Raising the Walls
In This Chapter
- Discovering flooring layout options
- Choosing the best framing system for you
- Understanding framing terms
- Connecting your tiny house securely to the trailer
If you’ve never built anything significant before, don’t fret. After personally teaching more than 2,500 participants at our construction workshops since 2006, one thing has become crystal clear. You can build your own house. We’ve seen it done time and time again by novice builders, so we have complete faith that you can be successful with your build, too.
Most people living in their self-built tiny houses have no previous construction experience either. What they did have was determination, passion, and a desire to learn a new skill. We can tell this describes you, too, because after all, you’re investing your time and effort right now by reading this book and learning as much as you can.
In this chapter, we cover tiny house floor frame systems and important framing terms, compare wood framing to other options, and learn how to fasten our tiny house to the ground, to the trailer, and to the roof.
You have two options when it comes to floors on a Tiny House On Wheels (THOWs):
1. Use a trailer frame as the base for your floor sheathing
2. Add a secondary floor system over the trailer frame
There are advantages and disadvantages to each approach.
By adding your sheathing directly to the trailer frame, you’ll maintain maximum ceiling height in your structure because you won’t have additional floor framing competing for interior space. The downside is that you’ll increase the potential for thermal bridging through the trailer frame into your conditioned interior. Thermal bridging refers to the process in which heat moves to areas that are colder. This is also known as heat loss. When materials such as metal are used in construction, they provide a path for that heat loss. When directly connected to the interior of a structure, these materials create a bridge for that heat loss.
DEFINITION
Thermal bridging is when noninsulated building materials such as metal or wood create a direct path for heat loss through an insulated building.
You can minimize thermal bridging by adding a framed floor system on top of your trailer frame. By creating space for additional insulation, your trailer will be much more isolated from your interior space. Your interior head height will decrease, but you’ll enjoy the benefits of warmer toes in the winter and be able to install utilities within the subfloor rather than through the ceiling.
You’ll want to create this floor frame with smaller lumber, such as 2×4s, to minimize the loss of ceiling height. Be sure to install the framing material either directly above the trailer frame members or perpendicular to them.
If you want to eliminate thermal bridging completely, consider using structurally insulated panels (SIPs) as your floor frame. SIPs, which are custom factory built structural systems with embedded high insulation foam, are very strong and provide a complete thermal break. They come in different options and the thicker you go, the better your insulation potential.
DEFINITION
Structural insulated panels (SIPs) are a high-performance factory-built system. Two panels—typically made of oriented strand board (OSB)—create an outside sandwich over sheets of foam insulation. They can be built to fit nearly any design. Building with SIPs is typically the same cost as wood-framed construction when labor is factored in. It’s also more efficient and thus can allow for smaller heating and cooling systems in a structure. SIPs make quick work of raising a wall and roofing system, especially when compared to wood framing.
Wall Systems
Various wall system options exist when it comes to tiny houses, ranging from conventional wood framing, steel, SIPs, and more. Some of them cost less but take longer to yield results. Others cost more, but reduce framing time by 90 percent. Factors such as your budget and time availability will greatly affect which option you choose.
Framing Defined
It’s important to familiarize yourself with framing terms. Not only will they help you understand the material we’re about to cover, but they’ll make it easier for you to discuss specific needs at the lumberyard or with building professionals. Bear in mind that terms may vary slightly by geographic location. Let’s go over each one and define it.
Learning these wall framing terms will make your construction process a lot smoother.
Wall Framing Terms
Following are some basic wall framing terms.
Wall studs are vertical framing members—typically a 2×4 or a 2×6—and are key elements in construction.
Cripple stud is a vertical framing member installed above and/or below doors, windows, and headers. Cripple studs never touch both the bottom plate and top plate at the same time.
King stud is a vertical framing member placed on either side of a door or window, running from bottom plate to top plate.
Trimmer stud is a vertical framing member placed on the inside (toward a window or door opening) of a king stud, running from the bottom plate to the bottom of the window or door header.
Header is a horizontal framing member placed above a door, window, or other opening.
Corner stud assembly is a vertical framing member placed at corner locations, typically built of three studs.
Rough sill is a horizontal framing member placed below a rough window opening. It attaches to the cripple studs below as well as the trimmer and king studs on the side.
Top (upper wall) plate is a horizontal framing member fastened to the top of the wall studs. A secondary (double top plate) is always connected to the top plate, overlapping at the corners, to increase the overall strength of the wall assembly.
Bottom (sole, lower wall, base plate) plate is a horizontal framing member placed atop the floor sheathing and to which studs are connected.
Rough opening (R.O.) is the space left open in a framed wall assembly to accommodate the future placement of a door or window. Check with manufacturer specifications for door and window R.O. callouts before framing the wall.
Roof Framing Terms
Following are some basic roof framing terms.
