# Backyard office, retaining, and privacy wall



## Team Scream (Jul 29, 2007)

Greetings everyone, I am an electrical contractor, I specialize in home theater, whole house audio/video, automation and networking environments.
I have very little (real world) experience in excavation, hard scape or drainage.
I have a fairly large project (my home) which seems like it could be Pandora's box if not thought out and/or executed properly please help me understand what it is I am up against.
Below are some pictures I took today after the landscapers cleared out every tree, bush, plant and root from the backyard in preparation for this project.

The scope of the project is as follows:

(A) build 100 linear feet of retaining wall (less than 5 feet tall) using Allen (or similar) block systems on west side of property incorporating low voltage lighting accommodations (pilasters?) as indicated in the attached images.
This wall will be built so that the TOP (final course) is 3 feet off of the neighbors wall toward my backyard.

(B) build (2) 16 feet by 3 feet conventional retaining wall segments against existing (neighbors) wall, at each end of the back of my lot where I will build two 10'x12' backyard office rooms (sheds). The south west office will require that 2 of its walls will be part of the retaining wall requirements for that portion of the lot.

(C) build Allen block retaining wall segments between each of the above mentioned "offices" to complete retaining wall along existing south side wall as indicated in attached images.

(D) build 60 linear feet (6 feet tall) of free standing block wall (privacy wall) from the back yard to the front edge of my house (north to south on the east side of my property line) incorporating pilasters and low voltage lighting accommodations.

(E) Continue the above free standing wall stepped down to 3 feet max height to the front of the property (47 feet) incorporating pilasters with low voltage lighting accommodations.

NOTES: The 60 linear feet as well as the additional 47 linear feet of wall mentioned above in section "E" are to be built on my property line which is level, however, 1 foot towards the neighbors side of this wall is on a 45 degree slope (downward towards his property). It is my understanding that since I am on the crest of this slope that I will NOT be required to "retain" any of the dirt going down the hill to his property. That it is in fact HIS responsibility to retain the dirt on the downhill side (which is his property).

(End Scope)

Questions:

(1) The MAIN existing neighbors wall on the west side which is over 100 feet long and 5 feet tall PLUS footing was permitted in 1962, it was NOT built to retaining wall specs. I am scared to death to remove dirt any closer than 3 feet to this wall for fear that the wall may fail and collapse.
It is the opinion of several of my contractor friends that this wall is actually causing my hillside to collapse into my yard. Is the neighbor responsible for this "damage" financially? how do I go about determining this and is it worth the hassle?

(2) since I am trying to build one of the proposed office structures right up to the property line, and up against existing (neighbors) walls, and since these structures will be built just like a bedroom in my main house, can I build the lower portion of the retaining wall to retaining wall specs AND THEN continue to build UP on top of this retaining wall to a height of 8 feet which will then become the actual walls of the structure?
I am sorry if I did not describe that properly but I hope someone gets the idea?

(3) I need to re grade the back yard portion of my property to get the drainage sorted out. As you can see in the pictures, EVERYTHING slopes towards the existing house now. How should I design the drainage so that water flows away from the house and then out to the front of the property?

(4) Does anyone know if I can get standard 8x8x16 blocks that look identical (texture and color) to the Allen Block I will use for the retaining 100+ foot wall on the west side of the house?
I do not want to use blocks that are noticeably different, I need some symmetry here and I am as confused as I have ever been.

Pictures:

This is the 100 foot wall on my neighbors property, you can see the exposed footing, this is the dirt that I want to retain with the Allen block wall described in scope (A).












Here is an image showing the size of the slope and the amount of dirt I am dealing with this view is north facing south:













This is the same side of the property but south facing north, I am kneeling down while taking these pictures to give you an idea of the elevations.












This is the same however I am east facing west:












Here is the rear most portion of my back yard, it is along the existing wall (seen on the right) that I want to build my office rooms, one on the far corner and one at the bottom right of this image, you can see the lines I have dragged out in the dirt to see where the structures will be, they are 12 feet long and 10 feet deep back to front (from the wall toward the house).











Here is the same image with some rough outlines (orange) showing the proposed structures:













Here is the reverse view (east facing west)











Thanks for any and all help offered up here, I will be building the structures myself, and perhaps laying the Allen block walls myself with the help of a buddy in the trades.


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## Tscarborough (Feb 25, 2006)

From the pictures, it looks like YOU are damaging HIS wall with the excavation on your side. 

You can get split face CMU that look exactly like Allen block, though they have a slightly different face size.

I would not think you could use SRW units as the wall of a house, since they weep water freely through the face. I would also check for setbacks and easments before you built theose rooms.

To solve your drainage issue, do as you plan, but make sure the final grade is from the house to the wall, and from the center of the wall to either side around the house.


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## dougchips (Apr 23, 2006)

Sorry for the post, just getting my post count up to 3000 so I can post streaming video.

Welcome to the site and good luck on your project! I couldn't resist after seeing your Post this morning.


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## Team Scream (Jul 29, 2007)

Tscarborough said:


> From the pictures, it looks like YOU are damaging HIS wall with the excavation on your side.
> 
> You can get split face CMU that look exactly like Allen block, though they have a slightly different face size.
> 
> ...


Actually there has been NO excavation, the undermining you see and the exposed footing of his wall has all happened naturally over the years but keeps getting worse every year.
This property has been in my family since 1986 and that little hillside just keeps coming toward the house.

I just got off the phone with the city planning department, and there are set back requirements.
One of the proposed structures can be 1 foot from the property line in all directions however the other proposed structure must be 1 foot from the rear property line and 5 feet from the adjacent property line.
This may actually work in my favor since the structure I want to build on the east side would be at the end of the pathway on the east side of the house which just happens to be 5 feet wide now.

