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Retaining Walls in San Francisco? Watch Closely When El Niño Starts Up Again

El Niño

Effects of El Niño on San Francisco retaining walls

When El Nino hit this year, you may have been looking forward to it. After all, it’s rain – albeit a lot of it – on ground that badly needs the moisture. What you may not have expected, and what some homeowners obviously didn’t expect, is the strong storm taking down the San Francisco retaining walls that hold the hilly landscape at bay.

A lot of the problems we’ve had here in San Francisco this year have been small compared to the two Bay Area homes affected by sliding hillsides at the end of January. However, retaining walls failed all over the city because of the rains. -And now the El Nino, although it’s one of the strongest in history, is on pause.

Rather than breathe a sigh of relief that everything held, now is the time to really take a look at your property. If you have retaining walls (and what San Francisco property doesn’t?), you need to have them checked to make sure they’re still doing their jobs correctly.

Why Do San Francisco Retaining Walls Fail in Rain?

It’s often believed that San Francisco retaining walls fail because of the pressure of all that earth being held back. After all, the Bay Area is just one big hill, right?

That’s far from the truth, however. It’s actually water – not dirt – that is the biggest culprit for knocking down retaining walls. More specifically, it’s water combating a wall with improper, or no, drainage.

When a retaining wall has proper drainage, water slowly seeps out, keeping pressure on the wall down to manageable levels. Without that drainage, however, water builds quickly behind the wall, causing hydrostatic pressure.

Hydro means water, and static means non-moving. So hydrostatic pressure is the pressure against the wall caused by standing water. To understand how this principal works, you can take a full cup of water and stick your finger in it. The pressure of the water against your finger is hydrostatic pressure.

The resulting additional weight of the water against the wall – with no outlet because of poor drainage – causes structural damage. In some cases, it causes cracks or buckles as the water forces its own seep holes into the wall. In other cases, it brings the retaining wall down, along with the soaked ground behind it.

Is Your Retaining Wall Failing?

Is there a way you can tell if your retaining walls are… well, retaining? Are they doing their job? Luckily, your wall doesn’t have to be horizontal to tell if it needs repair. Here are a few warning signs that your retaining wall may not stand up much longer:

  • Non-weeping weep holes – If your retaining wall has little holes in it, and those holes aren’t seeping after a rain (particularly a heavy rain), this is a sign that the drainage behind the wall is either inadequate or blocked.
  • Pregnant walls – If your retaining wall looks pregnant about a third of the way up, this is a sign that it may not hold much longer. Another good hard rain may be all it will take to knock the wall down.
  • Cracking walls – If your retaining walls have cracks, especially if the cracks are deep, long or wide, it’s a good indication that they need repair.

Repair or Rebuild Your Retaining Walls?

If your in San Francisco retaining walls are showing one or some of the signs above, it’s time to have them inspected by the professionals. However, none of these signs are definitive signs of doom; it may not take a complete rebuild to fix the problem. Luckily, there are several ways to repair a retaining wall without starting from scratch.

Tamate Landscaping will work with you to develop the best plan for your landscape and budget, whether it’s repair, renovate or rework. Contact us at 415-265-2697 for a free estimate.

Retaining Walls: 3 Types to Hold Back Those California Hills

Multi Terraced

Tamate Retaining Wall

In the landscaping world, retaining walls have the major purpose of providing stability to the earth, preventing erosion and the movement of soil. With San Francisco’s hilly grounds, retaining walls are an essential part of almost any household, apartment complex and business. Mud slides, ground seepage, crumbling dirt trying to take over your backyard – these structures are a barrier in the constant battle between man and nature.

Because of the ongoing war with gravity these structures are built to be burly and unstoppable. However, contrary to popular belief, these carefully engineered systems can also be aesthetically stunning. Not only do they hold back Mother Nature, but they also offer pragmatic benefits towards embellishing your home, such as providing privacy to your outdoor living areas and increasing the value of your home (which is a great return on investment, by the way).

Normally, retaining walls use their own mass, backfill anchoring systems to fend off the terrain behind it. They’re most commonly made with offset cinderblocks, angled stones, heavy blocks, wood or reinforced concrete frames, and then filled or backfilled. The fill source can be from just as many materials as the wall itself, but it has to have the necessary physical properties to act as a resistance to the natural earth pressures.

