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The Engineer's Notebook

The Engineer's Notebook is a shared blog for entries that don't fit into a specific CR4 blog. Topics may range from grammar to physics and could be research or or an individual's thoughts - like you'd jot down in a well-used notebook.

The Ziggurat Roofs of Bermuda

Posted May 27, 2016 8:00 AM by BestInShow

You're an island in the subtropical North Atlantic, with no freshwater lakes or streams. Nothing but salt water all around you. How do you provide fresh water for a population of 60,000 residents and more than 200,000 visitors a year? Your residents use technology that's nearly 400 years old. This technology not only catches and stores rainwater, it also helps keep buildings cool in hot weather and firmly on the ground during hurricanes. Despite changes in materials of construction, the Bermuda Roof - required by the island's building code -- graces the tops of houses all over Bermuda. The design makes so much sense it's used in other countries as well.

Bermuda Roof. Image source: Wikimedia Commons

Some history

The first English colonists arrived on Bermuda in 1609, rather by accident. The Sea Venture, a ship taking passengers to the Jamestown colony in Virginia, foundered on the surrounding coral reef during a hurricane. The passengers elected to remain on the island even after completing a replacement ship some months later. The lack of fresh water was readily apparent; although some water filters through the island's coral surface to underground lenses, the original settlers weren't prepared to locate and drill for it. So the new residents started harvesting rainwater.

The ingenious method Bermudians devised to collect rainwater is to create stepped roofs - hence, the ziggurat - that guide rainwater to a slanted gutter. The gutter connects via pipes to an underground cistern or holding tank, where water is stored until needed. Current building codes require Bermudians to make at least 80 percent of a roof's square footage a rainwater catchment area. With an average annual rainfall of 55 inches, that's a lot of water to catch and save.

The system

The rainwater-collection system incorporates more than just the gutter-to-cistern path. Several critical components lead to this system's success. These roofs, whether old or brand new, are nearly hurricane-proof; the Bermuda building code requires that roofs weigh 66 pounds per square foot (that's what the scuba boat pilot told Mr. Best in Show and me).

Roof composition: The original roofs were made of limestone "shingles," oblong slices of the island's native limestone mortared down over a hip-roof frame made of Bermuda cedar. The finished roof is then mortared over to fill in joints. Since the island can no longer supply limestone and cedar, contemporary roof slates are made of modern materials, such as expanded polystyrene (EPS), laid on a cement substrate.

Roof coating: Original roofs sported bright-white coatings of lime - essentially whitewash. This bright coating reflected the sun's glare, helping keep buildings cooler, and helped sanitize the rainwater. Today's roofers use white elastomeric paint. Although this material lasts longer than whitewash, homeowners still have to repaint every two or three years. This coating, like whitewash, helps prevent mildew and mold.

Gutters: Unlike conventional roof gutters, Bermuda roof gutters run slantwise across the slates, starting about two-thirds of the way down the roof, carrying rainwater through a pipe to the underground storage cistern. The gutters themselves are fashioned from cement.

Roof gutter on Bermuda Roof. Image credit: The A Position

Cistern: Rainwater passes through a filtration system as it funnels into below-ground cisterns. The cistern stores water, pumping it into a pressurized tank for distribution through the plumbing system.

Maintenance: Homeowners have to clean their roofs periodically to remove bird droppings and other foreign materials. As mentioned above, roof coatings last two or three years, necessitating re-coating at regular intervals. Public health experts recommend regular tank cleaning to ensure potable water.

Side benefits of the Bermuda Roof

A white-painted roof reflects sunlight back into the atmosphere, helping to keep the building it shelters cool. Something I didn't know is that, according to Lawrence Berkeley National Laboratory 1000 square feet of white roof has the equivalent effect of cutting 10 tons of carbon dioxide emissions. Multiply that by all of the white roofs in Bermuda, and the CO2 equivalent reduction is noticeable.

As mentioned above, the heavy roof prevents Bermudian homes from becoming airborne during hurricanes. The roof shingles, much less the entire roof, don't blow

off in high winds. Thanks to the mortar and roof sealant, these roofs are watertight, as well.

