Category: Concrete Design

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Drainage and Infrastructure Are Not Like Milk Duds

I’m still recovering from Halloween – 538 trick-or-treaters is a LOT Of kids – and it’s still framing how I look at things. Of the nearly $200 we spent on candy we have a bowlful left, and as I was pawing through the bowl for a mid-morning snack I kept encountering Milk Duds. Boxes and boxes of Milk Duds. They’re ok, I suppose, but I’ve never met anyone who got excited about them. It takes some amazing skill to be able to combine chocolate and caramel, two awesome flavors, in a way no one loves.

A lot of people look at the essential foundations of the landscape as if they were Milk Duds, something that you can’t avoid but don’t love. It doesn’t have to be that way! I’ve already gone on and on about dry streambeds as an attractive way to move water through the landscape. It’s also possible to move stormwater in a more formal way, using it as a water feature. When I took care of the grounds at the Salk Institute in La Jolla, California, I got to see a really neat way of handling rainwater. Here’s the wide-angle view of the buildings:

Every floor has a balcony overlooking the central courtyard, but what architect Louis I. Kahn did was he stepped each balcony back as they got higher, so that the rainwater flowed off the flat roof onto the edge of the balcony, through the scuppers, and onto the balcony below that, and on and on for the six floors of the building.

Source: tourguidetim.com

The idea was to create a series of cascading waterfalls, and it was a really cool idea. Now, ideas do come down to execution. If you worked at the Salk and wonder why you never really saw this, sadly, the reality check is that clearly the concrete company who poured the floors didn’t get the memo. In a heavy rain, water pooled on the balconies and flowed the wrong way, right into the labs. Rainy days meant all of us – landscapers, carpenters, plumbers – grabbed long-handled squeegees and saved Science from Nature. Hm. Is there an allegory in there?

Regardless, Louis I. Kahn’s design intent shows that drainage and infrastructure can be handled artfully. Where a lesser architect may have channeled the water into drains and hidden plumbing runs that daylighted in the scrub above the cliffs, he made them a feature. That’s a testament to what design can do. Thus inspired, I’m off to see if maybe microwaving Milk Duds makes them better.

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How Much Does a Retaining Wall Cost in Northern Virginia?

I recently spoke with someone who was looking for a retaining wall, four feet tall and ninety feet long. Before moving forward with a consultation he wanted a sense of what such a wall would cost.

He was surprised, to say the least.

There are a lot of design consideration for retaining walls in northern Virginia, and every site is different. Slope, soils, access, permits, and existing conditions impact the costs, so it’s not generally practical to create a proposal for a retaining wall based solely on square foot pricing. The best contractors examine the site, create a landscape plan (or have a landscape designer create a plan), work out all the materials needed down to the number of tubes of adhesive, and base the price on the labor and materials required to build that individual wall.

That said, I will use square foot numbers to at least start the conversation so I can help the client decide if they’re ready to move forward with the design. When we multiply the length of the wall by the height we get the total square feet of face, or SFF. Here’s how different materials can break down by SFF. Keep in mind that these are not absolutes, just starting points. Your site conditions may result in higher or lower costs.

Pressure-treated 6×6 retaining wall: Generally, a wall of this type will start at $35-45/ SFF. So in the example conversation with the homeowner who had a 90’x4′ wall (360 SFF), he’s looking at approximately $12-16K.

Segmental retaining wall: these are your interlocking concrete wall systems, EP Henry, Techo-Bloc, or similar. Depending on a lot of variables, walls average from $50/SFF to $75/SFF. For our homeowner with 360 SFF of wall, we’re looking at approximately $18-27K.

Concrete retaining wall with stone veneer and cap: This is the most attractive type of wall, and one I’m a huge fan of. Costs vary by site conditions, stone used, etc., but I generally ballpark $75-105/SFF when discussing budgets. My sample homeowner with 360 SFF would be looking at a range of $27-38K.

There are other types of walls (boulder, dry-stacked fieldstone, poured and stamped concrete, etc) but the above are far and away the most commonly requested and built in the DC Metro area. As you can see, retaining walls have the potential to use a good portion of the budget for a landscape project. This is why good design is key. Not only can a good landscape master plan ensure that the walls are where they need to be and and properly designed, it can potentially reveal options for using fewer or smaller walls – freeing up funds for the more exciting parts of the project.

 

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What is a Concrete Turndown Edge on a Patio, Anyhow?

Sounds so fancypants, doesn’t it? I have a few projects underway that need one, and it’s a simple concept that sounds more involved than it is.