Types of Retaining Walls (and Examples of Landscape Projects You Might Use Them for)

When you think “retaining walls”, you may picture the oh-so-popular gray, imposing hunk of concrete. There are several types, however, and each one has a better use compared to another. For instance, a gravity wall (which you’ll read about shortly) is great for short terraces, but not so great for retaining walls over four feet.

Gravity Retaining Walls are the oldest type of retaining wall, and are built to be bottom-heavy. Fatter at the bottom than they are at the top, they’re often built to lean against the ground they’re holding up. It takes math and a ratio to get them set right, but these walls are great for short terraces. At four feet tall or less, they won’t require mortaring or steel reinforcements.
An example of gravity retaining walls is this multi-terraced retaining wall and drainage project below.

Example of Gravity Retaining Walls

Cantilever Retaining Walls can hold a significant amount of dirt, and are good for tall slopes. They have a horizontal base that extends out to the back, and often to the front as well. For a cantilever wall to last and not come down eventually, it needs reinforcements (often steel) and some form of water drainage.

While a retaining wall with weep holes or a drainage system doesn’t very aesthetically pleasing, you’d be surprised to find out how beautiful it can be. Tamate Landscaping often uses stone facing and caps to turn a plain wall into a perfect backdrop for an Asian garden, or stucco covering to blend in with the Californian landscape like we did in Glenn Park. Click the link to read more about this retaining wall project.

Example of Cantilever Retaining Walls

Steel H Beam and Plank Retaining Walls are sturdy structures, and great for soft soil areas. They consist of beams driven into the ground at spaced intervals. Only about one third of the beams are above ground, with the rest below. They can be made out of steel, wood, concrete, or a mix, as we did in this Buena Vista retaining wall project in 2013. We buried the steel beams, then used treated wooden planks for the wall material.

Example of Steel H Beam and Plank Retaining Walls

Now that you are a pro at retaining walls you can consider having one built. These walls have been around for years and continue to offer myriads of solutions and aesthetic landscaping additions. Take care of the evil slouch in the yard where you wanted to build a pool but never got around to it. Beautify the atmosphere of your home in the back yard, front yard or all the way around the house.

Call Tamate Landscaping at 415-265-2697 to discuss your landscaping project. Find out how a retaining wall can beautify your view.

Backyard Landscaping: Private Sports Yard in the Sunset

Sunset District, San Francisco

Once upon a time, the Sunset District of San Francisco, California was known as the “Outside Lands”. Instead of homes and people, it was coastal scrub land full of sand dunes. No backyards; no backyard landscaping. It wasn’t until the baby boom that the last of the sand dunes disappeared, replaced by the tightly packed suburban style neighborhood it is today.

In February 2015, a backyard landscaping project took us to Inner Sunset, one of the four “micro neighborhoods” nestled in the Sunset District. The house was built in 1924, which may account for the unusually long backyard (most yards in the Inner Sunset don’t offer near as much room). The client looked at the space and dreamed of a sports-centered yard for two little boys – and maybe some adults, as well.

Before backyard landscaping

They opted for a large, artificial turf area for soccer and a padded sports court. For the sports court, they wanted basketball hoops, complete with overhead sports lights.

We had our work cut out for us. The retaining walls were crumbling, and the ground was taking back over poured concreate and a brick pathway. Weeds had destroyed most of the grass, and a gopher infestation was doing short work of the rest.  It took us three weeks to transition from a backyard disaster to a sporty backyard landscape.

Setting flagstones for an entrance into the home.

The first step was to set a concrete pad to provide a smooth, even surface for the flagstones. Quatzite flagstone went over the concrete base to create a small landing from the house to the backyard.

Digging down and building up: San Francisco cobbles used to build the retaining walls

Next, we dug out and replaced the retaining walls. Digging deeper gives the yard to very distinct levels: a turf area and a sports court area. Two benches were inset into the retaining walls to provide an area to watch the activity, and stairs going to the sports court. Plants along the terracing will eventually grow thick enough and tall enough to provide a privacy screen from neighbors.

Redwood bench set in recycled cobblestone retaining wallThe retaining walls are made with recycled San Francisco Cobble, which comes with interesting history. In or around the 1800s, these cobbles were quarried for use in the shipping industry. Old wooden ships would bob on the water like a cork once their goods were offloaded; the cobbles were used as a ballast to keep the now empty ships stable.

