But I am glad to say they won’t stare at me much longer. Bit by bit we knocked one item after another off the task list and we are finally ready to fill that gap with the open cell foam. It is time to call the insulation crew back in!
Spray polyurethane foam (SPF) doesn’t come cheap. To make this investment worthwhile, it is important that the SPF is applied properly, whether it is the closed or open cell kind. Getting the SPF installation right is more difficult than one may think. Here are a few observations that could help with quality control.
Lurking behind the studs
The saying is that open cell foam will fill all the nooks and crevices due to its extraordinary expansion rate (listed as up to 100 times it original volume for open cell foam). That is true, as long as the nooks and crevices are small enough.
The two inch gap right behind the studs is too big to get filled by the expanding foam, as you can see in the schematic section of the wall below.
To fill that gap, the spray foam must be applied to the surface directly behind the stud. If not one may end up with thermal breaks like the one shown below.
You can actually see in the video of the closed cell foam installation how the applicator carefully sprays a band of foam right behind the studs before filling in the open wall space.
Building corners are known as the most vulnerable areas in the thermal envelope. To add to the thermal integrity, we minimized the framing, which in turn allows for more insulation in the corner.
That, however, leaves us with a significant gap behind the framing. Unless properly filled with insulation, this can turn into a significant thermal break – a cold building corner – that could cause condensation followed by moisture and mold problems.
If open cell spray foam is applied along the framing with the assumption that it will expand into and fill the corner space, think again.
I learned this the hard way, by drilling a few holes into the corner framing so that I could peek into the gap behind.
Equally difficult are the areas where a perpendicular inside wall abuts against the outside wall. We structured the framing for the best insulation yield, which again creates a space behind the framing that is equally large to those at the building corners. The thermal break problem repeats itself, as can be seen in the schematic cross section below.
Whether a building corner or a wall junction, to fill the gaps, the open cell spray foam must be applied to the area directly behind the framing.
Even if done this way, it needs to be applied at a much higher rate to fully fill the depth of the gap. If not, the space ends up only partially filled and insulated, which is not acceptable, considering the investment at hand.
You’ll know when the space is properly filled, because the open cell foam will begin to squirt out from all the nooks and crevices in the corner or wall junction framing.
We applied a layer of open cell foam to the garden apartment and 1st floor ceiling to create an air seal between each unit. That air seal is not a given, as in some instances the open cell foam may begin to separate from the floor/ceiling joists, leaving behind a small gap.
This can be easily prevented by first spraying out the corners of the floor/ceiling joists.
Once the corners on both sides are sprayed, the remaining space in between can be filled.
I noted that this application strategy did not lead to any separation of the foam from the floor/ceiling joists, thus no small gaps.
Skill, sight and collaboration
One may assume that if you get an insulation company with a good reputation, you will not run into the above outlined quality control issues. I noted that this has less to do with the company’s reputation, but heavily relies on the skill and diligence level of the actual applicator (the guy with the spray gun) and his/her assistant (holding and dragging the hose).
Some individuals have the experience and attention to detail to provide a good product and can sustain a level focus while on the job. Others don’t.
Even if you get a good team, there will be glitches. The applicator and his/her assistant have a very hard time seeing because their full face goggles constantly get littered with spray foam. Even frequent cleaning of the goggles only partially helps.
To make things worse, bright construction lights or sunlight creates glare that makes it almost impossible to see. Even the best applicator can only do so much when operating partially blind.
I found that I am in a much better position, standing five or ten feet behind the applicator and his/her assistant. I have smaller goggles, have a clear unimpaired sight and can freely move around and look at the walls and corners from all sorts of angles. I was able to catch the missed spots in a heartbeat.
I began to tag team with the applicator and assistant, following them closely, and pointing out the spots they missed before they were too far along. But for that to work, you need a team that is willing to work with you. Those that did, appreciated my effort, because it made their work easier and faster.