View Full Version : Raised patio question.
10-15-2005, 12:41 PM
When using retaining wall block to raise a patio, say 2 - 3 foot height is there anything that should be used to tie the wall back into the base of the patio? Geogrid? Or will the water be a non issue with a compacted base within the wall. I guess my question is, is there anything that needs to be done with the wall to keep it from coming down? What if it is along the side of a driveway where it is bearing a more significant load? Thanks in advance.
10-15-2005, 12:53 PM
Use geogrid for sure. I like to connect opposite sides of the raised patio if I can. If not a 6' or 8' pull will be more than sufice.
10-15-2005, 08:12 PM
Is that a standard or just your practice Chris ? Just curious. I would not think you would need grid.
10-15-2005, 08:28 PM
Redbear, I'm not really sure what you're asking. Geogrid has nothing to do with drainage.
Usually, when we build a raised patio, there are sitting walls around the patio as well. In that situation, we will pitch the patio away from the house and install micro strip drains at the base of the sitting walls on the end where the water is directed.
10-15-2005, 08:58 PM
Mike, thanks for the response. I'm not figuring on using the geogrid to provide drainage but just to stabilize the standing wall. Let's say I have a patio that is raised against the house 2 - 3 ft. Should I provide a geogrid once the retainer is built to keep it from falling over in a few years or are you suggesting that as long as the slope is towards the front of the wall and drainage strips are provided that there would not be enough pressure on the wall to worry about tying it back into the base. Does this make sense??
10-15-2005, 09:02 PM
You need the grid to keep the back pressure from blowing the sides during the winter freeze cycle and to stabilize the load from the eweight of the pavers, concrete or dirt on top of the patio..
Along the side of a driveway you need strata-grid to support the wall because there is a live surcharge from the cars rolling across the drive. Kind of like using a jackhammer effect on the wall. Grid used on a driveway wall should be Strata 500, or 550.
10-15-2005, 09:49 PM
Redbear, how high is the tallest part of this retaining wall and what material are you using to construct the retaining portion?
10-15-2005, 11:45 PM
For our 2-3' raised patios, we do not use grid.
And we have been doing raised patios for 6 yrs.
There really is no surcharge on the walls for a raised patio, as there is for a wall that is holding a hillside in place.
Have you pavers installed with a pitch so the water rolls off.
Also we frequently have decorative planters at the fronts. With drainage pipe below, designed to take the water away.
Works for us!
10-16-2005, 12:12 AM
Using grid on raised patios is a standard. At least EP Henry recommends it. there is a lot of pressure on those walls and with the freeze/thaw...it just adds to everything. We always use it.
10-16-2005, 01:58 AM
Keystone engineering recommends grid as well. When we used Unilock in the midwest, the chaneled system would fail unless you used grid, because the freeze would push the walls apart. Lay in some grid, problem solved.
Put it this way, it can't hurt anything, and the cost is minimal. if the patio fails, then it costs alot.
10-16-2005, 10:14 AM
DVS, what type of drainage are you providing. Do you use "O" pipe in filter cloth below the A gravel base? Does the water really move through this to the drainage system or wouldn't the pitch of the patio just promote enough run off to not worry about drainage? I understand how water moves through the soil and clear gravel in a normal retaining wall system but when it is a raised patio or supporting a driveway where the base is compacted A gravel I don't understand your drainage system. Do you mean that the pipe is on the outside of the wall to carry the water away near the base as in a french drain? Can you explain a bit further. Thanks
10-16-2005, 11:02 AM
I just looked in my NCMA training binder for segmental retaining walls. NCMA specs call for a 4" SDR-35 perforated pipe sitting on the footing with the holes facing down, with some type of pitch. they like 2% but it is not completely necessary. If you have a sub drainage system the perf pipe should have a connection every 50' and that sub drain needs to either be connected to a daylighted hole, or a free flowing storm water system. If you have no sub drains or it is not feesable to install sub drains, then you need to pack the cells in the courses below grade with compacatable base, and set your perf pipe on top of that so you can core drill a daylight hole in the wall for draianage every 50'. The core hole should be sitting right at grade. We usually glue an unscrewable brass screen cap at the wall face to stop animals from building nests in the pipe.
The pipe should be sitting directly on top of geotextile fabric, and if you are using a solid block you need 1' of 3/4" clear stone behind the wall
If you use an open core block like a Keystone Standard, Century wall, or Compac, you can get away with 6" of clear gravel behind the wall. If you use grid, you have to wrap the geotextile around the gravel and create 2' high cells for every section that you install grid. We usually use a 6' wide x300' long roll of fabric to wrap with and where it needs to be cut, we overlap by 3' of materials. On a 1' wide gravel back fill, 6' fabric is just about right where you need litle to no cutting..
If you build your wall any other way than what I wrote, the NCMA has documented issues contributing to the failure and showed countless numbers of examples on the north american continent in their classes supporting their findings.
And, if you build it as I described, you are following a widely accepted guidline which if there is a failure, can be used to help stewer liabilities back at the designer rather than you. You will get dragged into it no matter what, but this way you free yourself when the case gets proved out in court.
There have only been two walls we have ever done that required a pipe outside the footing. They sat in the center 1.5-1 slopes and there was bedrock 4' below grade. We had to use soils nails every 5' to tie the grid to, and the engineers wanted both sides of the footing to keep completely dry.
