The Pros & Cons of Engineering Customized Modular Homes

At CVL Engineers, we’re no strangers to designing with modular units. One of our highlight projects included two and three-story modular structures built at the Kananaskis Nordic Spa.

We’ve also applied modular engineering techniques to residential homes. Like any type of construction, modular homes come with their own unique set of challenges and benefits. Engineering these structures can be complex when it comes to elements like foundations, structural systems, limitations in design options, and resistance to the elements. However, the benefits include financial cost savings, energy efficiency, and the option for complete or partial prefabrication.  

This modern style of home is becoming more and more popular in Western Canada, which is why we wanted to showcase some of the pros and cons, and dive deeper into how modular homes are built.

An Overview of How Modular Structures are Built

The individual components of the modular homes are built in a factory and shipped to the desired location to be finished and assembled on site. The modular units can be built using shipping containers and retrofit using structural steel or be purpose built using steel or wood. The main structure is typically made up of structural steel, and the flooring is created using timber joists. 

Standard Design Options

CVL Engineers helped create a generic structural design for six sizes of modular homes that could be built anywhere in Western Canada:

  1. One Unit Modular Home 42’-0” x 11’-9” 
  2. Two Unit Modular Home 42’-0” x 18’-0” 
  3. Three Unit Modular Home 42’-0” x 26’-0” 
  4. Four Unit Modular Home 42’-0” x 34’-0” 
  5. Five Unit Modular Home 42’-0” x 42’-0” 
  6. Six Unit Modular Home 42’-0” x 50’-0” 

The modular homes are designed in accordance with the Building Code requirements for Western Canada, which covers Saskatchewan, Alberta & British Columbia. To see some examples, check out our client Honomobo.

The Main Challenge in Standard Designs

Our main challenge was related to the distinct weather patterns across Western Canada. If the units were designed for extreme wind, seismic, and snow loading requirements, it would have resulted in a very expensive modular unit. To offset potential costs, we created a flexible design that would stand up to most severe elements, with add-on options for regions with extreme weather patterns.

To create the generic design that was both cost-effective and universally weather-resistant across all provinces, we performed analysis using various combinations of wind, seismic, and snow loading. Each of the units was designed such that it will cover around 80% to 85% of locations in Western Canada. For locations with extreme loading requirements, a small retrofit would be enough to satisfy the local building code requirement (such as adding a column or brace).

Main Structural System 

Our main challenge in designing the structural system of the units was ensuring the modules could be easily attached and that the homes could be expanded in the future.

The main structure for our modular homes consists of steel & timber combinations. The floor & roof is supported on timber joists. The rim joists sit directly on top angle trays. The angle trays are supported off HSS columns that are welded to the underside of the angles.

Each module has been designed as self-sustained for gravity loads. The modules can be easily connected (either in a fabrication shop or on-site) to create the size of home that has been chosen. These modular units are designed such that a four-unit home can be easily converted into a five-unit home by adding one module at the end of a four-unit home. 

Lateral Force Restraining System 

The lateral force restraining system for these homes is achieved through a combination of brace frames & shear walls. The brace frames are designed using HSS steel sections. For shear walls, we utilized the HSS columns & container walls. The container walls are made of corrugated steel, and when HSS columns are welded to them, they act as a shear wall capable of transferring seismic or wind shear to the foundation. 

Modular House Foundation

The modular houses are designed such that they can be placed either directly on the foundation or over top of the existing floor or garage. The foundation for modular homes ranges from spread footing to pile foundation. 

CVL worked on various foundation designs for these modular homes, ranging from high wind zone to extreme seismic zone. One of the challenges that we faced in designing the foundation was to design a reasonably sized spread footing in a high seismic zone when a six-unit modular home is sitting on top of a 6’ deep crawl space. The intermediate brace frame columns have to resist high seismic shear, and since the structure is located above a crawl space structure, it results in a huge spread footing due to the overturning moment. To reduce the size of the footing significantly, we decided to use a timber pony wall to act as a shear wall between two spread footing under the brace frame.

Learn More About Engineering for Modular Structures & Homes

For this project, we drew on our extensive experience in designing and engineering structures with multiple modular units. We’d be happy to share our experience with you, including the pros and cons of working with modular units for homes or commercial buildings. Reach out and get in touch with CVL Engineers today to learn more.

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