constructed smart level readings within 0.3% of code maximum as representing compliance, eg: 2.3% for "flat", 5.3% for "walkway", and 8.6% for "ramp".

 

[Jean Tessmer-HI]

When clearances have been really tight and we had no other choice, we've been designing as steep at 1.8% for "flat", 4.8% for "walkways", and 8.1% for "ramps". We do these only in concrete, not asphalt.

LA Housing Department and their Neutral Accessibility Consultant tested about a dozen digital smart levels. Stabila has been the most accurate, claiming 0.1% tolerance on their 2' long smart level, and it needs no calibration. These levels cost about $300 each. Most other manufacturers have up to a 0.3% tolerance, but they cost less than $100.

As a result of this testing, it is LAHD's / NAC's protocol that if the plans as designed meet code, they will accept as-constructed smart level readings within 0.3% of code maximum as representing compliance, eg: 2.3% for "flat", 5.3% for "walkway", and 8.6% for "ramp".

Hi Yikes,
Nice to hear from you. First, I hope you make sure that you are not responsible for any Federal ADA non-compliance. LA Housing should take responsibility. Second, I hope you are following flat work techniques some of which are laid out here: https://www.constructionspecifier.c...ble-predictable-concrete-flatness-techniques/. Third, I hope someone on your crews uses a smarttool. I have worked with David Ballasts and Eldon Tipping - ACI on flatness. It took years to find the sweet spot that did not put much additional length on ramps and was still buildable.

I am including an excerpt from the Stabila user manuals' error information below. The smarttool pro 3600 which is the delux version of the standard smarttool can get NIST certification. The MD smarttool and Pro 3600 all have the liquid filled gravity base sensors. I can stack 3 or four smarttools on top of each other and they all have the same reading. I can flip them 180 degrees and stack them and they all read the same. I take three of them on my jobs just to have a big smile when I stack them and they all read the same. They rarely need calibrating. I use the smarttool in federal and state court cases.

Last page of the Stabila digital user manual states: (by the way it appears Stabila has removed these instructions from the internet)
• The TECH level is very accurate in any angle or slope. In any angle or slope, if you were to spin your level 180 degrees to check an angle, you double your possible error. There is a quick way to minimize this possible error. Simply take each of your measurements and divide by two (2).

The errors only get worse when you are on any slope above 6% and rotate the level 180 degrees or turn it while walking it can read up or down more than a full percent. The hick ups from the stabila are me horrific because, they are not reliable, I had to go back redo a site that I used the Stabila on. Stabila used to use the Smarttool module, but decided their economical accelerometer module was good enough. Best thing is to have the MD Pro-3600 to check calibrations with inspectors using the Stabila, and they will see which tool is the smartest. Super Flat Floors use the MD Pro 3600 as their gold standard to calibrate the Super Flat floor inclinometer. I did training sessions with our county engineers showing them the Stabila on a more than 7% slope rotated 180 and it went to 9%. They ran out of the room and came back with their smarttools to check it the smarttool did that too. they did not. solid as rocks. The original smarttool is in the National Science Foundation's Museum has been since 1986. Here is the link to the Smarttools testing - comparison with MEMs digital levels. http://smarttoollevels.com/competitiveaccuracy/

 

[Jean Tessmer-HI]

You are being held to ~1/32" of deviation continuously on the entire ramp surface.

 

[bill1952]

I've been doing 1:12 aisle ramps in theatres for over 10 years and fairly sure no one has ever measured one. Of course a lot of those are parabolic slopes, starting at 1:12 and in 2 or 3 section of lesser slopes for a total of 30".

1:12 is barely acceptable for sightlines as it is and results in a stage higher than really desirable. Miss the days of 1:8 and 1:5 audience takes.

 

[Yikes]

Jean, I know we were talking about slopes, but what would you recommend for stairs, especially field-fabricated stairs (such as wood risers, treads and stringers)?
I've often spec'd 7" rise 11" run, but I realize in both chapter 10 and in ADA / CBC 11B it's max. 7" and min 11". The slightest misapplication of finish materials would make them noncompliant.

I'm currently thinking 6.75" max. risers and 11.25" min. treads.

 

[bill1952]

Just a related note. I did a lot of work on Chicago Public Schools. Their design standards are 29" rise max. between landings to compensate for bad work.

 

[Jean Tessmer-HI]

Thanks for your question. If you can maintain the average riser within the 1/4" tolerance in both rise and run directions at least you will have a fallback position showing you were under the maximums allowed under the ADA. You should document that in writing somewhere and that document should be sent to state or county agency that will keep the building plans showing the lower riser and longer run along with a couple of photos. That way you can say that on the day the steps or ramps were accepted by the client which should be the day the client signs off, you can say on that day you have the evidence of the correctly built site.
Remember ICC also allows a max. of 3/8", variation between the riser heights. I hope this helps. I generally set my ramps at 7.3% slope, 1.3% cross slope, and 4% for maximum general running slopes that are not ramps. Stairs I set for the palsy, crutch users, and elderly at 6" rise and 12" run minimums.

 

[Jean Tessmer-HI]

Just a related note. I did a lot of work on Chicago Public Schools. Their design standards are 29" rise max. between landings to compensate for bad work.

Bill were the ramps under 8.33% continuously along the entire length of the ramp. The technique used to measure the surface of a ramp is to take your samples ever 18 to 24 inches, photograph and log the data. The slopes are never averaged. If you end up over 8.33% in places, then the ramp is required to be fixed.

 

[bill1952]

I have only measured slopes for (aisle) ramps in buildings for purposes of designing a renovation. I have never witnessed nor am I aware of any ramp in any of the buildings I've worked on actually being measured. As I noted above aisle ramps are often a varying slope and sometimes curved, not the usual ramp.

 

[Yankee Chronicler]

I have checked the slope of ramps when they appeared "hinky" to my Mark IV Mod 1A calibrated eyeball. For critical situations I use a carpenter's level. For quick checks, I have a level app on my cell phone. We've only once had a ramp torn out. That was at my previous job. We went through multiple rounds of drawing submittals to reach a design we were comfortable approving -- and then the contractor's superintendent decided to build something entirely different.

 

[Jean Tessmer-HI]

i use the only digital tool which can get NIST certification. happens to be the same tool i see the doj inspectors using on their unannounced site visits. the sample rates i take are 24" with 12" overlap continuously on accessible routes including cross slopes.

 

[Jean Tessmer-HI]

the projects that doj showed up un-announced there were 5, all over 10 years to 20 years old. their routes and ramps were never measured before.

 

[Yikes]

Jean, I recently purchased the Stabila 36520T. Are you recommending I return ti for a different level? (I'm within the 30 day return period).
I just looked at the SmartTool 3600. I'm hoping to get a 2' long level, as that seems to be standard among accessibility consultants.

 

[Jean Tessmer-HI]

Jean, I recently purchased the Stabila 36520T. Are you recommending I return ti for a different level? (I'm within the 30 day return period).
I just looked at the SmartTool 3600. I'm hoping to get a 2' long level, as that seems to be standard among accessibility consultants.

Dear Yikes,
I cannot suggest or tell you what to do. I can only say what my experience has been when comparing the reliability of digital levels since 1991. I also look at what the folks who are promulgating the deficiencies use; they happen to be the DOJ inspectors. FYI info the standard field calibration check on a Smarttool is rotate it, 180 degrees in a horizontally plane and if it reads within 0.3% it is calibrated. 4 seconds. I have rarely if ever had to do the full-on recalibration. My Stabila gave out after two years. I have Smattools still working from the late 80's. The Smarttool started out as Wedge Tool Technology. It is your lifetime tool.