Plasti-Fab
EPS Product Solutions
Interior Insulation for Foundation/Basement Walls
Written by: Melissa Carruthers
Follow Melissa on Twitter @MelissaC_PFB
Last week I talked about how to insulate exterior foundation walls to improve the energy efficiency of the Plasti-Fab Home. The next step in insulating the Plasti-Fab Solutions Home is to insulate the interior basement walls. Below you can read instructions to get you started on insulating your basement using ***DuroFoam insulation. Remember, you can also use *PlastiSpan and **PlastiSpan HD in this situation as well.
When insulating a basement wall, make sure the wall surfaces are clean, dry and free of foreign materials and sharp projections. Start from a corner, and attach DuroFoam insulation to the basement wall using PL300. This is a foam safe adhesive. There are other foam safe adhesives you can use, BUT make sure they say “foam safe.” Measure and cut the DuroFoam to fit around windows. When cutting DuroFoam insulation use a utility knife or fine tooth hand saw like a drywall saw to fit openings such as windows.
You don’t need to wear gloves or a mask when cutting rigid insulation like you would with conventional fibreglass insulation. To create a vapour barrier, the DuroFoam insulation should be tightly butted together. Joints should be no wider than 1 mm. You can ensure this by applying adhesive between the boards (or tape the seams using any polypropylene tape with acrylic adhesive, also known as house wrap tape.)
Now to frame the wall, construct a separate wood framed wall and install it in front of the DuroFoam insulation to support the ½” drywall. The vertical framing should be at least 2”x2” and separated at either 16” or 24” on center. To attach the framed wall, fasten it to the upper floor joists and basement floor leaving a small gap between the PlastiSpan insulation and the framed wall. Electrical can be placed within the framed wall by running wiring in the small gap behind the framing. Shallow electrical boxes are the best fit in this application.
You can attach your drywall to your framed wall when this is complete. Following these simple steps for insulating your basement walls will help increase your energy savings and decrease your heating costs.
*Learn More about PlastiSpan Insulation.
**Learn More about PlastiSpan HD Insulation.
***Learn More about DuroFoam Insulation.
Next week: Building the Foundation using Insulated Concrete Forms
Plasti-Fab 
Why isn’t the reflective side of the insulation facing inwards? Wouldn’t if be beneficial for reflecting radiant heat back to it’s source?
Thank you
tex
That is a good question.
The reflective facer does not increase the nominal R-value of DuroFoam insulation. For additional information click link below Plasti-Fab PIB 253 – Facts About Thermal Resistance of Reflective Insulation:
Facts About Thermal Resistance of Reflective Insulation
The second link addresses specifically DuroFoam® Insulation for Interior Basement Applications:
DuroFoam® Insulation for Basement Applications
I tried to follow these links but got an error for both of them.
I am very interested to know why the reflective surface is not installed upward toward the house. Wouldn’t the reflective surface reduce radiant heat losses?
(UPDATE: Please check links above. They are now working.)
Good information. Lucky me I recently found your site by accident (stumbleupon).
I have saved as a favorite for later!
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I have a crawl space that is 4feet high. Can I install this horizontally?
Hello Jason, Yes you can install the product horizontally in your crawl space.
Is there a recommended thickness of Durofoam in this application for climate zone 6 when combined with a stud wall and 3.5″ fibreglass batts?
Hello Ben, That is a good question. There is a good web site that tells us what the required R-values are for the applications in the climate zones, found here: https://energycode.pnl.gov/EnergyCodeReqs/
So looking at the Basement wall R-value requirement for Climate zone 6, your overall R-value needs to be 15/19 (the reason there are two is one is for 40 degrees, and the other 70 degrees tested) Because the R-value on batt insulation varies on whether you used a faced material or not, I will use an example.
3.5 inches of fiberglass batt insulation gives you an R-11 when uncompressed. (meaning you didnt shmoosh (yes thats a very technical term) it into the wall cavity. If you compress it, it loses some of its R-value.
So now you have 11, and we have to get to at least 15. Regular Durofoam is 3.75 per inch. You need 1.5 inch thick DuroFoam to safely give you the required R-value for your zone.
3.5″ Batt (11) + 1.5″ DurFoam Insulation (5.6) = 16.6 R-value Wall
That being said, Make sure to check with your local building codes for specific requirements in your area.
I hope that helps!
Perfect, thanks. I will be sure no to “shmoosh” the batts.
Hello,
I am going to use the Durafoam product against the concrete interior walls then tuck tape for the vapour barrier. I would also like to use a fiberglass insulation for extra R value. Do I have to then use a Poly vapour barrier again before drywalling? I would think not as this would “trap” air within the cavity but thought to ask.
Thank you
I’m also asking this question
Good-morning, I live in London Ontario Canada (2 hrs North of Detroit). I’m planning on using Dura foram in my basement. a few question that I have. If I use 3/4 thick durafoam (the green stuff) and glue it right onto my concrete walls, and then if i use R14 fiberglass insulation, do I still need to apply a vapor barrier to the wall?
Also, if I use 3/4 thick durafoam on my basement floors.. do I apply a vapor barrier first onto the concrete floor and then durafoam or is it the other way around?
thanks for your help.
It depends on code requirements in your area. In my area (southern BC), you need to have a minimum of 20% of your R value in your foam vs fibreglass batts. I went with 1.5″ durofoam. 3/4″ sounds like it may not be enough. Durofoam has a low permeance due to the coatings it has, so it is a vapor barrier. I think it would work fine on a floor. Vapor barrier on a floor is not required in my area, but yours may be different. It’s worth checking your plans with your local code and inspector before starting.
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