Balloon Framing is Worse is Better
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A Brief History of the Balloon Frame
Today in the US, most houses and apartments are built using light framed wood construction. This system consists of load bearing walls made from 2x4s or 2x6s, which support a wood-framed floor or roof - usually either trusses, joists, or engineered i-joists. This system is a variant of a framing style known as balloon framed construction, and though it may not look particularly impressive, it’s one of the most important developments in the history of building technology.
Prior to the balloon frame, houses in the US were generally built using post-and-beam construction. This system is exactly what it sounds like - a structural frame made of heavy timber beams and columns, joined by mortise and tenon connections. Floor members would then span between the beams, and walls would be infilled using rubble, mud, brick, or stone. Crucially, the walls were non-load bearing - the weight of the structure was entirely supported by the timber frame.
The balloon frame, essentially, eliminates the heavy timber frame. Instead, the floor members sit on the walls directly, which become load bearing elements. The skin of the building, which previously only served as a barrier to keep the elements out, now also braces the wood stud walls, increasing their load bearing capacity. And instead of mortise-and-tenons, the light wood elements are attached using simple iron (later steel) nails. With complex elements removed and other elements performing multiple functions, the entire structure becomes more efficient and easier to build.
The balloon frame can trace its origin to Chicago in the 1830s. Accounts vary, but the most common story is that it was first built by George Snow, a lumber magnate, as the framing for a warehouse in 1832. At the time, Chicago was on the cusp of a huge population boom - it would go from 300 residents in the early 1830s to nearly 30,000 in the 1850s, and to nearly a million in the 1890s. Heavy timber, and the labor needed to work and assemble it, was becoming difficult to find.
Timber frames are a labor-intensive building system, especially in the absence of any sort of construction machinery. The timbers themselves are heavy and require a lot of effort to move into position. And the mortise-and-tenon joints that connected them took a great deal of time and skill to create.
Balloon framing, on the other hand, is built using lightweight members that are easily manipulated by hand. Instead of complex joinery, they’re fastened together using comparatively simple nailed connections. Learning to cut mortise and tenons took years of training as a carpenter, but anyone could be taught to swing a hammer. And by omitting the heavy timber frame, the balloon frame used 1/3rd of the wood as a post and beam house, and could be erected much faster.
Despite its advantages, the balloon frame took decades to fully displace post-and-beam construction. Though it spread quickly enough that it was known by name by 1835, carpenter handbooks don’t mention it until 1857, and it’s mentioned little up into the 1880s. Houses built in Chicago in the late 1800s often consisted of hybrid construction that was partially heavy timber, partially balloon frame. And by the 1940s, only between 60 and 80 percent of houses in the US consisted of balloon framed construction. Building technologies are very sticky - once one is in use, it gains a great deal of inertia that takes a long time to overcome [0].
Balloon frame has a few disadvantages. One major one is that the exterior wall studs all the way to the roof, which provides an unbroken path for fire to travel. After the Chicago fire of 1871 and the San Francisco earthquake (and subsequent fire) of 1906, preventing the spread of fire became more important for insurance agencies and nascent building codes.
The balloon frame addressed this by way of a variant known as “western style” or “platform framing”. Instead of wall studs that extend continuously up to the roof, in platform framing the walls extend just up one level. The floor above, instead of attaching to the sides of the studs, instead sits directly on top of them. This creates a platform on which to build the next floor.
Today, balloon framing (mostly in the form of platform framing) remains the default construction method for single family homes all over the world, as well as for multistory apartments in the US (contributing to our low cost of construction for these building types). It remains one of the least expensive framing systems for erecting a building.
The Balloon Frame and Industrialization
Why did the balloon frame take so long to appear? After all, wood and metal nails had been used for buildings for millennia. But the balloon frame required several things provided by the rapidly industrializing environment of the early 1800s.
First, there’s the lumber itself. In the absence of high-powered machinery, cutting logs down into dimensional lumber would be an enormous amount of work, and not worth the trouble. But in the early 1800s steam powered sawmills began to appear. By the 1840s there were nearly 500 of them on the Michigan peninsula, and nearly 1000 in the 1890s [1].
These mills could produce far more cut lumber than the water-powered mills they replaced. In the early 1800s, a water-powered mill could produce perhaps 1500 board feet of lumber per day. By the 1850s, steam powered mills were routinely producing nearly 30,000 feet per day, which increased to nearly 100,000 by the 1890s. Lumber production at this scale also allowed for production of uniform sizes, culminating in the first national lumber size standard in 1924.
Nail technology saw a similar trajectory. In the 1700s nails were hand-forged, and were precious enough that abandoned buildings were burned down to recover them - at one point nails amounted to 0.4% of GDP, roughly the same percentage that we currently spend on PCs or airline tickets. The industrial revolution saw the introduction of steam powered nail making machines, which could make tens of thousands of nails a day. The cost of a nail fell four-fold during the 1800s.
All this was facilitated by the spread of railroads, which first began to appear in the US in the 1820s. By 1850 the US had 9000 miles of railroad track, which increased to over 250,000 miles by 1916. Railroads allowed lumber to be shipped cheaply all over the country, allowing it to be used for construction regardless of local lumber availability. This allowed cities like Chicago to continue to grow and build as local lumber became scarce. What had once been a local, regionally-used material gradually shifted to a national commodity.
