Mobile Home Additions Guide: Footers, Roofing, And Attachment Methods

how to Build Mobile Home Additions

It’s much more affordable to ‘grow as you go’ than it is to buy a whole new home. In this article, we take a look at mobile home additions. We cover the basics of building an addition as well as the advantages and disadvantages of adding an addition to your mobile home.

The Basics of Building a Mobile Home Addition

There are a few basics you should know before you decide to build an addition onto your mobile home.

The most important thing a homeowner should know before adding to a mobile home is that the addition should never be attached to the home at all meaning the addition has to be built completely separate from the home with its own footers so that the weight of the build is distributed directly into the ground and not the home.

Additions Aren’t Actually attached to the Home at All

First and foremost, additions should never be attached to a manufactured home at all. The addition must be a completely separate unit that is simply butted up to the home and ‘sealed.’ You want the addition and the home to shift independently and only have a minimal connection that doesn’t impede the separate movement.

A mobile home addition must move freely from the home.

Additions post
Your addition or porch should not be attached to your manufactured home.

To put it simply, you aren’t attaching the addition to the home at all, you are building extremely close to the home and then sealing the crack between the home and the addition to prevent air and moisture leaks.

Footings for Mobile Home Additions

An addition needs a completely separate foundation from the home. And, like any structure, the footers must be placed below the frost line to keep them from shifting when the moisture around the cracks in the ground freeze causing the footers to heave and bow.

There are poured footers, cinder blocks, slabs, and piles. Footings for a mobile home addition should be determined by the depth of the frost line of your area, even if your home does not have the frost line footers so that shifting is minimal.

Here’s a map showing the frost line depths for the US:

Frostline depth - building mobile home additions - footers

Footers are installed below the frost line so that the addition doesn’t sink or shift.

Frostline footings
If you do not use frost line footings your piers can shift creating stress on the home and ultimately making it unlevel. If it’s especially soft ground the two sections can separate.

Financing and Insurance Issues for Mobile Home Additions

Additions to manufactured homes are not often seen as an ‘improvement’ – meaning it probably won’t increase the value of the home in most cases. It won’t change the classification of a manufactured home from personal property to real estate unless the home is permanently installed.

A big disadvantage of building an addition on your mobile or manufactured home involves financing and insurance. It may be harder to obtain both if your home has been modified in any way. If you didn’t get the proper inspections and permits you may run into serious issues if you try to sell the home later down the road.

Permits and Inspections

Some state mandates override local and county regulations when it comes to manufactured homes. Research properly for your location before you begin planning a mobile home addition. With some locations, you could run into so much red tape that the project ends before it even begins.

With all that said, mobile home additions are perfect projects for families that need a larger home but you must get permits and inspections done before, during, and after the construction process. Read about one manufactured homeowner’s experience while building an addition onto his single wide. He failed to get permits and inspections done and paid a price when he sold the home.

Addition on 1985 Liberty Single Wide

Sarah and Justin Wartick built an addition onto their 1985 Liberty single wide. You can see how they created the footers right up against the home and then framed the floor of it out (they were test framing the top in the first image). The second image shows the walls and roof have been framed and the floor joists being laid.

These next two images are the interior of the addition. The image on the right showing the door with the two steps is where the mobile home and the addition are attached. Technically, this is the only place the two structures meet other than where the roof and the siding are ‘sealed’ together.

HUD Guide on Manufactured Home Foundations and Support Structures

There are some great online resources about mobile home foundations. This guide about manufactured home foundations and supports is invaluable. 

For information about general construction footers, Front Porch Ideas and More has some nice illustrations that show the poured concrete and pier footings.

Mobile home additions - correct frost line footings and pier
Mobile home additions - correct frost line footings and pier graphic
Pouring a pier foundation - mobile home additions - correct frost line footings and pier

There are new products hitting the market to aid in DIY footings such as these square foot concrete forms.

Mobile home additions - correct frost line footings and pier - proprietary systems

Framing an Addition

You want the mobile home addition to having framing that is equal to or better than the framing that your home has. Of course, you’ll need to follow your local code.

Below shows a mobile home addition being framed out by SM Construction.

Framing of mobile home additions

A great blog called Dovetail Blog shares its mobile home addition process in detail. It’s a small addition but the end results are beautiful:

As you can see, they used poured concrete footings and extended the roofline down to the addition, keeping the pitch. The addition looks to be used as an entryway that houses the stove and is a few inches lower than the home, except for a platform that the stove sits on.