Aesthetically, the consistent use of this style of roof, coupled with the pastel paint used on Bermuda buildings large and small, contribute greatly to the charm of this British Overseas Territory. Bermudian indigenous architecture is considered by some to be the island's greatest artistic heritage.

The downside

Recent studies indicate that general cistern water quality isn't necessarily as good as one expects from a traditional municipal water supply or private well. Two years ago, a Canadian public health specialist from Universite´ Laval in Quebec alarmed Bermudians when he claimed that cistern water contains too much fecal matter to be safe to drink. Dr. Eric Dewailly based his statement on research completed in 2013. He proposed that bird droppings are the most likely source of fecal-matter bacteria, highlighting the need to clean roofs regularly. Dr. Dewailly encouraged residents to incorporate an ultraviolet treatment system to kill bacteria.

A study of the mineral composition of cistern water produced more equivocal results. Sediments that accumulate in cisterns can contain elevated levels of nasty stuff like arsenic, but the levels vary from tank to tank. The authors called for more research to clarify the picture.


Image credit:

Bermuda roof on building on Corfu. Corfu Blues Blog.

5 comments; last comment on 05/29/2016
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Grow Plants in Rocks! Innovative Horticultural Substrates

Posted May 20, 2016 8:00 AM by BestInShow

When I was researching my previous post, on living walls, I discovered that an inorganic substance, stone wool, is used as a growing substrate for some wall systems. Stone wool? I'd never heard of such a thing. The more I looked into this topic, the more interesting substrates I found. These all represent advances in the horticultural use of existing materials, some of them organic like coconut coir, some, like rock wool, inorganic. Improvements in substrate materials have no doubt contributed to the increase in living walls; the same improvements are a boon to horticulture in general.

What's a substrate?

Simply put, a horticultural substrate is a substance in which a plant's roots grow. Garden soil is a substrate. Vermiculite is a substrate. Plants do not need potting soil, or even organic matter, for growth. They do need something that holds roots firmly enough to enable the plant to grow up and that allows water and nutrients to reach the roots.

Why look for different substrates?

In the 1960s, a couple of factors impelled the commercial horticulture industry to seek out new types of plant growth substrates. The growing environmental movement awakened concerns about increasingly intensive use of farmland, which exhausts the land. These concerns led, among other actions, to the banning of methyl bromide, a soil disinfectant commonly used to prepare soil for planting. Finding new methods for crop culture would take pressure off of existing resources.

Stone wool

I'd never heard of stone wool, and I was baffled that something made out of basalt would be an acceptable plant substrate. Although mineral wool insulation has been around for a long time, a mistake - a bad batch of insulation - led to its use as a plant growth substrate. A Danish insulation manufacturer, the ROCKWOOL group, tossed the defective stone wool out on factory property. Lo and behold, sometime later staff noted that small plants were growing in the insulation batts.

The company worked with university researchers to perfect this stone wool for

use in horticulture. A subsidiary of ROCKWOOL, GRODAN, manufactures the horticultural version of Rockwool©. Plant propagators use cubes of the material for starting seeds or rooting cuttings. It offers several advantages for green walls and more general plant-growing applications:

  • The medium is consistent in makeup from batch to batch, and it's easily sterilized.
  • Stone wool is hydrophilic, which enables efficient circulation and recirculation water and nutrients, but it does not rot like organic substances.
  • Plant roots have plenty of room to grow between fibers.
  • Since stone wool substrate does not lock up or release any substances, growers can provide precise amounts of water and nutrients.
  • Stone wool is lightweight.

Coconut coir

Coconut or coco coir is the fibrous material found between the hard interior shell and the outer coat of a coconut. We're familiar with many of the products made of coir, whose production goes back as far as the 11th century AD: doormats, ropes, sacking, twine, among

others. During the 1990s, coir's advantages as a horticultural substrate attracted commercial growers, and it's popular today, particularly for hydroponics and mushroom cultivation. At least one company sandwiches coir mats into panels for vertical gardening. In addition to sheets and loose chopped fibers, horticultural-use coir is formed into bricks and cubes.

