SIPs "behave" differently than sticks when subject to loads; they are more akin to shell structures than assemblies of columns, beams and girders. Point loads are dispersed throughout the entire surface of a particular plane and may continue to be resolved across panel joints. This fundamental difference in how SIPs respond to imposed loads must be clearly understood by those who design with SIPs and those who are responsible for deciding both what size and how panels shall be oriented and where and how the joints between them shall go and what type they should be.

For simple structures such as a small gabled barn or flat or shed roofed box, the process is seldom complicated. When the forms start to get large, high and complex with several girders or purlins incorporated, we may then be talking about something else entirely.

O.K.  Here it is, I’m jumping in with both feet and will hopefully make just about everyone angry.  I believe that dealing with this question first demands that we look at the construction costs of conventional residential buildings, this way, we will discover the variables normally at work.  We may then substitute SIPs and see how this effects things.  Sound reasonable?

Let us also first determine what this animal is that we are setting out to price.  Most often we are speaking of a one-off custom residence.  This means that the house is a “prototype,” with novice Owners technically in charge of the process (because they are paying for this) guided by a Professional Builder.  The set up is just about as ripe for “fun and games” as can be.  Much of the time, miraculously, all goes well.  That is to say, that the final product meets or exceeds the undocumented expectations of the Owners, that it is completed more or less on time and on budget, and that the Professional Builder received his payments for the full amounts invoiced within a week of their issuance.

Mostly.

At the start, either consciously or unconsciously, both parties extend Trust to the other.  The Owners trust that the Builder will produce the best product he knows how at the lowest possible cost (plus his modest fee) and that the Builder will strive to do so as quickly as possible, that his full attention will be brought to bear so that at least three quotes are obtained for all subs and suppliers and that his constant presence at the job site will insure that only the highest level of craftsmanship is delivered.  The Builder trusts the Owners to appreciate his efforts and respond immediately to his invoices without question.  Their agreement, arrived at proceeding commencement of the work, usually consists of a permit set or plan service set of plans without specified finishes or with changes to those specified, and a one page proposal drafted by the builder that has a bottom line cost with perhaps a disclaimer or clause describing some provision for “extras.”  This weak documentation really relies very heavily on the Trust that each party extends toward the other.

Most likely the Builder will have arrived at his costs in the following manner:

1.    He will develop or have developed for him a material take-off
2.    He will secure prices for these materials.
3.    He will approach his favorite subs for prices for their work.
4.    He will derive his own estimates for several line items – both large and small – based upon his data bank of recent experiences, like cutting in an access road, electric service, etc.
5.    He will “temper” much of the above after assessing the attributes of the site.
6.    He will “adjust” much of the above reflecting on his judgements about the nature of the Owner – his partners for the project who are responsible to furnish him with the information he needs in order to proceed in a timely fashion.
7.    He will finally submit a total cost which is the result of all the above PLUS whatever fee he hopes to realize out of the project.

 

Of all of this, the cost of framing usually accounts for 10 % of the final cost off the project, that is to say for a move-in-ready $300,000 home, we are talking about $30,000.  This does not include dealing with access issues for large trucks and structural members or insulation.  It does include all interior floors and walls as well as the exterior ones.  The rule of thumb around here is that more than half of this is for labor, say two thirds, and the remaining third for material – framing members and sheathing.

 

Now for the SIPification.  What changes?  How does this impact the cost?  Essentially we always hear the same old stuff:

1.    SIPs cost more than traditional framing materials.  True.
2.    SIPs take less time to erect than the materials they replace.  True by a great deal.
3.    SIPs include exterior insulation.  Obviously true, therefore --
4.    SIPs allow for the down-sizing and/or redesign of the HVAC system.

So where does this get us?  Two important observations follow, distilled out of years and years of experience in the building world.

Observation One:

Talking about all these procedures in a general fashion gets us nowhere.  Don’t forget about the Statistician who drowned in a lake with an average depth of only two feet!  Each custom house is just that – a unique case, the particulars are what govern the outcome.  Each site is different.  Access may be a problem, maybe not.  The design of the structure may have innately buried in it all kinds of difficulties – or – more likely, the difficulties may be more numerous for SIPs than sticks or visa versa.  The stick framer uses (or doesn’t use) pneumatic nailers, the SIP manufacturer requires a 2x4 spline at all panel joints.  The electrician can’t get the special order rough-in kits until after the contract completion date!

