Pedro Tavares, AIA, of R&S Tavares Associates, on what gets modular projects into trouble

When a manufacturer says a model is "approved" in a state, what was actually approved, and what still has to be engineered for the specific lot? Where do buyers get caught by the gap?

For off-the-shelf plans, when a client comes to us and says they would like to sell a standardized plan throughout the state of California, it involves two things:

The model must be designed for the worst-case load scenario, which is often seismic. So that model will need to be able to be deployed state-wide no matter the seismic or wind load category. In some parts of the state, roof dead load also becomes a factor, due to snow.

Harder to satisfy, in my opinion, is the energy compliance required for a model to be able to be placed anywhere statewide, in any orientation. More often than not, when designing buildings we're accounting for sun angles, wind direction, and unrelated to this really, views. A plug and play model can't do those things and so must be designed for the worst-case scenario, which is often large amounts of glazing facing south or southwest.

In conclusion, for a model to be deployable and "approved" in the state it needs to be overengineered, or a few models deployable to specific climate regions must exist. As manufacturers really would prefer to take advantage of their manufacturing capabilities and find an economy of scale building the same “sprocket” repeatedly, this becomes a challenge. We'll often direct clients to focus on where their likely largest number of sales will come from, the denser metropolitan regions and those climate zones, and treat the extreme cases such as Death Valley, Truckee, Tahoe, Mammoth, as special cases.

What does a good manufacturer engineering package contain, and what is missing from a bad one? What should a buyer ask to see before signing?

It should have a complete set of construction documents, an approved calculation package, and an approved energy compliance report that matches the site it's going to. The seismic values, wind loads, and energy compliance must meet the criteria for where you want to install the module, but can exceed them.

Foundations: what do you design for a modular set versus a HUD code home versus a park model, and what happens when the site contractor pours something the manufacturer's drawings did not call for?

A modular building will nearly always be shipped with a floor frame, though floorless modules are possible and built all the time as well, just less common in residential modular. Because it's built with a floor frame, we'll nearly always design a raised, or crawl-space or basement foundation, which means a sunken pit with a vapor barrier and concrete or CMU stem walls. This gives the module space for the water, sewer and electrical utility runs beneath it to their points of connection on the site.

A HUD Code home doesn't need that but will often opt for it. Because a HUD Code home, or "Manufactured" or "Mobile" home as they're commonly referred to, doesn't lose its chassis when it's delivered and placed semi-permanently, it doesn't necessarily need a stem wall foundation and is often placed on piers and pads, and skirted to hide the chassis. Though from my understanding some lenders and FHA/VA lending guidelines will require a permanent foundation for them to be set on.

Park model homes are considered "recreational vehicles" and built to that code (ANSI A119.5). They always remain on their chassis and are stabilized with piers or jacks and often skirted.

If a contractor pours something the drawings didn’t call for it’s on them to fix it in most cases.

Which states are hardest to get a modular plan through, which are easiest, and what makes the difference?

39 states in the US have a modular program right now. Meaning in those states, the off-site portions of a project are approved at the state level rather than at the local jurisdiction level, more often than not by a third-party engineering company working on behalf of the state. This is a great benefit to modular construction because state-level approval is, in my opinion, often much more efficient than local-jurisdictional approval. Inspections of the modular portions of the project are also conducted in the factory by a third-party engineering company, and they arrive on site inspected and approved.

To answer your question, in those 39 states it's rather painless to get a modular plan through, with the caveat that the local jurisdiction where you're placing it knows about the state-level approval and inspection process. Many smaller jurisdictions aren't familiar with modular projects and can be resistant.

The 11 states that currently don't have a modular program are Alaska, Arkansas, Delaware, Hawaii, Kansas, Mississippi, Missouri, Oklahoma, Vermont, West Virginia, and Wyoming.

Eleven states have no modular program: Alaska, Arkansas, Delaware, Hawaii, Kansas, Mississippi, Missouri, Oklahoma, Vermont, West Virginia, Wyoming.