Learning these roof framing terms will give you a leg up when ordering materials and talking about construction with professionals.
Loft joist is a horizontal framing member installed to support the loads above it.
Ceiling joist is a horizontal framing member connected to the double top plate or to a ledger that creates a ceiling overhead. If the construction also results in a floor above, they may be referred to as floor joists rather than ceiling joists.
Rafter is a framing membrane that supports the roof sheathing. Rafters attach to the ridge (when present) and to the double top plate.
Ridge beam is a horizontal framing member—typically a 4× beam or greater—that supports the end of rafters at the ridge. The beam is supported by posts, which transfer the roof loads to the foundation. Note that a shed roof (roof without a gable peak) doesn’t have a ridge beam.
Ridge board is a horizontal framing member—typically a 2× board—that’s supported by the end of rafters at the ridge. The beam isn’t supported by posts, but rather the rafters themselves. Because it’s supported by the rafters, collar ties are necessary. Note that a shed roof (roof without a gable peak) doesn’t have a ridge board.
Collar tie is a horizontal framing member connecting two rafters on a gable roof. Collar ties are vital for roof safety and prevent rafters from collapsing when stressed by excessive loads such as snow or road rattle.
Wood Framing
Wood is the most commonly used material in residential construction. It’s forgiving, easy to work with, and any mistakes can be fixed with relative ease. Although power tools make the job easier, they’re not required because you can accomplish a lot with just a saw, a hammer, and some nails.
Another advantage to wood framing is that the materials (framing, sheathing, and fasteners) are readily available in pretty much every location across the country. Whether you shop at a local lumberyard or a big box store, you’ll likely find everything you need with ease.
The most common layouts for wall stud spacing are 16" on center (o.c.) and 24" o.c. This means that when measured from the center of one stud to the center of the other, the space is either 16" or 24" wide. Tighter spacing makes for stronger walls. However, wider spacing is acceptable and provides for better insulation values and less weight.
Residential construction in the United States calls for 2×6 walls in order to meet insulation code in most cases. For tiny houses, the most common framing size is 2×4 walls because of the space savings. You’ll have to decide if you want extra insulation value or extra floor space when considering which framing members to use.
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Be sure to lay out your walls correctly so that your sheathing lands on the centerline of your framing members. A 16" or 24" o.c. frame requires you to adjust your first stud location back by ¾" (half the framing member’s thickness) for the rest to be on-center. Measure your first framing member location to 15¼" or 23¼" and then strike a new measurement from that point every 16" or 24".
Screws vs. Nails
Although many people believe that screws are the better fastener for a THOWs, construction physics prove otherwise. The fact is that screws don’t have any shear strength, which is vitally important in a mobile tiny house. Let’s say you placed a nail in the wrong spot while attaching two pieces of wood. To remove the nail, you’ll have to pry it back and forth and work it out with some effort. This ability for nails to bend and flex is an integral part of their shear strength.
On the other hand, if you strip a screw while driving it into a wall, you simply need to give the head a whack with your hammer for it to easily snap off the body. This is an illustration of the lack of shear strength in screws. Whereas a nail can flex significantly, a screw simply can’t tolerate that same force.
All that said, there are two situations when it’s appropriate to use screws for framing and sheathing.
- The first is when you are using structural screws. These are specialized screws rated for structural use. They are not deck, drywall, or any other standard screw. You’ll know you’re getting the right ones when you just about keel over as you look at the price.
- Secondly, you can use screws in tandem with nails. Sometimes it’s handy to use a few screws to hold up sheathing before you come around and nail it all off.
It’s important to use wood glue wherever you can join two surfaces to create the strongest connection possible between framing and sheathing. Wood glue is considered cheap insurance and something you should add anytime you make a wood-to-wood connection. By using the right fasteners, your THOWs will be able to withstand all the stresses it will endure while being towed mile after mile.
There are various types of nails on the market and they vary in material, size, head shapes, and tip shapes, as well as shank texture (smooth or ringed). There’s some method behind choosing the right-size nail for the task at hand, but the best approach is to check your local building codes to see which nails are used where. This is important because using a 16d nail to toe-nail (or angle nail) a stud to a plate can actually blow out the stud and make the connection fail. (That location requires an 8d nail.)
A very basic approach is to use 8d nails when toe nailing and attaching sheathing to the frame, 16d nails for all framing connections other than toe nailing, and teco nails for all hangers and straps. You can use 10d nails for some specific applications, such as hangers and straps. However, it’s best to know exactly what nails are required where, especially when working with structural metal hangers and straps.
Nail sizes are typically called out by units of d. This harkens back to many moons ago in England when nails were named for how much it cost for 100 of each size. That means if 100 nails cost six pence, they were referred to as 6-penny nails. Today, the letter d refers to penny. Why? Because the d stands for the Latin name denarius, which was the Roman equivalent of a penny. Pretty neat, huh?