Observation Two:

Decisions about finish materials take precedence over almost anything else.  Granite countertops and plumbing fixtures and fittings are not justified by their “payback,” the same is true of electrical fixtures and appliances.  Even the ordinary HVAC equipment selection is not subjected to analysis and engineering.  No one ever asks, “What’s the payback on this sofa?”  The upgrading that a house goes through in it’s finish-selection-and-verification stage always more than offset what incremental upcharge that may have resulted from utilizing SIPs.

LCA (life cycle assessment) is never utilized to properly validate an envelope upgrade because it can’t be used to justify almost all the other decisions about a home, from where it is sited to what the locksets will be.

So, finally, after all the dust settles where are we?

A $3000 upcharge ( 1% of the project cost) that may be directly attributable to the SIP package will not be priced against the $4000 upcharge from fabric to leather for the living room seating.  Savings in the HVAC equipment will not be credited.  Increased thermal comfort will not be appreciated or valued, neither will be a smaller environmental footprint.  The philosophy of the Owner will drive all the aspects and attributes of the project.  The Builder will look to see that everything (the process) goes smoothly so that a decent profit is realized and that the Owners are satisfied so that a recommendation may be counted upon.

SIPs cost less and make sense.  Who cares? Not most Owners or Builders.  You can’t go out and force your client to use SIPs.  But those who come to you looking for the advantages will be happily rewarded.  The advantages  of SIPs are real and large in both number and value.  Their use in an integrated design which fully exploits their properties may also cost less at the outset.  Much less.

This is a report on where we currently are in our never-ending search for the lowest cost building envelope.  Be advised that is an ongoing project, and that our position may shift at any time.  Like anything else in the World of Design – Mother Nature included – when you go far out in one direction, the other elements of the design become “warped” from their usual aspect.  If you design a tree that can live in the desert, you get a cactus.  If you design a vehicle for maximum fuel efficiency; space, load, and speed performance are usually severely compromised.  This is certainly true in architecture.  What we are talking about here may have limited application because it produces a form/envelope that appears very different from anything in your lumberyard plan book.  These buildings are more barn-like than anything else which should not be a surprise, as their historic roots are in fact, well – barns!

Those who have investigated what the storage/commercial building industry is putting out – or those of us who just observe what is in the built landscape – are well aware of the ubiquitous metal building.  These structures consist of steel frames  - or “bents” – on some large regular spacing dimension called a grid or a bay.  These may run anywhere between 6 to 16 feet.  The steel bents are sort of hockey-stick-like; that is to say that the “business end” of the hockey stick is vertically positioned to be the building’s wall and the handle angles up to be the roof “rafter.”  They are thickest at the wall-to-roof joint because that connection is designed to be rigid and not “hinge” at all.

In a conventionally gabled and roofed box we know that the outward thrust from the rafters wants to push to walls out at the top plate.  We usually resist that in one of two ways.  The most common solution is residential design is to tie the top of the walls together with ceiling joists.  This creates our common attic. When this floor plane would go through a space that we wish to use, we remove it and put in a ridge beam.  By holding up the roof at the ridge we eliminate the horizontal thrust and we may safely remove the ceiling joists.  What the steel bents do is resist this thrust as a bending moment.  That is why the deepest strongest section of the frame is at the top of the wall; this is the derivation of the “hockey stick” shape.  (In fact, this is why hockey sticks have the shape they do.)  Now we need neither collar ties or a ridge beam.

The ordinary steel building has these bents erected at a regular distance – the bay size.  Steel “Z” section girts are installed horizontally connecting the bents.  Similar members are installed along the “handle” part of the bent and are called purlins.  Corrugated steel panels are then fastened to the girts and purlins becoming the walls and roof.  For insulated steel buildings, these panels may be double-skinned with urethane foam cores, but usually fiberglass batting is fastened and hung from the inside of the girts and purlins.  These buildings are one of the most cost-effective ways to enclose large spaces.  That is their strength and that is why they have become so popular in the agricultural and commercial landscapes – places where profit margins are notoriously slim.  This combination of large spans at low cost could not be resisted and the applications have spread.  One may now find them as school gyms, retail space – you’ve all been to Lowe’s or Home Depot, right? – swimming pool enclosures (“natatoriums” to the well-heeled), other warehouses and factories.  It’s no wonder that they shouldn’t be explored for residential construction.  We are now at a point where the curve of ever-increasing home size crosses the curve of large span structural technologies.

