Storm drain % question

[jackhewitt]

Hi. Im going to install some storm drain on a job. some is RCP and some plastic ( 18" 15" and 12"). I know how to calculate the pitch from one invert to the other, and pitch per piece of pipe. But this time I going to use a pipe laser witch is new to me. I see on the print it say 0.005% and on other prints it says 5%. Ive never seen it on prints before as 0.005% ,always as 5%. So if I input 5.00% on the laser would this be correct?

 

[RWF7437]

Sounds like an error. For this size pipe a slope of 0.50% would be reasonable. This is the same as a slope of 0.005 ft/ft. 5.00% sounds too steep. To be certain, ask the person who prepared the plans.

good luck

 

[jackhewitt]

Sorry I misplaced my decimal point. I meant .5%

 

[msucog]

you can always fall back on checking it manually. 0.5% is 0.5 vertical feet per 100 horizontal feet. 5% would be 5 vert feet per 100 hor feet. if the prints have conflicting info, double check the invert elevations to see if it corresponds to one of the slopes. i often see errors from inverts changed but the indicated slope is not or the other way around. as a former contractor, i always at least spot checked inverts and slopes to save the hassle of losing time in the field because the prints were wrong. quite often, the contractor doesn't always get money back or credit on the schedule for such errors by others. right or wrong, that's the way it is sometimes.

 

[jackhewitt]

Thanks for your help. I was making it harder than it should be. Just trying to get it right the first time.

 

[DarthSoilsGuy]

consider buying an electronic carpenters level for quick-checking stuff in the field. they are probably somewhere in the area of +/- 0.1% accurate. not the accuracy you need for laying out "tight" work, but it will quickly reassure you that you're in the ballpark. you'll figure out more uses for this little gizmo each day.

 

[Dozerman56]

It's been 20 years since I set up a pipe laser so maybe they're all set up the same now but it used to be some lasers you had to set up in slope per 100' and some had to be slope per foot. Easy enough to figure out but a pain if you've already put in 200 LF of pipe.

 

[eea]

Not to sound preachy, but NEVER just dial in a grade on laser. 9 times out of 10 the contractor will have set the manhole bases on both ends of the run. Make sure you are “painting” the target on both ends of the run before you start and adjust the beam to the real grade accordingly. A 5% run may actually be 4.95% between the as-built inverts. Allowing the contractor to adjust the last few segments of pipe on a “dialed” in grade run will reduce the effective capacity of the pipe. I can’t believe how prevalent this mistake is.