=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.