When installing a patio, you want it to have a slight pitch so water doesn’t pool on the surface. If we’re lucky, the grade slopes away from the house at a similar pitch as the patio, so we can prep the base and pour the slab on grade. If there’s a massive difference in grade, we may need a retaining wall at or just beyond the edge of the patio. What about the middle ground between the two?

A turndown edge lets us build up the edge of a patio without the expense of having to build a retaining wall under it. We simply form up the edge, shape the gravel under the slab to create a shape similar to the image, and pour the concrete. Now you know what a concrete turndown edge is, should it come up as part of your northern Virginia landscape design.

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Why Is This Retaining Wall Failing?

I walk by this wall whenever I walk to the post office in downtown Culpeper. Walls like this are pretty common in older neighborhoods like mine. Leaning and generally unhappy walls are, sadly, pretty common as well. So what gives? Why do these walls look like they’re ready to flop over on the sidewalk?

There are several possible explanations. The first is insufficient footer, or failure to tie the wall in with the footer. When building a masonry retaining wall in Virginia you generally want to dig down 24″ below grade, so you’re below the frost line. You then pour a beefy footer (thickness varies depending on application), often with rebar coming up from the footer to tie the wall to the footer. Our home was built in 1906 and renovated in the 1950s, and I can tell you with certainty that there was not a lot of digging to frost depth being done way back then.

Another possibility is insufficient drainage behind the wall. Water is a wall’s worst enemy. Hydrostatic pressure is a major cause of wall failure. The way we avoid a buildup of pressure is by using a “drainage chimney” of clean gravel behind the wall, along with periodic weep holes.

What makes this wall great for illustrative purposes is the fact that the wall likely started to fail because of hydrostatic pressure (water buildup behind the wall). This pushed the top of the wall forward, creating a gap between the wall and the slab. What’s right above the slab? Downspouts! So not only do we have a gap, we’re pouring gallons upon gallons of water behind the wall with every storm. Awesome.

So how would I fix this wall? I think we’re beyond the point of fixing something like this, and it needs to come out. Improper construction is hard to correct, and when it gets this bad – there’s no Band-Aid big enough.

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Elements of Design: Texture

Texture deals with how smooth or rough a surface is. When talking about elements of structures, smooth surfaces can often seem more modern and contemporary, while rough surfaces seem more rustic. Think of the difference between a rammed earth or concrete wall (favorites in modern design) versus a stone or splitface block wall.

Rammed Earth Wall. credit: ASNZ website (click to visit)

Texture has an additional role in landscape design, however. A pleasing planting design includes plants of different textures used in the landscape. Soft and spiky, narrow and broad, whatever the mix you choose the idea is to create some contrast to keep things interesting. This photo shows a really basic pairing of soft and spiky – something that’s actually quite common in container plantings:

An old trick I learned a long time ago was that if you want to be able to evaluate whether you have successfully blended textures in your planting design, take a black and white photo of the plantings. With the color removed, the textures become obvious. Brilliant. You don’t even need Photoshop anymore, just a vintage camera app for your phone. How cool is that? Yay, technology!

Texture is really effective, and it’s one of those tools that, when used properly, isn’t even readily apparent. It just “looks right.” The key to achieving interesting textures and relationships is knowing your options – which is where a good landscape designer can be a great asset.

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What Landscape Work Can Be Done in Fall and Winter?

I get this question a lot this time of year. I get my fall rush once the kids are back in school, it takes a few weeks to get through the design process, and suddenly we’re just past Halloween. Is it too late? It depends on what you’re doing.

Plants

Woody trees and shrubs can be planted almost year-round in Virginia. With the exception of last winter, I’ve had plants go in – and do well – all winter long. As long as the ground isn’t too hard for us to get a pick and shovel in, we can plant woody trees and shrubs. Perennials are another matter. They are generally too delicate to plant after about November 1st, because we’re pretty certain to get a hard frost after that point. I did a post a while back that talks about safe frost dates for northern Virginia.

Asphalt

Most asphalt companies in Virginia shut down sometime in December, and open up again in April. If we’re redesigning a driveway, we need to keep this in mind.

Concrete & Mortar

Concrete is going to be the happiest when the nighttime temperatures stay above freezing. That’s not to say that concrete work shuts down for the winter. On cold days, my masons have set up tents with propane heaters and laid stone all day long in t-shirts. At night, thermal blankets can be placed on flatwork to keep the temperatures high enough. Pointing up and cleaning can get slowed down a bit because the concrete stays “green” longer, but that’s not a problem as long as the mason knows what s/he is doing.

