Injection Foam: A New Tool in Our Insulation Toolkit
by Rachel White
Are the spaces open or closed? More often than not, our air sealing and insulation strategy hinges on the answer to this question.
Say you have a poorly insulated attic resulting in ice dams and high heating bills. How we remediate depends on whether the attic is finished (closed) or unfinished (open). If the attic is finished, best practice (and the only feasible strategy in many cases) is to strip interior surfaces, air seal and insulate the underside of the roof with spray polyurethane foam (SPF), and then put the finishes back. We have explored and priced other approaches, but none are as easy to install or as reliable.
The trouble is, this approach is tantamount to invasive surgery. It can also take four weeks or more to complete and cost tens of thousands of dollars. This is why most homeowners have little appetite for it unless they are planning to renovate anyway, or they have suffered really significant ice dam damage. It’s also one reason why we are exploring a new approach to insulating closed cavities using injection polyurethane foam (IPF).
IPF and SPF are very similar technologies. Both are manufactured on site by heating and mixing together two liquids to cause a chemical reaction the result of which is finished foam. But they also have important differences. Whereas SPF is spray applied, IPF is injected in a froth or liquid form. Unlike SPF, which expands and cures quickly upon application, IPF expands and cures slowly. IPF can thus be installed through strategically drilled holes into a stud or rafter bay. If installed properly, IPF will evenly fill cavities before beginning to harden into finished foam. It’s also possible to install IPF into cavities that already contain some insulation.
IPF has been around for decades but isn’t widely used by foam installers. One factor is the technical challenge of working within a closed cavity. Quality control is more difficult when you can’t see the product you are installing, and there’s a risk of popping off finishes if you overfill the cavity. Another factor may be SPF’s favorability for new construction, which has greater market influence than the retrofit sector (Indeed our foam subcontractor has offered IPF in the past but stopped because of insufficient demand). It’s also true that IPF won’t eliminate many of the costs of insulating closed cavities. For example. you still have to patch and paint all those strategically drilled holes. For these reasons, as well as our inherent conservatism and reluctance to experiment on our clients’ homes, we continue to use SPF whenever we need a large volume of foam (Our inherent conservatism also informs our investment in SPF safety and quality control).
That said, we are exploring IPF for projects where we need a small volume of foam, small enough that we can install it ourselves using kits. This would build upon our longstanding practice of using SPF to install small volumes of foam in open cavities. For a variety of reasons, it is sometimes more efficient and cost-effective for us to install foam ourselves using kits. By adding IPF kits to our insulation arsenal we’ll be able to insulate closed cavities and other difficult to reach spaces that we can’t get to with SPF.
The first step in this exploration was a training session with Henri Fennell, the foam expert with whom we worked to develop our spray foam protocols. Henri spent a full day with our crew, introducing us to IPF technology and leading us through a hands-on installation exercise.
The training was also an important opportunity to review general best practices for foam. For example, all foam needs to be heated to a temperature range specified by the manufacturer prior to installation. (For kits, Henri recommends a hot box outfitted with a waterbed heater and a probe thermometer.)
The highlight of the day was, of course, installing the IPF. Francis built a mock-up and everyone got a chance to try his or her hand at filling a closed cavity. As I mentioned above, one of the challenges of IPF is that you can’t see foam inside the closed cavity. So we also practiced using the infrared camera to quality control our work.
The training is already paying off. Francis used an IPF kit to insulate behind the boiler at my house, and we are planning to use IPF to insulate cathedral ceilings on an upcoming project. We're hiring Henri to oversee the installation.
Foam—whether SPF or IPF, bulk or kit—is a sophisticated and technically challenging material. It’s absolutely crucial that we remain current and in top form, even as we continue to expand our competencies. Thanks to Henri, we’ve added another tool to our insulation toolkit, which will allow us to solve more home performance problems than we were able to before—hopefully at lower cost and with less disturbance to our clients.