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LOBSTERS, ARCHITECTS, ENGINEERS, AND CUT-DRAWINGS

11/1/2014

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Originally written:  Nov 2003

This last week, after spending several sleepless nights wondering how I was going to write about architects and cut-drawings, I finally had a little “eureka” that brought me to my keyboard.  What I am always harping on are the structural differences between SIPs and sticks.  For most traditional building this doesn’t come into play, but for many structures it does and the importance of understanding exactly how your structure is working is essential to have in your head before you start laying out the pieces of your SIP-puzzle, which is actually what your cut-drawings are.  So let’s back up a little for some residential structural history…..

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BEING RESPONSIBLE FOR YOUR DESIGN

2/1/2014

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Originally written:  Oct 2001   

A client comes to see you. He may be a developer who wants three or four models for his 60-unit subdivision, a manufacturer with a tricky commercial project that needs some engineering, layout and detailing work, a representative from a church building committee, or a young couple with hopes for their dream house. In all cases, if you say, “Yes, I’d be glad to help out and do this design project for you - and how nice to hear you want to build with SIPs, I was just going to suggest we use them in this case,” you are accepting responsibility for proper specification of SIPs.

What does accepting this responsibility mean? It means that one should have a thorough understanding of the properties of the material so that only appropriate applications are utilized. By “properties” we mean the physical characteristics, the structural/mechanical aspects as well as perm ratings, resistance to ultraviolet light, ozone exposure, construction loading and handling requirements, manufacturing tolerances, and familiarity with accessory components - fasteners, splines, foams, caulks and assembly sequences. This is a lot to integrate, but it’s no more than what we deal with for all the other construction materials used all the time. (All the issues around cast-in-place reinforced concrete make me dizzy just thinking about them!) But deal with them we must or we are sure to suffer from either short term problems that might be “just” cosmetic, or long term problems that might cause structural failure. Essentially, we must be aware of the physics of the entire situation. We must be knowledgeable of code requirements, but also mindful of contextual issues that may not be anticipated by the code and arise from user patterns (normal or deviant, but foreseeable), or extreme conditions that arise from micro-climatic abnormalities (carpeting gets moldy and sick occupants – if they don’t sue - stop recommending you).

Buildings are different from how they were a generation ago. They are different because they are responding to the market that is requiring them to be different. Houses are now larger, but are also loaded with more appliances and features that tend to con-tribute to the increase of humidity levels. We take our cooking seriously; we do more of it and a lot of it on the stovetop. (Pasta rules!) We have hot tubs and whirlpools, steam showers and saunas. Greenhouses abound and so do active wood stoves and fireplaces. We like to think that all the products of combustion (of which water vapor is a large component) go entirely up the chimney, although this may not be the case. We are also more active, so we take more showers. Some luxury homes even have indoor swimming pools. All of this tends to put more moisture into our buildings. On the other side of the equation we are tightening up our buildings. Seems like all the talk about energy conservation is finally beginning to sink in. So we build ‘em tight –especially if we’re building with SIPs. After all, that’s one major reason why we decided to build our project with SIPs in the first place.

The savvy designer can see this coming. If he has done his homework, he knows that the perm rating of the SIP is less than 1 perm – lower than many waterproofing films and coatings. The tight SIP building with a high internal humidity will want to equalize the temperature and humidity of the gas (air) inside with that outside. In the winter, when the delta-T is high and the humidity is low, the pressure to equalize is very high. This is called vapor drive. If there are a few cracks in the building, especially high up where the delta-T is highest, the warm, moist air will find its way out. When it hits the cold outside, the water condenses out and – voila! – rot. The professional designer/architect/engineer knows this. He will design the building to head off this problem in several ways.

On the “supply” side, sources of moisture are controlled and limited. Swimming pools have covers, clothes dryers are vented to the outdoors (yes, especially in the winter!), and bathrooms, steam shower enclosures and saunas are also specified as vented to the out-side. For the energy efficiency extremist, all of these vents are passed through a heat exchanger that wrings out every last BTU before finally exiting the building. In fact, SIP structures are only considered properly assembled when a blower door test shows them to be so tight as to have less than 0.4 Air Changes per Hour (ACH). Many SIP structures test out at less than 0.2 ACH. ASHRAE recommendations, which are referenced by most codes, require supplemental mechanical ventilation for buildings with less than 0.4 ACH, so a Heat Recovery Ventilator (HRV) is almost a default specification for a SIP structure. Strictly speaking, ASHRAE calls for ventilation that will give the building at least 0.4 ACH, the heat-recovery feature is an option.

