A lot of people extol the powers of spray foam these days. When it comes to big gains in R-value and air sealing, there is really nothing else that stands a chance. But insulation doesn’t exist in a vacuum. It must not only be effective at stopping heat transfer in a lab but must also work as an integral piece of the house as a whole.
There are more than just two categories of houses 1) Insulated and 2) Un-insulated. An insulated house can also be either poorly or properly insulated. A properly insulated house cuts energy bills significantly and makes for very comfy occupants whether it is winter or summer. Whereas a poorly insulated house can quickly turn into a nightmare with problems on multiple fronts that can run the gamut from annoying to catastrophic.
Spray foam insulation when used properly can be very effective, but when used poorly can be one of the most devastation products for a historic building.
What’s Wrong With Spray Foam?
I hate to pick on a product that someone has given up blood, sweat, tears to create, but when it is misused on historic buildings it is truly a problem for us all. Spray foam is a modern product that doesn’t seem to mix with the functional design of old buildings. That difference in function is what creates the problems.
Problem #1 Not Easily Reversible
From a historic preservation perspective, reversibility is imperative. If you irreversibly change a historic building then are you really preserving it? This is readily apparent concerning the exterior appearance of historic properties, but the same applies to other pieces like structure, water management, and air management.
If you spray foam insulation onto the backside of your siding and it later needs to be removed, the task is almost impossible not to mention incredibly expensive. In contrast, if you paint your house one color it’s very simple for the next owner to change the paint scheme. Foam cannot be removed without monumental effort and usually it does damage to the underlying structure when it is removed.
Problem #2 Water Management
Foam poses a big problem here because it both decreases air flow and can trap water which prevents wood from drying naturally. Wet wood leads to rot and rot is house cancer. Old houses were not built with the same technologies and techniques to prevent water and air intrusion as modern homes. If a little water got into the walls of an old house it could always evaporate quickly due to larger amounts of air flow.
Spray foam insulation decreases that air flow significantly, which in it of itself is a good thing because it makes our homes tighter, but unless a detailed analysis of the building envelope is done prior to adding spray foam problems can arise.
The presence of spray also makes diagnosis of a leak more difficult since the usually water spots or wet wood are concealed underneath the spray foam. The problem only becomes apparent when the wood reaches a point of failure and needs replacement. Instead of quick leak detection and small repairs, you are left with no indication of an issue until the problem is huge and costly.
Problem #3 Fire & Smoke Dangers
Is spray foam flammable? Not anymore than a lot of other building materials, but when it burns (depending on the content of the spray foam) it can release extremely dangerous chemicals. Granted, you have bigger issues to worry about like a burning house, but the most common cause of injury in house fires is due to smoke inhalation. Add spray foam to that fire and you only compound the potential health dangers to occupants.
Problem #4 Off Gassing
There have been multiple incidents where the spray foam caused serious illnesses in the building’s occupants. Some of it may have to do with un-diagnosed sensitivities to the foam and others are clear air quality issues. The source of them are not 100% clear. Was it improper application? Maybe incorrect mixing of the materials? The answers are still not fully known, but until this is fully cleared up it makes me nervous to have it in my own house.
Some occupants have reported a constant smell of dead fish and others report constant headaches and migraines that won’t go away unless they are away from the house for extended periods.
Founder & Senior Editor
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.