Questions and Answers about Wrapping Mobile Homes

Kelly Hart is your host at greenhomebuilding.com, and has built his own home using a hybrid earthbag/papercrete technique, which can be seen on the Earthbag page. He has adapted the concepts popularized by Nader Khalili and his "superadobe" building, by filling the bags primarily with crushed volcanic rock. This creates insulated walls that are similar to strawbale, except that they are completely impervious to damage from moisture, insects or rodents. The earthbags are plastered both inside and outside with papercrete. Kelly has produced a video, titled Building with Bags: How We Made Our Experimental Earthbag/Papercrete House, which chronicles the adventure of building this house, and shows other earthbag houses as well. Another video program that he produced is A Sampler of Alternative Homes: Approaching Sustainable Architecture, which explores a whole range of building concepts that are earth friendly. One of the homes shown in this video is a hybrid strawbale/wood framed home. Kelly spent many years as a professional remodeler, and is available to answer questions about what he has done, or consult about other hybrid projects.

Questions and Answers

Q: I have been searching the web for any information on Exterior Remodeling an Older Mobile home. We have just been given a 1988 single wide mobile, which we are going to remodel the inside into a recreational room. Its the Exterior siding that I'd like to re-face into something that doesn't look like a trailer. We are thinking about strawbale, but not sure if its ever been done to the exterior of a trailer. Help. Do you have any suggestions. I feel like this is a subject breaking new ground. Since the housing market is off the $$$ charts, why not refurbish old trailers & mobiles and turn them into a useful living space that is befitting to a high-unique living style? Please if you can point me in the right direction I would sure appreciate it.

A: I have been asked this question many times, and the answer is yes, it can be done. It would be a rather major retrofit to achieve, since your trailer would basically need to be surrounded by an entirely new building. This means that an adequate foundation would have to be created, the bale walls (or whatever natural material you chose) would have to be built up in such a way that window and door details would function with the original ones (and detailed to avoid potential moisture problems), and then likely an entire new roof structure placed over the whole building/trailer to assure that the new walls are adequately protected. Given all of this, the trailer should be rather special and worthy of salvage in this way to warrant the work and expense; as you can see, you have nearly created a new natural shell. But I agree with you that salvaging these old trailers is a worthy goal.

C: (Bill Sitkin)I have been accumulating ideas from here and there and want to pass this compilation by you. There are plenty of repo modulars to be had. The perfect one for this project would be one with a high quality interior and a funky exterior.

R: I have put some thought into this proposition, and have had numerous questions from readers of GreenHomeBuilding.com about the idea of retrofitting manufactured housing in various ways. The most common exterior siding used on these things seems to be some sort of painted press-board that holds up fairly well if kept dry most of time. Unfortunately, many of these homes, especially the single-wides, have NO EAVES, and therefore leave the siding completely vulnerable to exteriorization from moisture. I have seen many instances of this problem. Obviously, any retrofitting of these sorts of homes must include a new roof that encompasses the entire unit with ample eaves.

C: (Bill Sitkin)Before setting the home a good sized thermal mass would be installed in the foundation ( at least 6 feet deep).

R: While a concrete foundation obviously provides a great deal of thermal mass, this is nearly useless as far as helping to moderate interior temperatures, since it is isolated from the upper portion of the home. Useful thermal mass must be located within the living portion of the building shell. This is true for basic passive solar designs.

Rather than creating a standard continuous concrete foundation around the manufactured home, I would suggest using insulating earthbags to do the job. They can start at ground level, or perhaps a foot below, if put on sand or on a rubble-trench foundation (depending on soil type). The perimeter stemwall on these things is really not the foundation for the building, since it actually rests on pillar supports located beneath the steel frames on which they are built. Again, this idea pertains more to conventional passive solar designs, than what you describe below.

C: (Bill Sitkin)The home is set and then strawbale walls are added. To protect the bales a second roof is installed with a 2 inch gap between the first roof and the second that extends several feet beyond the bales. The second roof is for a solar hot air system that connects to ducting in the peak that then heats the thermal bank from the bottom up all summer. By the time the bank begins to release heat the colder months have arrived. The key is in creating a control system for the heat source and directing it to the desired areas. A small detail is to use reflectex between roofs.

