What you need to know before spray foaming an attic

Before spray foaming an attic know there are many building components in a home that are hidden behind drywall or just out of sight.

As an architect in the Washington area, I’ve worked with numerous homeowners to help them understand what’s hidden behind their walls and ceilings and evaluate the right home improvement options. With colder temperatures upon us, it’s important to be prepared for the winter and the additional energy costs you’ll pay to stay warm.

Sure, you could just dial down the thermostat and wear yet another sweater to cut costs, but investing in the right home improvements can go a lot further to cut expenses and to improve your day-to-day comfort.

One of the places in your home where a little bit of attention can make a big difference in your comfort — and heating bill — is the attic.

According to the Department of Energy, properly insulating the attic can save 10 to 50 percent on a typical heating bill. In the Washington area, there are many styles of homes and roofs, but typically most have some degree of attic space, either walk-in or crawl space. For many homeowners, spray foaming the attic is the most effective method to save on energy costs.

Spray Foaming an Attic Out Performs Fiberglass In Attic Insulation 
For years SPF contractors have been frustrated by prescriptive building code requirements that mandated extremely high R-values in attics, particularly in cold climates. For example in Wisconsin, R-values of 49 are prescribed in attics. In order to provide more realistic evaluations of insulation systems, Oak Ridge National Laboratories developed a large scale, attic climate simulator that could provide data on how efficiently insulation systems rated R-values matched up to more real life performance.

In July, 2005, SPFA contracted with R&D Services to test low density, waterblown SPF and 2lb density HFC 245fa blown insulation systems in an attic thermal performance climate simulator at Oak Ridge National Laboratories. The SPF assemblies were compared to a typical blown-in fiberglass insulation attic application.

Three attic insulation systems were tested in the LSCS for both Winter and Summer conditions. The thermal test section has dimensions 8×8 ft. and area of 64 ft2.
Loose-fill fiberglass on
floor of attic (depth 14 in.)
Low-density foam between
rafters on the underside of the roof deck (depth 5.5 in.)
Medium (2. lb) density foam between
rafter on the underside of the roof deck (depth 4.0 in.)

Results:
The tests results demonstrate that both low density and medium (2 lb) density SPF installed to the underside of the roof deck in attic assemblies maintain a much higher effective R-value at both low and high temperatures than the fiberglass insulation system. The SPF systems maintained 74%1 and 83% respectively of reported R-value at low outside temperatures compared to 46% for the fiberglass assembly, and 61% and 67% of reported R-value at high outside temperature compared to 51% for the fiberglass assembly. (table 1)
Attic temperatures of low density and medium density SPF assemblies averaged 77 to 78 degrees F at high outside temperature and 60 – 61 degrees F at low outside temperature compared to an average of 107 degrees at high outside temperature and 7 degrees at low outside temperature for the fiberglass assembly (table 5).

1. During low density Spray Foaming, application anomalies were noted by observers that may have affected R-value performance.
This statistic is important for buildings that have ducts and HVAC units in attics. The
high and low attic temperatures require much more energy to heat & cool and contribute
to wider temperature ranges between levels of the building.

Here’s how to get started:

Read more: What you need to know before insulating your attic