An Engineers Role in Green Building

There is a myriad of construction methods available today. Some options include conventional wood frame of small dimensional lumber (2x4’s up to 2x12’s), timber frame, log, steel frame (from light gauge to structural shapes), concrete (as a frame or as bearing walls/roofs/floors), straw bale (either load bearing or as infill between a structural frame), rammed earth (in forms or stacked scrap tires), earth bag (a form of rammed earth), cob (another form of rammed earth using stacked balls/rolls of earth/clay), insulated concrete form (ICF; concrete poured into insulated forms that are not removed), structural insulated panels (SIPs; foam blocks sandwiched between sheets of structural plywood/gypsum board) to name a few. A modern home can be comprised of a combination of many of those methods. The foundation can be conventional or ICF concrete or wood (treated to resist moisture damage) bearing walls; the floor dimensional or engineered lumber, SIPs or concrete; the walls any of the frame methods, ICF, SIPs, straw bale, or any of the rammed earth methods; the roof dimensional or engineered lumber, SIPs or concrete. A future green/sustainable homeowner needs to become knowledgeable and educated in order to properly decide what types of home construction method to use.

While certain goals and criteria of the occupant’s needs and desires should be maintained in the design, these can be manipulated for more efficient use of materials. A recent design we participated in included a large lower level garage with covered parking outside the garage doors. A concrete deck was included over the garage and parking area to make that space usable and to allow the homeowners a panoramic view of their surroundings. The homeowner wanted some rooms added, which were placed in the deck area. The result placed loads from ICF concrete walls and roof over the garage and parking area, with no place for supporting columns. Hence, many large steel beams, the size of those used in high rise buildings, needed to be used to support the loads between column locations spaced far and few between. When this was pointed out to the homeowner, the response was that the design was too far along to significantly change. We were able to convince the homeowner to use lighter weight SIPs walls, transfer roof loads to other bearing points, use a lighter weight wood framed deck with a roofing membrane, and to place a few columns in locations that he could live with. Despite that, there were still beams over 25’ long supporting more beams over 25’ long supporting loads, which required those skyscraper sized steel beams, for a residential project.

Bringing the structural engineer on board early in the design can eliminate many of these problems when they most easily can be dealt with, before the “stone” stage. Structural engineers, by our training and experience, are able to look at a design and quickly assess the basic structural load path shape (how the loads are carried by the structural frame to the ground), spot critical areas, and draw attention to structural issues, whether major or minor. This is best done in the schematic phase of the design, coordinating with the designer and homeowner the optimal layout for their individual goals and criteria. A description of the design phases that an architect employs are as follows: The Programming, or Gathering Information, phase is where an architect spends time with the homeowner to determine how their current space is adapted to the way they live now, to better understand how future changes will suit their needs more directly, and finally a list of intentions and rough sketches of spatial adjacencies (what areas are adjacent) specifically derived from the homeowner and the building site is prepared; the Schematic Design phase is where the architect formulates a concept - a theme - which turns the written description and adjacency diagram into spatial definition; Design Development phase is where the architect and the homeowner continue to define - through plans, elevations and sections - the size of rooms, types of materials, and exact placement of the building; the Construction Document phase is where a set of detailed documents are prepared. According to architectural standards, this set informs the builder of the appearance and construction detail of the trim, built-ins, doors, and surface elements, with no mention made of the structural system (italics added). It is vital that the structural engineer become involved prior to layout of the rooms and major spaces, the Design Development phase, during or just after the Schematic Design phase, when the design can be reviewed with an eye to the structure supporting all loads surrounding those spaces. In the previous example, the design could have been changed to accommodate the extra rooms while providing for a simpler load path, eliminating the use of more structure than was needed and still meet the needs of the homeowner.

This is especially important in green/sustainable construction, where the homeowner has made a conscious and informed decision to do their part in assuring a future for coming generations by a reduced use of the earth’s resources, whether in construction or operation of their home. Again, in reference to our previous example, extra steel material was needed to meet the same needs of the homeowner that could have been met if the structure had been structurally reviewed earlier. This homeowner had to spend more money, both in material and labor, to build his home. That impact was directly felt, or will be when the construction invoices come in. In the larger picture, that spelled out by Robert Gilman and embraced by all concerned with our and our children’s future, our houses need to be built without the construction materials being “forced into decline through the exhaustion of key resources”. If even a small percentage of the homes designed use extra materials, that will quickly add up to resources that are not available for the rest of us on the earth. Looking beyond our national borders, groups such as Engineers Without Borders (EWB; ewb-usa.org) an international group of engineers helping those in developing countries achieve basic needs of water, sanitation and education, will not have steel available for water wheels to transport water to the fields for food production; Habitat for Humanity International (habitat.org) will not have the materials to provide basic shelter to those in developing countries; this highlights just two of the groups helping others who will have their work greatly impacted. What this actually means is that mankind will not be able to continue to exist and flourish if the resources we depend on are prematurely depleted. Participate in responsible green/sustainable design by consulting early in your design process with a structural engineer, and the earth will smile upon you.

