Purchasing SPF Trailers: Important SPF Rig Weight & Capacity Considerations

Below are things to take into consideration when choosing a spray foam rig. This is extremely important because if your rig is not built to industry standards, you could have issues down the road and lose your costly investment far too soon.

What carries your equipment is as important as what’s inside. After all, if you can’t get to the job, it doesn’t matter what you’re carrying! Use this resource to stay up to date on SPF rig and trailer best practices when it comes to designing your own rig or investing in a pre-built one.

SPF Trailer/Rig Weight & Capacity

SPF Rig Weight

How is the trailer constructed? Is it built to withstand the weight of heavy equipment and drums of material over time? Trailers should be built for spray foam contractors, not reused from other applications.

The reason we want these trailers to be specifically built for spray foam is because the interior components are very heavy. A 500 lb. drum is really only being carried over a few square inches when you consider the bottom ring it sits on. Trailers that are not built to SPF specs can eventually have sagging floors, or even worse, drums and equipment that end up falling through the floor.

Here’s a thought — a fully loaded 20’ tag-along trailer, without foam, can weigh over 9,000 lb. Now, add two sets of foam, and you’ve got 13,000 lb to carry. A typical 20’ tag-along is rated for 14,000 lb. This leaves 1,000 lb. of wiggle room for ladders, scaffold, or even a third set of foam. Let’s look at some numbers.*

Basic Rig Components & Their Weight:

  • 20’ Tag-along trailer: 4,100 lb.
  • Diesel generator: 1,500–2,100 lb.
  • Compressor: 700 lb.
  • Proportioner, hose, guns: 500 lb.
  • Aux equip. (heater, AC, air dryer), electrical, plumbing, insulation, hardware (barrel braces, hose hanger): 900 lb.
  • Toolbox, bench vice, wire wheel, tools, breathing air: 500 lb.

*To be fair, I’m estimating some of these numbers, but I believe they are very reasonable.

This rig could weigh anywhere from 8,000–9,000 lb. … without foam. Is your potential trailer capable of handling that? Or are you not even sure what your trailer is capable of handling?

Contact your local IDI if you’re unsure how securely your rig is holding the weight of your equipment and components. We host IDIREV rig evaluation events to help you manage these issues and any others that may arise.

As always, we recommend you follow all local and federal recommendations for weight distribution.

SPF Rig Towing Capacity

What is the cargo capacity? What is the Gross Vehicle Weight Rating (GVWR)? Can the trailer support two or three sets of material, as well as a generator, compressor, and one or two proportioners?

When considering an SPF rig, you need to take everything into account. Towing capacity is a huge consideration, and yet is one that’s often missed by suppliers who aren’t experts. If your trailer is not designed to the correct weight capacity, you can have issues with your axles bending or even breaking.

Trailer Structure

What is the interior height? Ample headroom makes it easier to change out a transfer pump without tilting the material drums. If you do not have enough interior height, this can make it very dangerous for your installers. Tipping the drums to get pumps in and out of the barrels can easily break or take off fingers in the process.

How is the floor of the spray rig finished? Spilled chemicals, sliding barrels and even foot traffic will wear heavily on a floor that isn’t built with durability in mind. Over time, this can cause the floor to rot. Without proper paneling on floors and walls, spilled chemicals can absorb offgas and promote harmful VOCs in your rig.

At minimum: walls should be thoroughly painted.

At best: walls should be paneled with a faced sheathing to help maintain cleanliness to limit VOCs.

Is the spray rig insulated? Does it have an air conditioner and heater?

Maintaining the chemical temperature is important to better control the reaction between A and B materials, which results in better material yields and more ROI after every project.

In warm weather, an air conditioner helps prevent material from overheating and expanding drums and keeps humidity at acceptable levels. In cold weather, a heater makes it easier to warm up materials to optimal spray temperatures. Your rig should have the ability to process foam according to the manufacturer’s recommendations no matter the conditions of your climate!

