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Foam Insulation board behind siding

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Foam Insulation board behind siding with Elite Home Exteriors NW

Can You Install Foam Insulation Board behind James Hardie Plank Fiber Cement Siding, Vinyl Siding or Cedar Siding?

It’s very common to install foam insulation board under Vinyl Siding but can also be installed under James Hardie Plank Fiber Cement. This does help with energy efficiency and approved per manufacturer guidelines but not as much as a blown insulation project.

James Hardie Plank and other siding manufactures allow up to 2” of foam backer to be installed. Remember when you are adding foam, you are building out away from the walls. Sometimes this can cause siding and window trim to stick out past the window frame. Contact us for more advice on what size foam board you should have installed.

Dow Foam Board can increase the R- Value of the wall by up to 20% and is made from Polystyrene. 2” Dow Foam has a maximum R- Value of 10 (4’x8’ sheet 2” thick).

Installing insulation board under siding can offer several benefits, but there are also potential drawbacks to consider. Here’s a breakdown:


  1. Energy Efficiency: Insulation board can significantly improve the energy efficiency of a home by reducing heat loss in the winter and heat gain in the summer. This can lead to lower heating and cooling costs over time.
  2. Improved Comfort: By reducing drafts and maintaining more consistent indoor temperatures, insulation board can increase the overall comfort of a home, ensuring that rooms stay warmer in the winter and cooler in the summer.
  3. Moisture Control: Some types of insulation board also provide a barrier against moisture infiltration, helping to prevent water damage and mold growth within the walls.
  4. Sound Dampening: Insulation board can help to reduce noise transmission through walls, providing a quieter indoor environment.
  5. Enhanced Durability: Adding insulation board can provide an additional layer of protection for the exterior of the home, helping to shield it from impacts and weather-related damage.


  1. Cost: Installing insulation board can be relatively expensive, especially when compared to other types of insulation such as fiberglass batts or blown-in insulation.
  2. Installation Complexity: Proper installation of insulation board requires careful attention to detail, including ensuring that seams are properly sealed and that the board is installed with the correct orientation and fasteners. This can make the installation process more complex and time-consuming.
  3. Space Requirements: Insulation board adds thickness to the exterior walls, which can reduce the amount of interior space available, particularly in rooms with limited square footage.
  4. Moisture Concerns: If not installed correctly or if moisture becomes trapped between the insulation board and the siding, it can lead to moisture problems such as rot or mold growth.
  5. Aesthetics: Depending on the type of insulation board and siding used, the added thickness may alter the appearance of the home’s exterior. Some homeowners may not like the aesthetic changes that result from adding insulation board.

Overall, while installing insulation board under siding can provide significant benefits in terms of energy efficiency and comfort, it’s essential to carefully weigh these advantages against the potential drawbacks and consider factors such as cost, installation complexity, and aesthetic concerns before proceeding.

Contact us for a FREE inspection and to get an opinion on your exterior envelope condition.

WA 360-605-9030
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Elite Home Exteriors NW also includes a LIFETIME Labor warranty to any Full Home or Full wall reside because we install all products to Manufacturer Guidelines and state building code. Committed to Quality Rain or Shine!

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Foam Insulation board behind siding

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