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Spray Foam vs. Historic Buildings

Spray Foam vs. Historic BuildingsA 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.

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10 thoughts on “Spray Foam vs. Historic Buildings

  1. Manufacturers of the spray foam do not reveal their mixtures of spray foam. But, from an anonymous chemist, responding to a CBC program:
    “That fishy smell is what most amines smell like… a catalyst in these foams. They are generally considered neurotoxic, among other effects….[there are] isocyanates in the foam. Many of these amines are slow to evaporate…in quantity they could take years to offgas. These properties are well-known to organic chemists..they would recognize that smell instantly on walking into the room…”. I had to stay in the house when it was installed, and inhaled a lot of evil solvent. Don’t do that. I will be using rockwool instead, to preserve my air quality.

  2. The air sealing properties of closed cell foam make it a superior product — properly applied it’s an effective VB that still allows wall structures to dry in both directions (inside/outside). Have used it in all my projects since first trying more than 20 year ago. My current project is rebuilding a fire damaged stone building from the 1870’s and replacing the stick built addition .. it underwent an extensive remodel back in the early 90’s that included spray foam. The foam actually hindered the spread of the fire — with no open voids the flames could not find openings to travel — it was only after rafters and studs became fully compromised that flames made progress. Most old home are 2×4 and often balloon framed — impossible to properly insulate. A layer of foam ….and you are done.

  3. I have 1850 Vermont farmhouse that i fully gutted. My newest plan is to do closed cell on exterior walls and under the roof. On most of the walls i just see the backside of the siding, some of which have lats holding a little plaster. In a cold climate zone like Vermont tightly sealing out chilling wind is the goal. Im not worried about water that might get by the siding. Whether you have closed cell foam or fiberglass bats, water coming through is bad and an obvious fail in the protective envelope of the house that has to be fixed. My biggest concern is the moisture from within that doesnt dryout as quick as it is created. Either air reclaimers or timers on the bathroom vents or a cross ventilation central house fan, i believe i can control the moisture. I’d love to hear from anyone who’s been there done that.

    1. Hey Greg, what did you end up doing? I am similarly gutting on old Victorian and am considering spray foaming the inside surface of the exterior siding, then reinstalling the interior wall coverings (1×12 redwood planks, then sheet rock). Also worried about the flow of vapor/moisture through the walls.

  4. A company named Aspen Aerogels makes a home insulation called Space Loft That is the best product out there. It is perfect for historic homes. It does not hold water. I think is thin yet has the highest r value of any insulation today.

  5. Look into mineral wool insulation, like Roxul, as a healthy and non-invasive alternative. It’s reletively inexpensive and easy to install.

  6. We had our crawl space encapsulated about 3 years ago with a thick poly on the ground and spray foam insulation up the foundation. It has been the best thing ever. No only has it saved us a lot on heating and cooling, but the house is much less drafty and less musty. We didn’t insulate the floors, just the foundation and piers.

  7. Hi Scott,

    I’m wondering if there are *any* ways spray foam can be used. I have an attic above my kitchen that I intend to turn into a walk-in closet. I will have to insulate between the roof joists. The head clearance is very low to begin with and the joists are narrow so I was thinking of using spray foam. Is this also a bad place to use spray foam? Is there a difference between different types of foam? 1897 Victorian. Thanks!

  8. Thanks for This! We are in the process of remodeling/restoring our “half story” which includes moving the walls back under the eaves and have talked to a few different people on the subject. What would you recommend for the eaves? Just bat insulation? It’s hard to find people who understand that we are trying to preserve the character of our 1920 bungalow (or, restore some of it within reason!).

  9. The smell may be formaldehyde from some other product used at the same time. I recently experimented with foam in my garage but wasn’t too impressed. Fiberglass batts and complete envelope sealing with adhesive and flashing are the primary goals. Foam insulation isn’t very historical as you point out and you’ll need a sawzall afterwards to cut up and throw away the pieces if you later replace them.

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