So you’re itching to begin construction on your Tiny House on Wheels?
Congratulations! You’ll have so much fun (I did). You’ll also lose a few hairs, though, and quite a few hours of sleep!
Hopefully, this guide will keep a few more hairs on your head. If you’re new to the Tiny Home world, you might not be sure how to frame a Tiny House on Wheels. In particular, should you use advanced framing for a Tiny House?
Now first, a disclaimer: I’m not a licensed contractor nor a certified structural engineer. But I am a design engineer with a background in the RV manufacturing industry. Plus, I designed and built my own Tiny House!
(This blog is usually about RVs, but I’m taking a break from my regularly scheduled topic to chat about my former hobby.)
Here’s why you should (or shouldn’t) use advanced framing when building your mobile Tiny House.
WHAT IS ADVANCED FRAMING?
Advanced framing was developed in the 1960s by the Department of Housing and Urban Development. The goal was to reduce upfront and lifespan housing costs, shaving off a few percentage points here and there.
Today, it’s more optimistically called Optimum Value Engineering (OVE) framing. For an official primer, read the EPA Advanced House Framing Guide.
Advanced framing is, quite simply, about doing more with less. If one stud will do, then don’t use two. It tries to pair down the wood used in a structure to the minimum.
Traditional elements of advanced framing include:
- 2×6 studs 24 inches on center
- Studs align with trusses or rafters
- Single top plate
- 2-stud corners
- No headers in non-loadbearing walls
- Insulated headers sized for load
- No jack studs; use header hangers instead
- No extra cripple studs
Now, let’s get something out of the way real fast.
Almost no one abides by all the advanced framing guidelines – and for good reason. In fact, later in this article, I’ll talk about some advanced framing features you should completely ignore. We’ll take the good and leave the bad (looking at you, header hangers!)
If you want to understand advanced framing, then you’ve got to understand stacked framing, also known as inline framing. The concept behind stacked framing is that loads are transferred from the structure to the ground in a continuous path, with all members acting as columns. In practice, this means that rafters, trusses, joists and studs should all be laid out on an aligned 2-ft pattern.
Finally, if you’re new to advanced framing, I recommend reading this seminal pro/con guide at Green Building Advisor. You’ll need to be a GPA Prime Member, but you can sign up for a free trial.
A RETURN TO REALITY: MISCONCEPTIONS ABOUT TINY HOUSE DESIGN
Before I begin, I want to alleviate some of the common concerns and misconceptions about framing a Tiny House.
After spending countless hours researching online, you might begin to lose focus on what’s really important. You can start hyper-optimizing, fretting over saving one or two 2×4’s.
Don’t do that. You’ll just give yourself anxiety. Stick to the fundamentals, and avoid these extremes:
- Don’t bother with extreme R-values. Aiming for Passive Haus standards for a Tiny Home makes no sense, mathematically speaking. The thermodynamics of conditioning and insulating a 200-square foot living space are wholly different than conditioning and insulating a 2,000+ square foot living space! Plus, in most houses, drafts are a much, much bigger source of heat loss than thermal bridging! Aim for at least R13 walls, R10 floor, and R19 roof.
- Don’t bother with extreme weight savings. You’re building a Tiny House, not an RV. If weight is a big concern, then stop learning about Tiny Houses, and start learning about RVs. You’ll never come close to the weight of a commercial RV with a Tiny House build, no matter how well-designed your home is!
- Don’t bother with commercial engineered wood products. Glu-lam, LVL, PSL, LSL – all these engineered wood products are primarily designed for large residential and commercial construction where big spans and heavy dead loads are normal. There’s little reason to spend the extra money to use them in THOW construction. Solid lumber framing is the
BENEFITS OF ADVANCED FRAMING METHODS
Advocates usually promote advanced framing for the following reasons:
- Less wood = faster assembly, more money!
- Minimal environmental impact
- Reduced construction waste
- Lower lifetime energy costs from better insulation
Some of these reasons don’t apply to the Tiny House world. So I advocate for advanced framing for wholly different reasons.
- Saves weight! Eliminating double top plates and switching to 24OC stud layout can save hundreds of pounds!
- Saves money. I remember when a 2×4 sold for $1.95. Today, with prices hovering around $7 (after dropping from $11), every stud counts!
- Easier electrical and plumbing. When you’re building your own Tiny House and drilling out every stud for Romex cable and PEX pipe, you’ll be thankful you’re drilling fewer holes!
Now, let’s get something else out of the way.
Some builders try to create a strange, polygamous marriage between mobile home, RV, and residential framing construction. Don’t do this.
I’ve worked in both the residential construction and RV manufacturing industries, and the two use very different methodologies!