Mobile home additions - after

Here’s the interior of the home:

 Opening Between the Home and the Addition

You’ll have to determine the size of your opening from the home to the addition. Doorways are easier to close up should the home ever need to be moved or the addition removed.

If you do opt for a wider opening between the home and the addition you will need to consider support issues for the opening. Wider openings, where studs would need to be removed, will likely require support beams. That’s not the smartest move for mobile home perimeter walls because those are your load-bearing walls. In other words, keep the opening small so that it’s easier to seal around the home and to keep from needing to support the perimeter wall with a beam.

Sealing Around the Mobile Home and the Addition

As stated previously, basic mobile home additions are not completely attached to the home. They are simply butted up to the home and then sealed all around to prevent leaks.

There are a variety of ways to seal the connection between the home and the addition. To seal the gaps between the home and the addition you can use weatherstripping, flashing, backer rod, caulking, and lumber. A backer rod is just a fancy name for round foaming that can be used as a membrane between the 2 structures.

There is a popular way to attach the siding of the home to the addition. Attach a 1×6 board to the home vertically so the addition will butt up against the middle of that board. You’ll attach another board with a lip to the side of the addition. Then, add weatherstripping and screw the lip of the addition to the board on the house – this brings the addition toward the home and helps seal it without overly damaging the home.

Flashing and vinyl siding will cover it all up.

Sealing the Addition Roof to the Mobile Home Roof

To connect the addition’s roof to the home if the addition is lower than the roof on your home, you will need to use flashing to seal the gap between the home and the addition.

For a metal roof, you would tuck a single length of 18″ flashing, that has been bent to the needed angle, place the flashing under the homes roof edge and over the addition roof. Attach to both with screws. Using 2″ neoprene flashing tape is always a good idea, and always seal the screws with weatherproof caulking (neoprene based). One note about the flashing, you want as long a piece as possible, but you don’t want it too long. If the flashing is too long it can cause cracks.

If the 2 roofs are at the same height, you just use flashing. Screw and seal.

There’s a rubber roofing that would work well. There is also a rubber membrane that’s 24″ wide that professionals recommend for this situation.

If the addition’s roof is higher than the roof on your home, you add the flashing under the lip of the roof of the addition and over the roof of the home (the opposite of above). This creates what roofing professionals call valleys and are problematic areas on any home. Special care should be made to keep water from sitting in the valley that is created.

The graphic below is based on a graphic found on Mobile Home Repair that shows a concept for sealing a mobile home addition. The top drawing shows a cap built on the home (labeled Alum Cap) and a piece of wide weatherstripping folded over to make a bulb shape and screwed into a board on the top edge of the addition.

Top view of addition attachment

The bottom drawing in the image above is showing the home and addition from the top, looking down. A flexible vinyl with fiberglass insulation is used to seal the sides of the addition to the home. It allows the needed movement required if your home is not set on a permanent foundation that is set below the frost line – the best method to prevent shifting of a manufactured home.

Amazing before and after mobile home remodel11
Justin and Sarah’s addition was built lower than the home so they have steps leading down into the new living room.

Examples of Mobile Home Additions

Below you can see a mobile home addition that passed inspection and can be found on The Inspector Blues blog.

Double wide with addition no source
An addition with a full roof over on

It is independently supported, has wired smoke detectors, an exit, sits on an 18″ grade, and is built with pressure-treated wood. It may not be great looking but it had what it needed to pass its inspections and current codes are not lax at all.

Mobile home additions - not the prettiest but it passed inspection

Here’s a park model manufactured home getting an addition built onto it. Notice how they’ve done the roof:

Mobile home additions - park model with addition being built

Another park model manufactured home addition and carport built by HorseFly Construction:

Single wide park model - building mobile home addition

The next photo shows a huge addition built onto a double wide manufactured home by Addon Rooms:

Double wide - building mobile home additions

We’ve featured a few homes with additions:

Questions and Answers about Mobile Home Additions

It’s not hard to grow out of a home. We had two adults, a child, and 3 fur babies living in a 1978 single wide with 696 square feet of living space. I often dreamed of building an addition onto the home! 

The following questions about mobile home additions cover topics such as adding a garage, living in a home while the addition is being built, and the cost of an addition.

