Non-combustible construction in relation to Tiny Houses
In response to Kim’s tiny house fire, I decided to write the following article that it may save some grief to others by discussing an alternative to wood for construction methods of tiny houses. While this article primarily discusses steel framing compared to wood framing, framing certainly is a major component in our construction. After we change our framing we can begin swapping out components and lower our combustible construction materials significantly by using items such as metal furring, z-bar and non-combustible siding. Inside we can replace wood pine surfaces with plastic laminates, gypsum or metals again. This is not to say we cannot use wood, but by using less we greatly reduce our risk exposure to fire and other problems that arise in tiny houses.
Many people are choosing to build with wood for their tiny houses due to the ease of use, availability and perceived thermal superiority over other materials. However, there is a better alternative that trumps wood in every category: steel studs. Now many people have concerns about steel studs which I will address on in order.
- Availability, Cost, Weight & Benefits of Steel
- Thermal Conductivity
- Ease of Use – How to Assemble Steel Framing
- Non-combustible Wall, Roof & Floor Assemblies
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I hope some people found this article informative and helpful in their tiny house building ideas. I encourage people to consider using steel framing as it truly can be a superior product if done well. It is not to say wood does not have its place and wood certainly can be used in conjunction with steel (particularly around door and window frames) but I truly hope steel seems at least less daunting as an option. I wish everyone the best of luck in their projects.
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Interesting article, thanks! I’ve enjoyed reading over the last few months since I found your blog.
I work as a structural engineer, and work with both cold formed steel studs and wood, so I’m pretty familiar with both.
The calcs showing better thermal performance with steel have not held up in real world tests. Side by side tests of nearly identical, average-size new houses are showing about a 5% additional energy requirement to heat and cool the steel version of the structure. This is my ball-park number to summarize a few tests, but you can find far more detailed info in the recent test report here: http://www.steelframing.org/PDF/research/02-Final_Report_Thermal-Beaufort.pdf
Rivets are more common for metal stud construction in Australia, but are very uncommon in the US. Construction here is usually with #8 or #10 galvanized self drilling screws. If you do choose to use rivets, which do have their advantages, I strongly recommend you consider using a high quality rivet. Almost all the rivets you can find at a hardware or local store are extremely low quality, and really aren’t suitable for this use. I’d even go so far as to call them junk.
There are actual structural pop rivets out there – I use Cherry Q or Cherry N rivets on my own projects any time I need a structural pop rivet, and they are easily available from Aircraft Spruce, Hanson Rivet, or any of a number of suppliers. I would recommend Cherry Q’s for a tiny house on a trailer, as they’re stronger by far, and more vibration resistant. You need at least a 3/16″ aluminum rivet at minimum to come even close to the shear strength of a standard #8 screw with an aluminum rivet, though. You can go down to around 1/8″ with a stainless rivet. Or you can use multiple rivets. Either way, really, you’re looking at about $0.25 per stud end to do the job with a combination of rivets that aren’t going to fail on you, and a single standard quality self drilling screw is faster, easier to use, stronger, and cheaper for this use.
The real advantage of steel studs is fatigue resistance when you’re working with a tiny house on wheels. Anyone who is doing their construction in nailed wood is likely to have nail pullout problems and loose joints over time, and screws would be my definite minimum recommendation for anyone doing wood construction.
Thanks Chuck! Excellent info here.
I found your article very interesting but can’t help but wonder how much this would increase the possibility of lightning strikes and if there needs to be included some form of apparatus to protect against that. I live in the southeast so want to be sure.
Hadn’t thought of that Rhonda but great question. I’d assume it would be fine and not worry about it since most of the steel will be unexposed.
Could use some more information on how this impacts the “glue and screw” method (road worthiness) if we change materials. Had originally thought about using steel siding similar to what I had on my former house but didn’t think it would work on the highway. Also, I would like to get your opinion for mineral/rock wool insulation for a tiny house on wheels since I’ve read that it is fireproof.
