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Comment by xnx | Hacker News Reader

Concrete is probably underutilized as a building material for homes in the US. Though there are high carbon costs for cement production, there are a lot of benefits to concrete: very strong against wind, very fire resistant, impervious to most pests, sound proofing, air-tight, good insulator when sandwiched with foam. https://www.iconbuild.com/ isn't yet 3D printing concrete homes at scale, but they have a small neighborhood of some really good looking homes going up in Texas.

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> there are a lot of benefits to

One disadvantage: much harder to do changes / remodelling down the road.

Cinder block may be better for later flexibility than poured concrete:

* https://en.wikipedia.org/wiki/Concrete_block

Most of the time, rebar and concrete is placed and poured in the vertical column created by laying the block effectively turning into a vertical slab. It’s so much easier to build a wood-frame dummy wall on the inside to house utilities.

Most of the world lives in concrete buildings.

There's a problem of where to put the infrastructure. If you lay pipes inside concrete, they're really hard to maintain. So, often plumbing, electrical, and HVAC just punch through the walls to outside equipment, plumbing, and conduit. Look at small low-cost housing in Asia. Mini-split air conditioners and pipes all over the exterior.

<So, often plumbing, electrical, and HVAC just punch through the walls to outside equipment, plumbing, and conduit.>

That's true for commercial bldgs, but almost all home dwellings in America with slab foundations have the plumbing and some hvac lines inside the slab. Repairing water and sewer lines in these homes is very expensive.

If I understand correctly from my neighbors’ experiences, they just cut up your walls and put new pipes in there and in the attic when the time comes that you inevitably develop a slab leak. it seems like this is probably a case where it has plenty of advantages for the first owner/1st 30 years (pipes neatly out of sight on the first floor) and when it eventually fails, it will be someone else’s problem besides the original builder or even original owner in most cases. Maybe this has changed in recent years though with the switch from copper to PEX, idk if they can just put that in the slab.

That's correct for water lines, and is expensive. But drain and sewer lines are in the slab. Just imagine the cost of removing your tile flooring, then cutting up the slab, removing the usually copper drain line (on older homes), laying new PVC, back filling with sand or gravel, THEN recovering the floors. Carpet would be a little cheaper.

In New Zealand PVC pipes are used in concrete slabs for sewage, which in theory should last something like 75+ years. Water, I think, is still put in the dry wall cavity.

Doesn't that just imply that a concrete home would have this problem everywhere, instead of just in the foundation?

In Latin America hollow brick is often used for walls. I'm not in the construction business, but I'm guessing it has to do with cost, insulation, and the ease of breaking in a crevice to lay conduit lines.

If you want to install a line and there isn't a pre-existing conduit in the wall, you do have to chisel one in. It's definitely more effort than with a "hollow" wooden wall, but it's not terribly bad.

> Look at small low-cost housing in Asia. Mini-split air conditioners and pipes all over the exterior.

I'd attribute this to the "low-cost", not necessarily the "brick/concrete". I'd imagine in the USA houses would be pre-fitted with more conduit, and homeowners could afford the installation of more as needed.

> If you lay pipes inside concrete, they're really hard to maintain.

I'd like to introduce you to a magical invention... it's called "ducts" :-)

You can have them behind walls, above ceilings, between rooms, between housing units etc. Of course, if the building was not build with maintenance in mind, or neglected to consider future potential needs (e.g. HVAC not catered to in buildings from the early 20th century) - then you have to run things on the outside; but even in those cases, new external ducts can often be constructed, using concrete or other materials (e.g. metal frames and whatever you like as cover, e.g. cement-board, sheet metal etc.)

Sure, if you were smart enough to have… all your ducts in a row. Ahem

Yes, you can, but people don't like it. There's classic Wiremold, but put that in a house and the value drops. There is an exposed plumbing as an aesthetic thing, but it's not popular.[1]

[1] https://www.graana.com/blog/concealed-vs-exposed-plumbing-di...

Didn’t know that was a thing. I love it.

The link gives me:

"The owner of this website (www.graana.com) has banned the country or region your IP address is in (IL) from accessing this website."

I guess maybe it's a protest against that genocidal war the government here is waging on Gaza.

You could do what they do in larger US buildings. Non load bearing walls are not made of concrete so vertical pipes go into those walls and are encased in drywall. Bathrooms and so on have their horizontal pipes below the ceiling of the space underneath, covered by drywall, so just need to punch a single hole in the concrete floor per pipe.