So the designer/architect/engineer will watch the other components of the building to be sure to control humidity levels within the envelope. From a health standpoint, the ideal is a band between 40 and 50% relative humidity (RH). This helps to prevent the growth of mold and mildew, which require higher levels of humidity to exist. On the “envelope” side of the equation, proper specifications call for the sealing of the SIPs with foams, caulks and gaskets. Ed Stahl of Sunworks in California suggests that intention-al vents be designed into the envelope sort of like “pressure-cooker relief valves” so that the moist air can escape without harm. Joe Lstiburek, preeminent building scientist advocates continuously running exhaust or intake fans working together with such vents as being economically competitive with HRVs.

Presently, the SIP industry is catching some flack about structural damage due to vapor drive. The panel manufacturer is not responsible for the improper application of the product. Let the design community take the responsibility for their own work. SIPs can make you look like a hero, but you have to understand their nature fully in order to use them correctly and with imagination. Specifications must deal with proper assembly and sealing. We, the design community, write the specs.

Originally written:  Oct 2001    
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BEYOND STICK TRANSLATIONS

1/1/2014

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Originally written: Sept 2001    
The SIP industry, as we all know, is very much in its infancy. Even though SIPs have developed an honorable track record that dates back to the early 1950s, the national market share percentage of new single-family residences remains down in the single digits when viewed against venerable wood and that upstart steel.

Since the founding of the Structural Insulated Panels Association (SIPA), the strategy has been to approach the builders and convince them to switch from sticks to SIPs. The thinking here was based on the correct under-standing that only about 5% of all new single-family homes were designed by architects and that the rest were all handled by builders. It was also determined that the largest market lay in residences although certain other building types were acknowledged as being ripe for SIP construction. Additionally, SIPA has remained relatively small and lacks the resources to launch a national campaign. In fact, the American Farrier’s Association (horseshoers!) has more than twice SIPA’s member-ship and budget. When one thinks of the market size for horseshoes and compares it to the square-footage of SIPs we should be installing, it becomes clear that we have to change how we are going about the business of becoming the preferred construction for quality projects.

I believe we have to recognize that the design community has been the main driver for the introduction of new technologies to the construction world. Architects and engineers have changed their specifications to introduce new materials and technologies when the new options deliver performance that eclipses the old standard, even when the initial price is higher. Builders are not properly equipped to perform the engineering assessments necessary to specify and size products of the new technologies. This can be seen with the recent introduction of composite joists. Architects and engineers started specifying them in their buildings first as they enabled longer, stronger, stiffer spans, even though there was a cost premium associated with the product. Architects and engineers were correct in forecasting that their clients – the building’s users – would be willing to pay a bit more for superior performance (perceived value). This “push” then created a consumer “pull” where savvy clients are now asking for designs that depend on composite joists for the enhanced span capacity that solid-sawn joists just can’t deliver. All the other extra performance features associated with the product - including the environmentally benign characteristics of the composites – are just frosting on the cake. The span ability alone carried the new product. The building community followed the lead of the designers and the demand of the customer.

SIPs offer us the same opportunity today. Although we welcome the contribution of the building community, which has historically been extremely conservative, it is time for the architectural and engineering community to step up and start specifying those SIPs! We know that many of the features that SIPs exhibit are important and can help the designer to create distinguished buildings that the consumer will ask for. Yes, SIPs are stronger than sticks, friendlier to the environment, etc. However, there must be a focal point to this message. One that is strong enough to make the design community think.

SIPs are capable of delivering forms and spaces that are not economically possible to achieve with sticks. SIPs can deliver curves, huge spans and cantilevers. They can be used as floors over unconditioned or outside areas that are warm and draft-free. These abilities should encourage the design community to create exciting, distinguished buildings that depend upon and exploit these features that sticks simply cannot deliver. So, I am throwing down the gauntlet to my colleagues. SIPs enable you to deliver better buildings to your clients; they beg you to boldly go where no sticks have gone before. It is true that the SIP industry has learned to pro-duce “stick translations” with some fluidity and competence. Standard colonials, ranches, capes and other popular eclectic styles don’t come anywhere near challenging the capabilities inherent in SIPs. The design community must go beyond stick translations to grab the attention of the public and focus the industry on upgrading the performance of our buildings to levels not economically attainable with sticks. New buildings that fire the imagination of the public can best be designed only with SIPs.

In future issues, I will be discussing in detail how SIP features enable the designer to create new forms. Some attention will also be given to how we may design and engineer the SIP components so as to aid the builder in their assembly. A new material should not hide behind tradition, but its strengths and characteristics should be fully exploited and celebrated. I hope to fully explore these ideas here and of course welcome the comments and contributions of those willing to join in the fracas. The SIP world can only hope to benefit from such discourse and in turn we hope to raise the quality of the built environment that we all share.


Originally written:  Sept 2001   
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    Bill Chaleff

    Registered Architect
    A.I.A., LEED AP

    East End Green Architect who has designed with 
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