Building with Earthwise SIPs

Before commencing construction on a SIP project, several important considerations must be addressed during the design phase.

Is SIP the Right Choice for Your Project?

Depending on the nature of the project, the designer or builder must evaluate whether Structural Insulated Panels (SIPs) are the optimal choice for walls, roofs, or floors. SIP floors are typically reserved for scenarios where the underside of the floor is fully exposed to the elements, as seen in homes constructed on pilings.

SIP walls, on the other hand, can be employed in virtually any situation suitable for wood frame construction. They offer enhanced strength compared to conventional wood frame walls, and their generous sizes provide various advantages in terms of design and installation.

The decision regarding SIP roof usage hinges on the roof design and the feasibility of incorporating a supporting structure. Certain architectural styles, such as craftsman-style homes, timber frames, Cape Cods, or A-frames, lend themselves well to SIPs, particularly for framing and insulating vaulted ceilings. In many instances, roof trusses may align better with the home's design than a SIP roof system. Hybrid systems, such as SIP walls combined with a truss roof or a SIP roof atop insulated concrete form (ICF) walls, are common approaches to creating high-performance homes.

• Do You Require a SIP Designer?

When working with pre-existing home plans or construction documents initially intended for conventional wood framing, these drawings must be adapted for SIP construction. Typically, this task falls to trained SIP design professionals or is a service offered by a SIP provider. The builder, client, and architect (if involved) will collaborate to review the SIP designs, ensuring alignment with the original construction documents.

Completed SIP layout drawings encompass all critical information essential for SIP package installation. In contrast to architectural drawings or construction documents, SIP layout drawings exclusively focus on the SIP building envelope and other structural elements necessary for SIP installation.

Is an Engineer Necessary?

It's advisable to consult with an engineer to determine whether additional structural engineering is required for your specific SIP project.

When opting for SIP floors, the SIP designer will determine the suitable panel thickness based on the span required for the floor panel. Additionally, they will craft a foundation connection detail (refer to diagram below) to ensure proper bearing on the foundation system. This detail serves a dual purpose by safeguarding against moisture intrusion through effective air infiltration sealing and incorporating a capillary break of treated material between the SIP and any concrete surfaces.

Point loads represent a crucial consideration when it comes to SIP floors. If a soft floor covering such as vinyl or carpet is specified, it's customary to add a second layer of floor sheathing over the SIP floor. Point loads within the wall system can also pose concerns over SIP floors, potentially necessitating blocking or direct support from the foundation.

The responsibility of determining SIP wall thickness typically falls within the designer's domain. The selection of wall thickness involves a delicate balance between insulating capacity and structural performance, where thicker SIP walls offer increased thermal resistance (measured by R-value) and greater resistance to lateral loads. Given that a significant portion of energy efficiency in SIP buildings stems from airtightness, it is advisable for designers to contemplate comprehensive whole-building energy modeling when establishing the requisite R-value for SIP walls.

Foundation Connection

SIP walls can be supported in two primary ways: atop a platform-framed floor system or directly on the foundation. Platform-framed floor systems sometimes introduce air leakage concerns, making SIP walls designed to bear directly on the foundation a preferred choice for enhanced airtightness. However, this approach necessitates a wider foundation with relatively precise tolerances.

In cases where SIP walls rest directly on a concrete foundation or concrete slab, it is essential to include a capillary break comprising treated plywood or treated lumber beneath the SIP wall. This crucial measure acts as a safeguard against moisture infiltration.

Where two SIP walls intersect at a right angle, dimensional lumber end plates are introduced into the foam recesses of both walls (as illustrated below). These walls are subsequently fastened together using panel screws. It's essential to bear in mind that this particular lap detail results in one of the walls being slightly shorter than the overall building dimensions.