Just wanted to pass this along in hopes it helps answer your questions.
10-16-2005, 11:04 AM
Bill, have you, or anybody else, ever seen a tech spec for a raised patio? I haven't. I've seen pleanty of specs from ICPI for various paver applications and pleanty of specs from NCMA for wall applications, but never one that incorporated walls and pavers.
10-16-2005, 11:13 AM
Good question mike. This was brought up in an off time discussion during the training. And, all you can really do is incorporate the core knowledge you gained from wall installations and apply it to your raised patio design. Since most of these are well under 3' in hieght, you don't have nearly the loads on them as a wall with a 3-1 slope behind it. however, you do m=have that freeze-thaw issue. Water, when trapped in the base or dirt fill will expand because you now have a lump of mass that got wet over fall, freezing just like a raised planter. And the grid will do nothing but help stabilize that. The other thing you have to look at is that you now have a 3 or 4 sided box you created, so depending on the grade at the outward side toe, you might need more embedment courses and actually need to excavate sub soils to install grid on the toe course. If it is flat, you really don't have alot to worry about.
I'll tell you, if you get a chance to do the NCMA training, go for it. Keystone fotted the bill for us all and put us up in Vegas for 3 days. It was an awesome experience to speak to so many other HUGE wall builders and engineers and we really gained alot of knowledge.
What I learned more than anything is the old "that worked for us for X amount of years" simply might mean it has not failed yet. Great class
10-16-2005, 11:59 AM
Bill, I did the NCMA in New Jersey last year. I over engineer my own raised patios and feel confident with what we are doing. I've just never seen a spec where the two applications are combined.
10-16-2005, 12:05 PM
Allegedly, and I saw alledgedly, the ICPI is writing some specifications on raised patios with SRW's. The guy to hook up with on that would be Rex Mann, he is on this forum and Groundtradsxchange.com
He is a trainer. I would love to see some specs myself.
10-16-2005, 01:46 PM
The raised patio tech spec has been in the works for about 2-years. However, they have to evaluate and re-evaluate the methodology suggested
by the committee members. Then it gets written and re-written and so on.
It is a very lengthy process, which has be accurate.
10-17-2005, 09:07 AM
I'll try to find some pictures. Although this is gonna be a busy week so it may not happen right away.
I can not tell you how many raised patios we've done. The water drains off without any problems.
I will say we mayy do a 3' raised patio. but 3' is not above ground. See we have building codes we must respect. And if the patio is to be 3' high, we will find a way to creatively step it down or if that is not possible we will backfill the outer perimter with soil so that only 18-20" is above grade :)
No offense directed towards Rex, but I do not agree with everything ICPI says :) Such as laying patterns for driveways and a few other things. For 8-9 years we have been using 2 seperate layers of geo-textile fabric where ICPI says not too - and all has been fine. Infact I got that idea after repairing a patio where the bedding sand intermixed with the crusher run base. Also ICPI states the use of geo-textile fab between the sub-soil and aggregate base is "optional". I do not believe that ingredient is "optional". In my eyes and my experiences - it is a MUST!
10-17-2005, 11:41 PM
I got that idea after repairing a patio where the bedding sand intermixed with the crusher run base.
How is that possible? Your base should be like a concrete slab....if installed properly.
10-18-2005, 09:26 PM
Yes a base should be like a concrete slab. Our bases are.
We repaired someone elses work. Who knows what happened.
We use 2 seperate layers. Its cheap insurance. And a great selling point.
You never know what can happen with the ground over time. I do NOT take this industry or our work lightly.
Its a hellava lot cheaper to lay a good geo-textile fabric at 8 cents / sq ft, than it is to come back and make adjustments.
And all I know is we have very FEW call backs for warranty work. So something is working!
10-18-2005, 11:56 PM
If you are that confident in your base why bother with the extra pull? I have too been installing patios, etc. for 9 years and I have had zero callbacks for sand migrating into the base course or anywhere else for that matter. All I'm saying is that if your base is installed properly.....save yourself some time and money and loose the second pull. Waste of time IMO. Put that extra to your bottom line.
10-21-2005, 05:08 PM
When you install the grid on your raised patios is there a rule as to how many layers you may need depending on the height and do you try to tie the whole patio together or is a pull of say 6' enough.
11-05-2005, 08:10 PM
I too will be trying my hand at a raised patio at my place.
Basically a 5' x 3' kidney shaped landing outside of a 8' sliding door.
the total length of the raised patio will extend beyond the non slid able door
two extra feet to the end of the house.The bottom of the door is approx.
2 1/2 ft. high.the 5' ft dimension will be off the non sliding door in hopes to include a small table and two chairs.The 3' dimension will be in front of the sliding door.From there i was thinking of having 50 or 55 degrees of steps,
four steps, I guess lol
I would like a planter to encompass the table and chair area.
I will be using country manor 6" block for the walls/stairs.(Paver's over the fill area)Pretty similar
photo at www.paversinstalled.com (photo 23)
So i guess my point is,Should I make a rectangle instead or will i be able to tye the kidney shape together properly, for a raised patio first timer.
Any one have any similar photos?
Thanks for taking the time to read:D
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