ECOURSE DAY 4:
TINY HOUSE FRAMING OVERVIEW
How a home is framed is one of the most important aspects of the construction process. Get this part of your construction right and the rest of your build will go smoothly. There are several ways to create a frame for your tiny home, and we will discuss the three most prominent here today: wood frame, steel frame, and structural insulated panels (SIPs). There are many factors to consider when choosing your faming material from overall material weight, to ease of construction, to local availability and more. Consider each factor well before you make your decision. For me, as a builder of roughly 20 years who has worked with wood framing for my whole career, the choice was easy, but not necessarily straightforward. I leaned towards SIPs for a while and then over to steel framing before landing back to conventional wood framing. Which you choose will be personal to you and there is no “right” solution.
The most common framing material here in the United States is wood. Within that, there are subsets like engineered lumber, kiln dried framing lumber, and free framing lumber. Most homes built with standard wood frames include a mix of engineered materials and either kiln dried or green framing lumber depending on where you live. The Northwest, for example, supplies mostly green framing lumber to supply yards, while the Northeast is known to favor kiln dried materials. If you have a choice between kiln dried and green lumber, my suggestion is to go with the kiln dried, even if it is slightly more expensive. There are two reasons for this suggestion. 1) Kiln dried lumber is lighter than green lumber. 2) Kiln dried lumber is more stable than green lumber (it won’t shrink as much) and so there is less chance of cracking in your finish materials as a result.
Engineered lumber includes LVL laminated beams, Glulams, I joists, and many other products. How each of them is used is typically called out by an engineer. That said, most of the larger engineered beam materials are designed to handle large loads spread out over large spans. One place where an engineered material might be used in a tiny home is in the roof. An engineered I beam roof system is lightweight and can handle the full span of the house easily. In addition, if you have a special roof design that has a section spanning over an open space below, the supporting beam could be called out as an engineered material. Finally, engineered wood is extremely stable and thus straight. If you live in an area where movement in wood frames is of concern, you might consider using engineered studs to create straight and stable walls with ease.
• Material availability. You can get all of the materials you need to build a home with wood framing from just about any local lumber yard. Although some lumber dimensions may need to be special ordered, a good supplier can get those delivered to you within a few days so there will be little if any delay in the construction progress.
• Ease of assembly. Wood framing does not require any special tools or skill sets. When push comes to shove, a wood framed home can be built with a tape measure, a saw, a hammer, and nothing more. The fact of the matter is that while other tools make the job much easier and more accurate, they are not a requirement. If you do choose to rent or acquire specialty tools for your own tiny house built (nail gun, router, miter saw, etc.), they are all pretty easy to learn to use. A quick side note here: Never take the matter of safety lightly. Learn how to use your tools properly from someone who knows how to use them safely.
• Environmental impacts. Sustainably harvested wood products are available in many markets today. If you purchase wood that comes from sustainable sources, you can help protect the planet. What’s more, when your house eventually succumbs to mother nature, it will be made of materials that the earth can recycle for you. Even during the construction process, the waste that is generated can be used elsewhere. Larger scrap pieces are easily used as blocking and temporary framing members during construction. Once complete, they can be burned as fuel for your wood fired hot tub, sauna, or wood stove. If you don’t have one of those, they can be chipped and used as mulch around your tiny house. My point is, the waste is not actually waste if used with intention.
• Easy to learn. There are lots of options for learning how to build with wood from videos to community college classes. If you are inspired to learn, there are resources to teach you no matter where you live.
• Mistakes are easy to fix. Wood is really forgiving when it comes to mistakes. Small mishaps can be patched and repaired while larger mistakes can be fixed by purchasing new materials with ease and using the mistake material elsewhere in the structure.
• Labor Intensive. Lots of pieces means lots of labor. Because the frame is made up of a combination of smaller pieces attached together, there is quite a lot of time that goes into assembling the structure. A nail gun and miter saw will greatly reduce the amount of time you spend on each section of framing; however, there will still be hours of labor to consider.
• Temporary Bracing. Because wood frames do not provide any lateral shear strength (ability to resist a force applied in plane with the wall), they require temporary bracing to be installed during the construction process. This bracing can end up as “waste” if not designed into the system elsewhere and can slow down labor. There are ways to avoid using bracing, i.e. installing the plywood or oriented strand board (OSB) to the wall assembly before lifting it into place; however, that adds significant weight to the wall and if you are working alone, may make it difficult to lift the wall into position safely.
• Splitting and shrinking. If you over-nail a piece of wood or nail it too close to the edge, it can split, rendering it useless (wood has to be properly fastened to provide strength to the structure). Green lumber is prone to shrinkage as it dries out. This can cause cracks in your finish materials like plasterboard or drywall if used.
When a tiny home is built on a trailer, the concern of weight become apparent. Trailers and axles are rated for specific weight restrictions and if you exceed that, the entire structure is at risk. As such, framing details need to reflect minimalistic approaches to the work. Whenever possible, eliminate excess wood from the structure. Some easy ways to do this are as follows. Be sure to check with your engineer to confirm that any or all of these options are available to you before you proceed.
• Use a single top plate. As long as the structure is framed such that the rafters land directly on top of the wall studs, the second top plate (typical to framed construction) can be eliminated from the design.
• Move openings. If a window or door lands near a wall stud in your layout, consider shifting the opening over so that the wall stud can be used as part of the opening’s frame.