We were approached by a local school to design their gym some years ago and were pointed by the building committee in the direction of these metal buildings.  I suggested we forego the limited life expectancy (20 year finish warranty) inherent in this building type, spend a tad more for an envelope that would last much longer and give superior performance throughout to boot.  In short, scrap the girts and purlins, scrap the corrugated steel panels and install SIPs directly onto the bents….well, not directly.  We recommend wood plates be bolted to the steel and the SIPs fastened to the plates.  There are now on the market self-tapping fasteners that are claimed to be able to be used directly into the steel bent top flange.  As you may tell from my tone, we have no experience with them and doubt this would work well in the field.  This gym was built in record time with out any difficulty and the cost was quite low.

We all know that SIPs are available as “jumbo” panels 8 feet x 24 feet.  We set the bents at 12 foot centers to fully exploit the economy of this size.  We used 6” SIPs for the walls and 10” for the roof (EPS core) for a very solid structure with excellent thermal properties.  We had the steel building manufacturer verify the engineering for the bents and fabricate and ship them to us.  The General Contractor had no trouble erecting them and “prepping” them with the wood plates.

We have a job now for a local sculptor who requires a building that has living quarters and workspace combined into a large barn-like structure.  We are recommending this same type of solution for his program.  The budget is tight, but the owner is no fool and wants an envelope that will deliver on comfort and energy efficiency. When you think about it, the larger your house becomes, the more you are mindful of the heating and cooling costs.  The SIPs will receive a drywall finish inside for fire-resistance and an exterior weather-skin of HardiPanels.  Special care has to be taken to detail the foundation/frost-wall/radiant floor/wall/bent connections.  We will need a proper thermal break between the floor and the outside.  Typical metal buildings on slabs do not usually consider this section of the building carefully and are erected on a monolithic pour of a thickened-edge slab which defeats the insulation of the walls and roof.  We plan to utilize at least 3” of XPS rigid foam for our frost wall insulation all the way down to the footing and the same under the entire radiant slab.  This is for a 5750 degree day climate.

Our client has need of the large clear span space that this system delivers.  Normally, for most conventional residential plans, SIPs may be satisfactorily deployed without need of any other structural elements except for perhaps a few purlins or a ridge beam.  However, when large spans – say 30 to 80 feet – are required SIPs alone don’t work.  Timber framing can do this, but at a far greater cost than steel.  Like most things in life, the greatest strength is also the greatest weakness.  To the degree that these structures are cost effective for large spans, they are the reason that for the “normal” spans called for in most residential designs – 12 to 16 feet – they are uneconomical.  Fortunately for us SIPheads, they are also structurally unnecessary.

Although this kind of system will have limited residential application, certainly with respect to “traditional” plans, there remain the few on the outer fringe who will find that this combo-package of SIPs on steel bents at 12 foot centers will meet their needs for large clear spans and a superior thermal envelope.  All at a very modest price.  For commercial applications, I think we are on the toe of an asymptotic up-swinging curve.  While this is written during a period of record-breaking low temperatures, I can only hope that those who commission commercial structures will take note of this and not fall back on those steel buildings that, like fast food franchises, make no contribution toward regional architecture.

In my small corner of the world we are seeing much more interest in SIPs both from the consumer and the architectural sectors than we ever hoped for.  It is poor science to make projections on such a small statistical sample, but interest from another entirely unlikely quarter gives me good reason to have my heart soar like an eagle when thinking of the immediate future of SIPs.

I (we, the SIP Brotherhood) have received endorsement from none other than Frank Lloyd Wright.  Well, not exactly.  He is dead.  In fact, very dead, having passed away to the great Architect in the Sky in the spring of 1959.  However; to the extent that he continues to live through his works and ideas, he is not only still alive, but arguably still remains the most progressive architect out there.

Wright, after the long drought of the Great Depression, in 1935/36 in his mid sixties, spread on the table for us all: Fallingwater, The Johnson’s Wax Building – each one of which could be seen as the zenith of one’s career – and a small $5,000 house; the Jacob’s residence.  Not in any way to detract from the contribution of the other two, I believe the little 1500 square foot building was his greatest work.  It launched his “Usonian” series and contained so many “firsts” that it makes your head spin;

          1. First radiant hydronic slab heat
          2. First carport
          3. First plywood panel non-load-bearing walls
          4. First “composite/built-up” roof system
          5. First lighting/electrical raceway built-in
          6. First compact central “chimney” kitchen

And that’s not all! But this is more than enough for our purposes. (I really recommend you do some research and check out these little Usonia jewels!)

…I guess you get the idea.  A real architectural and technological breakthrough!