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The most common framing nail sizes are:
- 8d: 2½"
- 10d: 3"
- 16d: 3½"
- Teco (for hangers and straps): 10d × 1½"
Steel Framing
Although steel framing isn’t as common as wood in residential construction, it’s a good option for a THOWs. Let’s go over the advantages of this material. Light-gauge steel framing is considerably lighter than wood. Some claim that 60 percent of the total frame weight can be saved on a tiny house by substituting steel for wood.
Steel studs are structurally very strong. In fact, they’re often considered to be stronger than wood. This means you can use less material to create the same strength rating. Steel studs aren’t solid like wood. Rather, they’re shaped like the letter C (thus the name C-channel) in a cross-section. This specific shape creates excellent strength while minimizing materials and weight. The hollow core provides an additional benefit by allowing insulation to be placed inside the studs, limiting thermal bridging.
One thing to be aware of is that steel studs are at risk for condensation issues. To mitigate this, it’s customary to wrap the exterior with rigid insulation. Unfortunately, this will reduce some of your interior square footage. If you use 2" rigid foam, your overall room width will be reduced by four inches.
Steel studs connect with structural screws, not nails. This process intimidates some novice builders. It’s not as forgiving as wood framing either. Cutting the studs leaves the edges of the material sharp and is either loud and full of sparks (if you use a saw) or slow and uncomfortable (if you use straight aviation cutters). You’ll have to decide whether the added strength and reduced weight of the material is worth the effort.
In fact, most people who choose to build with steel frames don’t do the work themselves but rather hire it out to professionals. It’s much easier to work with a custom steel frame through a shop or construction company that specializes in that type of work than it is to do it yourself.
Structural Insulated Panels (SIPs)
Many tiny housers are turning to SIPs for their wall and roofing systems. As discussed previously, SIPs are a sandwich system in which a foam insulation core is laminated between two skins of oriented strand board (OSB). SIPs are structural so they require no other wall or roof framing systems to support them. Because they include a foam core, they provide the insulation envelope for your walls at the same time.
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Though they might appear like a complex building option, SIPs are actually quite easy to work with. SIPs companies can take any set of construction plans, create a custom SIPs package, and deliver it directly to your jobsite. They factory cut all your window and door openings and provide channels for utility conduits as well.
SIPs show up on the jobsite as large panels. This greatly reduces the time it takes to frame and roof a tiny house. With several helpers onsite, you can realistically erect an entire tiny house frame (including the roof) in a day or two. Remember that this includes your insulation envelope as well, reducing your construction time even more. Insulating a tiny house can actually take a significant amount of time to do well.
Making last minute onsite changes to a SIPs house isn’t easy, but it’s not impossible either. That said, it’s best to invest adequate time getting the design just right and working closely with the factory to eliminate the need for changes in the field.
Some of the foams used in the SIPs industry are considered unhealthy by some. While one side argues that the foam is inert, others suggest that it emits unhealthy fumes. We highly recommend you research the foam your SIPs factory uses and ensure that it meets your needs and addresses your concerns. Two options becoming increasingly popular are polyurethane foam and graphite-based foams. Both claim to be inert and not to emit any toxic fumes. Ask your SIPs manufacturer if they offer either as an option.
There are currently a couple companies specializing in SIPs for tiny houses, but any reputable SIPs manufacturer can handle the job. They typically need a little lead-time to have an order delivered to the jobsite. Sometimes you can have your design delivered within the month. However, it could take longer depending on how busy the factory is, so plan accordingly.
Although SIPs might appear to cost more than wood framing at first glance, it’s important to remember that the insulation is also factored into the cost. Therefore, the price difference is not huge. In terms of weight, they weigh about the same as a stud-framed wall.
Tiny House Shells
Several tiny house companies are now offering dried-in shells for THOWs. This is a particularly attractive option for people intimidated by framing and also for those with a tight deadline. Prices are actually pretty reasonable for the most part, especially when considering you’ll be spared weeks and potentially months of framing, siding, and roofing.
DEFINITION
The term dried-in refers to the stage in construction when the structure is protected from the elements and the following are completed: rough framing, exterior wall sheathing, windows set, and roof waterproofing material.
Typically shells come with windows set, siding adhered, and the roofing material installed. The tiny house owner is left with tasks such as plumbing and wiring, insulating the interior, installing finish materials and cabinets, as well as fixtures and appliances.
One thing to keep in mind when considering a tiny house shell is that if you aren’t 100 percent certain where you want your door and window openings to go, you can simply ask the builder to not install them. Instead, you can cut them out when your shell is onsite, when you have a better sense of where you want them placed.
Once the shell is completed, you can either pick it up yourself or have it delivered. Because transit costs can be high, you might want to look for a shell builder that either builds locally or has distributors relatively close to you. Quality matters here, so choose a builder only after you’ve had a chance to inspect their work.
