The World of Insulation

The World of Insulation

As we have stated elsewhere in these Tech Talk product reviews, before any energy efficient systems can be effectively used, your building envelope needs to be optimized as effectively as you can. Previously, we talked about windows as one of the ‘big’ leaks and the topic of this review is insulation.

When the building envelope is done well, passive solar alone can contribute a lot to your home heating requirements. A number of specialty products have been developed to deal more effectively with the building envelope such as:

  • SIPS (Structural Insulated Panels) which are prefabricated wall panels of rigid foam plastic insulation sandwiched between OSB (Oriented Strand Board) sheathing. This product reduces convective air currents and thermal bridging which are the principle causes of greatly reduced efficiencies in conventional wall assemblies.
  • ICF (Insulated Concrete Forms) which are 2-sided expanded polystyrene (foam) insulation blocks that are stacked to become a concrete form then filled with concrete. They produce an airtight and solid home which has similar or even superior qualities to the SIPS system.

For our purposes we are going to be considering conventional construction systems which would be a framed wall using 2×6 studs with insulation and sheathing that are the standard of most new and existing housing stock.

Given a choice between fiberglass insulation and comparable options, I have been advocating the use of cellulose fiber insulation for many years. There is a premium to pay for this but with savings of your heating costs it does not take long to recover the differential. (Often 2-3 years) The National Research Council (NRC) did studies measuring the difference between fiberglass insulation and cellulose insulation. They measure the outflow of air to determine heat loss.

They discovered that the fiberglass insulation nominally R-20 in the wall actually performed closer to R13 and under certain conditions like 20 degrees below zero with a wind performed between R6-10. This is because of convective air flow in the insulation and thermal bridging. Additionally, the air flow from inside to the outside can create issues with moisture in the air flow, condensation and ultimately mold. I have opened many an exterior wall to see the black coloration of mold in the insulation.

The cellulose, by contrast, in the NRC testing: they could not measure any outflow of air at all. In fact they cut the vapor barrier at 18” and 7’ to encourage the outflow of air but still did not get a reading. Suggesting that, properly applied, there is no reduction of insulation integrity and no convective air flow to reduce efficiency or create issues with moisture. Cellulose is wood fiber (mostly newspaper) and it is treated to be fire resistant, bug resistant and mold resistant. It is most often used as a blown insulation that can be retrofitted in existing homes as well as new home applications both in the walls and attics.

Other batt type insulations include Roxul mineral wool and denim / cotton fiber batts They both have great sound attenuation qualities and thermal efficiency.

Another area where great strides have been made is with foam insulation. These include spray applications as well as rigid board applications. One of the applications used commonly in current home building practice is to install a layer of expanded polystyrene (EPS) foam insulation on a water resistant barrier (WRB – which can be an applied membrane material, building felt or Tyvk) on exterior sheathing, before putting a finish on top. This provides an air barrier and helps to mitigate thermal bridging. The building code in many areas also asks for moisture control for any incidental water that might penetrate the system.

EPS is an open cell foam that breaths a little and at normal room temperature it has a thermal resistance of approximately R3-4 per inch. Densities are typically ½ lb / cubic ft to 1lb / cubic ft. Some types of EPS are more dense for certain applications..

Foam insulation come in open cell foam like the EPS or closed cell foams. Many closed cell foams come in much higher densities than EPS and with thermal resistance running R 5 to R 7 per inch of thickness. Spray applications are very common in current building practice and really lend themselves to particularly challenging areas like vaulted ceiling, rim boards, bonus rooms over garages and other tricky areas to get good insulation and vapor barrier.

Closed cell foam does not require vapor barrier as it is its own vapor barrier and further National Research Council testing has confirmed that 2” of foam insulation eliminates the dew point which means condensation.

Spray foam insulation is typically more expensive but it has very good thermal properties, enhances structural capacity and provides other benefits. In my own building practices I use combinations. For example, I have used ICF Insulated Concrete Form systems for foundation and exterior walls up to the roof assembly. From there in one case I used cellulose fiber in attics and certain vaulted areas, then used spray foam in a vaulted turret roof that could not be effectively done any other way. And in another ICF home we sprayed the whole underside of the roof assembly with foam so that there was a complete thermal barrier.

When combined with triple glazed windows and thermal roll shutters or the In’flector screen referred to elsewhere,  these homes have amazingly energy efficient building envelopes

This website looks at a company in Maine that is building Passive Solar Homes that use EPS, SIPS and cellulose insulation. Viewing their Passive Home Blog access on the right hand column will take you to a detail view of their approach. They suggest they will be able to achieve a net zero house by starting with a very good building envelope

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