Pavers

Pavers (and segmental retaining walls) can be tricky in the winter. The problem happens when you have a significant amount of rain, sleet, or snow on the base or sub-base. If this moisture is allowed to freeze, you can have long-term settling problems. The solution is to keep the area as dry as possible, and use thermal blankets or other means to keep the base material from freezing. Again, the work can be accomplished in the winter, it just requires a knowledgeable contractor.

Ponds and Waterfalls

These can certainly be installed in the winter, but temperatures below freezing can make working with water less fun than on a sunny, 70 degree afternoon.

Decks, Porches, Pergolas

As long as snow’s not a problem, these can be built all year long

And what if you’re just starting to think about the design process? Winter is a great time to start the design process. I’m currently booking December and January projects. If you have a project you’d like to start planning, send me an email and let’s get started!

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Stamped Concrete Steps

In the post I just did about stamped concrete, I failed to mention one of my other issues with stamped concrete: the vertical surfaces (steps, turndown edges, etc) often look badly done- like a child’s attempt at making Fred Flintstone’s house out of Play-Doh. This is one more area in which I’ve been impressed recently. Here’s a shot of a set of steps that a stamped concrete contractor in northern Virginia just did for one of my clients:

I grew up in New England, where it’s not unusual for someone to use big slabs of stone for their front steps. This is actually pretty impressive, and I figured it was worth sharing.

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Is Stamped Concrete Any Good?

It’s funny- for the longest time, I would have said no. Emphatically, in fact. After all, there have always been several flaws with stamped concrete, many of which are still a negative:

  • Difficult to change- once a slab is poured, that’s what you have. To reduce it for any reason, you would need to saw cut and remove a portion. To add on to it you can pour a new pad, but good luck getting the colors to match. Pavers, brick, and stone are a little easier to change out depending on how they were installed.
  • Life span- Concrete doesn’t last forever. If you get a section that chips, cracks, spalls, or stains, you have the same problem previously mentioned that it’s difficult to patch unobtrusively.
  • Cracking- this is a big one. Concrete WILL crack; anyone who tells you otherwise is full of it. The reason is that concrete is strong in compression, but not tension. What does that mean? Imagine that a piece of styrofoam is a concrete slab. If we load it so that the forces are pushing down on the slab evenly, it handles it. Now, let’s put the styrofoam on the edge of the table and put a weight on the end hanging out into space. It fails, because it is weak in tensile strength- just like concrete. This is why we put steel reinforcing rods (rebar) in concrete. We’re taking a product (steel) that has high tensile strength and giving some of that to the concrete. However, even reinforced concrete will still exhibit surface cracking.
  • Expansion joints- this is my pet peeve. I’ve seen too many artfully done stamped concrete slabs where the contractor does a pretty convincing job of an irregular stone pattern, then strikes a joint right through the middle of it, ruining the illusion. To avoid this you need to find a good contractor AND let him know you don’t want to see this.
  • Surface finish- too many slabs are sealed with a glossy, fake-looking sealer. Also, sealed concrete can get slippery underfoot. There are sealers out there that have less of a sheen to them, and there are also additives that will make them less slippery (“up the coefficient of friction” if you want to geek out)

So Dave, you say, why on Earth would you let anyone use stamped concrete? Don’t get me wrong, I will almost always design with the idea of using brick or stone first. It comes down to a budget issue. In northern Virginia, the cost of stamped concrete is usually right around $15 per square foot, essentially half the cost of wet-laid stone or brick. That’s pretty huge. If it’s a pattern that translates well to stamped concrete I would rather see the project move forward than have the client take the plans, roll them up, and put them in the closet for a decade. Where’s the fun in that?

This project actually worked remarkably well with stamped concrete. It was designed to be 2’x2′ flagstone squares, laid in a grid pattern on concrete. Instead, we used a stamp pattern that makes the slab look like one big piece of stone and used a masonry saw to cut grid lines in the concrete. Even with natural stone used for the wall and firepit, the concrete still looks good. Apologies for the picture of an unfinished site, but we’re still working on this one.

So to answer the original question of the post, is stamped concrete any good? It certainly can be, with the right design and the right contractor. Make sure you have both of those in place and you can get a great finished landscape.

UPDATE: Here’s a pretty cool little set of steps one of our stamped concrete contractors did in northern Virginia.