I am considering the purchase of a double wide (2 section) manufactured home for retirement that will probably be in the 10 - 15 year old range.  Some have 2 x 4 exterior walls and the better ones have 2 x 6 walls.  Most have double pane windows. 

For those not familiar with manufactured home construction, most have vaulted ceilings inside which means that the roof structure is usually by trusses about a foot or so thick running from the exterior walls to the ridge beam.  During construction, they install the ceiling sheetrock before blowing in fiberglass into the cavity, then applying the roof sheathing.  Like cars, if yours is a T, W, T build, you probably got more insulation than if it was a M or F build!  Three tab is usually applied to the roof after the sheathing and felt.

The climate area will be Tucson, AZ.

What are your best suggestions to take one of these energy hogs, and make a silk purse out of it?

My experience with double wides indicate that the lack of quality in the materials and workmanship of the original build make them very expensive to remodel. There are no 'simple' fixes for one. The best idea I have ever seen was to set up a unit and build a pole barn around it. The added walls and dead air space adds additional buffering from the elements without major damage to the unit.

Before taking on bigger projects, exterior shades on the E & W sides, and awnings/shades on the S side can dramatically reduce the solar gain through the windows. If the landscape or buildings to the north are light in color, an exterior shade on the north windows can make a difference as well. About half the solar gain through windows in the SW is from scattered light, not direct insolation though the glazing. If the windows are not a low solar-gain low-e type, retrofit window-films can also cut the solar gain. Going with the ~40-50% heat-rejection type films is preferable to most, since the higher versions end up killing too much of the natural daylight, but on unshaded S facing windows with bright landscape & foreground a ~70% film might be used.

Insulation-wise the most-cost-effective thing to do is to make it as air-tight a possible. Use a window fan to pressurize it, run around with a smoke pencil or stick of incense and a caulking gun, can o' foam, and sheet of labels to mark every air leak that need more work than a quick squirt of caulk or foam. Then flip the fan around to depressurize it, repeat process. Pay special attention to seams where the floor meets walls, window & door casements,duct, plumbing & electrical penetrations into walls (even in interior partition walls)/ceilings/floors. You may have to pull some casings around doors & windows to foam-in some of the gaps properly (use low expanding flexible "window & door" foam in those areas if you do.)

The next big benefit is to earth-couple the building: Put down a 10mil poly vapor retarder on the ground, lapping any seams by 12" and sealing them with duct-mastic. Put insulated foam board around the perimeter wall with taped/sealed seams & edges, and mastic-seal the vapor retarder to the foam-board 12" up from the ground. Foam-seal the foam board to the sub-floor. Build yourself an access hatch/door with decently tight weatherstripping to make it fairly air-tight. In Tucson 2-2.5" ( R8-R10) foil-faced EPS (beadboard) with the foil facing the exterior would be about right. This takes less material & time than doing a perfect insulation job on the floor, and brings the high thermal-mass of the ~70F subsoil into play moderating both cooling and heating loads. You may/may not be required to make provisions for ventilating it, but the risk of moisture buildup is low if you've sealed it well. If ventilation is required, make it operable/closeable. If there is air communication into the living space you'll need to provide an thermal barrier against ignition on the inside of the foam board, but I doubt that's the case here. Hopefully there is sufficient structural stuff to attach the foam to already, but if not, it isn't tough or expensive to build a 2x3" studwall 24" o.c. screwed to the sub-floor.

Next, to lower the cooling load, a secondary roof deck mounted on purlins above the original roof deck, with either CA Title 24 compliant "cool roof" shingles above, or a layer of radiant barrier foil (or rb paint, or aluminized fabric) on the original roof deck under the purlins (or both). Make the purlins at least 1.5" (2x2") for more and long-screwed at least 1" into the trusses/rafters, not just the original roof deck. You need at least an inch to get much benefit out of the radiant barrier- 1x furring won't be enough. Leave the purlin cavities vented to the outdoor air at the ends, but you may want to staple in some screening to keep critters & bugs out. If the secondary roof is too rich for your budget, re-shingling with cool-roof materials will still make a difference, even without the secondary vented layer.

Buy a cheap infrared thermometer and use it to scope out wall & ceiling temps to find any gaps in the insulation. It's usually pretty easy to find the studs on a hot day (particularly in direct sun), but try to find any cavities that are more than 2 degrees warmer than the average. Mark them all with sticky labels/tags- if you have a lot of them, it's probably worth squirting some cellullose in there from the exterior, or having a pro do it. Cellulose would be preferred to fiberglass in this application since it blocks more radiated heat and has more thermal mass. If the walls are only insulated with R8 econo-batts in a 2x4 cavity (is that still allowed in manufactured homes?), there's enough room to blow cellulose in all wall cavities, which will dramically reduce the intra-insulation convective R-value loss at high temperature differences that low-density batts exhibit, more than doubling your true effective R-value on the sides that get direct sun.

Dana1

Thank you for the great, detailed reply! It does, of course, raise some additional questions.

1. With regard to window films, my only experience has been with films applied to the inside of the window which resulted in breaking of the seal in the double pane skylight that I had in a home about 8 years ago and resulted in replacing the window. Are there films for the outside which hopefully would avoid this problem?

2. Where do I get a 'smoke pencil'?

3. Could solar panels create a 'cool roof'?

4. I did see a company I believe in Tennessee, that was franchising a system to install a low expansion foam in each of the spaces between the studs on the walls of manufactured homes but they had no franchisees on the west coast. I'm really more concerned about the ceiling as they blow in that fiberglass before the roof sheathing goes on and it is probably compressed to 50% once it hauled down the road to the final destination. That area is also usually filled with hvac ducts.

About 1996 there was a code change that did upgrade a lot of the requirements like getting rid of the gray plumbing and requiring PEX or copper, but I don't know if it addressed insulation. One of my problems is that my wife wants to live in this particular manufactured home subdivision where some of the homes were even built in the 80's. I suppose that one could buy a real fixer, move it out and install a new home that would have many of these features. I sure wish that you could buy one made with SIPs panels!

I don't know of an window films intended for exterior application. The liklihood of damaging the seal is probably greatest on windows that get direct sun (where the heat gain is greatest), perhaps another good argument for exterior shades.

Smoke pencils aren't super-cheap- most people use other methods, but the pro-units can be had online here, or here.

Solar panels would shade the roof, but "cool roof" has a real specs for maximum solar absorption & minimum infra-red emissivity.  Most shingle vendors that are CA Title 24 2008 compliant will have that buried somewhere in the literature.

In Tucson blowing the cathedralized roof cavities full of cellulose blocking any venting will not cause any issues.  Don't  use "dense pack" methods where a hose is snaked into the cavity to acheive maxiumum density unless you know for sure the ceiling will tolerate the pressure & weight.  A pro could tell you what density & methods they're comfortable with, but if you think it was low density fiberglass that's settled a whole bunch, a cellulose fill of the roof cavities would be well worth it.