Grading around 30yo house

[bigballer]

I am having some drainage problems at one corner of my house and as a result the crawlspace has standing water in it most of the winter. I believe the problem is 3 fold. The house sits on a slope and we get alot of runoff from above all winter long. Behind the house (on the high side) there is a linear french drain that runs the entire length of the house (sits about 25ft from the foundation). Obviously it's not working properly because it should be catching the water coming off the hill (both surface and sub). The other problem is that I have 4% negative drainage. The grade at the foundation is 12" lower than the grade at the french drain (25ft from house). The last potential problem is that I believe (have not yet dug up) the corner downspout drains into the clogged FD via a 4" solid flex pipe. The first and 3rd problems are easy to overcome, clean out FD and dig up downspout flexpipe and reset. The problem I am having is weather or not to regrade around the house. If I can get the FD cleaned out and working properly, will that be enough to keep my house dry?? If I do the grading I will have to remove at least 35Cubic Yards of dirt to get a 6" drop from foundation to FD which is alot of dirt. I will also have to dig the FD deeper. One question regarding the FD, does it need to be lower (in grade) than the floor of the crawlspace?

These are the tools I have: Backhoe, BoxScraper, Landscape Rake, FEL with toothbar.

Any ideas/suggestions are welcome!
Thanks!

 

[nobull1]

Is this a problem that has just happened, or has it been like this all along. The more info you can provide the easier it would be to suggest a solution. Pictures would help a lot if possible.

Brian

 

[bigballer]

You asked for more details so here they are..

nobull - I have only been here 2 years but I am guessing this has been a problem for a while. The French Drain (they call it an Intercept Ditch) is on the asbuilt for the septic system so I assume that was built when they graded the land for the house in 1974. About 10 years ago the previous owner laid down a new roof and I am guessing at that time the downspout/gutter was added with the flex pipe leading to the FD. I dug a test hole into the FD and found alot of 1" stone about 16" down and 8" deep. No pipe. I also found what I believe to be the 1" stone they laid in for the downspout flex pipe but no sign of the end of the pipe in the main FD. Possibly they cut it short and finished it off with stone.

Egon - to answer your questions - We get alot of moisture all winter long - in the form of rain. Being in the Pacific Northwest we don't see much snow, just alot of rain. On different sloped places on my property (in winter) I can dig a 12"-16" deep hole and it will fill up with water in no time. Summers can vary, this one has been more "normal" meaning we have had more rain compared to the past 3-4 summers. Right now everything is pretty dry and the 24" hole I dug up earlier is still dry. At about 24"-30" I hit clay, some places it's deeper. On top of that is fairly gravelly/sandy soil. In other places (like in the woods) it's alot more mulch type soild before hitting the sandy stuff. Don't know about perc/perm too much.. I'll have to look that up..

So here are some pics. If you need more detail let me know I have more to post.. ;-)

On the left is the hill, the water that doesn't get picked up in the FD (most of it) flows along a low spot from about the row of sandbags (my futile attempt last winter to hold back the water) to the corner of the house where you see the downspout. You can sort of see the high spot along the FD where the brown ends at the blackberries about mid way through the shot. The brush cuttings are sitting pretty much on top of the FD. The hill is very steep up to where it levels off about 8ft above the lawn grade. Future plans are to remove all the blackberries on the top and put in two levels retaining wall using quarry rock or blocks. If I can keep the house safe one more winter that project should get much more attention next summer. <later> I cleaned up some more of the vines and discovered a dark spot right over the FD straight out from the deck. It was very soggy and spongy and when i stepped on it, water came to the surface so i dug the grass out and put a shovel 8 inches down. I noticed a trickle of water coming out of the hill and within 10 minutes the hole (about a half gallon size) filled up. I am guessing that this is a slow enough trickle now that it is just absorbed into the ground but come winter this is apparently where the problems begin. I think it's really bizarre to have water coming out of the ground that shallow, this late in the summer.. could this be a spring just 25 ft from my house???


This is from the other end of the house. You can see the deck sits much lower than the grass. In the middle of the lawn (dark strip) you can see the high spot, in either direction it slopes to the house or back to the FD. I am planning to remove this deck since it's in pretty bad shape plus it will help me grade that area closest the house if I need to. I also have an old surface well to deal with at some point that sits in the thick blackberries just on the uphill side of the FD (you can just make out the cement block sitting on top of the well cover).


btw, thanks bird for setting me straight on the etiquette of the boards, didn't realize crossposting was forbidden.. Is it possible for you to link that one on the "projects" board to this one?

Thanks!

 

[Willl]

If it were me, I'd pull that deck out and install a first class french drain all along the back and down both sides.

Give the water an easier route to go.

 

[toolsorbust]

the FD's highest point needs to be lower than the lowest point of your floor. Then you need a slight slope to where it comes out. Your down spouts should not come in contact with the FD. An ideal design would be to have the FD at the base of the footings then the grading slope from the house 6" ten feet from the house, at ten feet out create a valley to divert the water away. But in the real world, myself I would go out about 20 ft and dig a 12" wide trench lower than the floor around the house, put 4" of wash stone then 4" preforated pipe then fill the rest of the trench with wash stone to within 1" of ground level. This will catch a lot of the water run off plus help dry out the ground around the house.
Russell

 

[Egon]

The additional information surely does help. Can we assume that the hill slope continues on the other side of the house?

The best solution may be a visit from a Geotechnical Engineer who could give you a preliminary report.

Now for the amateurs:
To me it would seem that the entire area on which your house is sitting is saturated with ground water. The gravel/sand nature of the soil will make the ground very permeable with good water flow thru it. The frequent rains will keep recharging the hill.

