Why You Must Air Seal a Modular Home

One of the most important steps that a general contractor can take to make a modular home energy efficient is to air seal the gaps between modules. The manufacturer can control air infiltration within each of the modules, but when the modules are placed side by side or stacked on top of each other, significant gaps are created. It is just not possible to bring two modules together tightly when a cable is wrapped around each one while being lifted into place. In addition, even when the framing of one module is tightly butted up against the framing of another module, it is not possible to make the joint airtight. Very few set crews completely seal these gaps, so the GC should assume the job.

How to Properly Air Seal a Modular Home

A modular home that is properly air sealed is significantly more energy efficient than a typical site-built home. When a modular home is poorly sealed, however, it will leak more than a site-built home. The GC should make every effort to seal the following:

  • The basement and attic marriage wall
  • The interior marriage wall wherever there is a passageway, door, or clear-span opening
  • The exterior marriage wall along the gable ends
  • The exterior band between floors on two-story homes
  • The exterior sill plate where the first-story modules sit on top of the foundation

On the interior, the best way to air seal large gaps is with expandable foam. On the exterior there is a special technique that should be used before the GC completes the siding. Most manufacturers hold back a small piece of the exterior sheathing where two or more modules join. The GC must insert a piece of sheathing that bridges the space between the adjoining modules. The sheathing connects the modules structurally and creates a flat surface for the siding. By itself, however, the sheathing does not do a good job of reducing air infiltration, even when combined with the sill seal installed between modules by most set crews. But if the GC applies two beads of caulk to the back of the sheathing before nailing it to the modules, this will create what in effect is a gasket seal. The GC can then finish by caulking the outside edges of the installed sheathing to close the remaining gaps.

Shows all connections where two modules are joined, both side to side and top to bottom, as well as where the modules sit on the foundation. The GC must air seal these connections against air infiltration.
The general contractor must air seal against air infiltration where two modules are joined, both side to side and top to bottom, as well as where the modules sit on the foundation

The GC should carry out a similar procedure where the bottom of the first-story modules joins the sill plate and where the top of the modular wall connects to the roof overhang at the eave. He should also foam seal the gable-end triangle sections under the roof; he might first need to brace the sections from inside the attic. Completing all of these steps will create a significantly more energy-efficient and comfortable home, for a negligible cost.

For more information about why you must air seal your modular home, see The General Contractor’s Responsibilities for Building a Modular Home in my book The Modular Home.

Modular Home Delivery and Set

When I first starting selling modular homes I had a difficult time convincing customers to bring the right equipment to their modular home delivery and set unless the need was completely obvious, which it often is not. That changed after one nearly disastrous incident.

A Lesson about the Importance of the Modular Home Delivery and Set

My customers were building a two-story home made up of four modules shipped on four carriers. I asked them to have their excavator assist the delivery crew on delivery day, and they complied. It turned out that the bulldozer was not needed because the ground was dry and firm. This enabled us to position two of the modules next to the foundation and crane on the property with the other two modules stored in a staging area over night. I reminded my customers that they needed to keep the bulldozer on site for the next day’s set, but they said they didn’t think it was necessary. I pointed out that if it rained that night, we almost certainly would have a problem. My customers responded that it would cost them $500 for the second day, and they thought it was a waste of money. When it began raining that night, I called them at home to again ask them to supply a bulldozer. They refused.

A caterpillar loader ready to help with the modular home delivery and set
Make sure your GC provides the proper equipment for your modular home delivery and set

The set started off well. We got the first module onto the foundation quickly. While we were setting the second, we delivered the third to the site. But the transporters could not get enough traction on the wet ground to move the modules close enough to the foundation no matter what we tried. My customers called their excavator, who arrived two and one-half hours later. While we were waiting, a thunderstorm hit hard. My set crew climbed on the roof, in spite of the lightning, and tried to cover the two modules with tarps. They did OK, but while trying to position the tarp, one of the crew slipped and pushed his foot and part of the tarp through kitchen ceiling.Allof the water that had pooled on the tarp while it was being installed poured onto a row of cabinets. Fortunately, none of my crew was hurt and the damage was repaired. But that experience taught me that I had to explain to my customers all of the things that can go wrong if they do not provide the proper equipment for their modular home delivery and set. It also taught me to delay the start of a set if the equipment is not on site.

