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Old 08-24-2014, 12:23 PM  
floatr
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Default deck drainage/soil

I am replacing a old deck and have had issues with the water not draining out from under it well after a rain Its clay type soil..It is 15 inches above ground and facing a direction where the corner is that gets NO sunlight ever ,so that complicates the dry out much after a rain.It is in the southeast where its humid already so that only adds to the issue.
What are the best methods to use to prevent the high moisture or at least improve soil/drainage ?
I thought maybe slope it with a french drain at end but not sure about the water that goes into clay below deck.
Any other info is appreciated



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Old 08-24-2014, 12:39 PM  
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It is always importand that the landscape slopes away from the house. I would reshape that and cover it with sheep poly and a couple inches of graver so water would just run out. Then if you still have a problem after the deck is built you can just do your drain around the perimeter.



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Old 08-26-2014, 12:48 PM  
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Yes, make the soil even less porous and transfer the problem to someplace else that can handle it. A sump pump sort of does the same thing.

French drains have never worked for me but I've never done the calculations ahead of time. Lindeburg's books on taking the PE exam for civil engineering may help with this. My local library had a few of these books.

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Old 08-26-2014, 04:33 PM  
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Quote:
Originally Posted by Wuzzat? View Post
Yes, make the soil even less porous and transfer the problem to someplace else that can handle it. A sump pump sort of does the same thing.

French drains have never worked for me but I've never done the calculations ahead of time. Lindeburg's books on taking the PE exam for civil engineering may help with this. My local library had a few of these books.
Do a simple perk test before attempting a french drain.
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Old 08-26-2014, 04:52 PM  
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Quote:
I would reshape that and cover it with sheep poly and a couple inches of graver so water would just run out
if you can't find sheep poly, just use plastic

Otherwise neal is right on about this.
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Old 08-26-2014, 08:43 PM  
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I should try this myself
http://www.ianrpubs.unl.edu/live/g1472/build/g1472.pdf
or
http://www.todayshomeowner.com/diy-soil-drainage-perk-test-for-your-yard/

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Old 08-26-2014, 09:00 PM  
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Sometime raising the level of a down hill slope with better soil is all it takes.

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Old 08-26-2014, 09:30 PM  
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It's late so this may not be right -

A 12" dia hole, 12" deep has a dirt surface area of 452 + 113 = 565 sq. in. and can handle 2" of rain per hour. The hole is 113 sq. in. in area.

A 10' x 12' deck has a surface area of 17,280 sq. in. and so at this same rainfall rate would need a French Drain with a drain dirt surface area of 565x17280/113= 86400 sq. in.. For a cube shaped hole this is 44" on a side, roughly.

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Old 08-26-2014, 09:37 PM  
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Quote:
Originally Posted by Wuzzat? View Post
It's late so this may not be right -

A 12" dia hole, 12" deep has a dirt surface area of 452 + 113 = 565 sq. in. and can handle 2" of rain per hour. The hole is 113 sq. in. in area.

A 10' x 12' deck has a surface area of 17,280 sq. in. and so at this same rainfall rate would need a French Drain with a drain dirt surface area of 565x17280/113= 86400 sq. in.. For a cube shaped hole this is 44" on a side, roughly.
Convert that to to a ditch with perf pipe and gravel, more like a feild for a septic field.
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Old 08-26-2014, 09:42 PM  
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Quote:
Originally Posted by Wuzzat? View Post
It's late so this may not be right -

A 12" dia hole, 12" deep has a dirt surface area of 452 + 113 = 565 sq. in. and can handle 2" of rain per hour. The hole is 113 sq. in. in area.

A 10' x 12' deck has a surface area of 17,280 sq. in. and so at this same rainfall rate would need a French Drain with a drain dirt surface area of 565x17280/113= 86400 sq. in.. For a cube shaped hole this is 44" on a side, roughly.
I'm not disputing the math here (not qualified) but add this variable: the deck diverts some water and the ground underneath collects the rest.


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