Appropriate SIP Applications
Written by Dave Stevenson
Welcome again to the Insulspan SIPs’ blog. This time I’d like to discuss Appropriate SIP Applications.
I have heard it be said “if you can build it with 2x framing, you can build it with SIPs”. Generally speaking, I suppose this statement is correct. On a more practical level however, I think it’s important to understand the most suitable applications for SIP construction in order to achieve all of the benefits that led to the decision to use SIPs in the first place. I will be delving into the benefits of building with SIPs in future blogs, but suffice to say that the big 3 are energy efficiency, speed of construction, and factory built quality.
Any architect, engineer or general contractor knows that incorporating the right building product into a project is crucial to the project’s success. And choosing just the right product from all of the choices can be a difficult decision. The final decision usually comes down to several factors pertaining mainly to structural capacity, aesthetics, and ease of construction. Even though a homeowner may be ‘sold’ on a certain product, sometimes compromises are necessary to get the mix just right. To use a cliché, there is no point trying to fit a square peg into a round hole.
That brings us back to SIPs: Where they work best and where they don’t work.
For the most part, with the walls in particular, SIPs can be substituted quite easily for a stick framed wall. Some accommodations have to be made depending on seismic zone applications and heavy wind load areas, but the statement “if you can build it with 2x framing, you can build it with SIPs” generally applies. The roof however, is a completely different animal altogether.
I can’t tell you how many people have called to tell me that they have made the decision to use SIPs on their next building and then proceed to send me architectural drawings specifying a truss roof. When I call the customer back to confirm that their intention is to use panels for the walls only, the invariable answer is “no, I want SIPs for the roof, too.” Good grief!
It is important to understand that panels are not intended to be installed on top of standard trusses; they are intended to replace them altogether in order to create design possibilities more easily achieved with post and beam construction. This upper space can be left ‘as is’ for a vaulted ceiling above a great room, a mezzanine level can be added, or even an entire upper floor. This doesn’t mean that because the panels are structural they can support themselves, nor does it mean there are magical skyhooks holding the roof panels in place. In fact, the panels still need to be supported by beams or rafters of some sort, but the post and beam design results in an open space that would otherwise not be possible using standard trusses. The maximum span between the support beams depends on the snow load, the thickness of panel, and the spline connection at the panel joints.
So buildings designed with regular trusses and attics are not suitable to SIP roofs. What else?
Hip roofs are also tough to incorporate into a SIP building because the beams and posts required to support the SIPs are difficult and expensive to design and install. The hip beams typically obstruct head room, and the posts often have to be located right in the middle of the open space below the intersection of the hip beams and the ridge beam. Keep in mind that all beams and rafters need to be supported and this is usually accomplished by incorporating posts into the exterior wall panels. A house designed with SIPs on top of a hip roof can be a real challenge for the designers and engineers who want to keep the area open and post free.
On the other hand; flat roofs, gable roofs, shed roofs, winged roofs, gambrel roofs, and even roofs with dormers work very well with SIPs. It is important to get the roof support in the right location of course, but any designer or architect with a set of connection details and load span tables should be able to incorporate SIPs into their design and meet the three objectives of structural capacity, aesthetics, and ease of construction. (Link to pictures and roof plans) Keeping in mind that standard panel dimensions are 4’ wide and up to 24’ long, roofs built with SIPs can be extremely quick to install, with minimal thermal bridging.
I mentioned earlier that “for the most part, 2x stick frame walls can easily be replaced with SIP walls”. The one caveat to this statement is ultra-modern buildings with exceptional amounts of glazing. One of the benefits of using SIPs is that because of their 4’ modular nature they can reduce thermal bridging by eliminating much of the dimensional lumber that would typically be found in a stick framed wall. If thin panels packed with 2x material to support headers or massive shear resistance are being used between windows, then there really isn’t much point. SIPs are better suited to walls with normal openings and lots of wall area where the 4’ panels’ inherent R-value, air-tightness and reduced thermal bridging can fulfill their true potential.
That is all for this time but please be sure to comment or raise questions about this blog, or SIPs in general. I am interested in hearing your thoughts and want to encourage a discussion that will create more interest in the product and lead to a better educated readership.
Insulspan Division, PFB Corporation