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Need exterior insulation and air sealing options for this situation

Debra | Posted in Energy Efficiency and Durability on

I have some good friends that live in an old double-wide manufactured home (over 30 years old).  Their cedar shake siding is rotting and falling apart.  They used to depend on a wood stove for winter heat, but they are getting older and their health has deteriorated and they can’t physically handle that any more.  Now their furnace runs all the time and they aren’t comfortable in their home any more.  They also don’t have any air conditioning.

They want to replace their siding, and I strongly recommended that we work hard to air seal their walls and sill plate area (they have leaks big enough for snakes and mice to regularly invade their home).  They are in climate zone 4A, in Virginia.

The studs are only 2×4, with R11 fiberglass insulation (probably terribly installed).  Their interior walls are covered with a combination of paneling and some kind of thin drywall covered with vinyl wallpaper.  So, I wouldn’t count on the walls being able to dry to the inside.  The exterior sheathing is very thin OSB (well under 1/2″)  They aren’t sure if there is any WRB.

Ideally, after removing the siding, I think it would be best to remove at least some of the sheathing and determine if the existing insulation is bad enough to replace with mineral wool batts.  And find out if the existing sheathing is solid enough to leave in place. But they really don’t have the money or energy for all new wall insulation and sheathing.

So, we’re looking into trying to air seal the crappy sheathing full of holes from the shakes (if it’s not too rotted) with well-taped Tyvek, cover it with a layer of exterior insulation, install a rain screen, and then Smartside vertical panels.  

Far from ideal, but we think we can manage that much – financially and physically.  I want to help them as much as I can, as they helped me when I recently built our own home.  Unfortunately, I also have health issues that limit me, too.

So, are there any other affordable ideas for air sealing the old sheathing?  

And, any recommendations for vapor permeable exterior insulation?  I haven’t yet been able to find a local source for Rockwool Comfortboards.  They are either out of stock (long term) or aren’t carried at all (and may be too expensive).  And I’m concerned that most foam board insulation I’ve seen locally does not seem to be vapor permeable at all.  

Also, we won’t be able to redo the windows and doors, and will have to work around them and try to find a way to flash them better (no flashing tape was used when they were replaced 10 years ago).

I’d appreciate any suggestions you may have.  Thanks!


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  1. seabornman | | #1

    If the budget can stand at least 2" of XPS insulation, I think you could greatly lower the chance of interior moisture. For budget exterior, you can place the strapping vertical at 48" or even 64" o.c. and use a ribbed metal panel horizontally and quickly trim the doors and windows with breakmetal.

    1. capecodhaus | | #2

      Remember this is a 30 year old double wide trailer that's been in a humid climate for decades. It barely has a 3 pitch roof and likely sitting on a steel frame with skirt or a poorly detailed crawlspace.

      I don't think it's a good idea to wrap the exterior with a closed cell foam or any foam at this point in the buildings life, not to mention a 2 inch sheet of XPS is $50 these days. You'll very likely create a high humidity environment on the interior. I wouldn't do anything but remove and replace. Take a look around, do you see any doublewides wrapped in continuous exterior insulation, No. Most folks don't have any form of dehumidification in these homes either, a recipe for disaster.

      There is no mention of the undercarriage of this 30 year old beast. The trailer could be sitting on a steel frame with a decorative skirt wrapping (not ideal due to lots of environmental exposure) or could be on a crawlspace with dirt bed. This is an important detail to clarify.

      1. MartinHolladay | | #3

        Cape Cod,
        You're wrong. Wrapping the house with rigid insulation will decrease, not increase, the chance of moisture problems in the walls.

        1. capecodhaus | | #4


          You may be correct, but Seaborn suggested XPS. This is a poorly maintained doublewide that is getting a band-aid repair job. I wouldn't go beyond remove and replace as needed. Your thinking is too perfect. There is no continuity or even a chance of an air barrier in a double wide of this age, they have snakes (potentially venomous) entering their home.

          Remove any rotten sheathing, insulate, add new sheathing and a tight house wrap. Thats about it. I like Seaborns idea for metal roofing as an inexpensive siding.

          Perhaps the USDA has a program to help these people afford repairs.

          1. Expert Member
            BILL WICHERS | | #5

            Roofing polyiso is probably a good way to go here, since it is somewhat vapor permeable with a kraft or fiberglass mat facing. You can often find reclaimed roofing polyiso too for additional money savings over new material.

            I agree it's worth checking the underside for signs of deterioration, and possibly also reinsulating down there. I wouldn't be surprised if critters have made a mess of whatever insulation may have been down there originally.


  2. Debra | | #6

    Thank you, folks, for your feedback. I spoke with my friends, and the ground underneath their home is completely bare (not covered in plastic). And the floor insulation is pretty bad. They are not in any shape to work on that aspect, and neither am I. Plus, the ground underneath is full of craters and piles of soil and rocks. No effort was made to level and smooth it out before installing the home, along with a very rough full perimeter foundation. So, the house is likely taking up tons of moisture from that source. I'll pass on to them the link for possible financial assistance. Thanks!

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