About SIP walls and a residential flat roof, logic behind these alternative building methods

As our design is coming together under our structural engineer, Green Earth Engineering, I thought I should explain how and why we chose SIP walls and a residential "flat" roof design. They are
mostly because of cost-effective and energy efficient reasons, and I'll explain why in layman's terms.

First, SIPs are a composite building material. They consist of a sandwich of two layers of structural board with an insulating layer of foam in between. The board is usually Oriented Strand Board (OSB) and the foam either expanded polystyrene foam(EPS), extruded polystyrene foam (XPS) or polyurethane foam .


They are not commonly used in the building industry due to knowledge or resistance to trying new methods, which is very unfortunate, because they are superior to conventional stick framing and pay themselves back in cost due to energy savings.


So here's a breakdown of why we chose SIPs pulled from my architect's website:

Benefits for homeowners
* Extremely strong structure. There is considerable evidence that homes with SIP wall and ceiling panels have survived natural disasters like hurricanes, tornadoes, straight-line winds and earthquakes better than traditional stick-framed homes right next door.
* Lower energy bills. Discounting the "human factor"-thermostat settings and so forth-a number of side-by-side tests show that between 15% and 40% less energy should be needed to heat and cool a home with SIP wall and ceiling panels. In tests by Oak Ridge National Laboratory, SIP walls outperform fiberglass walls by over 50%.
* Improved comfort. Thanks to extra R-values and tight construction, the wall and ceiling surfaces in a SIP home will stay warmer than in stick-framed homes. The warmer those surfaces are, the more comfortable the home is.
* "Freeze proof." What happens if the power goes down? During the late 1990s, several New England SIP homes survived over a week without power or a wood stove and never came close to freezing.
* Indoor Air Quality. While there is no guarantee here, most homes built with SIPs are tight enough that builders can't ignore upgrading mechanical ventilation compared to that found in a standard home. In many studies in North American housing, the best indoor air quality is found in homes that are tight and equipped with upgraded mechanical ventilation.
* Green building product. On a life-cycle basis, a more energy-efficient house built with SIPs will be less damaging to the environment, in terms of overall resource consumption. Much less dimensional lumber is used in a SIP home than in a traditional framed structure.
* Interactive systems benefits: For example, a more energy-efficient home may cost slightly more to build but in turn can be heated and cooled with smaller equipment that costs less to install.

Benefits for construction
* Speed of construction. You can order the panels with all pre-cutting performed in a factory. They show up on the jobsite all pre-numbered, ready for assembly.
* Fewer framers. A crew can consist of one lead framer assisted by minimally skilled helpers.
* Shell installation option. If you're having a tough time locating skilled carpenters, a growing number of manufacturers have regular crews who will install a shell on your foundation for you to finish.
* Rigid frame. It's easy bracing SIP walls. In fact, once you have two corner panels up, you can lean a ladder against the panels when needed.
* Less jobsite waste. If you've ordered a set of panels with all rough openings for windows and doors pre-cut at the factory, the only true waste you'll have is taking a few cases of empty tubes of adhesive caulk containers to the dump.
* Less theft. While 2x4s and 2x6s are prone to "walking off" unsecured job sites, panels are too specific to the site's building system to be worth hauling off somewhere else.
* Cost competitive. While most builders say they pay a little more for SIPs than for the comparable framing and insulation package in a stick-built home, as a group they believe the benefits are worth the costs. The amount extra they pay varies; while a few say it costs them an extra $1 per square foot of finished floor area, the amount may be higher when roof panels are used. However, when roof panels enclose extra living space in a loft, the price per square foot is surprisingly competitive. If at the design stage you optimize a structure to use panels, the most experienced SIP builders then say a house framed with SIPs should cost about the same as a house framed with comparably sized dimensional lumber, and maybe even a little less.
* Easier to hang drywall. There is solid backing for all drywall against exterior walls, which means there is less cutting, faster attachment and less waste material.
* Fewer framing callbacks. Wall panels go in plumb, square and straight. Once in place, a SIP won't warp, twist or check.

As for our "flat" roof design, our architect advised us that a good way to SAVE MONEY is to get a commercial grade "flat" roof because you don't have to pay for those beautiful Spanish ceramic tiles found on Spanish/Mediterranean style homes, which can get extremely expensive. Besides that, the flat roof goes wonderfully along with our design aesthetic, it being modern and clean-lined. Now, many modern homes use metal roofs with overhangs, which are equally as nice, but we chose this design for cost reasons, having to be "cheap" but not compromise a good quality structure.

The way our roof will be designed is it will first be a SIP panel, then styrofoam wedges to give the roof a 1 to 12 pitch for rainwater drainage, then a thin membrane lining. There will be a parapet wall (wall that goes higher than the roof line) as shown below:


The reasoning behind the parapet wall is to both protect and "cover" all that is ugly on top of the roof. We will also prepare our roof to be solar panel ready.

As you can see in this design, we will not have a truss or attic space under the ceiling as the interior will soar all the way up to the SIP panel, creating a spacious looking living room with extremely high ceilings! High ceilings make any room look bigger, which is the effect we are after. The duct work from our HVAC will be in the floor of the 2nd story, thereby not needing an attic or truss at the ceiling.