At Tiny Green Cabins, we prefer the use of steel over wood. Our steel framing is 16 and 18 gauge cold formed steel and the use of a cut off saw is needed. Tin snips do not work, and our steel supplier said that 18 gauge steel is the minimum gauge they would recommend because of road vibrations. That works for us, as we also weld all the connections to add to the rigidity and tensile strength of the unit. We also add a thermal barrier to combat the heat/cold conductivity associated with steel.
Thank you so much, Jim!
I strongly suggest that anyone building a tiny or small house consider the REAL issues of fire; Life safety. Consult the national building code or the NFPA Life Safety Code re size of openings and appropriate hardware and instal one in each sleeping space (see Dee William’s tiny house). You will also find that wall/structural SYSTEMS not just their component parts are rated to survive long enough to get out. In small spaces it is likely the smoke generated by the interior finishes and furnishings that will kill people. I have heard of mobile home interiors charred while the dishtowels remained undamaged (that’s called a flashover fire). The light-gage steel studs used for residential construction will often buckle from the heat of such a fire while wood studs will survive…. Kim’s loss is a tragic accident. I doubt that it would have survived any better if it was built with steel studs. Consider ALL the factors. Play safe. Rich
Excellent point, Rich, thank you!!
This is getting fascinating, y’all!
Steel has massive ability to deform and still retain its strength. Tensile is marvelous. However, I feel like most of these discussions are stuck in the realm of relying on a stud frame for the strength.
An alternative? Skin on frame technology… it is nothing new, and it is precisely what you are doing when you build a shear wall. Tiny houses on wheels can take advantage of this for very light structures that are flexible and durable enough to move around. The weights of materials that work well for this do not fall in the standards of conventional building practice however.
But when you are talking about creating this type of structure, wood is a strong candidate for both web AND skin. Avoiding the combination of dissimilar materials minimizes stress focal points. And fatigue stress points. So, steel makes sense if you make both web and skin from it.
And using steel with aluminum rivets? NOt recommended. Even with pretty large rivets. There is also a small amount of galvanic corrosion that can happen here.
Fire is an ever present risk. But wood is also a time tested building material. It is also the most bio-compatible material of any mentioned above… when the house is done with its lifespan… you can just grind it up and use it in your composting toilet. Let nature do the rest, no?
Thanks Abel, very well said!
I’d been considering steel framing because of the weight reduction but what it ultimately comes down to for me is that I’m familiar and comfortable with wood. I started messing around with it as a kid with my dad(he was a cabinetmaker, carpenter and boatbuilder) not to say I’m all that great a carpenter, but I have a basic understanding of the materials and methods. Starting all over again with a new material isn’t something I’m willing to do with my home. I might try a test project sometime though.
Thanks Alice, great point. I’d be more comfortable using wood too if I were doing it myself.
No such thing as a non-combustible house!
Any material will burn or melt under intense heat. I recently had a camper caught in a field fire and burn to the ground. The aluminum and steel was melted into a puddle and frame totally bent by the heat.
Steel studs will reduce weight but for lateral pressure are not as good as wood studs and cost more.
May be useful in a house on wheels application but would probably require more lateral strapping.
In wood construction everything is glued an screwed to provide maximum strength and that same technique is used to build many airplanes.
You could not do that with steel framing and connection points for steel would be much weaker than a glued and screwed wood structure in my opinion.
Thanks, LaMar! Great points once again.
What conjecture mill cranked this refuse out?
