Learning about Structurally Insulated Panels
At the end of my day in the office, I had the opportunity to visit a local structurally insulated panel (SIP) manufacturer and learned so much about the both the structural capabilities and insulation values of this material. Until we met with the manufacturer, I’ve only heard of the material being used on some projects, but I’ve never learned about the material’s properties. Just like any meeting with a building material manufacturer, I was able to learn so much about SIP panels and understand the benefits of using it in some of our office’s architecture projects.
I’m sure there’s so much more to know about SIPs, but here are some of my general notes!
What are structurally insulated panels?
SIPs are a composition of rigid insulation that is sandwiched and glued between two oriented strand boards, which are better known as OSB. This combination of materials creates a panel that is both structural, insulated, and has an embedded vapor and moisture barrier. The rigid insulation can vary in thickness, but it will typically follow the standard sizes of lumber so that the lumber can be inserted on the tops and bottoms of the SIP panel for structural support.
How does SIP construction work?
When an Architect designs a project that will use SIPs, they will generally involve the SIP manufacturer from the beginning of the design process so that they can provide insight into the constructability of the design. The manufacturer will be able to point out any issues related to size, shape, insulation values, types of fasteners, and specific details for the project. Once construction beings on the project, the SIP manufacturer will produce shop drawings for each panel based on the Architect’s design.
After the Architect approves the SIP manufacturer’s shop drawings, the SIP panels are created in the warehouse and any openings for windows or doors are accurately cut out of each panel. The insulation at every opening is cut out of the OSB to the depth of a standard piece of lumber that will be inserted in the new void between the OSB. This will allow windows and doors to be screwed into the lumber for support.
Once each panel is constructed, it receives a code or label from the shop drawing set and is shipped out to the site. When it arrives, a small team of construction workers are able to lift each panel, bring them to their location, and tilt them into place. The top, bottom, and sides of the insulation between the OSB of every panel are cut out so that the SIP can be placed over a standard piece of lumber for structural support (as seen in the image above).
When two panels are connected end to end for a longer wall, floor, or roof, the insulation will be cut on both interior and exterior sides of the SIP. An OSB tab will be inserted, glued, and screwed on both sides to connect the panels together. This creates a rigid and continuous wall with no thermal breaks. To create a corner, a piece of lumber is anchored to the OSB at the end of the SIP panel and the OSB of the perpendicular SIP panel is placed over the lumber. The lumber and perpendicular SIP panels are anchored together and a rigid wall is created.
How are electrical conduits installed in SIPs?
After the shop drawings are created by the SIP manufacturer and the panel is constructed, it is turned on its side and a hot steel sphere is dropped onto the insulation. The hot sphere quickly melts through the insulation, leaving a cylindrical void through the entire panel. These voids are aligned in each SIP so that an electrician can install all wiring through every panel.
What about the structural capacity and moisture resistance of the SIP?
If we compare the standard 2x4 wall with wood studs every 16 inches on center with a similar sized SIP, the SIP is more than two times stronger than the typical stick frame construction. It’s also very simple to install and only requires a small group of workers to lift each piece into place. In most cases, one SIP can be installed up to a maximum of 12 feet in height and could be stacked on top of one another up to 36 feet. Beyond this point, a structural engineer will need to calculate loads and determine if additional structure will be necessary.
In terms of vapor barriers, the glue that binds the OSB to the rigid insulation naturally creates a vapor barrier within the material. The OSB and glue act as a vapor barrier for the SIP and any gaps are spray foamed on site. When materials are joined end to end for longer walls, more glue and OSB is added for both structural support and to maintain a continuous vapor barrier.
What are some things to consider when using SIPs?
One of the downsides to using SIPs is that the OSB finish for the panel creates a seamless and continuous vapor barrier and cannot be changed to finish grade plywood because of its size and finish. In essence, you can either keep the SIPS exposed with the look of OSB, or you can finish the SIP with a material like gypsum wall boards. The finish will also have to be applied on site because it can’t be applied in the manufacturer’s warehouse.
Regarding the turnaround time for producing SIPs, this generally varies, but will be no less than two weeks from the Architect’s final approval of shop drawings. However, if the Architect is working with the SIP manufacturer throughout the design and construction drawing process, the timeframe for constructing each panel is shorter because all parties will have a mutual understanding of the project.
The last thing to consider when using SIPs is that pipes and ducts cannot be embedded into the panel because it’ll take away from both the structural capability and insulation values of the panel. These will all have to be considered and built over the SIPs within a chase.
Structurally insulated panels are a fantastic building material that might appear to cost more upfront, but will save a project more money over time. When using SIPs in a project, construction teams are smaller and they’re able to finish projects in an exponentially shorter time period than the standard stick frame construction. Buildings constructed out of SIP panels are also about 60% more efficient in energy use because of the insulation values.
This meeting with a local SIP manufacturer was fantastic and my team and I were able to learn so much about this building material. I’m sure there’s a lot more to learn about SIPs, but I’m looking forward to potentially using it in a future project!
Let me know what you think and if there’s anything I might’ve missed in the comments section below. Until next time, thank you for reading and joining me on my journey as an Architect!