INSULATING GUTTED MOBILE HOME

QUESTION FROM MICHAEL MURPHY FROM
SWEETWATER, TN:


We have pretty much gutted a 14' by 66' mobile home in East Tennessee. It has only metal for a roof. When we were gutting it we removed, from a  small portion of the inside of the roof--the insulation directly attached to the metal. That insulation was installed between the trusses and the metal. After removing a few sections we realized we may be making a mistake, so we stopped tearing out it out. FYI, there was other insulation on top of the celing which we trashed.
 
So now we are wondering how to proceed, what approach to take, and some suggestions on properly insulating and venting the entire mobile home--which at this point is pretty much a house with a crawl space--but still with a mobile home roof.

 We would certainly appreciate some help.

 Thanks for your time,
 Murph

NOTE:  AFTER THE INSULATION DOCTOR ASKED MR. MURPHY  ADDITIONAL QUESTIONS TO HELP CLARIFY  BELOW WERE HIS ANSWERS IN QUOTES: 

Do you know what type of insulation you removed?  Was it rolled fiberglass material or a sprayed-on product or a rigid product of some nature?  
"Rolled Fiberglass"

I also need to know if the roof is sloped with an air space above the drywall line or if it is a flat roof? 
"It is a sloped roof where the bedrooms, bathrooms have a lowered flat ceiling, but the living room and dining area are more the shape of the sloped roof. So there is more space between the ceiling and the roof in  the bedrooms, kitchen, and bathrooms than in the Living and Dining area."

If it is a flat roof, how much space is between the under side of the roof and the drywall line? 
"Even though you asked for this info for a flat roof, I'll volunteer to give you the spaces between the lower ceiling and the roof -- about 2 feet, and the sloped ceiling and the roof -- about 8 inches."


SECOND QUESTION FROM MICHAEL:

We do have wooden trusses up there, so should we place blanket type insulation right up against the metal roof and staple it to the trusses??

And if we wanted to increase the R factor, could we just leave a space in between the roof (with attached insulation) and the bottom side of the trusses and staple new paper-backed insulation that would basically be sitting above the flat and sloped ceiling?? And vent that area with ridge vents??

And what about the 2 by 4 walls...we were thinking of putting R13 rolled fiberglass on the inside covered with 5/8" fire retardant sheet-rock. Then on the outside from the studs outward we were going to put up 1/2 sheathing, tar paper or house wrap, 1" rigid foam, and then hardi-board siding.

Does this sound like the way to go for the East Tennessee area--it can be very hot, very humid in the summer and very damp and cold in the winter.

Also, what do you suggest for insulating the crawl space?

Thanks Again,
Murph


  

ANSWER FROM THE INSULATION DOCTOR:

In the areas where you totally removed the insulation you would want to install a fiberglass blanket-type insulation with a vapor barrier (kraft-backed paper) attached to it.  It is my understanding that you may not have wooden rafters to staple the insulation to.  If this is the case, you would need to take a nylon banding tape, string it the opposite way that the metal rafters run and create a support system for the insulation.  The banding tape should be placed approximately 2' on center.  A lumber supply should have a banding type tape that is commonly used in a crawl space situation.
 
If you intend to increase the insulation value in those areas, you need to buy an unfaced fiberglas blanket to lay on top of the original layer of insulation.  It is also important that you install baffles, or proper vents, at the edge of the roof line to insure proper air flow into the attic (you can read about baffles on my website).  
 
In the areas where you have only the 8" space, it is important to maintain an airflow in that area also.  Therefore, you cannot install more insulation than 6" because you need to have a 1" to 1-1/2" of air space. (It is important to remember that insulation is guaranteed to be a minimum thickness not a maximum thickness.  In other words, when you purchase insulation and it states  it is 6", it will be at least that, however, it is not uncommon for it to expand above that thickness as much as an inch.)
 
Hope this helps you out!
 
Bruce Jones
The Insulation Doctor
 
















SECOND ANSWER FROM THE INSULATION DOCTOR:


OK, you have the right idea for the walls. (Rather than tar paper I would strongly recommend a Tyvek-type product made by Dupont).  
 
Regarding the crawl space, what I normally would recommend would be to insulate the perimeter with fiberglas blanket with a vinyl backing (commonly referred to as "curtain wall") and dump one heat run into the crawl space near the plumbing areas.  
 
Regarding the ceiling, I would not recommend insulating the truss holding the metal roof unless you put  proper vents between the roof and the insulation from the bottom to the top all the way from the eave to the apex of the roof continuously.  If you do this, you will need to purchase a flame-resistant insulation.  Normal insulation is applied directly above the drywall.  This cuts down your heat line and eliminates the need for a fire-proof product and allows you to backload the insulation with a second layer to increase the insulation value.
 
Bruce Jones
The Insulation Doctor