cheaper construction

=construction =housing

 

 

Housing is expensive. In America, one square foot of living space is often more than what people make from 10 hours of labor. How can so little be so expensive? Why does it take that much work?

Part of the answer is, "it doesn't". A typical single family home in America is more like 1 to 1.5 hours of labor / ft^2. People cost more per hour than they make, but taxes and health insurance aren't the main reason for the disparity. Material costs aren't either. As the Construction Physics blog notes, construction costs are not very correlated with labor and material costs. A lot of construction cost comes from bureaucracy, corruption, and developer profits enabled by bureacracy and corruption inhibiting competition. Apparent labor productivity in construction hasn't increased despite new tools like nailguns, so other costs must have increased.

Of course, there's more complexity in construction than is visually apparent. Still, more than an hour of labor for 1 ft^2 of house is kind of a lot, and maybe that could be reduced.

 

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Typical home construction in the USA includes the following steps:

- dig a hole
- pour concrete
- attach lumber every 16" to make a stud wall
- run joists across studs
- put planks on the joists
- nail/screw drywall to the studs
- run electrical wires through the stud walls
- tape, mud, and sand the drywall to get a smooth surface
- put primer then paint on the drywall
- put fiberglass insulation into outer walls
- attach siding to the outside to block water

 

If you want to reduce costs by adding new steps, you need to replace more work than you're adding. To do that, it's important to first understand what you're trying to replace, but when you do, variations are very possible.

 

 

What if, instead of pouring a whole foundation, you just have posts that each have a miniature concrete foundation? Yes, that works. That's called post-frame construction, and it's not a new idea but its usage is increasing because it's a bit cheaper, especially if you want large open spaces.

 

 

What if, instead of using drywall, you used hollow plastic panels that don't need mudding, sanding, or painting? Yes, that works. One such product is Trusscore. There are a couple disadvantages:

- Panels have seams between them.
- Noise transmission is probably higher.

Seams could be covered by painting over the panels. With some kinds of plastic, no primer coat would be needed. But Trusscore uses PVC, which contains plasticizers. Those plasticizers migrate to the PVC surface over time, weakening bonds to paint. They also slowly evaporate, and are bad for people. The solution to these problems is to not use PVC. Please, stop using PVC for indoor things.

 

By the way, since I mentioned painting walls, I'd like to say that US VOC regulations are very silly. Volatile organic chemicals are regulated because in sunlight they react with air to make smog. Chemicals with a vapor pressure below a threshold are exempt, because they don't normally evaporate much. Paint companies realized that chemicals with vapor pressure just below the regulatory threshold could be used as paint solvents, and they'd evaporate kind of slowly but fast enough. But if the chemicals are evaporating, it doesn't matter if they do it quickly or slowly. The point of VOC regulation exemption was to exempt things that won't be evaporating, not things that evaporate slowly. Either the slowly-evaporating paint solvents should be regulated the same way, or faster-evaporating ones (which can also be cheaper and/or less-toxic, in general) should have the same rules applied to them.

 

 

What if you replace the lumber, fiberglass, and drywall of outer walls with panels that are structural and insulated - some sort of..."structural insulated panels"? That's not uncommon now! Such panels are almost always made of plywood-styrofoam-plywood, because that's the cheapest option. Plywood is cheap, and polystyrene can be foamed to much lower density than other common polymers for complicated reasons beyond the scope of this post. Miscommunication can sometimes lead to the wrong panel shapes being cut; the multiple layers of contracting common in construction make that more common. That's gotten better over time, but there might be a trend towards on-site panel cutting machines. Still, this isn't considered a way to make construction cheaper: it's usually slightly more expensive than platform framing but gives better insulation.

 

What if you use something other than plywood for structural insulated panels? Plywood isn't very strong, and plastic is cheap these days, so polymer skins with foam core is probably viable these days, but I haven't seen it used in construction. Plastic doesn't rot and is generally less flammable, but maybe there's a problem with nailing stuff to panels being harder with plastic skins than plywood.