Wind, snow, seismic, flood: which site conditions change the design enough to change the price, and how does a buyer find out early whether their lot is one of them?

All of those site conditions can change the price quite a bit. Buyers should generally be aware of their site's nuances and know if they're in an especially difficult region.

Flood maps are a potentially surprising factor, and you can find those on FEMA's website. However, being in a flood zone can generally be managed by elevating the unit and providing floodwater openings in the foundation. Another surprising issue we often encounter is bad or difficult soils.

Someone seeking a modular build should be aware of logistics: where the modules will be “staged” or queued for craning, ease of access to haul a modular up the road and make the necessary turns, and staging access for craning, lifting, and pivoting, especially concerning trees and powerlines.

Install day: what goes wrong structurally when modules are craned and joined, who is responsible when it does, and what should be in the contract about it?

The most common errors are field errors where something is out of tolerance, such as a stemwall, holddown or bolt. They're inconvenient but usually easy enough to deal with. We've had instances where a pier was off the grid line it should be, which wasn't discovered until a 30,000 lb. module was coming down on top of it. Luckily, there was an ABS pad and a jack on site that could temporarily hold it up until a permanent solution could be put in place, without delaying the setting. The crane is a very expensive part of the production, and incurring extra crane hours leads to unwelcome change orders. Other errors, such as lifting straps causing too much strain, sometimes result in broken or cracked glass.

Who's responsible? Good question. I don't have a good answer. In my experience on my own projects that I've designed and built with modules, I generally treat it as a contingency and move on. I can share some errors I encountered during the setting of my house and how they were handled:

The most serious issue was my shipper telling me the day before my modules were supposed to be set that his trailers wouldn't be able to make the turn onto my street after all. It delayed my set by a day to a Friday, which ultimately meant if we didn't complete on Friday we'd have to use two days for craning, and the second day would be on a Saturday at time and a half. The solution was to get three of a different kind of trailer that could make the turn and use four forklifts to transfer each module to one of those other trailers in the staging yard. This meant my modules traveled about 100 yards over-height, but it worked. I deducted the cost of the forklift rentals from the shipping payout.

No insulation was installed in the factory in the ceiling of a lower-floor module that separates the ADU from my main house that was in the drawings. I had to buy insulation at the hardware store, change the order the modules were being set to buy time to get it in, and roll it out before the next module was dropped, with help from someone on my set contractor's crew. I received a change order from my set contractor for the help with that, and ultimately worked it out with the manufacturer in some extra work with the post-set finishing they performed.

My set contractor wanted to speed up the lifting and dropping of the modules by cutting square holes in the C-Channel floor rim near the ends of my modules to use hooks to pick them up. He had one of his guys start on that while I reviewed if it would be alright. Our drawings specify some specific guidelines for lifting the modules, which would have placed those holes 8' in from each end, so I ultimately abandoned the idea because the crane was waiting for the modules. He issued me a change order for the time he spent cutting those holes, which I rejected.

Consult your lawyer regarding what your contract should say.

Energy codes, fire sprinklers, and fire zone rules: where do these add cost or delay that the manufacturer's price did not include?

Everywhere. If your site has some peculiarity, I think you should be prepared to deal with that.

ADUs: which states or cities have pre-approved plan programs that actually shorten the timeline, and what does a manufacturer have to have done for a model to qualify?

I don't know about everywhere, but many cities in San Diego County have implemented something like that, and there's a public response process for getting a plan included in their list of pre-approved ADUs.

From the projects you have engineered, what did the buyers with the fewest problems do differently at the start?

I'm an architect and our company handles both architecture and engineering for primarily modular projects in-house. Therefore, I'll speak more to the architecture side, specifically regarding custom-designed and built modular projects.

Getting your design team and the manufacturer involved and interfacing early in the project is very beneficial, because many manufacturers have preferred details and preferred suppliers for things like cabinetry, plumbing and lighting fixtures, windows and doors, and maybe even appliances. You should be able to take advantage of their purchasing power by using their commonly purchased materials.