Coir offers several advantages as a growth substrate, not least of which is the attractive natural tan-to-brown color of coir sheets and bricks. Other advantages include that

  • Coir can hold up to five times its weight in water and release it slowly, yet it drains well and prevents water pooling and rot.
  • Coir is very slightly acidic, with good pH for plant growth.
  • Roots move easily into the pores between coir fibers.
  • Depending on its origin, coir can contain usable amounts of plant nutrients, such as phosphorus.
  • Coir has some anti-fungal properties and inhibits some other pathogens.
  • This medium is long-lasting and can be reused for three to four years.
  • Coir is a 100 percent renewable resource.

A problem recently noted with some coir products is the potential for inadvertent importation of exotic weed species. Ironically, gardeners can use coir mats to inhibit weed growth.

Felt systems

Patrick Blanc, the genius behind contemporary vertical gardens, started out using synthetic felt, irrigating plants with nutrient-laden water. Fast-forward to the 21st century for the introduction of an improved type of felt for vertical gardening. This new felt is made from 100 percent recycled plastic bottles, so it's environmentally friendly and durable.

At least two companies market pockets made from recycled-plastic felt, with two slightly-different pocket designs and configurations. Both designs make use of the felt's capacity to wick water throughout the pocket. Both designs also incorporate at least a minimum amount of another growth substrate, typically a soil-less mixture. Plant roots can penetrate the felt.

Florafelt Vertical Garden Planter Woollypocket Planter

These pockets make small-scale vertical gardening easy, indoors or outside. They can be hung on drywall without causing water damage, and gardeners can swap out and rearrange plants easily. Home gardeners that lack access to a plot of ground can use these pouches to grow vegetables and herbs - perhaps not squashes, but definitely lettuce and other smallish plants -- indoors or on a deck or patio.


Photo credits: Rockwool/Wikimedia Commons;; Florafelt; Woollypocket

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Behind the Scenes at the Museum

Posted May 08, 2016 12:00 AM by Chelsey H

I love anything behind the scenes! That's why I was so excited to see pictures of the storage areas in the Smithsonian Museum of Natural History (NMNH) in Washington, D.C.

The NMNH opened its doors in 1910 with wings added in 1960 and a storage facility in Maryland opened in 1983. To see old pictures of the museum click here.

There are over 126 million items in the growing collection ranging from ancient spear points to the bones of Tyrannosaurus rex.

Taken together, the NMNH collections form the largest, most comprehensive natural history collection in the world. The scientists who work in the labyrinth of hallways, vast storage rooms, and busy offices meticulously collects and studies the artifacts looking for details on vital topics, such as evolutionary relationships of organisms, biodiversity loss and global climate change.

2 comments; last comment on 05/08/2016
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Living Walls, Living Roofs: Old Ideas and New Technologies

Posted May 06, 2016 8:00 AM by BestInShow

The idea for this post came to me last summer, when Mr. Best in Show and I were in Avignon. The central market's north façade is a stunning living wall. Living walls and living roofs have been around for a long time. Sod roofs, the original living roofs, date back to prehistory [insert URL] in Scandinavia. The Hanging Gardens of Babylon might be mankind's initial stab at living roofs and walls. Gardeners have created green facades, formed when plants grow on a structure like a trellis or an arbor, for centuries, sometimes attached to buildings but often structures in themselves. Looking at the wall of Les Halles in Avignon, with its substantial size and artistic swirls of plant material, prompted me to investigate the engineering that makes these modern structures possible.

Les Halles Avignon, Flickr/TracyElaine

As usual when I get to sleuthing, I uncovered much more interesting material than I'd expected. This week's blog post will provide some additional history of living walls, plusses and minuses, and an introduction to Patrick Blanc, a French botanist who has designed and installed many walls in the past 15 years, including the one in Avignon. Future posts will cover some of the really interesting technology behind (literally) living walls, and the story behind a local, just-completed living roof.

A living wall vs. a green façade

The main distinction between a living wall - also known as a vertical garden or biowall - and a green façade is that with a living wall, the wall supports the growing medium, so the plants root in the medium and not in the ground at the base of the wall. Living walls can be installed inside and outside.

Some History

Sod roofs and arbors aside, Stanley Hart White, an American landscape architect, patented his idea for a vertical garden in 1938. White was granted a patent "for the Vegetation-Bearing Architectonic Structure and System" describing a method "for producing an architectonic structure of any buildable size, shape or height, whose visible or exposed surfaces may present a permanently growing covering of vegetation." As far as we know, however, White never constructed his vegetation-bearing structure.

