Building Homes or Extensions/Metal Building Insulation


Bruce, thank you for answering my previous question so promptly.

My other dilema is, I had a metal building built and my intent was to insulate it and finish the interior as a hobby room.  I was told by the builder right after he was done and I mentioned my intent for the building and he told me that I cannot use normal fiberglass insulation because metal the is no moisture barrier and the insulation would eventually mold and mildew.  He said the ONLY was to insulate it was spray in expanding foam because it leaves no space between the insulation and the metal siding.  This method is prohibitivly expensive.  

I have to assume that the guy knows what he is talking about he build almost 1000 buildings a year.  I would have thought that the metal sheeting would make a perfect vapor barrier.

The building is 12x24 wood frame construction with metal siding and a metal gable roof.  My intent is to air condition and heat the building.  I live in North Florida so the climate is very hot in the summer and very humid. The winters and mild and mostly dry.

I guess my question in a nutshell is am I going to be forced to use spray in insulation or can I use batted fiberglass rolled insulation.

Something I had considered was buying 3/4 foam sheets and using Great Stuff canned expanding foam as mastick to glue it to the walls.  I would be grateful for any insight.

Thank you sincerely,

Hi John,  I don't know why he gave you that information.  Cavity walls have been filled with fiberglass insulation for many years.  You can get fiberglass batts encapsulated in plastic wrap if you are afraid of moisture intrusion into the insulation. You can also line the wall cavity with house wrap or felt paper before insulation to give your wall,a vapor barrier.  In your case I would probably just use a foil backed insulation and install it with the foil facing into the room. For added protection I might use a house wrap like Tyvek or Typar in the cavity first and then do the foil backed insulation.

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Bruce E. Johnson


I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.


Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

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