• Eliminate headers. Window and door headers are only needed when roof loads are applied to them. If a window or door is located beneath another opening, use a simple frame for the bottom opening to eliminate the heavy beam that would otherwise be used as the header.
• Use lightweight materials. As mentioned earlier, kiln dried lumber and engineered systems can reduce material weight.
• Flat frame around openings. You need to provide nailing surfaces for siding and trim around openings. Rather than simply adding another stud or two, flat frame (turn the wood 90 degrees so that the meat of the wood is facing out) so that you can provide more nailing surface without adding more wood and weight to the structure.
Steel framing is common in commercial construction and is growing in popularity in residential construction in some regions. To be clear, I am not talking about large steel beams and heavy iron work. Rather, I am talking about C channel steel framing materials as shown in the image.
• Lightweight. C channel steel framing is very lightweight and as such, lends itself well to tiny home construction on a trailer.
• Weather resistant during construction. If you are like most builders, you won’t get your tiny house framed and closed in over the course of a single day. If you are new to building, it may take you weeks to get the building dried in. Steel framing members are not susceptible to the elements the way that wood is so they can handle the exposure a bit better. The main difference is that the steel will not absorb any water the way wood does. This will keep the frame dry and free of swelling.
• Environmental impacts. Although the waste is not easily used or managed on site the way wood is, it can be recycled.
• Speed of assembly. Once you break the learning curve of working with steel, the assembly process is quite fast. The materials are designed to fit into one and other with ease and the connections are relatively easy to make.
• Labor Intensive. As mentioned above, there is a learning curve to working with steel. For many people, it does not come as second nature as working with wood does. The frames are assembled with self tapping screws and a drill. This is loud and can be difficult on your elbow over time as it is a very repetitive motion made under a lot of constant force.
• Material availability. Steel framing is not as readily available as wood framing materials. You will need to find a supplier who can deliver or otherwise supply the materials to you. If you make a mistake, you can’t simply run down to the local lumber yard and grab another stick. This can cause delays in your construction timeline.
• Can be loud both during and after construction. Cutting wood is loud, but cutting steel is obnoxious. The same can be said about the sound of screwing self tapping screws into every piece of steel. It can also be loud when the joints move as metal grinding against metal is not a pleasant sound. This is something to consider in a tiny house on a trailer as it will definitely move when the wind blows hard enough.
• Corrosion. It is important to isolate steel channel framing from other metals as galvanic corrosion can set in if you don’t. This is a process in which the metals have a reaction to each other and start to break down as a result. Clearly this is not something you would want happening to your structural frame.
• Fire. Steel frame structures have excellent resistance to flames and are thus considered to be fire proof. On the other hand, they have a low resistance to heat. What this means is that even though they may not be themselves burning during a fire, once the fire heat reaches a certain temperature, the entire metal frame will buckle and collapse.
• Changes can be hard. If you decide at the last minute to move a window or door slightly within the design, it is not as easy to move the steel framing members as it would be if those changes were made in a wood framed structure.
• Steel framing can be more expensive than conventional wood framing, especially if it is not used as standard practice in your area. This is due to availability and it being considered a special order item.
• Environmental Impacts. I put this as a potential advantage of using steel; however, it can also be a disadvantage. If the steel framing you use is not sourced from recycled materials, then it is being mined and then manufactured. Both of those steps have large environmental impacts. Even steel framing members that have recycled material in them (even 100% recycled material) still needs to be reprocessed and remanufactured.
Structural Insulated Panels, or SIPs, are a sandwich of structural skins (typically OSB) over a foam insulation core (typically expanded polystyrene (EPS), extruded polystyrene (XPS) or rigid polyurethane foam). They are known to have high thermal performance ratings and structural strength and tend to assemble quickly under the right conditions. They are not a typical building material for those with limited experience; however, they can be used by a novice with a good sense of adventure.
• Modular assembly. SIPs panels are designed and built at the factory to meet your specific requirements and then delivered for on site assembly.
• Precision and speed. Because the panels are fabricated at a shop, they are cut to fit perfectly. This speeds the assembly process and an experienced crew could have the entire tiny house frame assembled in a day.
• Minimal thermal bridging. Because the structural elements of the envelope are a sandwich assembly of OSB-foam-OSB, there is very little thermal bridging (ability of exterior climactic conditions to transfer to the interior of the home). This means that the building will be very energy efficient.
• Minimal on-site waste. Because the panels are prepared at the factory, there is little on site waste to manage.
• Handling panels. You will need at least two people to handle and raise the panels. Sometimes, for larger panels and for roof panels, a crane may be required.
• Material availability. You will need to locate and work with a local SIPs company. If one does not exist, then SIPs will not be an option for you in a cost effective manner.
• Cost. SIPs are not cheap. You may save on labor because the speed of assembly can be very fast (if you know what you are doing), but the material costs are relatively high.
• Mistakes. Any mistakes in the assembly that damage panels will halt the job until a new panel can be delivered. If you made mistakes in your original measurements, the panels won’t fit and you will either have to creatively fix the problem by using what you have or reorder the panels to fit your actual measurements. In other words, as fast as the assembly can be, it is quite unforgiving of mistakes.
• Utilities. Because the wall system is a closed system, i.e. the foam and structural skins are already attached, all utilities must be installed in prescribed channels. There is no open wall space to work with.
• Changes can be hard. Changes or adjustments to the design are not possible as the window and door locations are already cut into the panels.
Hopefully you learned a lot about framing options for tiny houses in this lesson. Tomorrow’s? Electrical!