Need storm water drainage expert

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sh00ter

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I want to build a building (plan right now is 16x24) on the side of my house and it will be basically built over top the lowest point of the area (which already slightly holds water after a rain). Originally, I was thinking I'd make a french drain first and the intake grate would be under the building after it was built. However, my guy who is going to help build it wants to built a form from wood, fill with sand, then gravel, then some kind of granite powder over the gravel he says will make the pad almost like concrete, so in that case I can't really do the french drain idea since the water won't really be able to drain "under" the building as it would have if it was just built on skids with no raised pad.

If done this way, the raised gravel pad would be higher than the surrounding ground and then of course the building would be on skids on-top the gravel, so the building would not be at risk of flooding, but the water would all drain towards the the permanent wood form that outlines the pad and probably eventually rot it, not to mention if water got under it and kept the dirt below the pad soft/wet all the time?

I need someone who either can tell me someone, or is that someone themselves to come out for a fee and use instruments to figure the slopes, etc. and tell me exactly how best to approach this BEFORE I ever break any ground. What kind of person do I need to guarantee they know what they are talking about? Engineer, landscaper, grader?

Thanks fellas!
 

okierider

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Post a pic and let me see what you have going on, deal with these issues all the time.
What ever wood you use to hold in the pad is going to rot, why is your guy doing this? If you are already having water issues concrete would be a better solution. Barring that don't use wood use the composite decking, will cost a little more but will hold up to water for years.
 

NightShade

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Honestly I would begin with raising the low area up till it wants to drain naturally. After it will drain on its own the surface you want depends on what you want to do inside the building. I would expect something that size to be set on at least a concrete foundation with a gravel floor if not concrete. In this case a wood form would be put in place to pour the concrete and then could either be left to rot or stripped/thrown away.

And PLEASE if you have the area raised make sure that it's well compacted before you start building on top of it.
 

sh00ter

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Building up the area would be tricky because:

1.) If I actually added dirt to the low spot and compact it, then it would be even or higher than the ground along side the house and water would drain towards the house or stand in the area between the barn & the house.

2.) Raising the area too much will cause too much of the barn to stick up over the roughly 8.5ft tall fence. I was hoping to keep the crest of the roof to be as close to level with the house eves as possible which would mean the barn would only slightly stick up over the fence.

Also, I was originally just going to do a french drain but the area has more than one visible low spot (where I see small puddles for a day or two) so the drain grate would likely only collect some of the water since that area is so flat (con-caved from right and left but still flat once those slopes stop at the low area). Also, if I want to do do some sort of pad instead of just building on skids placed on blocks, then that eliminates the french drain being able to be under the barn.

I will post a pic later when I can. I have one now but it isn't hosted and I thought I could upload it as an attachment?
 

okie362

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As mentioned before you will be much happier long term if you fix the drainage issue first then pour a slab. A building of that size built on skids will end up not being sufficient for what you'll dream up to use it for in the future.

Just my opinion. That and $5.00 will get you a Starbucks.
 

Boehlertaught

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In 1996, I had a 16 x 24 skided building built behind our house. I don't live there now but the building is still there and still looks OK. That building was also in a storm water wet area that drained well. And it continued to drain well for the twelve years I lived there. The building was built on concrete blocks set/leveled on compacted soil. The rain water went right under the building and into the drain area between the two side neighbors back yards.
 

sh00ter

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As mentioned before you will be much happier long term if you fix the drainage issue first then pour a slab. A building of that size built on skids will end up not being sufficient for what you'll dream up to use it for in the future.

Just my opinion. That and $5.00 will get you a Starbucks.

You are probably right, but I still need to figure "how" to handle the drainage if my slab would be pour over the low spot that everything drains towards. I know with a form, the slab would be up enough that the building would not flood, but water would be draining towards the building from 3 directions (Front, left, right). It would try to drain around the foundation/pad but I don't think it all could. I suppose I could trench along each side of the foundation/pad to allow it to drain on the sides of the building but I'm not an expert on this.

The other factor is cost and HOA..I might not have the option to build as big as I want nor do concrete so any way you slice it, I basically need to figure how to fix the drainage regardless of what I build there or not.
 

sh00ter

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I have a similar building in a similar poorly drained area. I simply set the skids on cinder blocks...water runs right under it and all is well.

Thanks for the reply, does any water stand under it? My issue is not just that the building would be build over the low lying area, but that some of the low flat spots hold water...it dries pretty fast in sun but underneath a building, I'd be worried about mold, etc. We are talking less than an inch of water that doesn't drain well, not a 6 inch deep puddle or anything.
 

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