Exterior XPS upgrade on a manufactured home?
We are replacing the siding on a double-wide manufactured home, and so think it might be a good idea to add a layer of 1.5’ XPS to the exterior walls at the same time. However, we will not be changing the windows (recently installed, but lower quality double-pane gas-filed vinyl sliders), nor updating the floor or roofing assembly. (The installer sticker in the electrical box claims R-38 in the ceiling, R-36 in the floor, and R-21 in the walls–and the insulation seems pretty well installed.)
Can this home benefit from the added XPS on the exterior walls with the existing windows and flooring and roofing assemblies? Or, is this degree of insulation a waste if the windows and entire envelope are not upgraded? Thanks!
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There's no concern about it being a waste without upgrading the entire envelope. The cost has a lot to do with the detailing of flashing and trim at the windows. If you have a solid plan to do that without too much labor, it's probably worth it.
Standard XPS is far from being green--it's made with an extremely potent greenhouse gas more the 1000X worse than CO2. But the good news is that there are alternatives available that cut that impact way back or even eliminate it. Those include EPS, GPS, polyiso, and new versions of XPS such as Owens Corning's "NGX". OId style bad XPS is still allowed in Oregon (if that's what the OR in your name means), but not in Washington or California, so it shouldn't be to hard to get NGX. But GPS is likely cheaper for the same R-value and polyiso offers more R-value for the same thickness.
Thank you, Charlie! Yes, OR does stand for Oregon. I will definitely look into the XPS alternatives, for sure. Much appreciated!!
If it were me, I would remove the new windows if possible, and install window bucks the thickness of your insulation board. So that the windows are not inset, requiring trim that could leak and allow water to get behind the insulation.
To assess the climate impact of different types of foam insulation, you can use this new, free tool: https://www.buildersforclimateaction.org/beam-estimator.html. We will be discussing it with the developer on this week's BS + Beer Show. Using it, you'll see that while NGX has less up-front carbon emissions than standard XPS, it's still among the worst products you can use in a building when it comes to climate impact. EPS, GPS or polyiso are better choices. Even better, you might consider rigid wood fiber insulation, though it currently costs more than the alternatives, it is roughly carbon neutral.
Thanks so much Mike, and Michael! Super helpful info!