Want to learn all about SIP building?  These frequently asked questions are a good place to start.  Contact us to discuss your own design, build and renovation questions. We always look forward to talking about the benefits of SIPs.

1. What is a SIP ?

Structural Insulated Panels (SIPs) are a high insulating sandwich of OSB (Oriented Strand Board) skins and EPS foam ( Expanded  PolyStyrene) bonded with a continuous film of durable and water-proof urethane adhesive.

2.  How much insulation is really needed in my walls VS roof?

There are many answers to this complex question:

  1.  In a total SIP home, the amount of insulation in the roof need only be slightly more than the walls. When a vented attic is present, roof insulation is much more than walls simply because of attic losses of R-Value due to moisture and drafting. It is also easy to pile in more insulation in a big empty cavity –so why not.. Walls usually make up a much greater area so two level homes will lose more than double the heat of the roof so wall insulation is usually the first place to look for thickening.  Of course in the planning stages of a home this is easy!
  2. How much insulation to use is based on geographic location and the cost of energy to heat or cool your home.  A home in Vancouver will be less demanding versus a home in Prince George. It can be shown that cost effective R32 wall systems in Vancouver creates payback, so 8 ¼” SIP walls in Prince George should be a minimum, and a 10 ½” (R40) wall is also easily justified.
  3. By code, both the 6 ½” SIP walls and 8 ¼” SIP roof work. A builder that builds to code minimums are a sure sign that energy payback calculations are not done or not understood. At today’s low cost of money, it pays to finance thicker SIP’s.   i.e. – Many of our energy audits may show a scenario like an $8.00 per month increase in your mortgage for thicker walls, while saving $20 per month in energy savings.  This is the first month the owners are in the house –not the “payback period”. With the rising costs of energy it only makes sense to insulate your home with the best system available on the market.  A well-insulated home can also decrease the required size of the heating system. In defense of builders deciding against SIPs… on the basis of bill of materials only we add to the building costs, and eliminate a high percentage of framing labor for exterior walls, roofs and floors. So why does a builder want to spend more on materials and reduce his money making labor factor when he is not living there to pay the heating or cooling bills?


3.  What thickness of SIP = the performance of 2×6 framing 24” o.c.?

4 ½” SIP panels exceed the performance of a 2×6 structure with stud’s 24” o.c. Strangely, most framers still work on 16” on center studs so the losses would be that much greater. Window and door losses are also much higher in framed structures due to multiple studs supporting bulky framed headers taking away a lot of area that could have high insulation values from SIPs.  The cost of thickening SIPs is very low compared to thickening a framed stud wall.  Our only cost is top and bottom plates and foam thickening.  Note: 2×6 framing will soon not make the new energy building code.


4.  Why are SIPs better than Trusses?

 That is not necessarily true in all cases. Trusses have their place and benefits. What panels achieve better than trusses is that they insulate much more efficiently and greatly reduce potential for condensation and ice damming at eaves. They also create a very comfortable space at the high reaches of the ceiling. SIPs are also more effective than blown insulation in the attic. Smart building seminars sponsored by the Home Owner Protection Office (HPO), tell us that an R40 SIP roof performs approximately the same as an R65 insulated attic and this is because the attic is gone and so is that moist and hot area in summer and very cold and drafty and icy in winter.  Roofers also LOVE the solid feel of the top side of SIPs –especially for steel roofs and the symmetry is very much appreciated by steel roofers.


5.  How is electrical installed in the walls?

 There are 1 ½” diameter chases located in the middle of the walls and roofs. For walls, there is a vertical chase every 4’ from top to bottom and horizontal chases at 16” and 45”.  Furthermore we also cut in electrical plug boxes and set pull lines to exterior lighting locations so that electricians can get right to work instead of dealing with cutting the boxes out and hoping they have hit a chase.  This eliminates extra charges that most electricians have levied on SIP home owners for figuring out where the chases are and cutting boxes. In some cases the pre-cut boxes actually make SIPs quicker to wire than framed buildings.


6.  I like the idea of warmer SIPs, but for windows and doors do I have to pre-consider and lock into all of my decisions?

 Doors and windows in most cases are very easy to change after panels are installed –though structural verification must be done for such changes. Modifications are much more easily done in a matter of seconds on the computer model than expensive site time that holds up completion.

We provide perspective drawings and elevations of your home to see the windows in a ‘reality’ setting as well as put passive solar gains as a design priority. This pre-planning is much easier and less costly than going through the house later with changes needed after it is built. Also framed wall changes cost more than changes on a SIP wall.


7.  Can I add windows or change the size later if it looks too dark?

Very easily – though again with our 3D imaging we can do sun studies to see internal lighting effects during the days if these decisions are important.  The little things that matter are often suggested by us like putting a window in the walk-in closet.  We often suggest small changes in window sizing or location to further improve the preparation time of the SIP package. This translates into savings in labor for the cost of the package.


8. How is plumbing run through the panels?

Plumbing vents can be accommodated with a special chase.  Water and drain pipes should never be run within any exterior walls since the potential of freeze and failure can occur. In the event of pipe leakage potential wetting of a lot of insulated wall area is high and you would not want that to be going through your exterior walls on any type of construction.


9.  How is condensation in roofs and walls avoided and how does this improve R-value?

The presence of solid foam at the outer 3” to the cold side creates a complete absence of air in the zone where dew point temperatures can trigger condensation. This eliminates the potential of wetting, unlike batt insulation which is designed to trap air and use the air as an insulator. The daily heat up and cooling cycles within walls and attics develops condensation on most days that demand ventilation to avoid wetting and rot. In a framed wall with batt insulation when the air in the wall heats from sun heating the surface the air’s ability to hold more moisture increases.  When the surface loses sun and dew point is reached the moisture in the cooling air condensates in the wall or attic. Furthermore the venting and motion of air from venting also displaces the air that is trapped in the insulation and increases the loss of effective R-value since the air is not truly trapped. Solid foam 3” deep on the cold side will avoid condensation conditions. Batt insulation efficiency drops as it is moistened and this also is the start of ideal mold growth conditions.


