How Much Insulation is Too Much?
The single most cost effective way to make your home highly energy efficient is to have the right insulation selected and installed corectly in your home.
Doing this will make everything else work better. The design, money invested in your windows, and a better return on solar panels.
Firstly, make sure that your insulation product has been independently tested. There are still a number of insulation products on the market in Australia that have not been independently tested and actually overstate their values.
In Australia there are only three certifiers that insulation products can be certified through: Benchmark certification, SAI global, and Certification solutions. So make sure that your insulation product is independently certified to achieve the performance it claims it does.
Remember also that foil insulation is great for reflecting back radiant heat but like most insulation products does not perform as well at keeping convective heat under control. Radiant heat (i.e. from the sun) is the significant factor when protecting your roof from heat intake.
To effectively keep your home cooler in summer always use foil sarking under your roof whether you are using Colorbond or a tiled roof. Using effective double-sided reflective foil insulation in your walls is successful for containing heat loss during winter.
Another factor to consider is that some insulation products really are not suited to your floor because they simply are ineffective stopping winter heat loss.
How Much insulation is too much? If you have R2.0 insulation in your ceiling, by increasing it to R4.0 even though you double your insulation level, the effectiveness of the insulation does not double.
In a report in 1981 by the CSIRO titled Builders and Insulation, it stated that Builders should, therefore, have a general knowledge in respect to the application and economics of the insulation materials available. Unfortunately most builders do not.
The report goes on to say that the money invested in insulation: soon pays off the original cost of the insulation. In general, the higher the thermal resistance of the insulation the lower the heat leakage will be, but there is an economic optimum.
In a separate report by James Fricker B Mech Eng, CPEng, MAIRAH, M.IEAust, where Fricker also reported on the diminishing returns of insulation he provided some modelled cost savings for insulation. Fricker then tells us that the correct choice for insulation depends on local climate, insulation and energy costs.
A similar analysis was modelled for a home in Brisbane with air conditioning: Using the figures in his report the added benefit seems to drop more dramatically after installing R4.0 batts in your ceiling.
Fricker’s report finishes by saying that the CO2 generated to make the insulation vs. how much is saved by installing the insulation in your home is likely to be similar to the cost savings.
The number one ingredient of sustainable housing is a sustainable budget. Put your money where you get great bang for your buck, and as you see after R4.0 insulation in your ceiling there is far less bang.
Even if you have R3.0 insulation in your ceiling or R1.5 insulation in your walls, but if it is not installed correctly then you may really in effect only have half of what you think.
Another key factor to insulation is using a composite system. That is use both reflective foil and bulk insulation to get a better oerall performance and go one step closer to having a zero energy house
About the Author
A recognized authority on energy efficient, healthy and sustainable homes, Libe has developed Tasmania’s First Certified GreenSmart home and produced the Homes For Living! on line newsletter and The Better Building Guide. His awards include the 2007 Australian GreenSmart Professional of the Year; Builder of Tasmania’s First Certified GreenSmart House and MBA Tasmania Award For Excellence in Energy Efficient Housing
(ArticlesBase SC #580022)