Give Spray Foam a Fighting Chance: Top 10 for Good Foam

Bulk two component spray foam is applied to almost every new home or renovation in southern Ontario. It is a widely used product that has a high R-value density and is often expected to do double duty as an air barrier system. It’s the “go to” product to cleanup or hide the most complex areas that batt insulation and poly can do, but often not with grace. Now that some foam products have a low Global Warming Potential (GWP of 1), why do builders make it difficult for the installer to apply it beautifully?

Set up the Foamer for Success 

Too often we see builders setting-up the foamer for failure. Somehow, many builders expect foamers to spray in tight spaces, behind ducts and around wood framing details that are clearly impossible to spray through.

When spray foam is applied properly, it forms a nice, fairly uniform smooth, tough crust. It looks air tight. The conditions for spraying include above freezing weather and a dry, clean substrate. So if that salamander heater is creating condensation on the substrate, it might be a good idea to talk to your foamer and use a heat source that doesn’t create humidity indoors at least for the duration of the spraying.

Humans not Robots 

While robots are now spraying large open areas, such as commercial roof decks, humans continue to spray homes. We must therefore allow for the human factor. To optimize the human foamer, s/he needs to have at least three feet of clearance between the substrate and the spray gun; that means adding two feet for the human behind the gun for ergonomics and to ensure that foam is applied nearly perpendicular to the surface. The foamer must wear a full-face mask, especially if fresh air is not pumped into the area.

To set yourself up for success, think like the foamer. Substrate that can be seen and touched has the best chance of getting nice even foam. Note that adding furring on the inside that’s perpendicular will slow the sprayer down as they typically like to make long even passes of spray. 

To be successful when spraying the sheathing from the inside of the building:

  1. Delay the ducts: There should be no ductwork along exterior walls. Having clear access to the substrate means the sprayer can install the foam more uniformly with fewer blisters and bald spots.
  2. Delay the soffits: bulkheads along exterior walls or ceilings need to be constructed after the foam is sprayed.
  3. Pushed wires back: all wiring should be pushed to the back or touching the sheathing. This will ensure the foam has fewer voids created by wires. Also, if you have to scarf excess foam, knowing the wires are all on the cold side of the foam should give you a degree of confidence.
  4. Pull plumbing in: Keep the water supply lines well on the warm side of the foam.
  5. Can’t avoid attic ductwork? Prior to installing the drywall, invite a third party inspector to test the sprayed product for completeness (air seal) and thickness. Mastic the joints in the attic before you spray.
  6. Rim joist areas: Floor joist that run parallel to the wall can make for awkward spraying. It gets worse in the basement when the below grade wall thickness pinches off the view. When assembling your floor cavity, consider lining the outside edges with board foam that can be sealed in place or using an insulated rim board.
  7. Hot Roofs: All sistered rafters or laminated trusses that form girts should have exterior edges sealed together with acoustical sealant prior to installation. Ideally, cross purlins are installed between the roof sheathing and rafters so that a full, monolithic coat of spray foam is applied directly to the underside of the roof deck.
  8. Clean Me: Spray foam can’t form an air seal against a dirty substrate. Besides, debris makes for bumpy foam that is more likely to have defects in it.
  9. Wood Moves: Have your foamer lap the foam’s edge up the wood for a solid bond with the wood that will allow for some movement.
  10. Won’t Stick: Foam can’t be applied to 6 mil polyethylene, and many other shiny substrates. Note too that some sheet metal has a thin film of oil on it. Spray foam may not stick well to ductwork either.
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