Unfortunately, concrete production is a pollution problem.

Cement industry accounts for about 8% of CO2 emissions

https://www.cbsnews.com/news/cement-industry-co2-emissions-c...

This number keeps growing because all of the other emissions are finally going down. I memorized it as five percent a decade ago.

It's a point source of carbon, which is the best case for capture. Some of the carbon could be made into plastic (particularly polyoxymethylene would be easy) although you might find that demand is saturated well before you have used up all of the capture.

Bigger problem is that due to the extreme temperatures required (the essential crystal structure, called alite, can only form above 1250 C) the facilities are large, expensive to construct and difficult to modify. Because the reaction produces a dust plume, they are often sited in less regulated jurisdictions, which compounds the problem. But capturing the carbon and capturing the dust likely require some common components.

This is arguably an opportunity for Latin America, which has historically had low local cement production due to tighter environmental regulations vs Asia. Its road and rail infrastructure lags as a result. (The durability of PC is also highly desirable in tropical environments!) But a proper implementation of clean cement is not yet well understood, and economic incentives for cleaner imports are merely theoretical at this point.

Cement is so c02 intensive largely because the chemical reaction which occurs release a large amount of c02. From what I remember the energy use for the furnace is 10% compared to 90% from the fundamental chemistry.

This is what I remember from working for a start up that was helping make low carbon cement, the numbers could be wrong, but it's more complicated than just the energy to reach the high temps.

We need to bioengineer vines or something, actually bacteria would be best, to grow insanely fast. Then grow them while the slab cures.

Then after grind them up as mulch abd fertilizer.

We can outfit the bacteria with a natural inhibitor. Maybe a lack of lysine.

Yeah. That'll work.

Some researchers are experimenting with additives of various sorts to use concrete for carbon sequestration: https://news.mit.edu/2023/new-additives-concrete-effective-c...

The obvious economic quirk about capturing carbon in concrete is that given time and pressure you can convince carbon to harden. Concrete that continues to pull in carbon in its process in theory has good chances to be stronger and hardier. If it continues past the initial set, you get "self-healing" concrete.

You joke about plants, but yes plants have been doing variations on that for epochs now, there is probably some more lessons to apply from them if we want to build a "diamond age" with all the excess carbon we've spewed as a culture.

Additives might be useful, but there is potential to weaken the concrete, and that'd make things worse, not better. EG, forcing rebuilds too often.

The reason I diverged from vines, is because multi-cellular is too slow. I think what we'd need to do, is create some sort of thin mat you lay over the concrete, just unroll it, and it has dormant bacteria along with whatever input(food) it requires to consume CO2.

So it then, much like yeast in bread, multiplies quickly, and you're left with a thicker mat to roll up and dispose of, grind up, say for fertilizer.

I envision the mat to be thin, akin to plastic rolls you get to keep insulation in place. They could be comprised of entirely organic materials, food for the bacteria. You know, such a thing should be possible, but would the bacteria multiple quickly enough? And likely water would be required as an additional.

Too many contractors can’t get concrete right. I see so many new builds with cracks and spall damage. So many basement or garage slabs with a few big cracks in them. Stick frame is more fool proof for sure

The problem is too many contractors are crooks.

High carbon cost of cement for sure (until we find viable new materials to bring that down which companies are actively investing in). That said a concrete home, if properly built, lowers the lifetime costs of CO2e as you have better heating and the product life is exceptionally longer!

Here's a detailed walk through of the Lennar development from last month by a pretty detailed home builder/contractor:

Revisiting Lennar & ICON's 3D Printed Neighborhood 6 Months Later with Matt Risinger

https://www.youtube.com/watch?v=fPTps7e9SqY

Here's one of the homes at the level of a lay person's level of knowledge:

Inside a 3D Printed House That's Actually (kind of) Affordable

https://www.youtube.com/watch?v=qG7KMjV8zMk

That Matt Risinger video is exactly the one I watched that educated me that this process has gotten beyond the prototype stage. Great videos, but I usually watch on 2x speed because the information density is kind of low otherwise.

Wood is also very strong against wind if engineered correct. Both need something else to air seal as air will go through. Yes it is fire resistant, but unless your insulation and other building material is also fire resistant you gain nothing important: either way a fire will gut the house and need expensive work to repair. Wood is also a good insulator when paired with insulation.

Concrete is a useful material to build with. However it isn't the miracle that many advocates claim.

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