Plus, all three areas – mobile homes, RVs, and residential domiciles – have their own construction codes (HUD, NFPA 1192, and IBC, respectively).
If you’re looking for a code to follow, use ANSI 119.5, the Park Model RV code. This is one of the standards also adopted by NOAH, the unofficial reigning Tiny House certification program.
Personally, I recommend framing a Tiny Home like a brick n’ sticks house, more or less – especially if you’re new to building! You’ll find lots of online tutorials (like this) to help you get started. If you decide to blaze your own path, you’ll have to understand all the little ins and outs of construction and design all by yourself – and you don’t want your first design project to be A) your permanent home and B) something that moves down a highway at 60 mph!
YES, USE THESE ADVANCED FRAMING TECHNIQUES ON YOUR THOW!
Frame Your Layout 24OC
Yes, you should frame your THOW 24OC!
And you don’t even have to use 2×6’s! 2×4 studs on a 24-inch layout is more than sufficient for 95 percent of all THOW builds.
Run full-length studs. If you’re building a single-pitch roof, you might be tempted to extend your shorter with a little kneewall. Don’t do it! Spend the extra money and use 10’ or 12’ studs that run up to the top plate. Then install wall blocking to fasten the unsupported sheathing edges.
I made this mistake. I built my THOW with a shed (single-pitch) roof with a 10-ft tall sidewall, built out of two sections. It was a massive pain to assemble and did not want to lay flat. Oops!
Use a Single Top Plate
A double plate is not necessary if your studs align with your roof rafters or trusses (a half-inch off center is usually allowed). You’re throwing away lumber, otherwise.
Contractors sometimes gripe about single top plates because fastening a single top plate together, at the joints and the corners, is kind of a pain.
Thankfully, when your house only has four corners, splicing the top plates together really isn’t much of a concern.
I recommend using a 2×4 as splice blocks for butt joints. It’s easy, cheap and simple. The splice should span the entire width of the stud cavity. Use at least 4 8d nails per side.
You can also use a steel plate (minimum size 3×6 inches) with six 8d nails per side.* Or a specialty structural hanger. These can be a little expensive, though. I recommend using these metal connectors at your corners.
Also, I recommend offsetting your sill plate and top plate splices by at least two feet! And four feet is even better. Otherwise the splice can act as a hinge point.
DO NOT USE pronged connectors (aka truss plates, mending plates!) Those are designed for trusses (and to be pressed in by a machine), not for framing plates!
Choose a 3-Stud Corner
I wouldn’t recommend dropping all the way down to a 2-stud corner. You really need to reinforce those corners in a moving, shaking Tiny Home! Plus, 2-stud corners are an absolute nightmare for hanging drywall or installing paneling.
A better solution is a 3-stud corner: quick to build, easy to work with.
A 3-stud corner is still relatively strong and secure. It minimizes thermal bridging by allowing lots of room for insulation. Best of all, it’s easy to chase wire through! Use a spade (aka paddle) bit to drill holes for Romex and other wire.
Insulate Your Headers
Yes, you should insulate your headers above doors and windows. Otherwise, these blocks of solid lumber create cold spots in your wall.
There are several ways to build and insulate your headers. Most solutions, like boxed headers, are too time-consuming for the home builder. If you’re framing with 2×4 studs, the easiest solution is just to sandwich a ½” thick foam board between your two doubled headers.
And of course, you should only use headers in the load-bearing sidewalls. Don’t worry about them in the end walls.
Speaking of headers: Should you use 2×4 or 2×6 headers?
Traditionally, this question would be answered by a span and load table and a structural engineer.
For a tiny home limited to 8.5’ wide, though, in most circumstances, you can get away with a doubled 2×4 header for openings up to 48 inches. Personally, I recommend a doubled 2×6 header when framing wider than 48 inches – not so much for the load-bearing strength, but to minimize flexing in the wall frame, which could damage the window.
Try to Keep Windows on Layout
A technique that will make your life easier is to position windows and doors inside the 2-ft layout, or at least one side. That will reduce the number of studs and cripples you’ll need to install.*
*Note: If you use jack studs, you’ll normally only be able to line up on edge of a window with the common layout.
If you’re looking for more construction details, such as how to connect a partition wall, check out this guide from Building Science Corporation. Also, this article from the BSC goes even more in-depth.
DON’T BOTHER WITH THESE ADVANCED FRAMING FEATURES
Some elements of advanced framing have fallen out of favor with the construction community at large. These detailing elements save a modicum of wood, but cause a whole lot of hassle!
- Header hangers: Header hangers are expensive, finicky, and difficult to level. Just use jack studs.
- Cripple studs: Go ahead and use cripple studs underneath hung windows! Cripple studs, when cut to exact length, help to level a window. Otherwise, you have to manually level and nail the window sill plate in place.