I must have mis stated myself somewhere, so let me clear things up a bit, I never intended to use Allen block as part of the structural wall of the room(s), I wanted to build conventional retaining wall segments which I would incorporate as part of one of the structures, however now that I understand the setback requirements that plan is out the window.

Thanks for the heads up on the drainage, that is consistent with what I had imagined.
My question is this:
Will the drainage (perforated) pipes be placed behind the footing of the wall or on the house side of the footing?
Also, is it necessary to vent the drain pipes vertically to daylight every 50 feet? or do you vent them to daylight at an angle through the face of the wall somehow?
Please help me understand this or better yet, can you guide me to a website with illustrations?
Thanks guys!

P.S. streaming video requires 3000 posts? jeeeeeebus I got a long way to go.....damn!:jester:


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## concretemasonry (Dec 1, 2006)

You will have to maintain the integrity of your neughbor's wall. Fortunately, it appears to be well built.

You cannot excavate and remove soil that reduces the bearing capacity of the soil supporting the wall. This includes excavation that is totally on your property, but deep enough to cause a loss of support.

The erosion of the back of your yard that was permitted to contunue after the home construction and any additional excavation could jeopardize the integrity of the wall depending on the depth and distance from the property line.

Any retaining wall you build will probably have to be engineered. Most municipalities require this for any wall retaining a level area of soil over a specified height. Usually this height varies between 3.5' and 5'.

Different retaining wall block systems also place the un-engineered or gravity limit at between 3.5' and 5' for a level area retained. Because of the slope and distance to the property line/wall a "equivalent soil surchrge" could be added to the loads on your wall.

You would probably need a site survey to determine if an engineered wall is required. In any case, a segmental wall would still be the most economincal when conpared to a rigid reinforced block or reinforced concrete wall since segmental wals do not require footings, grount and reininforcing steel.

Your project is very do-able and should result in gaining some very valuable space.


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## masonking02 (May 13, 2007)

nice blockwork il leave the answers to the smarter guys.


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## Team Scream (Jul 29, 2007)

concretemasonry said:


> You will have to maintain the integrity of your neughbor's wall. Fortunately, it appears to be well built.


Well thats good news, The neighbor and I get along just fine, I have seen situations not unlike this where good neighbors end up hating each other.
My intention is not to create a rift of any kind, and I should have worded the related statement I made to reflect that. After re reading my original post, I would write it again differently



concretemasonry said:


> You cannot excavate and remove soil that reduces the bearing capacity of the soil supporting the wall. This includes excavation that is totally on your property, but deep enough to cause a loss of support.


I understand that completely, my intentions are to build the SRW 3 feet off of the existing wall to a height just above the footing and utilize that space as a planting area. Is it still your opinion that if I do not excavate vertically closer than 3 feet to his wall, on my side, that this wall will still need to be engineered?

The SRW will top out at 4 feet and according to Allen block "should be built with Geogrid, however "can" be built without it", for the $300.00 or so required for this wall, I will use Geogrid.

The city tells me no engineering required for my wall as long as it is under 4 feet. A permit is required however.



concretemasonry said:


> The erosion of the back of your yard that was permitted to contunue after the home construction and any additional excavation could jeopardize the integrity of the wall depending on the depth and distance from the property line.


I hear ya loud and clear, and yes sir, the operative word in that statement was (is) "permitted".



concretemasonry said:


> Any retaining wall you build will probably have to be engineered. Most municipalities require this for any wall retaining a level area of soil over a specified height. Usually this height varies between 3.5' and 5'.
> 
> Different retaining wall block systems also place the un-engineered or gravity limit at between 3.5' and 5' for a level area retained. Because of the slope and distance to the property line/wall a "equivalent soil surchrge" could be added to the loads on your wall.


Can you elaborate on the "equivalent soil surchrge" part of that? I have no idea what you mean here, is it an imaginary number referring to "potential" soil pressure(s) based on things like the weight of the wall above my proposed wall?



concretemasonry said:


> You would probably need a site survey to determine if an engineered wall is required. In any case, a segmental wall would still be the most economincal when conpared to a rigid reinforced block or reinforced concrete wall since segmental wals do not require footings, grount and reininforcing steel.


My thoughts exactly, however the main thing I like about SRW's and the block system concept is the aesthetic value, the wall has a finished look to it straight, let alone add some elevation changes, stairs, landings, planters etc, I think it is really visually appealing stuff.



concretemasonry said:


> Your project is very do-able and should result in gaining some very valuable space.


Thank you for taking the time to reply Dick, I do appreciate it, I am not completely green when it comes to this stuff, however it is a bit daunting, and since this is going to be a fairly pricey little upgrade to the place, I really want to measure thrice and cut once.

I would really like to forgo the costs of engineering, if you know how to guide me through the process of evaluating the weight load of this (existing) wall and the weight bearing capacity of my proposed wall/retained earth to determine if I fall reasonably within the acceptable limits or not, I could then make an educated decision based on that information, as to whether or not I truly should spend that (engineering) money.

Again thanks to everyone who has replied and to those who may.


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## Driftwood (Feb 15, 2004)

*We do many different types of walls in the Bay area*

That 100 ft wall has a surcharge , How much ,I can't see the grade on the other side. You need a soils and structual eng. AS is ,it will rotate in time ,if nothing is done. non engineered walls in this case may very well fail in a short time.
If You do a lot of this ,You'll understand My red flag ! Good luck


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## Driftwood (Feb 15, 2004)

*One more note*

The load is going out at a 45 degree angle,down hill. Retaining walls are holding back everything up hill in a 45 degree angle , not out level into the hill. I have some good people I work with on projects. One is 28 years with Bechtel all over the world.


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