Comment by monkmartinez | Hacker News Reader

Comment by monkmartinez | Hacker News Reader

Being a firefighter, I am tangentially intimate[1] with construction methods for dwellings, be they commercial or private. I am fascinated with concrete and the myriad of ways it is formed. My nerdy side really wants to build a concrete 3D printer and print a compound for my family. My profession reminds me that building codes and laws are mostly written in blood and are codes/laws for a reason.

How could we speed up the process of adopting codes across the US? 1 hour to my south in Mexico, one can basically build anything they want in concrete and there really isn't a regulatory body that would stop them. The probabilities of earthquakes and hurricanes in that area are quite low, no really reason to build for snow loads, but definitely for wind. Yet, on the other side of that imaginary line, in the same desert with the same probabilities; Contractors must build houses that can withstand loads and forces that will likely not happen if the house was around for 200 years.

Todays homes are not generally built with concrete except for the slab on grade. They burn hotter and faster than anytime in the history of shelter.[2] This is mostly due to the contents we place inside, but a large part is the gluing of structural elements out of fractional lumber. We seal and insulate these newer houses up tight, because they have very little thermal mass, with petroleum based products that contribute to fire load as well.

Concrete would be a better choice for homes in the US, but its cost prohibitive due to labor and materials. I don't know for sure, but the price for building with concrete seems like it is mostly artificial. That is, using 8 x 8 blocks for walls seems excessive when compared to the layered 2 x 4 -> 1/2" OSB sheathing (only on corners) -> Foam/chickenwire -> Stucco sandwich. Why don't we see tilt-up concrete homes? Or columnar concrete homes? It all just moves so slowly...

[1] New phrase? I am not an architect or contractor, but I know my way around most building systems past and present to include mechanical, electrical and structural.

[2] https://www.nist.gov/fire

> Why don't we see tilt-up concrete homes?

When I was a kid, my dad was in commercial construction. During the 80s I was old enough to remember things my dad talked about work, but not really able to fully understand them. I have distinct memories of my dad always dissing prefab concrete constructions that became popular, but I don't remember why they made fun of them. My dad also taught building trades at a local high school for a time, and he had stories about how the houses the students built were of such better construction than modern houses because they were learning the proper ways of construction vs learning how to cut corners and speed up the process while saving money. There were definite comments about how home builders were interested in using prefab walls so that they were always the same vs variance between crews. He was not a fan.

The beauty of stick-build houses is that they are easily modifiable. Move a wall. Build an extension. Move the plumbing. Add new fiber runs. All very incremental, marginal-cost work.

I'm very curious about your statement about insulation leading to faster fires, though. Like you say, codes tend to move very conservatively - are these new insulative house wrap products and such not getting fire tested as part of their approval?

How to spot an HNer in a home construction conversation:

Add new fiber runs.

There are competing concerns ever since the 1970s energy crisis insulation has been required. The people doing that often didn't talk to the health and safety guys. Some insulation doesn't burn, but some burns fast. Some safe while others are toxic. We discover issues and adjust code to fix it. Them Someone discovers something new and it looks great until years later we discover something we didn't know and codes have to adjust to something we didn't know.

Stick built is also more flexibility in terms of timetable. The roofers, can be on site before the framers are done. The electricians and plumbers show up right as the framers wrap up their work and before the roofers are done. Or they can wait a week because as long as they gets done before drywall nobody cares. Insulation can happen concurrent with plumbing and electrical or after. When you consider that all these parties have N jobs that need doing this added flexibility to show up early or late in the process helps a lot. Concrete is somewhat flexible but isn't that flexible in terms of timetable of all the steps.

Some have worked around the barriers for non traditional building by getting an approved frame, then ensuring that the approval process is ok with any form of 'infill'. For concrete, the frame of wood or steel could be approved, then you pour/print the rest which is not officially 'structural'.

I don't think we should be moving in the direction of insulating our dwellings less at this point since we are actively trying to reduce energy/emissions and heating/cooling is a big factor in that.

But maybe concrete structures are more insulating than I realize?

Thermal mass is great to smooth diurnal variance

Thermal mass inside the conditioned envelope is.. less so on the exterior of the house. Especially if it thermally bridges from outside to inside.

Thermal mass is great for hot days and cold nights in areas near the equator. Most people live where sometimes they day doesn't get hot enough at least once in the year. Even when day of not enough balance and you either deal with the cold (frozen pipe is the big issues, humans can wear more clothes), and insulation is the only answer. Well you can just turn on the heat, heat but without insulation you need a lot. (Such areas tend to not have modern furnaces, burning tires is common for heat despite the toxic fumes)

In short, thermal mass is overrated.

It has an R value of less than .5 per inch. Which is pretty much terrible to the point that it's negligible. A typical wall may have an r-value of 20, and a roof is 30+.

Reply on news.ycombinator.com