The Arts and Crafts movement of the early 20th century, followed by Art Nouveau, favored plants that climbed up the sides of buildings and thus bridged the junction of lawn and built environment. Their favored plant? Parthenocissus tricuspidata, also known as Boston ivy (not to be confused with Hedera helix, English ivy). Whether the ivy is Boston, English, or some other species, ivy-covered walls are ubiquitous. They're not living walls, though, despite ivy's propensity for covering up nearly everything in its path. Like kudzu.

Why bother?

Construction of a living wall isn't inexpensive. Why go to the expense and trouble, other than the aesthetics of the finished design? These walls have several advantages, some obvious, others more subtle.

Reduced costs for air conditioning and heating: External living walls absorb sunlight, preventing sunlight from striking and warming the building. The cushion of air between the building and the plant support frame provides insulation. Plants also provide shade and evaporative cooling.

Reduced air and noise pollution: Both interior and exterior living walls reduce air pollution, by using carbon dioxide in photosynthesis and absorbing other compounds, such as nitrogen dioxide and particulates. Plants help absorb sounds, providing an acoustical advantage.

Improved aesthetics: Living walls are often planted in patterns. Small green "pictures" can be incorporated indoors or outside.

Improved quality of life and job satisfaction: Some studies have shown that seeing nature in the work environment can increase job satisfaction.

Depending on choice of plant material used and living-wall accessibility, some vegetables and herbs can be grown on living walls.

Types of Living Wall Systems

Living walls have two basic construction styles:

  • Pots or pouches assembled on a framework and filled with growing medium, with irrigation provided
  • Panel systems that combine irrigation and a growing medium, mounted on a support framework

Both types of garden systems can be used indoors and outdoors. My next blog will dig into some of the interesting materials used for these systems.

Image credit: Vertipak

Patrick Blanc: Father of Modern Living Walls

The Avignon living wall that so entranced me is the work of Frenchman Patrick Blanc, the inventor of the modern vertical plant wall. Blanc started his botanical career as a specialist in tropical forests, writing his Ph.D. thesis on understory plants in tropical forests. In 1982, he signed on as a resident scientist at the prestigious Centre National de la Recherche Scientifique (CNRF), making field trips to Southeast Asia in search of new plant species. He discovered Begonia blancii , one new species, in the Philippines. Working for CNRF is still Blanc's day job.

Blanc's claim to international fame, however, is his championing of living walls. In 1986, he installed his first living wall, at the Cite des Sciences et de l'Industrie de la Villette in Paris. In 1988, Blanc patented his vertical garden system, described as follows:

On a load-bearing wall or structure is placed a metal frame that supports a PVC plate 10 millimetres (0.39 in) thick, on which are stapled two layers of polyamide felt each 3 millimetres (0.12 in) thick. These layers mimic cliff-growing mosses and support the roots of many plants. A network of pipes controlled by valves provides a nutrient solution containing dissolved minerals needed for plant growth. The felt is soaked by capillary action with this nutrient solution, which flows down the wall by gravity. The roots of the plants take up the nutrients they need, and excess water is collected at the bottom of the wall by a gutter, before being re-injected into the network of pipes: the system works in a closed circuit. Plants are chosen for their ability to grow on this type of environment and depending on available light. []

Since 1988, Blanc has designed and installed dozens of these "vertical tapestries," as Kristin Hohenadel of the New York Times describes them.

Blanc's designs often incorporate plants that create not only an aesthetic but an educational experience. For example, the installation at the Musee de Quai Branly in Paris, completed in 2006, incorporates 15,000 plants of 150 different varieties, representing countries whose artifacts are included in the museum's collections.

Could vertical gardens also grow food? Sure. Several years ago, a group of high-school students in the Bronx successfully grew many pounds of fresh vegetables for their school cafeteria. The Bronx group partnered with Green Living Technologies, which claims to be the inventor of "edible green walls" and a mobile edible wall system. Other commercial enterprises offer living wall systems that could adapt to growing lettuce as well as ferns and pachysandra.