The “new” alternative construction methods mentioned earlier carry the same external loads as conventional construction, but the load paths can be significantly different. A structural engineer experienced in and willing to work with such construction methods is an invaluable member of the design team. Different materials carry loads in different ways: load bearing straw bale walls cannot sustain even a small point load and must have a load spreader element on top of the wall; rammed earth walls of all types can carry a limited point load and must have the same load spreader, or an integral load carrying vertical element; SIPs can carry high uniform loads, but also need an integral load carrying vertical element for point loads; all of the alternative methods have their individual idiosyncrasies which must be understood and properly designed for. The loads paths need to account for where the loads act on the supporting elements. A wide wall, such as straw bale, tire, or rammed earth, cannot simply bear on the outer rim of the floor, which in turn is resting on possibly an 8” wide concrete wall. If that load path is not considered, the floor joists may easily become overloaded to the point of failure. The different types of methods also exert unique loads according to the weight of each. A conventional 2x6 and drywall/siding wall 8’ tall weighs 120 pounds per linear foot (plf), while a straw bale wall exerts up to 320 plf, and rammed earth walls can exert 800 plf. These must be accounted for in the design.

There are many experienced architects and designers available who can lay out a design making the best use of your alternative materials: straw bales are between 3’ and 4’ long; wood panels are 4’ wide; tires are an average of 30”-32” diameter; ICF forms come in 48” to 96” lengths with 12” to 16” stack heights; all of these need to be accounted for in the dimensions of the home to avoid unnecessary cutting and fitting. They are familiar with room layout to make the best use of the space you have. They can design in essential elements such as proper window locations to make the best use of daylighting and natural ventilation. They can lay out the utilities so that heating and plumbing runs are efficient and not oversized. There are many factors that come into play in the design of your green/sustainable home. However, only a structural engineer can assure that it will safely withstand the forces of nature, and do so in the most efficient manner possible, with the least use of our earth’s resources. Contact a knowledgeable structural engineer early in the process of designing your home, and you will have the “greenest” green/sustainable home available.

Mark Benjamin, P.E., M.ASCE, SECB is president and principal engineer for Crown Jade Design and Engineering, Inc., a structural engineering firm specializing in green/sustainable housing design See us on the web at www.crownjade.com; email jademail@crownjade.com; or contact us at 970-472-2394.

Is carbon a waste product?

Let’s keep this simple, atmospheric carbon is a waste product as a result of our modern lifestyle and energy choices. Here is the definition of a waste product: ‘something that is taken out of the earth but not capable of being reintroduced.’ The logic is very simple. One half of the carbon we emit will last in the atmosphere for geologic time. This is an actual fact, and even though it is not a famous one it is central to the issue of where does civilization go from here? This is about the time when the grandfather in Moonstruck says “somebody tell a joke.”
We know what a waste product is very well because of the nuclear power debate. You can take the uranium out of the land but can’t safely reinsert the stuff after it has done its enrichment and fission thing. Interestingly, Steven Chu, our energy secretary, now sees nuclear waste as less of a hazard than the greenhouse gasses we are now emitting. We can wait around for some particle physicists to harness vacuum energy, dark energy, dissect and manipulate M-theory to extract energy from the 10th dimension, call it holographic energy, or capture all of our coal plant carbon (as seen on Sixty Minutes), and send it towards China via the Earth’s core. In the mean time we can stop wasting so much energy. The last option sounds a whole lot cheaper. Call it the low entropy revolution.

Tax rebates out the window? True or False

Ye-haw, we got energy efficient tax rebates!
Now you can upgrade your home and get the fed to help with the bill. Here is a quick quiz about those new windows you want to get:

1. A Champion Windows TV commercial claims that your average house leaks as much air as an open window. Should you get new windows? True or False

2. Your rebate is only for specific window types that conform to u-factor and solar heat gain limits. Should all your new windows then be applicable for the rebate? True or False

3. Should you replace all your windows regardless of the type? True or False

4. Will installing thermal curtains be equivalent to new windows? True or False

5. Should you save your money for solar panels instead? True or False

6. Are sliders worse than single hung windows? True or False

7. Are new windows the most important thing to consider when doing an energy upgrade? True or False

Extra credit: Are clad windows better than vinyl? True or False


Answers:

1. F This Champion Windows commercial rightfully says that many homes leak approximately 4 sqr ft of air. Getting new windows will often have a minimal effect on air infiltration issues. Many window manufactures are falling all over themselves with misleading information. Please be wary.

2. F See “Dude, tune your windows”

3. F Many existing double paned fixed units with a min ½ inch air gap are only a little less efficient than new windows, especially on the south and north side.

4. T A sealed thermal curtain has the same r-value as an average energy-star rated window.

5. F Reduce your energy consumption first! Its pay back and carbon reduction per dollar is at least 7 times better than solar electric.