My suggestion would be to consider a new perimeter trench, say 15 to 20 feet away from house and at least 3 or 4 feet deeper than the house footings. The trench should be around 3 to 4 feet wide, have perforated hose on the bottom and be back filled with coarse round aggregate. For water removal daylight the trench on the downhill side or have pumps installed. Originally there should be lots of water but this should taper off after a period of time as the saturated soil starts to drain.

How this trench fits in with the retaining wall I'm not sure but I think I'd place it downhill from the wall. The wall should also have drainage. Perhaps the two can be integrated??

Several years ago there was another fellow in your area with the same type problem. He did not have the benefit of a hill to work with. Inveresk, a fellow member gave him very good advice.

Please note, these thoughts only deal with surface items. The Geo tech Engineer will also consider slope stability and volumes of water etc.

 

[bigballer]

The current FD is u shaped around the house. This is is a long FD (easily +200ft) and the downhills begin at the turn on either side of the house about 100 feet out (well out of the way of the house).. One downhill side of the FD is an open channel which empties into my pasture below (entire property has about a 3-5% grade depending on where you are standing). This flows fast most of the winter, the water comes out of the FD and hits this channel and just flows. I haven't measured the flow but would say it's several gallons per minute. It's now dry as a bone. The other end is buried and empties into a dry well that overflows and bubbles the sod due to the amount of water coming off the hill. It's now dry as well.

But the fact that I found that soggy spot over the FD right behind the house last night concerns me alot. I dug a hole a foot deep and it filled up pretty quickly.

Egon - thanks for your response, the width/depth of the FD you describe seems like a massive job that only a large excavator and truck loads of aggregrate could accomplish.. I would like to consider another approach that's not as aggressive but hopefully would do the job. I don't really want to dig out the existing FD since there is alot of cobble in it already and it does catch "some" of the water. It seems that simply digging a new trench 15-20ft off the house would be better. If I go 16"-20" wide and 3-4ft deep (2ft lower than the crawlspace floor) that *should* allow the water to drain well.

I am also attempting to find a GeoEngineer that will come out and do a survey.. that might change things a bit..

Thanks!

 

[Egon]

Please, my sises are just picked out of the air. No design basis whatsoever.

A man with the qualifications is the one to listen to.

 

[Highbeam]

Oddly, I am in the middle of fixing almost the identical problem. House built in the 60s into a hill and the grade of the surface actually toward the home and a wet crawlspace. I just moved into the place this winter and temporarily dropped a sump pump into the crawlspace to keep the water from touching the joists.

I have found a few causes.

1) The downspouts all tie into a perimeter footing drain that is made of clay tiles surrounded in gravel. There is no fabric and no outlet from this system. I guess it is supposed to perc out.

2) Soil surface graded towards house and in places touching the siding. Lots of uphill drainage area.

3) Back in the day they used wooden boards to hold the forms together that made the footing. Then they uses metal straps for the stem wall forms. The footing form ties were left in place when they poured the stem wall. Well after 40 years the ties rotted out creating a "perforated" foundation that sits right next to my perforated footing drain which receives downspout water as well as surface water as well as groundwater.

You've got to drain the crawlspace. In place of the sump pump I, just this weekend, dug under the foundation and installed a crawlspace drain. On the inside I will trench and install collection laterals as needed, if needed. I know that the water will not get high this year. This drain should be daylighted as a dependable release of actual damage.

You've got to grade the yard. Current building codes require that the surface be graded away from the foundation for so many feet. I chose 2% or 1/4" per foot for no less than 15 feet given my site constraints. Yes, this was a lot of dirt to move and yes this created a 2' vertical drop at the 15 foot line which will be "retained" by a low rockery. I actually dug down to 2 inches below the crawlspace vents and then ran at 2% away from the foundation. Buy a laser level from HD, your eyes won't work for this. Surface water- check.

I've got a guy coming on Saturday with a serious ditch witch. 8" wide trench and 4 feet deep. This trench will be placed close to the base of the 2' vertical drop and will be filled with a little gravel, a 4" perf pipe to act as a FD and be daylighted below the house, then a 4" solid pipe to carry all of the downspout water, then gravel almost to grade and then either sand or fabric and loam. I haven't decided how to top the trench. Groundwater check, downspout water check.

I will abandon the old clay tile system in place.

I have been advised to go into the crawlspace and mortar shut the rotten form ties in the foundation to deperforate the foundation as another level of protection. The only damage done in my case was the bottoms of the wooden colums are getting rotten. Easily replaced.

Don't worry about the dirt moving being too hard it goes very quickly with a boxscraper. That was the easy and cheap part. It is second in importance to the downspout water. Most of the wet crawlspace and basement issues are due to poor downspout water disposal.

Winter's coming.

 

[Highbeam]

Picture time. Imagine your photos and then apply my fixes as you see fit. Ignore the file name numbers and use the below numbering.

1) My crawlspace outlet. Below the footing beneath a non-load bearing wall. 4" pipe. Note also the clay tile that they just butt together.

2) Looking uphill at where they dug out of the bank for the house and how I was able to lower the grade at the house and then slope away from the house for 15-20 feet at 2% which made a vertical wall of about 2 feet.

3) Looking away from the cut bank down grade to where all of this will be routed. I have plenty of fall thataway.

4) I used the excavation spoils to level out my pasture. At least 30 yards. It moves really fast when you realize that scooping it into the loader is much faster than dragging it away with the box scraper.

Let me know if you could use any more photos. I am in Buckley in the south sound if you want to stop by. This weekend will be the big pipe day.