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Comment by MS90 | Hacker News Reader

There's also the fact that there's only about six inches of dirt here, dig any deeper than that and you hit solid limestone. That's why none of the houses here have basements.

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Uh you have that backwards. Limestone is rock, but it’s an easy one to carve through (unlike Manhattan Schist, for example).

It also has an advantage over soil that the remaining bits don’t need much extra support for the load above. This doc talks about it: https://stateimpact.npr.org/texas/2012/11/21/why-texas-doesn...

It also has a disadvantage in that it's extremely porous and allows water to seep through it, which expands and contracts with temperature changes and causes the limestone to crack. There's areas around town where roads have been cut through hills, and if you drive through these after a big rainfall you can literally see water pouring out the side of the rock face. Chunks of limestone breaking off and falling onto the side of the road is a pretty regular occurrence.

There's other issues, too, such as the lake that runs through the middle of the city, the underground rivers and cave networks in the area, and the unstable clay on the East side of town that expands and contracts with rain, causing all sorts of problems.

Do you actually have any sources or are you just making assumptions based on how you see limestone behave on the surface?

I don’t have sources myself but to me the porous nature of limestone seems like a benefit since water would easily flow to the water table instead of flooding in the tunnel.

Erosion seems like it would be a far bigger problem for tunnels in soil or sand than it would be for limestone.

Water generally flows down. If you have a high water table building basements is usually foolish.

Limestone, because it dissolves in contact with acidic water (and rainwater is slightly acidic) is also prone to sinkholes. Best to keep the ground stable by not exposing it to more water. It happens so often in Florida there’s an FAQ page. https://floridadep.gov/fgs/sinkholes

there is no one reason why we dont have basements, but it is more likely to do with the fact that up north they have to dig deep (3-4 ft) for the frost line. If you are digging that deep anyway, you might as well go an additional 4-5 ft and build a basement.

Excavating limestone isnt that hard. Instead of one day to dig a basement in soil, it would take about 14 days to dig a typical basement in limestone (based on digging pools in limestone). It costs about 1500/day for the crew/equipment so an extra 21K for the excavation.

East austin has no limestone and basements are still rare.

It might not be 'that hard' to excavate limestone, but an additional 21,000 dollars added to the cost along with 14x longer work time is not an insignificant difference.

East Austin doesn't have them because of the unstable clay that expands and contracts with rains, same reason the track surface at COTA has had so many issues. The ground doesn't stay put.

Couple those things with the frost line issue you mentioned, along with the likelihood of flooding, and it probably comes down to the fact that it's just too much work to be worth it.

The reason you don't have basements is because you don't have to worry about the Frontline.

If you did, land would be worth $21k less per lot - to make up for the cost to dig a basement.

> East Austin doesn't have them because of the unstable clay that expands and contracts with rains

Which is why most people water their foundations to ensure the soild maintains steady state of dampness- rain or shine.

It may be different in Hill Country but in Dallas and Houston the water table is just too high in most places to make a basement realistic.

There are basements here in Houston but they're rare and typically have multiple sumps and pumps.

> there is no one reason why we dont have basements, but it is more likely to do with the fact that up north they have to dig deep (3-4 ft) for the frost line. If you are digging that deep anyway, you might as well go an additional 4-5 ft and build a basement.

In Minnesota, where I live, basements are definitely a byproduct of structural requirements. You have to dig 48 inches so that your foundation is under the frost line. But also consider that you don't want your front door to be at ground level, because then it might not open after a massive snowfall. So if you add up all that vertical space, you get about 7 feet, which is about the ceiling height of an unfinished basement.

Alternatively its roughly 3 days of work to drill, blast & dig out a basement excavation, but explosives are scary so such work is often blocked outright.

East Austinite since I was a teenager, family has had the same parcel of land since the 1880s. It's all caliche and limestone boss 6 inches down boss.

How do you put down fence posts? A brief googling says they should be 36 inches deep.

Depends. Some combine the fence posts with concrete (adding weight), some add reinforcing metal posts, some do nothing. Watching fences collapse after a strong wind storm is a common sight.

Its worth noting you can generally still drill a hole into caliche.

I use an 8 foot, iron digging bar ahead of the post hole digger.

That may be true in some areas of Austin, but in most cases, it's about cost and expectations. Austin straddles the border between dry, rocky west Texas and wetter, black soil east Texas, but houses have traditionally been built without basements no matter what kind of soil they were built on, in Austin and in other parts of Texas. These days, a lot of newer, more expensive houses are built with basements to maximize usable square footage.

Houses used to be small, built of wood, and hardly attached to the ground at all. It was fairly common practice to pick up a house and move it to another plot nearby.

I think once cities get older and more ossified in their shape is when basements start to appear.

Assuming there is no other reason to avoid it like flooding, hard rock, earthquakes, etc.

> It was fairly common practice to pick up a house and move it to another plot nearby.

To me that sounded fishy but I looked it up and you seem to be right! https://www.brownstonedetectives.com/the-ancient-art-of-movi...

Yeah no kidding, when I had a tree planted in my front yard they had to use jackhammers to make the hole deep enough. I had no idea.

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