4 comments; last comment on 05/09/2016
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Time to Plant Some Trees

Posted April 25, 2016 12:00 AM by joeymac

Well its spring time and I'm sure you're getting the itch to be outside and working on your garden, pick up your yard, and get ready for outdoor projects after the long winter, especially up here in the Northeast. One outside project that people like to do and is the perfect time to do right now is planting a tree. There are multiple reasons for planting trees such as: saving a household's heating and cooling energy consumption, trees also clean the air by absorbing pollutants and carbon dioxide while producing oxygen, they provide shelter and food for wildlife, help save water by slowing evaporation, and provide food when planting fruit or nut trees.

Choosing the right tree is where your homework comes into play. Once you've decided on the reason why you're planting a tree, you need to figure out what type of tree will best fulfill your needs. If you're planting for energy savings, then you need to select a large deciduous tree, which will shade your home spring through fall while allowing the sun to shine through in the winter once its leaves have fallen. If you're looking for shade, choose a tree with a broad canopy, and if you want shade year-round, then select a tree that's evergreen and won't lose its leaves in winter. Make sure to pick a tree with the right color in mind for summer and fall foliage that fits your liking. Fruit trees give a double bonus by providing food and beauty with their spring flowers and fall foliage. Also keep tidiness in mind when picking out a tree, some trees are messier than others. If you're planting a tree near a pool, select one that won't produce messy flowers, seedpods, or both. If planting near a pool an evergreen would be ideal for keeping the water clean.

Planting is best done while the tree is dormant. This is either in the fall after the leaves have dropped or in early spring just before the leaf buds begin to swell. Planting trees during this time gives the roots time to grow before the warmer weather stimulates new top growth. Trees can be planted at any time of the year but extra care is needed to be sure they are adequately watered during their first summer.

When planting a tree, the hole's size plays a major role in how quickly a tree establishes itself and grows. The hole should be three times wider than the trees root ball and shaped like a saucer. This allows for good root growth and development, because the majority of a tree's roots grow outward into the top foot of soil where oxygen is at high levels. The hole should be the same depth as the root ball or even slightly shallower. Trees don't like to be planted too deeply because it decreases the amount of oxygen available to the roots. Also, trees tend to settle a little lower after being planted. When picking the planting site remove any excess soil on top of the root ball, place the tree in the center of the hole. Fill the hole with the same soil that was dug out, after filling in the hole create a berm around the hole which will hold water to help it permeate deeply around the tree and water immediately after planting to settle the soil and get rid of air pockets. No fertilizer or any other amendments should be added during planting or for the first year, as this could hurt the tree's roots. New trees will need more water for the first year to help them get established, especially the first few weeks after planting. Add a 2 to 4 inch layer of mulch, compost, or wood chips around the tree. Keep the mulch 6 inches away from the trunk to prevent fungal disease or insect problems.

16 comments; last comment on 04/27/2016
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Let Them Eat Weeds: Foraging in Urban Food Deserts

Posted April 22, 2016 8:00 AM by BestInShow

This week (April 17 - 23) is Wild and Feral Food Week. I'd planned to follow last week's blog about eating invasive plant species with a post about eating non-invasive wild plants, like ramps and fiddleheads, which come into their own at this time of year. Scratch that idea. Instead, let's celebrate Wild and Feral Food Week by examining the premise that urban foraging can be an effective method for improving fresh food availability. Solar Eagle's humorous response to last week's blog post got gave me the title for this week's blog: let them (or us) eat weeds. This notion is discussed by Mark Bittmann, at the time a visiting fellow at Berkeley Food Institute, as he joined Philip Stark and Tom Carlson of the University of California, Berkeley, for a walk around Oakland, CA, finding weeds to eat.

Gourmet chefs on a foraging expedition. Image credit: The Gourmet Forager

Food Deserts

First, some background. Many of you have heard of food deserts. For those of you who have not, the US Department of Agriculture's definition is "[food deserts are] parts of the country vapid of fresh fruit, vegetables, and other healthful whole foods, usually found in impoverished areas. This is largely due to a lack of grocery stores, farmers' markets, and healthy food providers." The definition specifically calls out lack of a car plus no grocery store within one mile as main factors in the food desert definition. The map in the link above shows that we can find deserts in rural areas as well as urban environments.