Yes, I know this is an article about SIPs.  I’m getting there, a little patience, please.

So the items of great interest for us are numbers 3 and 4.

Wright actually designed these babies to built “upside down;” that is, from the roof down! There were masonry piers and short walls – usually brick – that were built first on top of the slab and then the plywood and plank composite walls were to be inserted under the roof.  Apprentices who “cheated” on Wright and reversed this process and were caught were severely dressed down and sometimes – fired!  These walls were seen as enclosing panels that completed the thermal envelope, but were not structural where clerestory glass ribbons sat between them and the underside of the roof.  They were of sandwich composite construction, comprised of horizontal 1 x 12s and battens screwed together over a ¾” plywood core.  Today, I’m certain Wright would have welcomed SIPs as superior thermal enclosures that would accept the fastening of his unique exterior weather-skins and interior paneling.  Wright was clearly into the large sizes his composite wall panels could attain, and I’m sure he would have great affinity for the jumbo SIPs.

Most interesting of all are the Usonia roofs, number 4 on our “Hit Parade” of firsts.   Wright developed a “composite” roof structural system consisting of three layers of 2 x 4s with the center layer perpendicular to the other two adding up to a nominal 12 inch deep structure.  This enabled him to have a wooden space-frame-like “panel” that could span in both directions or even work with his hexagonal grids at 60 degrees.  These roofs were the technological “key” to the Usonia designs.  Glass could go from floor to ceiling and other traditionally required beams, girder, purlins and framing was – for the most part – eliminated.  This system allowed for glass clerestories to be located at the top of almost all walls.  This “floating ceiling” effect was exploited by Wright to create paradoxical spaces that, with their thick roofs and large overhangs, conveyed a powerful sense of shelter and security, yet at the same time, with the eye travelling from inside to outside along the ceiling plane, delivered a sensation of strong engagement with the outside.  When Wright proudly proclaimed that he had “destroyed the box,” he was really saying that his spaces did not have the overwhelming sense of containment that was the hallmark of traditional western building.

Now it’s perfectly clear to me that there are d—n few roof framing systems out there that give you the opportunity to catch ‘em up and support ‘em wherever your fluid plan just happens to let you!  One can see why Wright had to invent such a system when you experience his buildings.  A brick pylon here, a short wall there, a chimney, a post wherever!  Not much in any regular position holding up the roof!  I have tremendous sympathy for those apprentices who, out of frustration, thought to put the walls up first.

Aside from a true space frame or curved shell construction SIPs can deliver this kind of span capability without even breathing hard.  I know in my heart of hearts that Wright would have loved ‘em!  His Usonia designs are so magical because they deliver experiences and sensations that ordinary stick framing just can’t economically match.  The proof is that these built-up bi-directional roofs were trouble for Wright and his clients.  Their structural performance depended upon the strength and stiffness of the connections between the layers of 2 x 4s and the stability of the wood framing members.  Toe-nailing wasn’t a great way to achieve a really good connection and the wood itself experienced considerable shrinkage across the grain equal, of course, to the 12” of total depth.  While the concept was more than clever in that it also allowed Wright to specify pitch into the build up so as to avoid ponding water on the roof, deflection due to connection movement would be excessive.  Thus SIPs would have performed beautifully for Uncle Frank ( as we affectionately refer to him in our office ) as none of these problems would have occurred.  I guess this is a clear example of being ahead of his time.

It wasn’t the only time Wright designed and detailed for materials that weren’t yet available.  The Johnson’s Wax building had skylights and clerestories of glass tubes sealed parallel to each other.  Too bad this was well before silicone caulk/sealant was invented.  They leaked like crazy until they were finally sealed, decades after Wright’s death, with the silicone we now take for granted.

The issue here is that modern buildings, which are defined as those that don’t have a particularly strong sense of containment ( a solution based on the presumption that the outside world is not hostile ), and that encourage the occupants to engage their environment, use glass and opaque planes under a “floating” roof.  SIPs excel as thermal and structural wall planes, but they can also be utilized as multi-directional roof planes.  Supported on seemingly random points, as Uncle Frank would say, “ As a waiter supports his tray on the tips of his fingers,” SIPs can help you to create a home with a terrific sense of shelter, but also one that is in tune with the contemporary social outlook.

There are some folks who appear to have it all in the housing department.  They’ve got the location-location-location, they’ve got great grounds, a terrific view, southern exposure, all energy-star appliances, first-rate windows, and a bone dry basement.  Just sittin’ on top of the housing world!

Then…