Home Builder Canada - Insulation

Insulation
Evolution, experimentation, claims & research

By Jon Eakes

There are two cardinal rules in the world of insulation:
1. Insulation is always part of a system that has to control thermal loss or gain, air flow and moisture movement. Don't think of insulation by itself.
2. Always use the least expensive insulation system that gets the job done - or you could use specialty insulations only when their special characteristics justify the increased cost for equivalent thermal insulation. Don't forget to calculate total installed costs, including air flow control, moisture control, absence or presence of secondary products like studs or strapping, and, of course, labour.
Rule 2 explains why the most widely used thermal insulations in Canada are simple glass fibre batts or low-cost blown-in materials like cellulose, which fill existing structural cavities, or polystyrene panels that cover structural cavities. Building a wall just for the purpose of holding insulation is usually a waste of money and space.
There are many other insulation choices out there. Not only do we need to determine whether their special characteristics justify their cost, but we also need to see them in a systems context against rule one and judge their advertising claims against realities, including climatic differences.

Climate makes a difference
There was once a popular insulation in Southern California that was simply a roll of aluminum foil that popped open like one of those 3D Christmas cards and was stapled to the studs: aluminum foil, air space, aluminum foil, air space, aluminum foil. That's it - the wall was insulated. When it was tested at the National Research Council in Canada many years ago, working against cold outdoor temperatures rather than the hot southern California sunshine, the convection loops inside the air spaces was so great that it produced negative R factors, effectively cooling the house faster than if there was nothing in the wall at all, one of the primary problems being that the aluminum air "tubes" were open at both the bottom and the top. Definitely not appropriate for a heating climate. Its not much good in Canada and can even reduce our invaluable winter time solar gains, potentially increasing our heating costs. Insulations that perform well in cold climates primarily resist conductivity, not radiation, help (or at least don't hinder) the avoidance of convection looping in or around the insulation, and may even contribute to the blockage of air flow and moisture flow.

Sound and fire resistance
When would we change from regular glass fibre batts to some other type of cavity fill? Heavier batts, like Roxul, can resist sound transmission, or provide an accrued level of fire resistance. Simple cellulose insulation provides surprising fire resistance, partially because of its density. Air Krete is probably one of the most fire resistant of the spray-in-place insulations with a great ecological reputation as well.

Dollars per inch
Expanded polystyrene may replace batts for about the same cost and the same R-value per inch where the rigidity of the panels is useful, but generally we do not use a panel product between joists or studs. It's simply a question of the cutting and fitting complications. Where thickness of the insulation becomes important, like small rooms or cathedral ceilings, we may go to products with a higher R-value per inch.

Sprayed-in-place insulation
Polyurethane really begins to justify its cost when sprayed-on polyurethane is used for insulation, air sealing and vapour retardation all in one shot, or simply fitting into irregular spaces. Some will use this for a whole wall, others will use it locally; such as in the header space or over the double header of outer walls to get maximum insulation while leaving an air passage during re-roofing jobs. Cellulous wet spray and the light weight concrete Air Krete are two air tight spray-in-place products that have the extra property that they will not burn or smoke. Sprayed-in-place insulation always requires experience because when products are created on site, under extremely variable conditions, the performance of the final job can vary a great deal. CMHC research in the Atlantic provinces thoroughly documented how too much water sprayed into a cavity in a climate with little drying potential can cause problems. Hence some sprayed-in-place products could work well in a dry climate where exactly the same product could cause problems in a wet climate. Although most sprayed-in-place products make great claims about air sealing, some can shrink or separate with building movement and negate this added value.
Icynene, a low density polyurethane spray, is one of the few spray insulations that adheres well to all surfaces and remains flexible after curing, assuring great airtightness despite potential building movement. Icynene even provides a special "pour" for filling existing cavities with little pressure on the drywall, or lathe and plaster.
Fomo Foam Products has a new Slow Rise polyurethane foam being used in the U.S. and its promoters claim the ability to simply pour it into a wall during renovations and fill the wall - without danger of pushing off the drywall. They even outline a procedure for adding insulation to a wall cavity partially filled with batts. For renovations that could prove very interesting, once we get enough data or experience with it we'll see if it is really true, as well as see the Canadian pricing.
In the meantime, it is interesting to note that Dow's foam product, Great Stuff, in the blue can and labelled for window and door use - unlike all other window and door foams except Icynene - does in fact cure to a soft sponge consistency, greatly reducing pressures that can distort frames or blow off drywall.

Remove vapour retardants in basements?
How about all the rumours of National Research Council studies on basement insulations and moisture control? Although the final report is due out in the spring of 2006, several interim reports have already given us a lot of information. They were basically experimenting with the use of house wraps on the concrete as a permeable moisture barrier, then a stud wall shimmed off the floor to allow the flow of any water rather than trapping it behind the wall, and then the same house wrap up over the insulation on the inside in place of a vapour retardant. The question was: would it be better to let moisture move slowly in and out of the wall in both directions depending on the season rather than trying to concentrate on the cold weather winter dynamics of the basement? The bottom line seems to be that this idea worked well, as long as the basement humidity levels remained rather dry during the winter, but if an occupant installed any significant humidity source in the basement, then moisture would accumulate inside the wall were it ran into the cold house wrap that is up against the cold concrete wall. Hence, with real people doing what they do in basements, the Canadian research does not support removing the moisture control system that we call a vapour retardant.

Keeping out of trouble
When builders or renovators consider trying an insulation for the first time, they should first of all look for third party verification of advertising claims. Be sure that any technical data you are looking at is for a heating climate, not an air conditioning climate. CCMC evaluation reports should be read to see if it was really tested for the use at hand. Talk to other contractors in your climatic region to see about application problems or long-term durability problems. If you are the first to use it in your area, ask the manufacturer to work with you on a pilot program. It is in their interest to have successful local projects. Like R-24 paint, if it sounds too good to be true, it probably is. HB