 

 

What if you use something besides wood for joists? That's not uncommon: steel is the most common alternative, because steel is cheap. Now, pultruded fiberglass is also a viable choice. Of course, this isn't going to solve high construction costs.

 

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You maybe have noticed that I haven't been discussing cast-in-place reinforced concrete flooring, which is the most common system for taller buildings. That's because the theme of this post is reducing costs, and that type of construction is more expensive than platform framing with lumber. Somewhat recently, wood apartments up to 5 storeys became allowable, and now 5 storey wood apartments are a common type of construction. Previously, that wasn't allowed because of fire safety concerns, which is actually understandable: fires in wood apartments are a serious concern.

I also haven't been discussing prefab modular homes.

Doing something in a factory doesn't automatically make it cheap. Aircraft are made in factories and they're expensive. A fixed indoor location is usually somewhat better for workers and material handling, but for prefab construction to be significantly cheaper, it needs to be done differently in the factory than it is on site, and the cost savings need to overcome the costs of shipping mostly empty space. If you look at what's actually done in prefab home factories, it's very similar to what's done on site.

It makes much more sense to make flat panels in a factory, and then assemble those into buildings. There's progress to be made in making the panels easier to assemble, but people do that now.

Structural insulated panels are viable. Precast concrete wall panels are viable. Flat stuff is easier to automate production of, and easier to ship. Building whole sections of buildings in factories does not, in general, reduce construction costs more than it increases shipping costs...unless there's cheap labor on one side of a border, and demand for buildings on the other side.

Yes, mobile homes are cheap, but you can't just buy land and put mobile homes on it. There's a whole permitting process and they need utility hookups; trailer parks have significant fees despite being in undesirable areas, but people still use them. Holding land factors constant, and adding in the cost of connecting modules to make something bigger than a trailer, the cost advantage of factory construction is questionable. (Here's a Construction Physics post on Toyota's failure to reduce costs with modular construction.) There are also large tooling costs to making things more like cars: setting up to make a single type of car costs around $1 billion, and building modules can't be economically shipped around the world like cars can.

Of course, even if you make flat panels, they still need to be cheap. The Broad Group made a 30 storey building in 15 days but their floor modules are too expensive, and they also had construction going 24 hours with a lot more people than is normal. It was a publicity stunt, not a better way to do construction.

Because those floor modules were too expensive, involving lots of labor, they have a new system with more automated production: B-Core, which is 2 steel sheets with lots of steel tubes between them. That's also much too expensive, as this Construction Physics post notes. But I think the concept of such floor modules isn't terrible, if you could make them cheaply somehow; a much cheaper way to make structural panels is the EconCore approach.

 

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putting it together

 

Let's try combining several of the variations I mentioned above to make a novel approach to construction. What might that look like?

Let's start from current post-framed "barndominium" construction, since that's one of the cheapest types of residence in the USA today (around $125/ft^2) but let's change it to use more kinds of materials and more new stuff to make things more interesting.

So, let's start with steel posts in the ground, with standard poured concrete footings, and a standard 8' spacing. Then let's use pultruded fiberglass joists with maybe 30' spans across those, since fiberglass seems more high-tech. And then, instead of another layer of joists and planks, we could use EconCore honeycomb core boards with glass fiber filled polymer skins, which can feasibly span the 8' between joists at a cost of perhaps $5/ft^2. So, probably more than using lumber for that has historically cost in the USA - which shouldn't be surprising - but water resistance and lower weight is worth something, and wood is more expensive in some places. Also, a closer post spacing than 8' might be better if making a building with multiple floors, maybe 64".

We haven't used wood yet, so let's attach wood between the posts for mounting wall panels. You can't hammer nails into steel, so maybe the posts come with brackets welded or cut into them to mount stuff. Then, instead of using drywall, we could use something like Trusscore but with something other than PVC, maybe polypropylene. That could then be painted without further work or a primer coat.

Most siding is PVC these days, so let's use polypropylene or PET instead.

Is that cheaper than current construction? Well, it plausibly could be, which makes it worth trying, right? I mean, on a societal level, rather than for an individual company. Perhaps governments should subsidize initial attempts at construction with new potentially-viable techniques.

 

 

 

 

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