Let’s imagine that we are Martians coming down to earth and seeking to build ourselves a new home for our new life here on this jewel of a blue-green planet. We are, as Martians of course, well connected to an extraordinary knowledge base and extremely rational in our behavior, but also passionate about the arts. We therefore approach this project almost like a science experiment, but want it to come out looking drop-dead gorgeous! As well as being concerned about performance-under-fire, we are also extremely cognizant of and sensitive to energy usage and environmental footprint issues.
Masonry – a first class building material able to withstand eons of weather and it is also rot-resistant and non-combustible. There are some thermal issues and cost issues. If in a hot-dry or hot-wet climate, and if thick enough, this stuff works pretty well, but in climates where heating is required, masonry by itself doesn’t work; it needs to be augmented with a layer of insulation, preferably on the outside. Masonry is usually expensive. It is available pretty much only as a site-built material, and if it requires the insulation layer, the package price can be, …well, pricey. Masonry for roofs is a whole other expensive issue. There are pre-cast concrete solutions, arches and vaults with masonry units, but all of these are difficult and therefore expensive to install. The only exception I know of for this are described in the book “Architecture for the Poor,” by Hassan Fathy. These solutions yield forms that may be considered by some to be culturally unacceptable. The clay masonry products (bricks) have a much smaller ecological footprint than Portland cement based products.
ICFs are close cousins of masonry, in fact they are masonry-with-insulation turned inside out. This helps a bit with the price, particularly for owner-builders, but interior and exterior finish options are a little more limited and/or a little more expensive to install. We also have a serious roof problem. ICFs are currently not designed for roof or floor applications. During a fire, there is no danger of structural failure, but all interior and exterior finishes will have to be replaced.
Log constructions may be culturally appropriate in some locations, but not most. We include them here because they still out-number SIPs for new construction each year. There are also rot issues on the outside and limited finish options on the inside. The interiors tend to be pretty dark, if not initially, then over time. Most owners are reluctant to paint the logs or cover them up with painted drywall. Roofs might be solid logs similar to the walls, but are usually log rafters or trusses with SIPs as the insulated roof deck. So, both log and ICF construction are really limited to walls only and most such structures wind up being roofed with SIPs. People who select log construction give a great deal of weight to appearance over performance. The initial log home revival born in the 1970's paid little attention to infiltration resistance and such homes were drafty as all get out. Though this has changed dramatically for the better, and the thermal mass of the logs does help to reduce heating (and cooling) loads, this type of construction still does not hold a candle to the conductive and infiltration resistances of the other technologies we are discussing here.
Ahhh, Timber-frame, who can deny its beauty? Its main attraction is its “frozen history” aspect. It is, in “architect-speak” transparent; that is, it makes the rational of the structure visible and tangible – we see what and how is holding up what. We find transparency to be full of meaning and thus it delivers great satisfaction. If hand-wrought, we reach out to touch the tool marks, thus almost touching and connecting with the human maker. With all this, timber-frame construction is expensive, and leaves 8-foot wide and high voids that are generally covered up with – you guessed it – SIPs! In fact, if the usual interior drywall skin of such timber-frame wrap panels is changed to the same structural skin as used on the outside of the panel (thus making a true structural insulated panel) then one may pluck out and remove the timber-frame from the remaining envelope and it won’t fall down! One may also rightfully express concern over the use of prime timbers and the environmental impact their use engenders. Secondary growth forestry products really don’t perform as well as the old stuff does. The new timbers twist, shrink, split, check and otherwise move much too much, stressing the connections between the frame and its wrap.