- Drywall clips: See my recommendation for the 3-stud corner, instead!
- 2-ft Modules: Don’t freak out if corners, soffits, or windows fall off the 2-ft pattern. Following the layout is a guideline, not a rule.
I recommend sheathing your entire THOW in 7/16” OSB sheathing. This eliminates the need for any let-in bracing or other bracing.
Yes, it’s heavy. But it’s also one of the most versatile construction methods. Continuous sheathing, properly installed, acts as a:
- Air barrier
- Column stiffener
- Racking bracing
- Siding substrate
Most modern types of siding, like vinyl, are designed to be installed over continuous sheathing.
Don’t get hung up on whether to install siding vertically or horizontally. Yes, horizontal sheathing performs better in wind loads. Is it worth the extra blocking? Probably not. Pay more attention to the nailing pattern than the grain orientation.
Use high-wind nailing patterns when sheathing. I highly recommend using ring shank nails! These nails hold almost as well as screws and don’t work loose unlike the more common smooth shank nails. At a minimum, you should nail 4” on edges and 8” in the field with 8d ring shank nails or screws.
If your sidewalls are taller than 8 feet, consider using 4×9 or 4×10 sheathing panels rather than 4×8. You’ll eliminate the need for a row of blocking to support the edges, and that can save quite a bit of time!
OTHER FRAMING AND CONSTRUCTION DETAILS
General Things to Know
- Get a pneumatic power nailer! Cough it up. Hand-nailing your tiny house frame is a rubbish waste of time. If you don’t want to spend the money, rent one from a home improvement store or a contractor friend.
- Frame your walls on the ground (or your subfloor deck). Then raise them into position. If possible, sheath your walls on the ground, too, but beware! – they’ll be heavy! But if you can sheath them on the ground, cutting out the windows and doors is as simple as running a router around the opening.
- Mark your layout consistently. Some frames mark to center, to near edge, or far edge. Use symbols to indicate exactly what you’re measuring from and to.
- You’re not building fine furniture. Usually, a 1/16 to ⅛” tolerance is just fine. Just don’t allow tolerances to stack up!
- Use your best lumber for top plates, wall studs, corners and door openings. Keep the bowed lumber for cripples and jack studs.
For more information on learning framing, read this Fine Homebuilding guide.
If you’re installing extra-wide interior trim around your windows, then you may find that jack studs alone aren’t wide enough to accommodate your trim fasteners.
The conventional solution is to add a king stud. But that’s heavy and increases thermal bridging. A better solution is to use a 2×2 nailer, which allows for insulation behind.
But you’ve got to choose something! Otherwise you’ll be screwing or nailing into drywall or paneling, which do not hold fasteners well, especially with the vibrations in a Tiny Home!
Don’t bother with header hangers. They are finicky, easy to drop, and surprisingly expensive! Just use jack studs to support the headers.
Also known as “fire blocking,” wall mid-span blocking is when you install 2×4 crossmembers between studs about halfway up the wall.
In a typical house, this is usually done to prevent fire from traveling up the wall framing, especially in balloon framing. At one time, blocking was installed in the walls to reinforce the wall shear bracing. This practice is now considered archaic; properly installed sheathing has adequate strength and rigidity to resist buckling and racking.
However, wall blocking might have a use in your Tiny House!
If you are using thin (5/16″ or thinner) paneling for your interior walls, then adding wall blocking can reinforce the paneling.
If you are hanging cabinets or a ledger board off the wall, then the added blocking is necessary to provide extra fastener strength.
End-Nail or Toe-Nail Studs?
I chose to end-nail my studs to the plates with 3-½” 16d hot-dipped galvanized ring shank nails, two (sometimes three) nails per end, shot at a slight angle and staggered so they resist pull-out.
End-nailing is faster and more accurate than toe-nailing for lay people, in my opinion.
If end-nailing makes you nervous, I’d recommend skipping the toe-nailing altogether and using structural lag screws with pre-drilled clearance holes. You don’t get more overkill than that!
You can also use structural hangers, like Simpson SP1 and SP2 connectors. This is what’s recommended for Tiny House construction by NOAH.
Anchoring the Walls
Anchoring the walls will vary depending on your trailer chassis design. As a bare minimum, however, you should anchor the sill plate plate to the chassis with ½” galvanized anchor bolts no more than 4’ on center.
Pressure-Treated Sill Plate
I chose pressure-treated 2x4x12’s for my sill plate. I felt the extra insurance against rotting was well worth the extra dollars.
However, if you use pressure-treated wood, you have to protect your fasteners from corrosion! The easiest accepted method is to use hot-dipped galvanized (not electroplated) fasteners: that means bolts, washers, nuts, everything!