Spline joints are employed for connecting panels in the same plane, applicable to both wall and roof panels. Within a SIP layout drawing, spline connection details also indicate the precise locations where sealant must be applied to establish an airtight seal. The sealing process stands as one of the pivotal elements in SIP installation. Panels that are not sealed correctly can give rise to issues like moisture damage, mold, rot, and even structural failure.

A surface spline connection, as illustrated below, comprises two strips crafted from OSB or plywood. These strips are inserted into pre-made slots within the foam core of the SIP. Subsequently, they are securely fastened by nails driven through both faces of the panel, establishing a reliable connection. One notable benefit of this panel connection method is its ability to circumvent the thermal bridging issues that can arise with lumber connections.

An alternative approach for intermediate floors involves employing a hanging floor system, as illustrated below. This method incorporates a top-mounted joist hanger fastened to the upper portion of the first-floor wall. Hanging floors are often preferred for their enhanced energy efficiency, as they effectively eliminate the possibility of air leakage through the floor system or rim joist area.

The connection between walls and roofs can be established using either a bevel-cut SIP wall or a square-cut SIP wall, contingent on factors such as roof pitch, roof system type, and the Earthwise preference.

In a bevel-cut approach, the SIP wall has been precisely cut to match the pitch of the roof. Top plates are inserted into the foam recess at the upper section of the wall panels, serving both as support and as recipients for the panel screws used to affix the SIP roof system.

Alternatively, when a SIP roof is situated atop a square-cut SIP wall, framing teams must introduce bevel-cut solid lumber at the wall's uppermost section to align with the roof pitch and provide adequate bearing for the roof panels. Regardless of the chosen method, it is essential to recognize that the wall-to-roof connection constitutes a pivotal sealing area in the construction process.

In numerous instances, window and door openings within SIP walls can be created without the necessity for a structural header. Opting to forego structural headers whenever feasible not only reduces thermal bridging but also streamlines the construction process. SIP manufacturers have conducted extensive testing and released load tables specifying the maximum permissible spans for door and window openings without requiring the addition of a structural header. These determinations factor in the opening's width and the structural forces exerted on the wall.

In cases where these prescribed limits are exceeded, designers will prescribe structural wood headers, which can be constructed from dimensional lumber, engineered wood products, or even pre-manufactured insulated headers. These headers are adequately supported by posts or dimensional lumber that are integrated into the SIP wall panels on both sides of the opening.

A pivotal decision undertaken by the SIP designer revolves around the selection of roof panel thickness. Thicker SIPs offer superior R-values and can span more extensive distances. In determining the appropriate panel thickness, the designer must take into account various factors, including the overall design loads, comprehensive whole-building energy modeling, the required span distance, and the project budget.

When addressing roof spans, designers must also evaluate the type of spline connections utilized between the roof panels. While dimensional lumber or engineered lumber splines enable panels to span greater distances, it's essential to acknowledge that these products introduce a thermal bridge, potentially impacting energy efficiency and project costs.

Multiple options exist for supporting a SIP roof, with ridge beams, purlin beams, and load-bearing walls being common components in designing a system that effectively upholds the SIP roof panels and aligns with the building owner's interior space requirements.

Ridge Design

A frequently employed detail in SIP roof design involves the merging of two panels over a ridge beam at the roof peak. Roof panels are securely fastened to the ridge beam using panel screws. This region is another critical point for air sealing, and many Earthwise recommends the use of specialized SIP tape in conjunction with expanding foam or mastic sealant to ensure proper sealing.

Certain geographical areas across the country are subjected to extreme conditions such as high wind loads, heavy snow loads, or seismic activity, necessitating additional design deliberations for SIP structures. SIPs remain a feasible choice for nearly all scenarios where conventional wood framing is employed, provided that the structure undergoes thorough and appropriate design and engineering processes. The intricacies of these techniques extend beyond the scope of this book. Therefore, if you find yourself constructing within one of these regions, it is advisable to collaborate closely with you Earthwise Manufacturing and building code authorities to ascertain the specific design requisites.