Of course, they were then off loaded, and San Francisco ended up with a whole bunch of cobbles. They were eventually turned into paved streets, the streets were covered in tarmac, the tarmac in asphalt and the cobbles were buried. So now the client can tell people their retaining walls have a long, established history. If nothing else, it’s a good conversation starter!

Sports backyard: basketball court has benches to watch the game play, as well as halogen lights

We brought in the Sports Court Company to install the special foam sport court. The two galvanized poles seen will be used to install halogen overhead lights.  Also, on the stairs, we installed LED down lighting for times when the games go late into the night.More redwood benches were installed here, for spectators, and another right off the flagstone porch.

Artificial turf, especially strong for soccer playingThe artificial turf we used is call S-Blade 90, from a long-term partner, Global Syn Turf. S-Blade 90 is a high-end, thick, realistic-looking material that will stand up to the rigors of soccer and other harsh activities.  It has brown thatch woven into the turf to make in look more real. The turf is laid over 3″ of compacted baserock for stability. In addition, we added heavy landscape fabric, to prevent weeds, and a layer of galvanized wire mesh to deter gophers.

The finished backyard landscaping project: sports centered, with strong turf, basketball court and room for soccer

Above: Our finished project! It did take three weeks, but at the end of that time, we were all extremely happy with how it turned it. A far cry from old, crumbling walls and a struggling weed patch!

Retaining Walls | Whitney Street – Glenn Park

Whitney Street Project

Glen Park Neighborhood

Glen Park, a wonderful neighborhood in San Francisco, could provide an entire semester of architectural material if you took the time to walk up and down the hilly streets. Spanish Colonial houses sit side-by-side with Mediterranean Revival homes, which butt up against homes built in Mission Revival style. It’s an interesting place with an interesting history, which was one of the reasons we were happy to take on a landscaping, garage stuccoing and retaining wall project on Whitney Street.

When we were called out for this project at the beginning of 2015, we were told that the client wanted a drastic change in improving curb appeal. We knew we had to keep the charm of the landscape consistent with the charm of the home. For a house on Whitney Street, full of 85-year-old (and older) homes, this is no small accomplishment. Although the home is modest, the front really makes it stand out from the dwellings on the street.

Another challenge was stuccoing the equally old garage and adjoining retaining wall in a way that would keep the stucco looking fresh and in one piece a few years down the road. Thanks to four years of little rain in the Bay area combined with San Francisco hillsides, stucco has a tendency to crack, and retaining walls can shift. Obviously, we don’t want either of those to happen.

We started as almost every landscaping project starts – with a little demolition, watched over by my work dog, Dukey:

Dukey Dog

Once all the old was out of the way, we could start the real work of beautifying the front of the home. Although a retaining wall was part of it, we also replaced the stairs and patio, add added a deck to the garage. We poured a new slab for the patio garden, built new stairs for the front porch and for the new deck over the garage.

Pouring New Slab

Bison Decking System

For the deck over the garage, we used the Bison Deck System, which ensures a smooth, even foundation for the wood tiles. This also provides a level step, rather than dipping and swaying when people walk on it.

We also installed new steps of black limestone and black slate. At night, the steps are lit by wall lights with a solid brass face plate. As always, we used FX Luminaire 12-volt lighting fixtures to illuminate the garden/front. FX Luminaire has always provided excellent products for landscape lighting.

Steps and Wall

Limestone Steps

To ensure the stucco on the retaining wall and garage doesn’t crack under the dry heat, we fortified it with metal lathe. Next is the process of applying the stucco, starting with a scratch coat.

Coat_4_stucco

As a final touch, we added custom iron fencing to the retaining wall, deck and stairs. This not only helped keep the style of the home, but also to set it apart from its neighbors.

Gate in Iron

Iron Work Steps

The Finished Project

We were really pleased with the final results. Within three weeks, we’d designed, installed and finished a flattering front entrance for the client. Tamate Landscaping did all the carpentry, electrical and stucco, which kept the price lower than if we’d had to go to outside contractors.

As well, we used an ironworker with long ties to the company to provide custom iron fabrication and installation.
Whitney Street Project

It was quite a job, but I think it’s one for the “well done” books.