R: This is an interesting idea, that I am not sure I completely understand, but I believe I get the picture. In this instance you are using the thermal mass of the concrete "foundation" to store heat for release later. This might work in the Crestone area climate, which doesn't really get very hot in the summer. It would likely need an active component of a fan to force the collected hot air down into the area under the floor. I think to be effective, such a system might need considerably more mass than just the concrete...like what the earthships attempt to do with their vast insulated earth berm on the north side, or possibly bins of stones down there. Maybe the actual foundation support for the steel frame could double as thermal mass.

Another considerable challenge with this idea is exactly how to interface the bale wall with the existing door and window openings in such a way that it looks good and is durable over time with all of the potential water issues. The devil is in the details. Probably, the only way to find out if this works, is to try it out on some project.

R: (Owen Geiger) I think Kelly's right.  It's easier (less labor intensive) to add thermal mass inside the dwelling space.  If used as seating, floors, etc. it's very practical. Also, I recommend using trusses to build a new roof on the old structure.  Trusses provide lots of space for insulation. Matts Myhrman's book Build it With Bales briefly mentions wrapping modulars with bales.  I've also been privileged to see his proposal for a Native American community in Arizona.  (The project never took place as far as I'm aware.)  Using his ideas, families would be able to stay on their land and continue living in the modular throughout the renovation process.  The end result is a beautiful, super-insulated southwestern style home that's doubled in size by adding a sun space addition on the south side.

C: (Bill Sitkin) I remember seeing a video that showed a house being retrofitted with strawbales. The windows and doors were relocated into the bales. The depth of the window sills could be varied depending on where they were located. I have to disagree about the thermal mass located inside the building since there is already limited space in a modular. One could pop out the south facing side with a greenhouse that has the mass incorporated into the stem walls and foundation. The cost variable of building rafters would be a negative in my mind. One would still have to bear the cost of a new steel roof whichever way is decided upon. At any rate, I think that retrofitting modulars could be lucrative. I have been looking at the repossessed websites and they are very affordable.

R: (Owen Geiger) Put all doors and windows flush with the outside of the bales to prevent any moisture problems.

R: I actually think that adding a solar greenhouse/heater addition to a modular is about the best of all ideas. I also agree that the larger trusses are unnecessary. There are ways to get mass inside, such as with tile floors, rock-work surrounds for wood stoves, etc., that don't take up that much space. Clearly, money can be made with fixing up those cheap repos in sustainable ways.

Q: I bought a old doublewide mobile home with a foundation and basement. It was the only thing I could afford in the Bar Harbor Maine area when I wanted to move to the coast I love. I saw a lot of potential in the home. I want to reconstruct the roof and bump it up so it has a pitch on it to give me more room. I want to open the front so it has windows and put in double doors and a porch as I have a great view of the bay from my front. I want to do bales of hay around the house and then put on a regular house over that and then redo the interior. I am I being a fool? This will be all that I can afford to live in as the prices of homes here are out of control.

A: What you describe can be done, but there are a number of details that will need to be worked out, especially dealing with an appropriate foundation (as described in another Q and A below) and the need for a roof that substantially covers the new walls, as well as all of the door and window details.

A: (Jeff Ruppert) One of the main pitfalls associated with retrofits is the foundation. If you are in an area with frost heave, you will need to put down support for the bales to frost depth. The other alternative is to sink piers along the wall length and span with a grade beam which incorporates a void form for soil expansion during frost events. If you do not have frost heave issues, it is a fine approach to rehab. The windows work best when on the exterior not only in a retrofit. Good luck!

Q: We had very little money or time to build so we gutted a single wide HUD mobile and are doing low/non-toxic renovations to it. Now we realize that we are going to need a larger place as we will be adopting four foster care children with-in about 6 mos. Do you know of any "green" manufactured/mobile home suppliers or have any ideas on green renovations to an older mobile home?

A: If I were to renovate an older mobile, I would consider adding thick, insulating walls to the outside, using either strawbales or earthbags filled with rice hulls, vermiculite, perlite, or crushed volcanic rock. This would mean creating an appropriate foundation for these and extending the roof to go over the walls and creating appropriate door and window openings...so it is still a lot of work and some expense, but possible.