10.  How can SIP BC guarantee zero drywall cracking?

The stability of the walls and window headers is attributed to four things that lead to good drywall performance.

  1.  1. With lack of internal wall condensation there is no movement across the wall thickness that occurs in framed walls as lumber takes on and lets go of moisture.
  2. The anti-racking stability (wall movement lengthwise) from SIPs due to OSB each side and a full adhesive bond stabilizing it makes the wall naturally stable to high wind loads and seismic.
  3. During extreme cold cycles the lack of cold to hot gradients stabilizes the response of the wall.  The lack of lumber in the wall and the fact that there is no off-gassing of the EPS –it does not contract either.
  4. Our 8 ¼” and 10 ½” SIPs utilize zero thermal bridging panels around windows and doors and full insulation headers also warms up the linings around windows to eliminate condensation in this critical area.


11.  Why do you promote SIP panels to run high through the floor joist level?

Better structure, thermal, air seal, labor: This improves the thermal performance at the floor joist area, which can lose more heat than the whole area of a warm SIP wall since it is a challenge for insulators to deal with.

Properly  apply insulation and air seal.  It also improves the structure by getting rid of the rim board box joist which is difficult to fasten well to the walls and eliminates a shear failure area. Labor to install top mount joist hangers is less than setting a rim board. It also shortens the total length of the floor joists which may allow less material purchased.


12.  TALL WALLs -How are SIPs better? 

More strength, better insulation, straight, lower labor factor. SIPs can rise high with precision straightness while tip-up weights are less than half of a framed wall. Framed tall walls require studs closer together and a lot of blocking which robs insulation and increases labor.


13.  How can HPO smart building seminars claim that solid foam at the outer area of a roof outperforms attics?

Attics –even well ventilated attics get very hot in summer. This increases the temperature that the insulation must work against to keep the home cool –so R40 solid foam at the exterior is more effective than R60 in the attic.  Furthermore there is daily condensation especially in summer and this condensation sits and collects on the vapor barrier supported by the drywall.  Ice damming is eliminated –which quickly ruins shingles and can result in internal wet damage from the roof leaking.


14.  How do SIPs get their strength?

The full bond of OSB to foam each side plus the amount of area of the wall makes the wall function much like a really high strength I-beam where the OSB is the flanges of the I-beam and at the middle of the core of foam there is neutral stress.  The OSB keeps the wall straight and strong.  A SIP is tested to easily exceed the strength of framed walls.


15.  How do you deliver lumber splines and zero thermal bridging at the same time?

We turn the lumber to the faces of the panel. This doubles the opportunity for gasket sealing as well.  This also provides lumber inward and out for additional thickened hard points to fasten to. Where we have beam point loads we double the lumber on the side the beam is coming from.

16. Can I use SIPs for the whole house?

Walls, Roof, Floor. SIPs can work everywhere that insulation is required.

  • Walls needing insulation –SIPs cannot be beat on a $cost / R value basis –of any system. Our Canadian climate winter or summer justifies a R32 to R40 wall assembly winter or summer.
  • Roof assembly in SIP makes sense for many areas. Compared to hand framed areas –extremely cost effective. For long spans trusses may be more appropriate –though ganging of trusses to make girders over a long span area is a great way to support SIPs.
  • As a floor SIPs are extremely comfortable to walk on, but are only cost effective when placed over top of exterior zones or over a garage area. The comfort of a room with a cold floor zone is at the expense of a lot of heat being poured into that room.

17. Why should I choose SIPs over a traditional stick built home ?

SIPs will eliminate 98% of thermal bridging associated with stick framing. This increases the net system R-value delivered. Example –a 2×6 framed wall at 16” o.c. with R20 insulation will deliver R-15 at best and worse where openings exist due to cripple and header support losses.

18. What is the cost comparison between a SIP Home and a stick built home ?

Final installed cost of SIPs similar thickness will be about $1/ft2 more than framing –However the SIP will also deliver at least 40% more R-value and a better start to delivering an air tight home. If the framed system adds foam on the exterior to match R value the materials and labor would make the framed wall more expensive as well as much thicker.

19. What is R-Value ?

R-value can be thought of as the resistance to exchange heat in the presence of a heat difference inside to outside.  For R-value, the higher the number the better the insulation. You may also see “U-Value” or factor which is the inverse of the R value number so lower is better. Window and door assemblies use this and the number is used to include the net total insulation of the pane and frame assembly.

20. Are SIPS insect resistant ?

Premier SIPs are resistant to insects by way of a component of Borate in the foam when it is formed. This will ‘slow down’ insects –but is not a warrantee per say. EPS will never be a food of preference for any bugs or insects –but like any insulation are is a desired nesting material. The borate component lowers its desired value to bugs to nest in it or use it for nesting. Local prescribed anti-insect measures will be necessary to mitigate effects of insect infestation.  There are also improvements available to the sheathing with use of treated OSB for special applications. Topical treatments of BluwoodTM to OSB contains a borate component and it also eliminates molding potential as well as takes the OSB to a ZERO flame spread rating.


21. How long does it take to get SIPS delivered to our site ?

Under normal circumstances four to six weeks should be anticipated. Simple and smaller jobs can one to two weeks. Larger more complex residential  or commercial jobs may take 6 to 12 weeks depending on seasonal demand and engineering required.


NEXT : 10 Reasons Why SIPs are Better and Why You Should Build a SIP BC Home