4 Common Questions about Mobile Home Additions

These questions were asked in the comment section of our very informative article about building mobile home additions found here.

Can I Add a Garage Beside My Manufactured Home? 

I have a 1300 sq ft home on a permanent foundation in rural Colorado. Last year I had cedar log siding put on the outside (big improvement).

Is it possible to add to the end of the place an attached double car garage with a small apartment above? My building department told me if I add 33% SQ footage to the home, it changes from mobile to standard construction. I am thinking of a 20 x25 addition. An apartment could be rental income.

You should have no issues building a separate garage with a second story beside your manufactured home assuming it meets your local codes.

Additions aren’t truly attached to manufactured homes. They must be built as a completely separate structure with its own foundational support. Typically, an addition to a manufactured home will be close to the home and then sealed together at the roof and sides. Siding is then wrapped around to create the illusion of a single home. Structurally, the manufactured home will move, settle separately from the addition of any size.

Structurally, the manufactured home will move and settle separately from the addition.

Make sure to research insurance and tax increases if your home changes to real property. Manufactured homes usually have low taxes so if you transition the home into real property your tax liability may increase significantly.

The Directory of Mobile Home Manuals may help you find more information about your specific builder’s suggestions here.

Questions about mobile home additions - manufactured home remodel - new garage installed beside the home
This home has gorgeous cedar siding and a one-story garage. Click here to see the interior.

Related: How to Make Your Manufactured Home Look More Like a Site-Built Home

How Much Does a Mobile Home Addition Cost? 

I’m looking to add a bedroom to my mobile home. Can it be done at $2000 or under? I’m thinking of either a nursery or the master. Thinking if I’m going to add might as well get a bigger bedroom. I’m assuming I have footings because I don’t have blocks.

I’m thinking of either a nursery or a master bedroom. Thinking if I’m going to add might as well get a bigger bedroom. I’m assuming I have footings because I don’t have blocks.

The simple answer to your question is no. There is little chance that you can legally build a complete bedroom addition for less than $2000. Materials alone will cost at least $2000 and then you have labor and inspections to pay for.

The foundation of your manufactured home will not matter because the addition must be built as a completely separate structure. New footers or slab foundation (depending on code) will be required for the addition.

Here is a great resource from HUD about manufactured home foundations that explains everything. 

Can you Live in the Home While Building a Mobile Home Addition? 

Is it possible to live in the main home while the addition is being built and sealed or is there a certain point when you have to move out for a bit? Even if hiring contractors and builders.

Yes, you should be able to live in your home while building a mobile home addition. Since the addition is a completely separate structure you can absolutely live in the home during construction. Only when you are cutting through to ‘attach’ the two together will there be any activity done to the home itself.

Can I Move a Mobile Home Addition? 

Can the addition be moved together with the mobile home when we have to move? Or will the addition have to stay?

If the addition is properly built it can typically be moved. It will be transported via a flatbed truck (assuming it’s not too large). Then it will be installed beside the home once the foundation or footers have been laid for each.

Transportation companies will charge extra for that service so make sure to factor it into the overall cost.

Summary

The basic concept of mobile home additions is to keep the addition separate from the home, while still allowing a connection that is weatherproof and leak proof.

Inspectors and building consultants are available at your local and state agencies, use them to your advantage. You want a safe, long-lasting addition that will make your homework better for you and your family.

If you have any questions, please comment below and I’ll try my best to find you an answer. As always, thank you for reading Mobile Home Living!

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107 Comments
  1. Patsy Simpson says

    Looking for a contractor to do large extensive additions and remodel to a double wide in the Campbell county Lynchburg va area

    1. Kim Alley says

      Right now we don’t have a directory of contractors (but we are working on one). You might be able to call a mobile home dealer and ask for a recommendation or just start calling places from the yellow pages. Just make sure you ask for references, and that you don’t pay them all their money upfront.

  2. Teresa Hewitt says

    Hi this is Teresa. Hope you are doing well! I have found one of really nice homes for sale, it is a single-wide home that is for sale out in a rural setting. Can I put an additions to the home like family room, office and a bigger closet? The home that is currently for sale, it does not say about den or family room so I really would need that for installing a stove and also for an office. I live in the state of Virginia in Spotsylvania county. Please let me know by send me an email at tkilby2009@hotmail.com all lower cases. Have a great goodnight!! Teresa