The West Oakland neighborhood through which Bittmann, Stark, and Carlson took their tour has long been considered a food desert. A 1960s-era freeway project split West Oakland from the rest of the city, hastening the neighborhood's descent into poverty. Several supermarkets have come and gone; currently, West Oakland is waiting for yet another supermarket project to get off the ground. A food-co-op and a couple of smaller enterprises are helping improve the food scene, but these stores cannot adequately serve West Oakland's population of around 37,000.

A Walk on the Wild Side (you saw that coming)

Stark and Carlson are principal investigator and co-investigator, respectively, for Berkeley Open Source Food, an initiative that, among other goals, seeks to increase foraging for

urban wild-grown greens. My first reaction to eating a plant I pulled up from a sidewalk crack was, as you might think, yuck. The uber-foragers address the yuck factor directly. Yes, these plants can be dusty. A dog might have watered them. However, plants are washable; no one says you have to eat them as soon as they are picked. An interesting point in the weeds' favor is that these plants are free of the pesticides commonly used on field crops and even in home gardens and lawns. Free-range weeds have several other plusses:

  • They're free.
  • They're organic. Think about that: organic weeds!
  • They require no cultivation or other care.
  • They're drought-tolerant.
  • Many are nutritionally superior to cultivated counterparts.
  • They're ubiquitous

The foraging trio quickly found a basketful of greens. All of you readers who have lawns will recognize some, if not all, of these usual suspects. The New York Times published a guide with pictures and serving suggestions (see link in Resources).

Please note: if you are interested in foraging, do your homework on plant identification before you taste anything. When you taste, start with a small bite and wait to ensure that you are not allergic to the plant. The Berkeley Food Initiative web site has a good guide, and there are plenty more on the internet.

  • Chickweed (Stellaria media): "tastes like spring," according to Bittmann
  • Sweet fennel (Foeniculum vulgare): milder and sweeter than commercial varieties
  • Yarrow (Achillea millefolium): sagelike flavor
  • Wood sorrel (Oxalis acetosella): lemony and crunchy
  • Sheep sorrel (Rumex acetosella): a "bright" taste
  • Nasturtium (Tropaeolum majus): peppery and succulent
  • Wild radish (Raphanus raphanistrum): mustard-hot and slightly sweet
  • Bristly ox tongue (Echioides helminthotheca): beefy or mushroomy flavor

A Cool Smart Phone App

Urban weed foraging in the East Bay has a nifty technological assistant. Berkeley Open Source Food encourages use of the iNaturalist smart phone application designed to make foraging easier and safer. Foragers provide a real-time weed inventory/mapping/visual index for Berkeley, Oakland and Richmond. iNaturalist exploits smart phones' GPS capability and cameras to enable individuals to post locations and pictures of various plant species. There's a competitive aspect to posting information: current leaders in "most species" and "most observations" are listed on the site. The screenshot below illustrates the "leaderboard."

The iNaturalist plant-mapping project is a testbed to determine the feasibility of urban foraging. The website claims that participants have found "vast quantities of delicious fresh natural greens in economically challenged parts" of the three cities covered. How "vast quantities" translates to number of people who get to eat fresh salad, and who those people are, are questions that the research project seeks to answer. Even if an urban area produces enough weeds to feed everyone in the city, who will eat them? Food carries all manner of socio-economic and cultural connotations, in addition to the yuck factor. Will an urban family eat weeds if family members feel this reflects negatively on them? Are there cultural barriers to eating some of these plants? Given the general opinion that California's East Bay is way out there, can it be replicated elsewhere or will the association doom it to implementation in few other locations.

I'm not immune to weed prejudice. A few years ago, I got a pile of purslane in my CSA (community-supported agriculture) weekly bag. Since I'd just spent a lot of time pulling purslane out of my flower beds, I wasn't happy to have paid for a fresh batch. After reading Bittmann's favorable reactions to most of the weeds he tasted, though, I'm inclined to give purslane a taste. After all, the cultivated plants we eat all started out as something wild.

Image credits: Berkeley Food Institute, iNaturalist


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