Retaining wall – how high can I make it
Francorosso
| Posted in Construction Techniques on
My backyard slopes down from the house and I would like to build a retaining wall to reduce the slope and increase my useable backyard. I have two questions, first, what is the cheapest material to use(it won’t be visible, so cosmetics don’t matter). Second, how high can I build it and have it still be structurally capable holding back fill dirt(code isn’t an issue). I realize that there are multiple considerations but I’m just interested in general answers.
Thanks,
Frank
Replies
How high to you want to go?
the modular blocks can go 4 ft without an engineer, with I think about 20'.
how long will the wall be?
lots of parameters to guess at.
bobl Volo Non Voleo Joe's BT Forum cheat sheet
Thanks for all your replies. I think I would like to go about 5 or 6 feet tall, anything more is going to create an incredible amount of work getting the dirt to fill in(I'll have to get it dumped in the front yard and rent a Bobcat or similar tool to get it in the backyard.
I don't think I'll be using old broken concrete, my neighbors would get nosy really fast if I did that.
I looked at the cast concrete at Lowes and HD, but those things get really expensive if you use enough of them.
If treated wood is the cheapest I may go that route, but the chicken wire filled with gravel is an interesting idea.
Oh by the way, there is a mostly dry creek at the bottom of the slope which fills to the rim during storms and seems to be eroding it's bank toward my house, so I need to know how far to set back the wall from the creek to avoid causing further problems.
... the chicken wire filled with gravel ... would be my first choice for a wall of the height you're looking at. Two rows and you'd be done. J-u-s-t it's not really chicken wire and gravel The product is known to stream engineers as a rock filled gabion. With the right mix of wire size and opening and rock size and shape, you end up with a really big free draining building block - say 3ft high x 3ft deep x 6 or 9 ft long - that you can stack like bricks. But the rock has to be the "right" size and the wire the "right" guage. The beauty is that the baskets can be filled in place and used to reinforce the stream bank to stop further erosion into your yard. BTW, you should be able to get plastic coated wire that is good for 70+ years.
And this is less expensive than wood? My lot is small, the total width I would need is about 50 feet. Where do I get the materials?
3 to 4 ft is also what many codes will allow a home owner to with needing engineering and/or permits. Also the same height as most of the modular blocks without engineering.
Instead of one big wall you might go with severl smaller ones in a stair step fashion. You will need much less fill that way. Also it makes for a lot more versitiliy in materials and designs.
For example you might make a 3 ft rip rap wall down on the creek and then have several feet of landscaped terrace with benches and the behind it 2 steps of wood walls. Or maybe grade it to 30 degrees for a while and then have ground cover. And then a final wood retaining wall.
NOTE - if you use wood, be careful of "landscape timbers". A lot of them are not fully treated and don't have the certication stickers.
I can give you can specific sites now, but when I was looking for a different application I found tons of stuff on the internet. Some commercial, but also lots from state highway departments, departments of natural resources, and ag extensions.
St Louis has information on design of non-permitted retaining walls and it should show up on a google search. Also try googling on RIP RAP, ERROSION CONTROL, RETAINING WALLS, STREAM BANK ERROSION CONTROL, and similar titles.
Also in the last few years there have been several ariticles in FHB and/or JLC about this. You can buy the individual articles online for a few $. Go to FHB, then archive and jlconline.com and the Research.
I know "code isn't an issue"
but do you have any restrictions on building near water? Particularly since you are filling.
are you in a "flood plain"? this can cause permit type difficultiesbobl Volo Non Voleo Joe's BT Forum cheat sheet
I don't know about any restrictions about building close to water, I didn't really think that applied since the creek is dry most of the time. But now that you mention it, I'd better call the county before one of my neighbors does!
And they will.
Quittin' Time
Treated lumber near a part time stream is not allowed in many areas, you best checkup on it as lots of work might need to be undone. Use the rocks in a basket if you can. Maybe you could use old bricks or broken (small pieces) concrete? (low cost?)