Here are some money-saving SPF rig temperature tips:

  • Most climates in the US will fall under 45 degrees and rise over 95 degrees throughout the year. Both ends of this spectrum are problematic when processing SPF.
  • Insulate your trailer: If it’s not fully insulated, it doesn’t matter much what mechanicals you’re using; the foam will be damaged by harsh climates.
  • Practice what you preach! If we believe SPF is a premium insulator, shouldn’t we start by believing it should work in our own rig? This is overlooked by some rig builders in an effort to reduce the price. Think of selling an expensive car (I consider SPF the high-end car of insulators!), would the salesperson be driving a beater?

A Commercial Trailer Just Won’t Do!

Is the trailer equipped for proper weight load distribution?

Proper weight load distribution keeps tongue weight at an acceptable level, promotes safe towing conditions and prevents swaying.

Pro tip: A rule of thumb is to keep tongue weight between 9%–15% of the loaded weight of the trailer. Remember that trailers pull much differently when fully loaded (to the job) and empty (from the job). A properly balanced trailer will pull safely both ways.

This issue is more prevalent in a tag-along trailer. The reason is the weight rating of a receiver hitch vs. the weight distribution of a gooseneck. This problem is solved by placing the axles in the correct position on a tag-along trailer.

This is why not just any trailer will do when building a rig. We work closely with our vendors to make sure the trailers are ordered with the axles mounted in the correct position, meaning there’s a specific measurement from the tip to where the axles are mounted. That way, we are under the 15% rule when loaded going to the job, and over 9% when empty coming home from the job.

Consider this: Look at the label on your pickup’s receiver hitch:

Even a Class 5 hitch on a 1-ton dually is usually under 2,000 lb., with non-duallies closer to 1,400–1,600 lb. The diesel generator alone can exceed this weight limit, not to mention the trailer weight itself, or other equipment placed over the tongue.

“We put the drums over the axles so it balances out”… that’s fine if your rig is sitting in your shop! Most of us don’t want that — foam shouldn’t be a fixed weight! When we’re busy, our rig can fluctuate 3,000 lb. on any given day, whether we’re fully loaded or empty on our way home from a job.

Insulation Equipment Housing & Installation Within the SPF Rig

Where is your equipment located in the rig? Is it somewhere where drums will consistently hit your proportioner and eventually cause damage to your machine? You and your crew must make sure your hoses are out of the way and on a hose rack (built specifically for spray foam hoses) so they don’t get snagged as well.

You also need to make sure your rig is plumbed and all electrical is run by a certified electrician. This is very important because if someone is wiring your SPF rig or trailer and they don’t know what they’re doing, they can fry your machine!

Considering an SPF Rig but Unsure How to Get Started?

In short, make sure your rig builder is someone you trust and are completely comfortable with. This is a lifelong investment, and cutting corners usually ends up costing you more money in the long run. It’s crucial to work with the pros — contact your local IDI Distributors to get started!

By: Ken Allison, Director of Business Development

Ken specializes in business development and building science. You can find him at any of our training events around the country helping local contractors grow their business. Contact your local rep about the next training event near you to hear Ken’s advice first-hand.

Read the Full Series:

Read our full rig series to determine what type of rig you should invest in to get the most ROI. Learn about the important factors that should go into your rig purchase decision — and how they could affect your rig’s performance on the job … and your profitability!

  1. Introducing Our Mini-Series (what you should know about owning a spray foam rig)
  2. Important SPF Rig Weight & Capacity Considerations
  3. How to Choose the Right Air Filtration System
  4. Air Pressure & Volume — Is Your Equipment Sized for Optimal Performance?
  5. Choosing SPF Equipment With the Best ROI
  6. Choosing Power and Auxiliary Equipment
  7. Other Cost-Saving Considerations


Have a question on anything insulation, pricing, or want to place an order? With hundreds of products and countless services, our experts will help walk you through the process of getting ready for your next project. Get in contact with our team today for help and guidance on the right products and best techniques for you and your business.