Construction Techniques: Spray Foam Insulation

Spray Foam insulation comes in many styles and mixtures. The most common form of spray foam insulation is rigid polyurethane that comes in a liquid and is sprayed into the building’s exterior envelope. This the same method used to insulate the ELEMENT. The benefits of spray foam insulation are seemingly endless: it helps reduce air and moisture infiltration, helps increase the thermal performance of the building (it has a much higher R-Value per square inch when compared to typical Fiberglass Batt insulation) thus saving on energy costs, it can help add strength to the building’s structure being that it is compact in nature, the fact that the insulation is rigid helps prolong the thermal performance of the building (typical insulation, and also other forms of sprayed-in or blown-in insulation, have the tendency to sag or settle over time leaving insulation voids near the top of the wall, and the insulation also helps to ensure air tight construction which while helping reduce air infiltration will also help keep other harmful air pollutants out of the building.

A Test of Three Different Insulation Methods Set Up By the Insulation Company

However, there are some downsides to the use spray foam insulation. In most cases, such as is the case with the ELEMENT, the spraying can be very hazardous to the health of present during the spray. For this reason, spray foam insulation must be installed by a trained professional and in a well ventilated area. Because the spray foam has a chemical base, when it is sprayed it also releases these chemicals into the air. There are several spray insulation methods which use water as the base compound which makes the installation much safer for the environment; however, these tradeoffs typically results in a lower R-Value per square inch of insulation. Also, most spray foam insulation is very dangerous when on fire (in some cases it is impossible to extinguish with household fire extinguishers or water). For this reason, proper fire protection must be incorporated into the envelope design when using this type of insulation.

When looking at the insulation installation used in the ELEMENT, there are several problem areas that came about through the design and detailing of building’s exterior envelope. The first problem area came about when detailing the electrical and plumbing systems. To keep the tubing and conduit out of sight, they were placed inside the walls; the majority of these walls being exterior walls. The greatest issue which will likely arise from this detail will be the fact that the energy models of the building have no way of accounting for this reduction in insulation thickness. While there are ways to designate a specific reduction in the amount of insulation, it is very difficult to model the unique thermal bridge which will occur from the conduit running through the envelope.

Running Plumbing and Wiring Through Building Envelope on the Bedroom Module

Conduit Running Through Exterior Wall After Insulation Has Been Sprayed In

The second issue arose when the insulation was physically sprayed in. To make the installation easier for the professional insulators, the interior sheathing was installed first and the exterior sheathing was left off. This way the insulators could simply walk around the outside of the building spraying as the go. The problem can be seen when this process is looked at more carefully. When the insulation is sprayed out, it hits the back side of the interior sheathing as a thin film which then expands very rapidly (typically to 100 times its volume in roughly 8 seconds). This is a fact known by the professional insulators, so they spray very quickly and move on so that the insulation does not expand too much past the wall studs. In a perfect the world, the insulation would expand exactly to the outmost point of the wall studs and stop. This way the exterior sheathing could then easily be installed over the insulation. Obviously, this is not possible so the insulators spray in the foam insulation so that it does not reach the outmost point. If the insulation would expand beyond this point, it would need to be cut off. This process is very labor intensive and the insulation often breaks away in chunks, not a clean line. This too will become a problem in the computer modeling of the house. The model assumes that the insulation fills the entire wall cavity. Unfortunately, it does not. Again, there are ways to compensate for this lack of insulation; however, as you can see in the image below, the insulation is not uniform in shape. If there was a discrepancy in the thickness of the insulation, ideally it would be thickest at the wall studs and other areas where thermal bridges occur. However, it is almost completely reversed in this case.

Spray Foam Insulation after Installation, Notice the Corner Where Insulation is Hardly Present

Another Example on the South Wall Where Insulation Is Severely Lacking

The easiest method to avoid this issue comes in the planning stages of construction. If these facts are known, there effects can be minimized. One method to limit this problem would be to install both interior and exterior sheathing before the insulation is sprayed in leaving a hole in the exterior sheathing where the insulation can be sprayed down into the cavity. This method is clearly more time consuming for both the insulators and the builders. However, if the building’s systems rely heavily on computer modeling, this is one of the most effective ways to ensure a uniform insulation thickness when using spray foam insulation.

Detailed Section Sketch Showing this Process with Both Interior and Exterior Sheathing Installed Before Insulation is Sprayed In