Have you considered using concrete block? It's relatively inexpensive and you can have it stucco coated if looks become an issue.
I would really recommend you check with the building department. Generally speaking, 3 feet above grade is the highest retaining wall you can build without a permit. That is, also only if you are not cutting into an engineered slope. It doesn't sound like you are.
A neighbor of mine cut back 18 feet into a slope to build a 12 foot retaining wall without a permit. The inspector appeared just as the 3 full concrete trucks drove up. Turned all of them away.
It is really worth having a structual engineer draw up plans. You can never overbuild a retaining wall. Especially if you intend your family to play around it.
Good luck.
Len
I live in earthquake country and have seen to many things fall down...
Whatever material you choose to use, as important as the material that you choose is supplying proper and ample drainage. Water runs downhill and that creek is there for a reason. I live on the lakeshore of Erie and have seen every known material used for retaining, some with sucess some a bust. I'm not sure of the amount of water is draining on your property now is but as soon as a wall is constructed chanelling will become an issue to be sure.
The shoreline builders have chosen to use landscaping cloth as of late to minimize silt losses due to drainage. The jury is still out on that stuff. PVC perforated weeping line is what we use here.
Choose what you wish, as long as it is not made of wood. Wood rotts, eventually, treated or not. The material that will be the cheapest for you will be the material that is readily available close by. Around here limestone quarries are local. If you can get "rip rap" where you are, for a short wall 4'x50' rip rap will do it. It is small limestones smaller than 1 cubed foot. They are placed by hand or a small Bobcat.
Don't use wood my freind unless you plan on doing it again in 10 years.
Good Luck
Edited 3/12/2003 6:20:22 PM ET by canuckguy
Cheapest material broken concrete slabs. usually you can get it free of charge or pay just for trucking. Although not the must attractive. But with proper plantings after install you can pretty much ,make it disappear over time. High end, precast concrete modular blocks. labor intensive getting first course set and level. Middle ground pressure treated timbers, use timbers that are treated to .40 as these are treated under pressure, where as some others are treated to point of retention. Difference being if the wood is wet when treated cells are not going to accept the treatment hence they will rot over time. As to height need to know how high to plan on going and I can lead you in right direction. In previous life I was a Landscape Architect and contractor and have designed and built walls from 2' to 15' using all different types of materials.
I read somewhere of a retaining wall built of old tires. It wasn't verticle. The tires were laid out in a row, next course was set back about half the diameter of the tires. Plantings were made in the tire centers after the work was done. Tires must be roughly the same size.
I like Dan's suggestion of broken concrete. Dan, was that said in mortar, or dry?
Average Joe says:
I'll wait here while YOU go wrestle the wild alligator.
Dry
I had a similar problem on a lot with a very steep slope. The volume of retaining wall was enough to constitute a major expense. I did a bit of research in concert with my neighbor and we determined that we could best solve our problems with retaining walls constructed of gabion baskets. These are wire cages that are filled with large gravel (stones really) and stacked with a slight setback to each row. These can be stacked quite high and fairly steeply and they are very economical when you have a lot of wall to create. These products are also used for stream engineering (to create wing dams and weirs). The wire lasts a long time and if you plant ivy and other climbing vines (we used some trumpet vines and honeysuckle too) it will make the walls pretty nice looking within a few years. Hopefully, the walls will have silted in and become sort of a natural conglomerate that will be stable, even when the wire eventually erodes.
I did once build a retaining wall approx. 4' high 250' long with railway ties. You can go quit high if you put in the T-bracing.
if you live where there are rocks, the cheapest would be a battered dry wallMike Smith Rhode Island : Design / Build / Repair / Restore
Check out materials for gabion baskets by searching for gabion baskets at google. Also your local landscape suppliers will likely get them for you as a special order item.
Does anyone have a picture of what a retaining wall looks like made out of these materials?
This article has a couple of pics. Good reading too. http://www.forester.net/ec_0105_project_gabion.html
Bunch of really nice ones here.
http://www.ieca.org/public/articles/details.cfm?id=576