Tiny Tuesday: Raise Performance, Lower Bills

Let’s face it – most folks can’t build a new house to reduce their energy needs, not even a tiny one. It’s expensive and time-consuming, it throws a monkey wrench into your lifestyle, and it’s counterproductive if the building materials have a high embodied energy. If you are like most of the population, a more appealing proposition is to retrofit the home you already have. That’s where Home Performance with ENERGY STAR comes in.

First, ENERGY STAR helps to connect you with a local certified contractor who will perform an energy audit of your property. Then, based on the results of that assessment, the contractor helps you schedule improvement projects to reduce your heating/cooling needs and improve your air quality. The result is savings for you (due to lower utility and medical bills) and increased comfort for all occupants, not to mention a positive effect on the environment.

Components of the initial assessment include reviewing energy bills, a visual inspection of the building’s envelope and mechanical systems, and safety tests to identify leaks or moisture issues. The contractor follows up the assessment with a cost-benefit analysis of all possible improvements, such as adding insulation, upgrading mechanicals, and sealing leak points. They’ll work with you to prioritize projects accordingly.

Rebates are available on a regional basis. (Efficiency Vermont offers up to $2000 off the cost of improvements.) So you save money twice. If you’ve never taken advantage of Home Performance with ENERGY STAR, you can start here.

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Tiny Tuesday: Callie’s Coop

Callie is a fifth grader from Atlanta who designed and built a homeless shelter for a school project. As described in this inhabitat article, she conceived the shelter to demonstrate the power of solar energy.

Made from inexpensive, weather-resistant materials like corrugated metal and Tuftex (much of it salvaged), the shelter cost Callie about $10 to build. It’s small and light enough for a person to tow like a wagon, yet encompasses a sleeping area, a sun-powered oven for cooking, a composting toilet, and ample storage. A small solar panel powers a lightbulb, and a rainwater-collecting roof enables the shelter to operate off-grid. Callie showed her prototype at the Georgia Tiny House Festival last week – let’s hope it’s her first of many creative housing projects.

Thanks to Deek Diedrickson, who posted a video about Callie’s house here.

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Callie shows off the doors of the shelter she built.

Tiny Tuesday: Support Talented Teens, Win a Tiny House

The Way of the Bard is a group of high school students who gather regularly in Shelburne, Vermont to practice storytelling, dance, music, and dramatic performance, in the tradition of Shakespeare and Chaucer. The group hosts an annual fall retreat called Borderlands, where families follow a trail through the woods and meet the young bards along the journey. They also run the wildly popular Enchantment Camps, already sold out for this summer, immersing children 7 and up in an imaginative world of magic spells and mythical creatures – plus a daily game of Quiddich.

The current group of 18 has been together for four years, and as they graduate high school they plan to culminate their experience by visiting Ireland. To raise money for the trip, the group built a tiny house on wheels and is giving it away through a raffle. At 6 feet by 7 feet with no utilities, the structure would make a great office, playhouse, or warm-weather guest house. Right now it’s furnished with a twin bed, table, and bench. Visit the website to watch a video of the construction and to buy raffle tickets for $10 apiece.

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The Teeny Tiny House under construction.

Rising high school students in the area can also apply to form the next Way of the Bard group in the fall of 2017.

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Monthly Mechanics: Columns

Just as the vast majority of bridges are beam bridges, the vast majority of buildings are post-and-beam buildings. Horizontal and vertical elements are easy to build and maximize use of space, making them the only rational choice for all but deliberately fancy buildings like stadiums and opera houses. The horizontal elements are the beams, and they work mainly in bending. (We’ve explored beams a few times already.) The vertical elements are the posts, or columns.

(Smaller buildings, including most houses, have loadbearing walls as their vertical elements. You can think of a loadbearing wall as a spread-out column.)

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If you peel back the finishes of a typical building, you’ll see a grid of columns like this one.

A well-designed column is subject to dead loads and live loads from directly overhead, based on the tributary area of the floor above. With no horizontal or eccentric (off-center) loads, a column acts in pure compression. In this way, columns are sort of the opposite of cables.

But unlike cables, which fail only by yielding, columns can fail in two ways. One is crushing, the compression equivalent of yielding. The other is buckling. Even without horizontal forces to induce bending, long unbraced columns will bend anyway.

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Crushing | Buckling

How do you know if a column will fail by crushing or by buckling? The answer brings together many topics from previous Monthly Mechanics articles. Crushing is governed by the equation Pc=fc*A, where fc is the material’s compressive strength and A is the column area. Buckling is governed by the equation Pb2*E*I / L2, where E is the elastic modulus, I is the moment of inertia, and L is the unbraced length.

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Let’s investigate the above concrete column. (Concrete columns are almost always reinforced, but for compression the rebar is negligible.) Crushing load is Pc = 4000 psi * 144 in2 = 576 kip. Buckling load is Pb = π2 * 360000 psi *1728 in4 / (120 in)2 = 426 kip. So this column fails first by buckling. A shorter or stockier concrete column would fail first by crushing. Steel columns almost always fail by buckling.