View Full Version : Grading and drainage

imported_John Smith
07-27-2007, 04:41 PM
Seems like all of the houses in the Houston area have decent grading and drainage on the front and sides, but the backs are almost completely level (at best) or somewhat slope towards the house and form a valley about 4' from the foundation. How are others measuring slope per IRC (6" in 10'). Its kind of tough to actually quantify the drop when the ground is muddy and the grass is tall.

Jim Luttrall
07-27-2007, 05:04 PM
I would recommend getting familiar enough with the proper slope that you can spot it without a tool. Improper grade is pretty easy to spot.
I never use a level to measure the actual slope and call out poor drainage/grading on most inspections. I explain verbally and have a standard paragraph inserted into the report to give clients something to shoot for.

Jerry Peck
07-27-2007, 05:15 PM
I measure it this way:

- R401.3 Drainage. Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection so as to not create a hazard. Lots shall be graded to drain surface water away from foundation walls. The grade shall fall a minimum of 6 inches (152 mm) within the first 10 feet (3048 mm).

- - Exception: Where lot lines, walls, slopes or other physical barriers prohibit 6 inches (152 mm) of fall within 10 feet (3048 mm), the final grade shall slope away from the foundation at a minimum slope of 5 percent and the water shall be directed to drains or swales to ensure drainage away from the structure. Swales shall be sloped a minimum of 2 percent when located within 10 feet (3048 mm) of the building foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped a minimum of 2 percent away from the building.

Measure out level (as best you can) until you can measure down 6". You should be within 10' of the foundation/slab.

Except ... "Where lot lines, walls, slopes or other physical barriers prohibit ... " that fall. In that case - first, though, "prohibit" does not mean "makes it difficult" - the slope needs to be at least 5/8" per foot fall AND "directed to drains or swales to ensure drainage away from".

How many times have you seen a limited slope "directed to drains or swales"? Not many, I'd guess.

imported_John Smith
07-27-2007, 05:21 PM
Jerry, do you have a 10' level or do you have something different?
I was thinking of making something that could be easily broken down.

It sounds nit picky, but I would like to actually report some type of measurement.

I know what Jim is saying, I too have always called out improper draining where it was evident from a visual inspection. Some of the newer construction Im doing is a little tougher.

Jerry Peck
07-27-2007, 05:44 PM
Jerry, do you have a 10' level or do you have something different?

Two screw drivers and a 12' piece of string with two knots tied in the string 10' apart. Use long shaft screw drivers, say 9" shafts or so (one can be a shorter 6" shaft). Tie the string around the shorter screw driver at one of the knots in the string, stick the screw driver into the ground all the way to the handle next to the foundation. Now stretch the string out and tie string at the other knot to the longer screw driver (which already has a mark on it blade 6" down from the handle, a file works for this mark), stick this longer screw driver into the ground to the mark.

Your string is now the 10' distance, and the minimum slope is the 6" length of the screw shaft above grade.

Stand back and look at the string.

Does the string look level? If so, you have met the minimum slope.

Does the string go downhill? If so, the slope is greater than minimum by as much as the string goes downhill.

Does (gulp) the string go uphill? If so, then the slope does not meet the minimum slope required. Okay, now to the exceptions ...

Is there a wall, lot line, or other physical barrier which prevents meeting minimum slope?

- If yes, is the drainage directed to a drain or swale?

- If yes, it meets the exception.

If EITHER answer above is 'no', then they screwed up. (Check this as your default, it will be the most common answer. ;) )

imported_John Smith
07-27-2007, 05:49 PM
Jerry, thanks again for the excellent advice.This board is lucky to have someone with your knowledge and expertise.

Usually when I see a long post, I kind of scan through it until I get to your response. You always apply logic, common sense and a true understanding of the codes.

You would never get along with my wife. Shes always right!!!!!