I have been through two house fires in regular sized homes… One was a 110 year old farmhouse, which was totally destroyed, and I only just got the kids out of their beds and outside in time… It took SIX minutes for the entire house to be alight… and this was a huge sprawling five bedroom home…
My second house fire was in a house that I was renting… again full sized… This fire was caused by the insulation in the roof smouldering against the chimney… luckily the children were not at home this time… but I only escaped the fire by climbing out a bedroom window… I’ve been told that it is a miracle that I even woke up and managed to get out…
BUT… as we are now in the process of designing out own tiny house to put on the land where our previous home was… I am concerned with many having loft style bedrooms, and only one access… – usually a ladder… and then through the home… Ours will have windows that will enable someone to be able to climb out of…
I never want to be caught in a house filled with smoke again and be disorientated and unable to get out via the main enterance…
Wow, Ruth, thanks so much for sharing those experiences with us. I believe all lofts should be required to have a window you can crawl out of. In fact, it may even be required but I think it’s also common sense and hope everyone takes it into account when building theirs. Thanks for bringing it to our attention.
Of course there is the Terma-Steel panel system that does all the good stuff and if you face both sides with Hardi Planks you will probably fix most of the fire problem.
Great info! Thanks for putting this together.
Aluminum (excuse my spelling) would be a lot lighter than steel.
I think step one (especially for those who already have a wood framed/wood construction tiny house) is always fire prevention. There are enough combustible materials inside a “non-combustible” tiny home to gut the home and cause serious injury or death before you even worry about the wall studs. Some of my suggestions include:
1. A human-sized exit at each end of a tiny home (some kind of rapid kick out window in a loft and similar at main level at the hitch-end of the home and a door at the other would do). I see too many lofts that would be deathtraps in a main floor fire at night.
2. Common sense cooking and heating options (light lacey curtains in the kitchen area-not for me).
3. Choose fire resistant materials for bedding and furniture.
4. Know your electrical system and it’s limits. Cook in stages instead trying to cook and heat and compute all at the same time with a nest of with extension cords.
5. Small fire extinguishers strategically placed.
6. Battery powers smoke alarms.
7. Have a fire plan and if others live with you, have a few fire drills.
Be safe, be happy, live tiny.
It’s wood for me! maybe some corrugated roofing 🙂 but the rest would be wood or SIPS and wood frame. That’s kinda the whole point of TH for me, besides the freedom is the fact it takes less of a footprint and breaks back down when I’ve done with it or can use the parts for the next TH and compost the sawdust from the first. Whole new twist to self – sustaining:)
We used all wood framing and wall coverings in our tiny home, due to weight concerns as well as cracking joints on the drywall. However, we were very concerned about the fire potential in our tiny home, so we used intumescent paint on the walls, floors & ceilings before we painted them or covered them with our flooring. It was an inexpensive (compared to metal studs & drywall) solution to our problem.
The only time I’ve seen this amount of misinformation in a comments section about this topic was by a man that worked for a logging company. So I really feel the need to clarify even though my husband said that people don’t really believe all the misinformation (he thinks it’s common sense). The major thing I’d like to point out here is that wood is FUEL for a fire while steel is NOT. You don’t throw pieces of steel into a fireplace to warm up your house, in fact a lot of the time the interior of the fireplace is is made out of steel and the rack that you put your logs on is made out of steel. Does steel have a lower melting point than wood? YES!! But good luck getting it to that point as it’s not combustable i.e. wood is FUEL…steel is NOT. You have to have a massive fire with lots of combustable materials in a house to melt steel (gas explosions do it) for the amount of heat to get hot enough to melt it. A wood framed house will burn no matter what and drywall isn’t going to stop it like the retired fire captain said in an above comment (every single house I’ve ever heard of burning had drywall in it….I’ve never seen a house that didn’t have drywall in it). To the guy that said “there’s no such thing as a non-combustable house!” Not true at all. Go try to burn down an earthbag house, an ICF, or a monolithic dome. You will be there for awhile. I own a red iron steel framed house and there have been reports of fires in houses like mine. They haven’t been known to spread, just smoulder (electrical fires). Under the right conditions though I’m sure it’d be possible to melt. As far as lightening goes steel provides a pathway for it to travel, wood does not. So if you live in a wood framed house and your house gets struck by lightening it just burns down, with steel it goes into the ground. If you prefer wood over steel because of cost that’s fine but it’s definitely not safer than steel.