SIPs 101

Steve Maxwell

Canada’s Handiest Man

Questions and Answers about SIPs

Steve Maxwell

Canad’s Handiest Man

Are Structural Insulated Panels More Expensive?

Short answer – No.  Comparing the costs of Structural Insulated Panels to stick & batt is not an “apples to apples” comparison.  A Structural Insulated Panel wall systems includes all of the elements required in a standing finished wall section; exterior sheathing, structural elements, insulation and vapour barrier.

Whereas a stud wall is cut and framed then sheathing has to be installed, insulation must be installed and an air vapour barrier must be added. Now with new Energy Codes in place in many jurisdictions a layer of rigid EPS foam must be added to the exterior to meet Code.

We have to mention that EPS insulation used in SIPs and other IPB products provides 30% more insulation than fiberglass batt insulation. SIP construction has superior air tightness.when compared to wood framing and provides double the strength.

The savings for the builder comes from significantly reduced labour hours.

The savings to the building owner comes from reduced building operating costs because of built in energy efficient construction.

What is an Advanced wall system?

“Advanced wall” or “Advanced Building” systems combine energy efficient insulation and air barrier tightness with structural properties into a building code compliant material.  There are 5 recommended systems recognized to be Advanced Building Systems: SIPs, ICF walls, double wood frame, wood framed / fiberglass with rigid foam added and panelized.   As you can see, four of five use rigid foam.

For more information on this see “The Benefits of SIPs”

Does it take longer to build with SIPs?

University studies comparing side by side construction of two identical size houses in Ontario, one wood framed and built with Structural Insulated Panels (SIPs) proved that building with SIPs is approximately 50% faster.  Empirically, building contractors that have used our SIPs, tell us that they can stand the walls of a medium size home in 7 to 9 hours, plus when they add a SIP roof they can have the roof on the next day and locked up on the third or fourth day.  That’s well under half the time it takes to lock-up a wood frame home.  Equally important, DIY home builders have similar experiences building with SIPs.

see: R.S. Means SIPs versus Wood Frame Construction

For more information on the advantages of IPB insulated wall panels Panels go to: “The Advantages of Building with SIPs”

What is the R-value of SIPs? / Is it about the same as wood frame construction?

The measured R-value of EPS is approximately 30% more than the R-value of fiberglass insulation.
R-value is the measure of thermal resistance calculated in a laboratory using specific values under perfect conditions.  So for instance a bag of R-18 fiberglass insulation, intended for installation in a 6 inch wall cavity, has a measured or material R-value of 20 – 22.  The same size SIP wall has a measured R-value of 27.

New building codes no longer accept measured R-value, compliance calls for “effective” or “whole wall” R-value.  Effective R-value measures the performance of the whole wall after it’s constructed.  Effective R-value is obtained by calculating the insulating elements in the wall and then subtracting the thermal bridging elements in the wall.  A wall constructed with SIPs will have an effective R-value of  R-24 while the wood framed / fiberglass insulated wall will be around R-14.

In fact new building codes require builders to add EPS to the outside of  wood framed walls in order for them to achieve compliance standards. Our question is: why wouldn’t they just use a SIP wall to begin with?

Does EPS foam insulation off gas or contain CFCs and HCfs?

Decade long studies prove that EPS foam insulation does not shrink (in scientific terms – drift).  Which means it does not off gas.  Some rigid foams drift but not EPS.  EPS  is 98% air & only 2% is a plastic. which is why it makes great insulation!  EPS insulation can return up to 200 times the amount of energy required to produce it, and reduce emissions by up to 100 times the volume produced during the manufacturing process. In fact EPS has the highest Life Cycle Benefits for all insulation products and its recyclable.  EPS is manufactured using a low-environmental impact process of steam expansion that uses pentane and contains no CFCs (Chlorofluorocarbons) or HCFCs (Hydrochlorofluorocarbons)..

Does OSB contain formaldehyde?

Urea formaldehyde is no longer used as the bonding agent in the process of manufacturing OSB and has not been used for many years. Phenol formaldehyde is a naturally occurring chemical found in almost all trees, apples, toothpaste and even blood. Minuscule amounts of phenol formaldehyde can be found in  in OSB but levels are so low that it is nearly impossible to measure.

Why not build with conventional wood framing?

Testing shows that a 61/2 inch wide SIP manufactured wall, with 51/2 inches of foam, has an R Value of R-27 compared to a 2 X 6 dimensional framed wall assembly with fiberglass batt insulation which has an R Value of R-14 because of lower r-value of  the fiberglass insulation and thermal bridging at the studs.  Thermal bridging happens when heat and cold is transferred from the inside of an exterior wall through a wood or steel stud to the outside.  Continuous foam insulation in a SIPs panel eliminates the bridging effect.

Airtightness is also a major factor in comparing a SIP wall to conventional construction.  Air blower tests show that a SIP wall measures approximately 0.2 air changes per hour compared to 2.0 air changes per hour for a wall built with studs.

Why are SIPs more environmentally responsible?

When you build with SIPs, you are constructing a building that can save 50% or more on energy costs when compared to conventional stick frame construction. That means less fossil fuel consumption and less greenhouse gas emissions. SIP technology provides higher “whole-wall” R-value, tightens the building envelope, and reduces air infiltration. That allows you to downsize the heating and cooling equipment. It is the combination of these systems that makes up the technology of a high-performance SIP home. You will also enjoy the green building benefits of less job-site waste, better utilisation of material resources, and more environmentally friendly building practices.

How do SIPs save so much labour?

Cutting and fabricating, based on your construction drawings, are done for you in our manufacturing plant. Panels are delivered to the project site ready to assemble. Site labour is reduced because of less measuring and cutting lumber to fit, no installation of sheathing and fiberglass or spray foam insulation plus vapour barrier seal. As well the time building materials are exposed to the weather on the job site is reduced.  In general the project is “dried-in” sooner. That means other subcontractors can get a head start on the jobs they need to do, interior finishing is faster. drywall installation is quicker, windows and doors installation is quicker, and installation of cabinetry is quicker. 

How do you wire SIP houses?

IPB standard wall panels come with four wire chases in every panel, two horizontal and two vertical.  Wire chases are marked on each panel. During wall assembly bottom and / or top plates and wall connection splines are bored to match up with chases to pull wires through. An electrician simply “fishes” the wire through the chases as required, standard electrical boxes are installed either using a router, jig saw or hole saw.

In the event that an electrical box needs to be added, it’s easy, a series of short shallow cuts are made into the wall panel, EPS foam is removed wiring is installed and the cut is covered.

What about plumbing in SIP walls?

SIP walls are generally used for exterior walls only and plumbing is not usually installed in exterior walls, but rather through the floor into the bottom of cabinets.

Where exterior wall vent-pipes are necessary, chases can be formed in the foam cores.