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DIY Spray Foam Insulation


Insulating with spray foam insulation provides an R-value of up to R-7.0 per inch. DIY kits from most home improvement outlets and online let you do your own foam insulating. This article helps you decide if DIY foam insulation is the right choice–and how to use it.

DIY Spray Foam Insulation

Differences between DIY and Contractor Applied

Here is a comparison of DIY spray foam and professional installation.

Do-It-Yourself Applied

  • Convenient. Spray when you want where you want.
  • Ideal for smaller areas or jobs that take an extended period of time.
  • Best choice for remote locations.
  • Temperature-sensitive. Typically must be sprayed at over 65 degrees F.
  • Cost. $1.25 – $1.60 per board foot.

Contractor Applied

  • Preferred choice for large projects.
  • Usually have heated trucks for cold-weather applications.
  • Usually have a minimum charge.
  • Have to stay out of the building for 24 hours after completion.
  • Cost. $0.85 – $1.00 per board foot.

Open Cell Or Closed Cell Foam?

There are two types of spray foam kits available–Closed cell and open cell.

Closed Cell Foam

  • Approximately R-3.8 per inch.
  • Expands to three times its sprayed size.
  • Great sound barrier.
  • Best for hard-to-reach areas because of the expansion factor.
  • Requires a vapor barrier.
  • Cost. $0.45 – $0.65 per board foot.

Open Cell Foam

  • R-7.0 per inch.
  • Preferred DIY foam. Easier to control.
  • Low expansion. Dense.
  • Provides vapor barrier when 2” thick.
  • Cost. $1.25 – $1.60 per board foot.

Plan Your Application

Make sure you are ready to spray. Clear the area. Have a ladder or step stool handy. Set up a fan to clear out fumes. Cover anything that you don’t want to be sprayed–including the floor. Pick a starting point and proceed in an orderly manner.

Keep spraying. After 30 seconds of non-use, the product will harden inside the nozzle. Once clogged the spraying tips have to be changed. All kits should come with extra tips but make sure you get them.

Smaller Kits May Have an Advantage

Most kits are labeled with a number like 200 or 650. These numbers represent the number of board feet each kit will cover. Bigger kits have two large tanks that usually require two hands to move or shake. Buying three smaller kits that cover the same amount of board feet is more expensive but much easier to handle.

Measuring the Amount of Foam Needed

Spray foam is sold and measured by the board foot. A board foot is 12” x 12” x 1 inch thick–or any area that covers 144 square inches to one inch thickness. A 200 kit will cover 200 square feet to a thickness of one inch or 100 square feet applied two inches thick.

Buy the Correct-Sized Kit

Most products only have a shelf life of about 30 days (manufacturer’s recommendation). The kit can be used and reused regularly within that time if the equipment is cleaned after each use and new tips are installed. Buy a kit that will insulate the intended area. Buying a larger kit because the price per board foot is lower may be a waste of money.

Check the Surface Moisture

Spray foam will not adhere if the surface moisture of the wallis over 20%. Older dry surfaces should be fine but new construction or any place that has been wet recently could be a problem. If in doubt buy an inexpensive moisture meter to make sure your foam sticks.

Protect Areas Not being Sprayed

Spraying foam can be a messy and inexact project. Foaming windows, electrical boxes, or the floor just adds work. Trying to remove wet foam just spreads the mess. Cover the floor, windows, and doors with light poly taped in place. Use painter’s tape to keep from filling electrical boxes and other fixtures. You want the foam to seal around the exterior of the boxes–not inside.

Protect Yourself

Wear a full protective hazmat-type suit c/w hood and boot covers. Your gloves should be taped to the sleeves. Use a respirator with changeable filters and wear goggles. Spray foam tends to splatter and is difficult or next to impossible to completely remove.

Spray foam is a combination of isocyanurate and polyol along with blowing agents and fire retardant chemicals. The mixture can be toxic when breathed in. They are also flammable in a gas state. Make sure that there are no sources of ignition when blowing foam. Remember to turn off the water heater and furnace pilot lights.

Protect the Equipment

Follow the instructions that come with the kit. Shake the cans before starting to mix the contents–then every few minutes while working. Before attaching the nozzle, spray into a disposable container to ensure that chemicals are mixing correctly.

Lubricate the nozzle before the first tip is installed and with every tip change. Petroleum jelly lubricant is supplied in each kit. If you run out, use the jar in your medicine cabinet.

Spray a Picture Frame First

When spraying between wood framing members–studs, rafters, trusses–spray a picture frame against them around the perimeter; then fill in the center. Spraying the picture frame with ½” foam allows it to penetrate any gaps between the dimensional lumber and the wall or roof sheathing. The ½” will expand to one inch thick.

Give your picture frame a few minutes to start curing. Then spray the center to ½” thick. This application method also reduces the risk of a heavy layer of foam curing quickly and creating bulges in the sheathing as it cures completely.

Spray In Layers

Spray foam layers are called “lifts”. Never spray a lift more than 2” thick. If additional insulation thickness is desired, wait to apply the second lift until the first is cured. Adding a second lift before the first is cured can result in lower R-values.

Recommended lift thicknesses vary by manufacturer. Not waiting for lifts to cure and spraying too thick are the two most common DIY spray foam mistakes.

How to Deal with Obstructions

When spraying your picture frames in the stud cavities, spray behind obstructions like pipes, wires, ducts, and electrical boxes. Just spraying over them can leave an uninsulated void between the sheathing and the pipe, wire, etc.

Know Spray Depth

Following the manufacturer’s recommendation for lift depth requires you to know how thick your spray is. You can buy spray foam depth gauges but homemade tools work just as well–and cost less. Wrap a piece of tape around a screwdriver, awl, or stiff piece of wire to check the depth as you spray.

Removing Overspray

Overspraying foam is a common occurrence–especially when first starting. Once the foam is dry, run a straightedge such as a carpenter square down the face of the studs if you have filled the entire cavity. Not only will it take the excess foam off the face of the studs, but it will also show you any high spots between the studs.

Depending on the size of the lumps, they can be removed with a utility knife, hand saw, or wire brush. The wall should have no protrusions that interfere with applying drywall.

Combining Spray Foam and Batts

Spray just enough foam into the cavity to end up with about 1 ½” of cured product. Split fiberglass batts lengthwise to finish insulating the cavity. This system combines the air-sealing properties of spray foam with the money-saving use of fiberglass. Using R-13 batts results in about R-17 wall insulation.

Do not compress the fiberglass. It loses insulation value as air is squeezed out of it. Do not spray less than one inch of cure foam. It will lose its air barrier properties.

Cured spray foam must be covered in all living areas with a thermal barrier such as drywall. An exception is rim joist cavities. Non-living areas such as attics and crawl spaces can be left uncovered. Exposed foams must have a Class A fire-resistant rating. If not, they must be covered with drywall.

Rim Joists and Bottom Plates

Uninsulated rim joists are one of the top heat loss areas of a house. Spray foam is a popular and easy way to solve the problem. Spray the foam at least 2” thick onto the joist and down over the bottom plate to cover the joint with the concrete foundation. No need to picture frame these small areas.



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