Q: I was looking through your website today because I am in dire need of fixing my inadequate house..1972 mobile home with 2 inch walls. I can't afford to replace it with a new one and I want to try to cover it up with something for more insulation. I saw the cob building and was fascinated by being able to mold and shape; a person could be really creative! I was also looking at the lightweight concrete and the beautiful form it can be molded into. Is there any recommendation for something I can put around this trailer... I was wondering if the cob would dry if it was placed next to the trailer? My property is in Cripple Creek, Colorado, elevation 9494. Any advice would be GREATLY appreciated. I have all winter to read books and try to figure this out!!!

A: There has been a lot of interest in upgrading older mobile homes with better insulation. People have done this with strawbales, which are especially good for this, since they provide such good insulation (about R-30).  The strawbales (generally placed on the outside in this scenario) need their own substantial foundation, and then the roof structure needs so be extended to cover them. Cob would not be a particularly good choice for this, because the insulation value is rather poor. Lightweight concrete could be a reasonable option, if it is done thick enough. You get about R-15 for 6 inches of vermiculite or perlite concrete...so this plus what you already have would definitely be an improvement. At that altitude in Colorado, you want every bit of insulation you can get!

Q: We live in Central Washington State and own a nice manufactured home. I am wanting to go greener but I really do not want to start over completely since I am happy where I am at. I was wondering if it would be possible to wrap the existing home in earthbags to make it more efficient? I imagine that a vapor barrier may have to be placed between the existing siding and the earthbags.

A: This is certainly a possibility, especially if the earthbags were filled with an insulating material, such as crushed volcanic rock, perlite, or rice hulls. There are a number of technical details that would need to be worked out, like proper foundation, roof overhang, and how to deal with windows and doors. A vapor barrier between the earthbags and the siding may not be a good idea, because it could become a point of condensation that would adversely affect the siding and interior insulation. It is usually better to leave the wall system as breathable as possible.

Q: I have been reading on earthbag building for many years and have always wanted to build my family a group of domes. However, we now live in an older mobile home that I have almost completely renovated from the inside out and hate to waste the time and materials invested. I have read your page of info regarding wrapping the exterior of a mobile with earthbags or strawbales but I still have some additional questions. I would like to use bags of rammed earth instead of straw bales or filling bags with pumice, scoria, etc. The reason for this is because I am hoping the bag walls could support flat roof trusses with a living roof over the length of the trailer. Is this possible? Also, since the trailer is 4 ft off of the ground at the high end would it help to build a double wide bag foundation wall up level to the floor of the trailer and go single wall from that point on? I do know that buttressing will be involved but I'm still concerned about the bags being able to support the weight.

A: You could certainly wrap your mobile home with bags filled with compacted adobe soil, and this would be plenty firm to support a heavy roof. You would lose the insulative value that either strawbales or scoria would provide, but this may not be a primary concern if your mobile is already fairly well insulated. Also adobe walls that thick will help moderate interior temperatures considerably. On the other hand, I believe that bags filled with pumice or scoria could also support a heavy roof... You could make a double-bag stemwall foundation, like I did for the base of my Carriage House, and it would help with the stability of such a high wall. If you can figure out a good way of periodically attaching the bag wall securely to the sides of the existing mobile, you could probably get by without do this, or even adding any other buttressing.

Q: I was wondering if it's possible to use earthbags around the MF home with the possibility of a gap in between to fill with that foam insulating material (which would also cover the earthbags as one cannot get in-between to plaster. Would there be the need for a membrane? a cement foundation? Not sure. However, plaster the outside and sides etc.

A: (Kelly) It is possible to surround a manufactured home with earthbags, and this can enhance thermal performance. Probably the best type of fill for the bags in your area would be some form of insulation, like pumice or volcanic stone, rice hulls, or perlite. This also has the advantage of being much lighter to work with. Such bags can be placed right up against the existing exterior siding of your home.

The easiest foundation would be a simple rubble trench dug around the perimeter of the house for the bags to rest on. You would need to somehow extend the existing roof out over the new bag wall, and there are various ways to do this. And, of course, the bags will need to be plastered to protect the material and provide a pleasing appearance. The details for how you will deal with door and window openings also needs to be worked out. Altogether, this would not be a simple process to accomplish, but it might be well worth your while.


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