Balloon framing is thus an early example of industrialized construction. It relied on machine made mass produced, uniform products (dimensional lumber, nails) which could be produced in large volumes at production facilities far from where they’d be used. It allowed the replacement of custom, one-off components with nearly interchangeable parts, and shifted construction from specialized, skilled craftsmanship towards semi-skilled, repetitive labor. And it allowed construction to occur much faster, at lower cost, and using less material.
Balloon Framing is Worse Is Better
In software development there’s a phenomenon known as “worse is better”. Roughly, it states that what matters most for the success of technology is how easily it can be implemented. Inelegant, ugly, inefficient or feature-incomplete systems - systems that use hacks or kludges - that are easy to install will beat out elegant systems that are harder or more expensive to put in place. The balloon frame is a classic example of a worse is better system.
First, balloon framing is extremely tedious to fully engineer. It’s not especially amenable to the mathematical tools engineers use for analyzing structures [2], which are better suited for either discrete elements or continuous materials. The fastening together of many small elements in many different locations results in complex connections, circuitous load paths, and highly indeterminate elements. Much of wood design is prescriptive, based on empirical tests or what’s performed well historically, rather than rational any sort of rational analysis.
Design is further complicated by the fact that wood is a highly variable material. It has hundreds of relevant material properties depending on the species, grade, size, direction of loading, duration of loading, temperature, moisture, and so on.
And beyond that, as a structural system, it lacks any sort of aesthetic elegance or simplicity. It’s made up of lots of flimsy-looking members [3]. Balloon framed buildings are rife with imprecision - lots of gaps between members, lots of elements slightly askew or not perfectly straight, lots of contractors failing to follow the plans. And despite using less lumber than post and beam construction, it still uses a lot of ‘extra’ members, to the point where an entire field of design exists to remove them.
It’s not the sort of system an engineer would design from scratch.
It’s undesirable from an architectural perspective as well. Balloon framing has largely been used for simple residential structures (or worse, mobile homes) that have historically had little architectural involvement. The size and strength of dimensional lumber makes it difficult to use it to create large or architecturally impressive spaces - it’s better suited to simple, room-sized framing. The architecturally influential residential buildings are more often built from more flexible materials such as concrete or steel.
But according to worse is better, none of this matters. What matters is how easy the system is to implement. And this - how easy it is to actually build a typical building - is where the balloon frame really shines:
It doesn't require specialized, expensive labor - no welders, masons, or crane operators.
It doesn't require heavy or specialized equipment to erect - buildings (even large ones!) can be built with nothing more than simple hand tools and a large forklift.
It’s easy to accommodate services - The voids between the studs means there’s room for things like switches, piping, and insulation. And using wood makes it easy to drill holes to run lines wherever you need to, or fasten whatever you need. Something as simple as installing a lightswitch all of a sudden becomes a major piece of coordination if your building is made of concrete.
It can be easily adjusted or fixed in the field - This lets it accommodate imperfect or incomplete upfront planning, or late stage project changes. And it means mistakes are less likely to result in massive cost overruns. This is something many prefab systems really struggle with.
It doesn't require perfect logistics - if a shipment is late, you can source needed material locally, or even pick something up at Home Depot.
It can’t scale up to huge structures, but can scale up to the sort of buildings that are most likely to be built (low-rise residential ones).
It can’t easily accommodate large, architecturally impressive spaces, but it can accommodate the sort of spaces people are likely to actually want (room-sized ones).
Often the trajectory of “worse is better” systems is that they gradually catch up to more elegant systems - bugs get ironed out and features get added. We can see this with balloon framing as well. Things like platform framing, FRT, and sprinkler systems have reduced the risk fire poses. Truss plates and engineered lumber have made it easier to frame large spaces. And steel hangers and ties have made connections stronger and easier to analyze.
Balloon Framing and Prefabrication
Balloon framing is an industrial building system, but it’s an extremely low level one. We see mass production or prefabrication of low-level components (dimensional lumber, nails, trusses, roof deck, etc.) that are relatively simple to combine together. But the final assembly work still takes place on site, and remains time-consuming. The rest of the construction industry is in a similar situation. Prefabrication of larger components, outside of a few building types optimized for it, remains elusive.
Buildings see something of a catch 22. There’s often an attempt to decrease site work by means of increased prefabrication. But larger prefabricated elements often need to be custom-designed to fit the site and the specific building requirements. It’s difficult to get both large prefab modules AND large production volumes.
[0] In Japan, a large percentage of the houses are still built using post-and-beam construction.
[1] The spread of sawmills quickly exhausted the lumber supply on the Michigan peninsula, and by 1910 they had closed.
[2] Or the software tools - wood framing is notorious for having little software available to aid the process.
[3] Supposedly this is how the name balloon frame came into being, as the buildings looked so flimsy they might blow away in the wind.
This highlights a challenge I hadn't really thought about before. Prefabrication sounds simple in theory, but balancing standardized production with the unique requirements of each building is clearly much more complicated.