Question

I'm converting a school bus into a motor home. What's the best way to insulate?

Asked by josh jackling
Perris, CA

I want to insulate with closed cell foam. I have approximately 3" of room to fill. What R-value is that? I want to fill the roof but I'm not sure if it will expand and deform it. Also, where do I buy the product? Or where can I find a company to do it? I live in Perris, CA.

Answer

Cynthia Phakos

Answered by Cynthia Phakos

Los Angeles, CA

Koffka Phakos Design

January 6, 2011

With more natural disasters rendering people homeless, and with the trend in repurposing used items that would otherwise go to a landfill, this question has relevance in many applications. Architects are experimenting with shipping containers for housing components to deal with the very same issues.

Insulating for heat loss, heat gain

School buses typically have an integral chassis with a body frame made of a vertical C-channel frame (3" as in your case) with horizontal steel members serving as crash protection at the floor, and below and above the windows.

Between the frame members would be where you would apply blown in insulation.

If heat loss is an issue, insulating the floor would be critical and you might ask your mechanic if there is anything that can be done at the chassis. At the interior, I would recommend a carpet and a thick pad as insulators.

If heat gain is the primary issue, the walls and the roof are the areas of concern. The floor not being insulated would actually work well, with the underside of the bus allowing for air movement.

I recommend cellulose

Closed cell spray foam insulation, a superinsulator (R 6–7 per inch, yielding an R 18–21 wall), expands approximately 100 times its initial size and can deform a wall or, in the case of a bus, can seep out of panel joints on the interior, the weakest points of the wall and roof construction.

For a blown-in insulation, I recommend cellulose made of pulverized newspapers with an R-value of 3.8 per inch, which will give you an R-value of 11.4. The cellulose is treated with boron, which is fire and pest resistant. To prevent settling, an adhesive can be added.

Build out the wall if necessary

If you require more insulation, you could build out the wall on the interior below the windows and then use the spray foam insulation.

I would recommend using metal studs, flat framed, spaced an inch from the exterior wall. This gap will prevent thermal transfer through the exterior wall construction and the metal studs. After installing the foam (be sure to open all of the windows and use a fan for ventilation during installation), the wall could be finished with drywall, with a ledge at the sill of the windows.

A good installation company (referred to me by installers that I have had much success with) very close to you is Apple Valley Insulation Contractors in Hesperia, CA (760-244-8848). They can give you pricing as well as recommendations as to whether your wall construction would work for the spray-in foam.

Other ways to deal with solar gain

As furring down the roof would not work since height is an issue, another option is adhering a product such as AYR-FOIL. This is a 3/8" thick, 7-layer, reflective insulation which comes in rolls of varying widths.

  • The two outer layers of aluminum foil will reflect 97 percent of the radiant heat.
  • For heat gain, this might be your most economical solution, and might be something you experiment with.

The foil will certainly change the aesthetic of your interior, but it can be covered with drywall. If you are planning to go in this direction you might speak with a local representative of the product.

Solar gain through the windows will also impact the comfort of your mobile home, and you might contact a glazing contractor for a window film that would serve your purposes.

Other factors that will affect the heat gain would be the color and emissivity of the exterior finish.

Tagged In: insulation, spray foam, reuse

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