Help Your Dealer Protect Your Home During the Modular Home Delivery and Set

When your dealer tells you to provide equipment for your modular home delivery and set day, remember that he isn’t just protecting his interests; he is also protecting your house.

For more information about the modular home delivery and Set, see The General Contractor’s Responsibilities for Building a Modular Home in my book The Modular Home.

Preapproval for Modular Home Warranty Work

Sometimes a general contractor with limited modular experience can turn a “couple of hours” fix of some minor modular home warranty work into a “couple of days” project.

Obtain Preapproval for All Modular Home Warranty Work

A stamp approving the modular home warranty work
Always obtain preapproval for modular home warranty work from your dealer before attempting to fix a problem

I had a customer whose master-bedroom ceiling was not level at the marriage wall. My set-day supervisor should have noticed this and told the customer that we would come back to fix it. But he missed it, and my customer, who was acting as his own GC, decided to fix the problem on his own. He ended up tearing down half of the bedroom ceiling before he contacted us for help. The problem, we discovered, was that the ceiling framing on one of the modules was hung up slightly on the other module, preventing the first module from settling all the way down. All that needed to be done was to free up the first module, which we were able to do in two hours. When we finished, the ceiling framing was even, but my customer now had to replace a lot of drywall.

Independent GCs Must Obtain Preapproval for Modular Home Warranty Work from the Dealer

It is very important that your GC understands that they should always obtain preapproval for modular home warranty work from your dealer before they attempt to fix a problem. If they do not obtain proper authorization, both of you are at risk for not being compensated for the GC’s corrective actions.

For more information about why you need preapproval for modular home warranty work, see Warranty Service for a Modular Home in my book The Modular Home.

Imperfections in Modular Home Sales Models

No sales model is perfect, regardless of who builds it.  Even modular home sales models have minor imperfections.

What I Learned about My Modular Home Sales Models

Soon after starting my business, I built a two-story model home with several upscale features. For example, I dressed up the first floor with oak trim and doors, all finished in clear polyurethane, so that my customers could see what this option looked like. The first customer who ordered this upgrade called me soon after we set his home, very upset. He said that some of his oak moldings had a much darker grain pattern than the others, which he felt was not the case in my model home. Without first looking at my model, I went to his house to see what made him unhappy. When I saw the variation for myself, I ordered replacement moldings. Unfortunately, the new moldings came in with as much variation as those installed in his home. Finally, after ordering three sets of replacement moldings, we were able to match all of the moldings in his house almost perfectly. (In retrospect, I cannot believe that my manufacturer provided me with all of these moldings for no additional charge.)

A couple of months later, the manager of a custom woodworking shop visited my model home. I told her about the problem with the oak moldings, and I showed her the rejected moldings. She then walked me through my model home and pointed out that it had the same “problem.” Even more surprising, she said that all of her high-end, custom stick-built customers had the same “problem” when she provided them with naturally finished wood moldings. She added that most customers actually prefer this natural variation.

Notice the Imperfections in Your Dealer’s Modular Home Sales Models

An open house sign to modular home sales models
Modular home sales models are never perfect, since all new construction has minor imperfections

In addition to teaching me about the natural qualities of wood, this experience taught me how easy it is to miss the true appearance of a home’s features. Over the years, I’ve noticed that while most customers do not look closely at our modular home sales models, they put a microscope to their own home. And when they do, they see both real and imagined imperfections that they do not realize are typical of all homes, including their dealer’s modular home sales models. I strongly recommend that you make an effort to notice the imperfections in your dealer’s modular home sales models and expect them in your home.

For more information about imperfections in modular home sales models, see Modular Home Specifications and Features in my book The Modular Home.

© The Home Store, Inc., 2021