What Are Structural Insulated Panels (S.I.P)?

Structurally Insulated Panels (SIPs) consist of an insulating polystyrene core sandwiched between two structural panels. The exterior panels are often oriented strand board (OSB) but can be other products like plywood, sheet metal, or cement board.

Structurally Insulated Panels (SIPs)

The interior insulating material in SIPs is usually rigid foam board insulation. Expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (ISO) are the most popular products. Other options are Polyurethane foam (PUR) and composite honeycomb.

How S.I.P Panels Are Made

Most structurally insulated panels are manufactured in factories and shipped to construction sites for erection. Recent technological advances allow SIPs to be manufactured on job sites. On-site construction allows for better control of custom-made components, but size, space, and logistics can make it difficult.

The manufacturing process depends on the type of insulation used in the sandwich– either rigid foam board or liquid injection.

Polystyrene S.I.P Panel Manufacturing

Processes vary by manufacturer, but in general, manufacturers cover the faces of the rigid polystyrene with adhesive and apply the exterior rigid panels. Each panel is clamped, heat is applied, and it’s held in place until the adhesive is cured. Manufacturers use the same system regardless of the exterior panel.

Polyurethane S.I.P Panel Manufacturing

To create Polyurethane S.I.P. panels, manufacturers inject Polyurethane and polyisocyanurate insulation between the structural panels as a liquid. The panels are set into clamps and act as the mold. Once inside the mold, the liquid expands to fill the void. They allow the foam to cure and then remove it to complete the process.

Indoor Air Quality of S.I.P Houses

Airtight SIP buildings prevent air infiltration. Tighter draft-free buildings allow for better control of incoming air with an HVAC system rather than depending on gaps, cracks, and holes for proper air exchange.

Ventilation system designs vary by climate – all have filters, some have dehumidifiers, a few have air-to-air heat exchange systems, and most have automatic controls. Choosing the proper HVAC system will help make any SIP house comfortable and mold-free.

S.I.P Environmental Sustainability

Structural Insulated Panel buildings are environmentally responsible. They eliminate onsite labor costs by up to 55%, reducing waste, vehicle costs, emissions, and many environmentally harmful products.

R-Values of Structural Insulated Panels

R-value is a measure of a material’s thermal resistance. The cost of heating and cooling a house can be as much as 50% of the total energy cost. The choice of insulating material and how airtight the building envelope is can save thousands of dollars during the building’s lifespan. It also impacts comfort.

R-values are assigned as the result of controlled tests conducted at 75 degrees F. Each product is tested individually; rather than a test of the entire building envelope. Whole house R-values are affected by all of the building components.

  • Thermal Bridging. The R-value of softwood studs is about R 1.4 per inch. So, even with R-20 fiberglass batt insulation, the 2 x 6 studs create a thermal bridge every 16”–with an R-value of around R-9.0– reducing the overall R-value.
  • Air Infiltration. R-value measures heat conduction. Air infiltration or exfiltration is convection. Air leakage is responsible for up to 40% of a home’s heating or cooling loss.
  • Thermal Performance. Thermal performance is a description of how insulation and building envelopes act outside the laboratory. Some insulations lose the R-value as the temperature decreases. As shown by the following chart, the SIP wall’s R-value will increase as temperatures decline.


How are electrical wires and boxes installed in SIPs?

Wiring is pulled through chases–precut channels in the foam-  according to the house wiring diagram.

Do SIPs require ventilation?

Yes. When properly constructed, SIP buildings are extremely airtight. They do not meet the required 3 air changes per hour without HVAC assistance.

Do SIPs meet fire codes?

SIPs with a minimum of ½” drywall or other non-combustible material have the same fire rating as stick-framed houses.

Does an attic with a SIP roof system require ventilation?

No. It does not require vents. The attic may be ventilated by the HVAC system.

Do SIPs meet building codes?

Yes. SIP construction is covered by Section R610 of the International Residential Code (IRC). This code is the basis of most US building codes.

How is siding attached to SIP homes?

Most siding manufacturers recommend attaching siding every 16’ into studs. SIPs have very few framing members, so siding requires more nails, screws, or thicker sheathing to provide proper attachment. The siding manufacturer, an architect, or an engineer can decide the appropriate fastening frequency.

Can you install plumbing in SIP’s walls?

Plumbing can’t go in a SIP’s walls because of the possibility of freezing. Designers should locate plumbing on the interior walls or build a box around wall-mounted plumbing if it must be on an outside wall.

Are SIPs mold and mildew resistant?

Yes. Properly constructed SIPs are airtight and watertight, which eliminates mold growth medium.

Are SIPs susceptible to termites?

Termites do not feed on the foam in SIPs but could hollow it out for nests. Some SIP manufacturers offer Borate-treated foam and/or wood panels.

Can you use asphalt shingles on SIP roofs?

Yes, but some shingle manufacturers will not warranty their product when installed on unvented SIP roofs. Look for an asphalt shingle product with a warranty, or choose different roofing materials such as steel.

Do SIPs contain harmful chemicals?

No products in SIP house components contain harmful chemicals or Volatile Organic Compounds (VOC).