Studies show that out of 8,000 homes that underwent tests over a 10-year period 50% failed to achieve the standard ACH or air changes per hour that were set for E80, traditional built standard houses. And, only 0.2 percent performed better than the set rate.


It is possible to achieve the standard ACH rating using traditional materials but the pain of achieving this is not worth your time and effort. There are easier, better way to make your house as high performance as it can be.


Current building systems rely primarily on timber framing.  Good old 4 x 2 (90 x 45) framing has been around for a long time and is the cornerstone of all residential & light commercial building.

With recent changes to the building code focused on increasing the thermal efficiency and warmth of homes, and reducing the costs of heating, the limitations of traditional framing and the insulation ratings they can achieve have become an issue. Currently the highest insulation rating achievable in a 90 x 45 exterior wall is around R2.8. This rating is very much dependent on how well the insulation is installed and the type of insulation. Over time it may also sag, further reducing your rating.  In addition to this the exterior wall often has a vented cavity behind the cladding, which allows cold air to circulate. Given that the only things separating us from the cold air is building paper insulation

and Gib board, heat loss is inevitable.


SIPs replace the traditional 4 X 2 framing and incorporate solid urethane foam insulation sandwiched between two sheets of orientated strand board. The panels vary in thickness and have an R rating starting at R2.8 for 115mm thick panels and rising to R8.3 for 315mm thick panels. The panels can be used for all the exterior walls as well as the roof and internal walls should you wish. 


A study was made by the Brock University, located in St Catherine’s Ontario, comparing two almost identical houses. They were built at the same time, but one was made with conventional 6x2 (140x45) studs and batt insulation, while the other utilised 4 1/2" (115mm) SIPs.


The highlights and conclusions of the article as are follows:


  • Insulation is usually rated under controlled variables in a laboratory under controlled conditions in order to use R-values to measure the energy efficiency of a home.

  • SIP walls perform at their rated R-Values as a result of it being tight as a system and its tight construction neutralizes moisture and air circulation found in stud wall framing.

  • Infrared imaging exposed the deceiving nature of R-values via infrared imaging on both structures. Energy loss measured a higher rate of R-20 insulation at the conventionally framed building PERFORMING AT ONLY AN R-4 EQUIVALENT. The SIP home on the other hand PERFORMED AT THEIR TRUE R-17 RATING, using only 4 1/2" walls with R-17 rated insulation.

  • Thermographic analysis  also demonstrated that the STUD HOME CONSUMED NEARLY  4 TIMES AS MANY BTU's AS THE 4 1/2" SIP WALL HOME at an outdoor temperature of -10.5 ºC (13.1 ºF).

  • The SIP house is shown to be much tighter than the stud house in air leakage tests. The SIP house had 1.55 ACH (air changes per hour). It was found that THE STICK FRAME HOUSE HAS 68% MORE LEAKAGE. This means that the SIP house would use less energy for heating, would be more comfortable, retain heat better and be less drafty, considering that all other factors are equal.

  • The Brock study involved air leakage tests, hourly temperature readings over the course of a year and thermal photography. The SIP house outperformed the stud house in energy efficiency in each case. 2 x 6 Stud Wall 4.5” SIP Wall.

  • On an average winter month, the SIPHOUSE WOULD SAVE $88 A MONTH on its heating bill, based on heat loss data collected in the study. Considering increases in our energy costs since the study, using SIPs may now give $100/month range savings and this is using only 4 1/2" SIP walls, typical construction calls for 6 1/2" walls which provide more insulation value.

Two houses were built side by side in Albert Town (near Wanaka). One was a standard stick frame home and the other was a SIPs house.  Although Anne didn’t measure it herself, the builder of the SIP house told her: 


Outside temperature two degrees.


Inside temperature 14 degrees (empty and unheated house) … raised to 16 degrees over the period of an hour when sun came into the house, due to passive solar design (good orientation, insulated concrete slab),  and the excellent insulation and air tightness provided by the SIP panels.


Code insulated house next door was five degrees.


Although the SIP house was not heated at the time the temperature was taken, it does have a wood burning stove and a fresh air ventilation system with heat recovery and stays comfortable.  When the new owners went in to have a look at it, they couldn’t believe there was no in-slab heating operating.


A lot has been said comparing traditional building materials and SIPs, so how do they really stack up? The main point you will need to consider is your build cost. Traditional materials eat a lot of resources just to be able to frame and insulate the house.  SIPs eliminate this issue by being an insulated panel.  SIPs may seem to be a bit more expensive up front but if you factor time and labour costs (for construction), you will then realise the savings SIPs bring.


Probably the most important factor to consider is the ongoing monthly operating costs. Using SIPs on your next project will save you a lot of money on heating and ventilation costs, whilst also providing a very warm and healthy living climate in your home.


All in all, using SIPs for your next project not only saves time and hassle but saves you a ton of money in the future.


Kevin Turley

Director, Green Abode