 

Current Project 2014: West Portal Custom Front & Rear

By On January 18, 2014 In Completed Projects, Ponds and Waterfeatures, Retainingwall With Comments Off on Current Project 2014: West Portal Custom Front & Rear Permanent Link to Current Project 2014:  West Portal Custom Front & RearPermalink

Our first project in 2014 brings us back to West Portal and its a large one for San Francisco Standards.  Below is a shot of the rear before construction. We’ll be constructing new fences and sunken patios with contemporary concrete retaining walls that are becoming so popular these days.  Also included is a gas fire pit, stainless weir waterfearure, decks, lights and much more.

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The end of 7 days.  After removing about 40 cubic yards of debris, concrete and dirt, you can see the forms for the new wall going up.

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January 24, 2014, the end of week 2, we pumped 12 yards of  colored concrete (silver smoke), removed the forms on the same day and hand troweled for a smooth finish.

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Also being installed is the rear wall stonework and water feature.

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January 31, 2014:  Day 18.  

Things are moving along as planned and we should be done in about 7 days.  Below you see a test fire of the natural gas fire pit.  We installed a 30″  H- burner but now I’m thinking I was over ambitious.  The unit puts out so much heat that I’m concerned it may create superficial fissures in the concrete where its narrow.  Although the fire pit is a big chunk of steel re-enforced concrete, expansion and contraction of such material may cause an unsightly effect.  After a discussion with my clients, we are downgrading to a 24″ T-burner.  Stay tuned for a night shot.

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A photo of Manuel in the background working on the “stainless weir” water feature.  Also, Mario in the foreground, ripping a piece of black limestone for installation.   A word about these two dedicated workers:  From the pueblo of San Mateo, Mexico,  they’ve been with me for 12 plus years and are the single greatest asset to my operation.   They are skilled, dedicated and with an unmatched dynamite work ethic.  Without them,  I simply would not be able to do an installation like this.

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A photo of stair stringers made from 4″ pressure treated material.  All cuts have been sealed with “copper green”.   I’d say its elephant proof.

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February 7, 2014:  2 shots of “Almost Done”

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FEBRUARY 14TH, 2014, PROJECT COMPLETE

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Concrete

Concrete

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Completed: West Portal Renovation Aug.2013

By On August 12, 2013 In Completed Projects, Retainingwall With Comments Off on Completed: West Portal Renovation Aug.2013 Permanent Link to Completed: West Portal Renovation Aug.2013Permalink

Below is a before shot of an uninviting, underutilized backyard.

chung before

We started with demo of the entire yard and concrete forms for a raised concrete planter which has become popular for todays contemporary styling.

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Planter number one with concrete forms removed.
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Concrete planter number two.  This shot was taken 3 hours after the concrete pour.  Timing is crucial here.  Remove the forms too early and the whole structure will collapse.  Too late and it will be too hard to hand trowel a smooth finish.

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Winter 2013, Project Complete

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Completed Project: Outer Sunset Makeover, 6/2013

By On June 23, 2013 In Completed Projects, Retainingwall, SF Dept. of Building Inspection Permits/decks & retaining walls With Comments Off on Completed Project: Outer Sunset Makeover, 6/2013 Permanent Link to Completed Project: Outer Sunset Makeover, 6/2013Permalink

This residence in the outer sunset currently has crumbling concrete retaining walls/steps, terraces that slope and no foliage excepts for weeds.  Not a very inviting environment for a young couple with a new baby.  We were asked to provide a makeover, with a set strict budget and to include a deck, new steps, fix up the walls, turf and plants.  We were shown some photos of elements they liked and we took it from there.  Below are two photos of before.

We started with demo, relocating steps and reinforcing the existing walls.

Below is a shot of a massive concrete bench that we formed and poured.  It serves as as a safety barrier between the two terraces, a platform in which to tie the deck that we will be installing and also seating.

sunset forms

sunset deck

Adding new concrete to existing concrete must be done with great care.  The natural tendency is for new concrete to pull away from old concrete due to poor bonding and expansion and contraction of concrete.  We minimize this by anchoring rebar to existing concrete with a epoxy resin as seen below.

We also coat all surfaces of existing  concrete  with a bonding agent called Weld Crete as seen below.

Job complete.  Three new level terraces, new steps, an organic vegetable garden box, TREX deck and artificial turf.  Also installed were auto irrigation, lighting and plants.