6. T Slider type windows are notoriously leaky after installation, avoid them if at all possible.

7. F Always consider the entire thermal envelope of your house before you begin trying to fix it.

Extra credit: T Wood clad and fiberglass usually have a better U-value, but also consider the growing consensus of vinyl as a carcinogen.

Dude, tune your windows (and other simple stuff to make a better building)

May 2009

I’ll have to start this sustainable line off with an apology. I was having a conversation on Earth Day with a builder for whom I have great respect. I was talking to him about building orientation and how important it is and he told a story about how he talked a couple into facing view windows to the west, to make the clients happy. These are the type of stories that make a green building consultant’s heart sink. So I chastised him. I felt bad and want to say I’m sorry. But then I think about it again and my blood pressure goes up. Its Earth Day 2009 and I have to teach a builder who has built off the grid homes how important good orientation is. If he doesn’t get it, then what about your typical builder/ developer? What about you?
So what is wrong with view windows to the west? In Colorado, where I live that’s where the view is and it makes sense, we have such nice mountains. NO! Not about our mountains being nice, no to the seemingly irresistible urge to make a home an energy idiot. West facing windows gain a lot of heat in the summer months. You need a lot of ac to make it work and probably shades to reduce that late day heat, even with your fancy pants low e-4 glazing. So now you have a view of your shades. These windows give you the view in the winter but you’ll have to subsidize it with a lot of heat, aka money. The home I live in was originally set 20° west of solar south and now I wish I got a crane and turned it before I put in an addition. 20° makes that much difference and the view is still there, really.
Studies have shown a 30% energy savings in just good building orientation. This is not cheap, it’s free! So when I am driving through the country and see houses sitting alone and their windows are everywhere but solar south I know their owners 401k is dedicated to keeping the home from being unlivable for the rest of the homes existence. Just to help dissuade rumors, the LEED commercial green building system does account for building orientation, but currently only if you chose to peruse it in version NC 2.2.
So let’s dig a little deeper. You know all this solar orientation stuff but what’s with the “tune your windows” part, and “dude?” I’ll have to apologize again, that was uncalled for. This subject gets me a little emotional. Tuning your windows simply means that with modern glass you can actually select the amount of solar heat that comes through the window. The big commercial buildings would be in deep trouble if they couldn’t dramatically reduce all the heat that hits the surface. They have glass that can cut 80% or more of the solar heat gain. This keeps the occupants from throwing file cabinets through the windows in overheated despair, thus resulting in the collapsing of the economy (even more.) The housing window manufacturers and dealers followed suit and sell their fancy pants low-e windows as energy savers.
So what’s wrong with low-E glass? It keeps the winter heat in and summer heat out. We are smart and our windows are south facing with good overhangs so in the winter we can heat our house up and the low-e glass will keep our rug from fading. NO! The window folks, I will refer to them to as ‘Dude’ for this conversation, are not correct. Dude will tell you about the U-factor, basically a measurement of how much heat escapes the entire window unit, and low-e eliminates fading (it doesn’t). Dude will talk about low-e2 glass, and how low-e4 glass is even better, aka more expensive. But look at the National Fenestration Rating Council (NFRC) sticker on that new window, over on the side, see it, next to the U-factor number. That’s the solar heat gain coefficient (SHGC) rating. In the building world you have to get used to acronyms. That number is basically a percentage of heat that comes through the window from the outside. Large commercial buildings are very keen about heat gain.
But you are building a house where you want heat gain in the winter and out in the summer. Summer is easy, limited west and east facing windows, overhangs to shade your southern windows. Winter is long here in Colorado and some free sunshine heat would hit the spot, but not according to the sticker on that new window. An average low-e2 window is reducing about 60% of that solar heat and low-e4 is up to 80%. The lower the number the more radiation that is blocked from the outside. Don’t be discouraged though, you have the ability to purchase glass with a different SHGC. Dude doesn’t talk about this but there are two types of low-e, a hard coat which has a low SHGC .30-.45, and a soft coat which has a higher SHGC, around .60-65 and hence more heat gain. So all you need to do is order the soft coat low-e with a high SHGC for your southern windows and a low SHGC for the other sides of the house. It may take a little more effort but you will be well rewarded with a smart house (except in Phoenix). Computer modeling could show that you may even be better off without low-e glass. For extra credit figure out the shading coefficient (and then email me at andrew@baosol.com, because I don’t get it).
How much southern facing window? Rule of thumb is 7% fenestration (window area) on the southern side, and if you really good at this green building thing 20% fenestration with distributed direct gain thermal mass.
Ok, next month is “Why green building is for the conservatives”, and bowing to the blogosphere and its rapacious appetite I’ll be adding an extra post or two a month to the sustainable line: blog such as “Is carbon a waste product?” and “Tax rebates out the window? True or False”.

Thanks to igreenbuild.com, Otherpower, and treenex.com for letting me banter on to their websites.


Andrew Michler, LEED AP