There are quite a number of Proprietary Construction Systems that are out there utilizing many different materials as their base. There is light gage steel and aluminum framing and different factory-produced panels with different cores and skins. There are hybrid systems with minimum framing components and panel wraps that are engineered to take the torsional and other loads that a building must resist. Our Martians might well fall in love with one or more of these systems, but we don’t have the time or space to evaluate them all here, so we will just quickly look at steel framing. This has much to commend it in terms of Price, Strength, “Green-ness” and Flexibility, but for exterior wall construction, it behaves as cooling fins – conducting our precious heat directly through to the outside. When the thermal short-circuiting is addressed remedially, the costs go up too much. Some systems have low racking resistance and must be used with care, or supplementary diagonal members must be utilized before the walls are closed up. I don’t like to give up all the advantages, so I recommend that Light Gage Steel be utilized for all interior framing.
Sticks are last on my list. I can’t believe most of my colleagues out East still design and specify this system. Sticks are made from the best trees of the Pacific Northwest, cut and fashioned into “2-by” material and then shipped to our lumberyards three thousand miles away! When originally used for low-rise construction in the 1840’s to quickly build out this country, it produced flimsy structures, though flexible and redundant, that were the most flammable ever devised on the face of the planet.
These buildings, though superior in thermal performance to most of their masonry brethren, were still difficult to insulate and nightmares of infiltration. When remedially updated to provide the insulation and infiltration resistance that today’s homeowner requires, the cost goes ballistic and quality is difficult to control. If thermal performance upgrades are done half way, half-well – as is the predominant practice – these structures become mold and mildew factories. Oh, and did we mention the fact that stick structures are highly combustible? Our Martians are quick to pick up on these issues and also marvel at the flexibility born from the redundancy inherent in the system. This encourages an undisciplined approach to structure that is more “Folkloric” than akin to the true engineering that Mother Nature practices and architects and engineers dub “elegant.”
At last we come to SIPs. The physical and mechanical characteristics of SIPs are best found by contacting the various manufacturers listed at SIPS.ORG and SIPWEB.COM. Suffice it to say here that they are structurally and thermally superior to most options discussed above and also feature a remarkably small environmental footprint. Our Martian friends carefully and methodically constructed a matrix to enable them to exercise proper judgement about what they have learned about the various options in front of them. Down the left side are performance categories, each with a value from 1-10, with 1 being the worst value and 10 representing the best. Across the top are the Column Labels of each of the candidate Systems.
Please note that most of these ratings are highly subjective, reflecting my personal assessment of value relative to performance. I do not know of any objective testing that assigns importance to various performance categories; for example: whether or not it is important for the building to be of fire-resistant construction beyond code requirements is a matter for each individual to prioritize. The values in the “Evaluation Matrix” have relative significance rather than absolute significance. These are not scientifically derived, but empirically – based on many years of working with all the systems listed in the capacity of an architect.
a. Assumes Structural SIP skins.
b. Assumes adequate rebar for racking & seismic resistance.
c. Assumes minimum Portland cement.
d. Assumes logs from prime trees.
e. Due to Portland cement.
f. Life Cycle Analysis.
g. Products of combustion and resistance to combustion.
h. Rebar throughout is standard.
i. Assumes small openings.
j. Framing upgraded to equal SIP thermal performance. ( R and infiltration )
Back in the real world, we are not Martians, meaning that we don’t make all our decisions in a purely rational fashion. When it comes to decisions about houses, just like with cars, we actually function in our most irrational mode. We care far more about appearances than functionality and performance standards. While high field labor costs and increasingly higher standards of finish will force housing construction into the factory and off the site as much as possible, we don’t know the time frame for this transition, just the certainty that it will happen. Because the housing stock doesn’t turn over at anywhere near the rate of the automobile fleet – 100 years versus 10 years – we should be producing only the best housing we know how to build as it will be around for a long time and the cost of correcting shoddy or code-minimum construction is extremely high.
When the extra-terrestrials finally do arrive, we don’t want them going back to their home planet reporting that they “found no intelligent life on the third planet from the Sun.” As we praise the pyramids of the Ancient Egyptians and judge other past civilizations by their buildings, we should be prepared for a similar accounting by those who will write the history of our time on the planet earth.