Perimeter drain - can only get 1% over 86 feet.

[fufu]

I’m running a new foundation drain down a garage and out to the street. I’ve got a couple questions.

1 – The total length of the run is 86 feet. Because of the topography of the yard I can only get the pipe to drop 12 inches. That’s a little over 1%. Is this OK? If not, does anyone have any suggestions on what I can do?

2 – Should I rent a level to make sure I get the grade right along the full 86 feet? Or is there another way of doing it?

Thanks.

[LazyPup]

You will be okay if you run 4" pipe.

Under the International Residential Code all lines 3" or less in diameter must be run with a 1/4" per foot pitch, except a 3" line may be run at 1/8" per foot with the expressed consent of the local inspector.

Under both the International Residential Code (IRC) and the Uniform Plumbing Code (UPC) a 4" line may be run with a 1/8" per foot pitch.

To convert a fraction to a decimal divide the numerator by the denominator, thus 1/8" is 1 divided by 8 = 0.125" per foot.

the length of the run is 85" so the required drop is 85 x 0.125 = 10.625"

to convert .625" to 1/8's of an inch we multiply 8 x 0.625 = 5 so 0.625" = 5/8"

To run 85' of pipe with a 1/8" per foot pitch the total drop is 10 5/8" thus your 12" drop exceeds code minimum for a 4" line.

You can very easily make a pitch level to check your pitch as you go. You simply add a spacer on one end of a level equal to the required pitch for the length of the level.

By example, Assume you have a 3' level. At 1/8" per foot the drop for 3' would be 3/8". Simply cut a small square block of 3/8 plywood equal to the width of the level and tape it on one end of the level.

See the attached illustration.