Anchoring Systems
No matter what framing system you choose, you’ll need to ensure you have adequate anchoring to connect the house to the trailer. Without it, a tiny house could literally disconnect from the trailer frame and that would be a terrible start to a road trip. Next, we’ll discuss the three major points of connection to consider.
The first type of connection to consider, even if you’re building a THOWs, is attachment to the ground. By residential building codes, all forms of housing, except for recreational vehicles, are required to anchor to the ground in some capacity. The intent of this provision is to minimize damage and injury caused by high winds, earthquakes, or other natural disasters.
There are several options for connecting a Tiny House On Wheels (THOWs) to the ground and which one you choose will be affected by site soil conditions, topography, regional natural disaster potentials, as well as climactic influences. Your local building department can help you identify the best option for you. You can also speak to local contractors and engineers.
The most secure way of attaching a tiny house to the ground is by connecting it to a perimeter concrete foundation. This requires the removal of the wheels and potentially the axles as well. Though tedious, removal of the tiny house from the foundation is possible if relocation is necessary. However, this isn’t the best option if you plan on moving your house with any regularity. In fact, if you plan on moving it more than once or twice, this may be a burden not worth implementing.
Another option is to pour a concrete slab with engineered anchors embedded into the foundation and to then attach the tiny house to those tie-down locations. It’s important to also use strategically placed jack supports under the trailer frame that can take the weight off of the wheels while parked. This is a relatively simple solution compared to other options because the axles and wheels can remain on the THOWs.
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It’s important to provide support for your loads (dead and live), as well as resistance against uplift and tip over. This is why both anchors and jacks must be employed together. In terms of what foundation system to use, there are several options available other than those listed here.
If you plan to move your house often, a permanent foundation system is not a great option for you. Instead, consider using something that can quickly and easily be put into place and removed. A common approach is to place the trailer on jack stands while parked. You can also ask your trailer manufacturer to weld hooks onto your trailer that can be anchored to ground anchors in your location. There are screw-in ground anchors available on the market that can be perfect for temporary anchoring.
Trailer-to-Wall Frame Connections
The next level of support is the connection of the house to the trailer. When done correctly, the house can’t disconnect from the trailer, no matter how many potholes the driver manages to drag it through. There are several ways to accomplish this task.
A common anchoring system in the park model industry is the use of metal strapping. Each piece is installed behind the siding and in front of the framing/house wrap. The straps run from one side of the trailer frame up and over the roof, and all the way down to the other side of the trailer frame. Each strap is then welded to the frame and further attached to the stud framing with nails. These straps are typically only installed in two to four locations across the entire house.
If using metal straps is too cumbersome or expensive, you can choose anchor bolts. Where to place them and which ones to use varies with the tiny house, so please consult with an engineer or purchase plans that specify this information.
The most common anchoring system for THOWs is anchor bolts. Depending on your trailer manufacturer, they will come installed upon delivery or you can install them onsite.
Most commonly, anchor bolts are welded to the frame in pre-determined locations designated by the architectural plans. These bolts extend up from the trailer frame and through the bottom wall plates. They are secured in place with heavy duty metal brackets (Simpson HTT4). The HTT4s are then tightened down with a locking nut and nailed to the studs in line with the manufacturer’s specifications.
This connection attaches the wall frame to the trailer with incredible strength. The HTT4s are what’s used in high seismic risk areas around the country and are thus resilient enough for a THOWs application.
Some tiny house trailers can be custom built with frames that allow for the installation of anchor bolts after the walls are erected. If your trailer doesn’t have that feature, you’ll need to lift your framed walls up and over the bolts, which are welded in place on the frame.
One important point to mention with any of the anchoring systems is that once your walls are enclosed in finish material, you’ll no longer have access to the nuts and bolts. For that reason, you’ll need to be 100 percent certain that everything is fully tightened before you close up your walls. Be sure to use locking nuts, thread locking fluids, or any other time-tested fastening system.
Wall Frame-to-Roof Connections
Now that your walls are connected to the trailer, you’ll need to ensure your roof doesn’t fly off while in transit. The best way to do this is by using hurricane clips. The most common clip we see in residential construction is the Simpson H2.5. It’s easy to install (nailed on to framing members with manufacturer’s recommended nails), very strong, and relatively simple to hide behind most wall finish materials.
The Least You Need to Know
- You can minimize thermal bridging in your tiny house by installing a raised floor system atop your metal trailer.
- Though wood framing is the most common for tiny house construction, other options such as steel and SIPs are being used with increased frequency.
- When building a tiny house, you need to securely anchor your wall framing to the trailer and the roof to ensure it doesn’t all come apart while driving down the highway.
- There are several anchoring systems options ranging from metal straps, to hurricane clips, to HTT4 anchors.