New curb lower than pavement level?
September 10, 2022 2:26 PM   Subscribe

A new apartment block is being built a few blocks from my home. The sidewalk/curbs were poured significantly below the level of the existing street pavement. Why might the new curb be installed this way?

The construction site is fenced off, so I can't measure, but by eye from across the street, it looks like the flat part of the curb that the pavement should eventually abut is several inches below the edge of the existing pavement. The top of the curb/sidewalk looks like it is about even with the existing pavement. From my admittedly ignorant perspective, it doesn't look like the pavement could be made to line up with the curb unless the city tears out the pavement and repaves / changes the profile of the street. Before the apartments were built, the site was an empty lot being used as a parking lot by the city, and it had existing sidewalks and curbs. Maybe it has to do with drainage? But the existing street seemed fine, so that doesn't seem like the right answer.

The street's pavement seems to be in reasonably good shape, so I'm curious why the construction would be planned this way. This is an utterly trivial question, but I'd like to understand the logic behind the way this is planned/executed!
posted by Alterscape to Grab Bag (9 answers total) 1 user marked this as a favorite
I’ve seen some things like this get carefully finished wrong and then get fixed a year later. Or just leave a terrible puddle every winter until I moved away. I guess sometimes the builder is using a point inside the property to level from and some plan is just wrong about the relation of that point to the rest of the world.
posted by clew at 3:21 PM on September 10

Sometimes they do that so they can build a block wall that winds up above street level and acts as more of a retaining wall. Then the lowest blocks are mortared in below street level, making the whole thing more secure. The thing that look like a curb is really just a footing for the block wall that will wind up higher than street level.
posted by happy_cat at 3:37 PM on September 10 [6 favorites]

So the pavement isn't currently touching the curb? It's not clear from your post how far away it is, but if they are widening the street it would make sense to have a lower curb. Many streets curve upwards in the middle.
posted by yohko at 5:35 PM on September 10

Response by poster: Here's a couple of photos. The street is not being widened. I'm just wondering how they plan to make this work. If they just fair out the current profile of the street, there's going to be a very low curb. If they try to meet the edge of the poured concrete, there's going to be a very steep drop-off. I think clew's answer is likely correct, but I'm wondering what the fix is.
posted by Alterscape at 6:23 PM on September 10 [1 favorite]

That is weird.
It's not a curb, but the curb usually goes in first so that is strange.
I've also known of mistakes getting made in the survey, or not bothering to survey but this is so close to the road it seems extra dumb. Is the sidewalk sloping away from an entry to the building that's flush (no stair)?
posted by sepviva at 7:23 PM on September 10

Oh! Sorry I missed this when I first looked. What they did is pour new concrete road base past the new sidewalk. That's part of the road and will get covered with a layer of asphalt up to the curb and ramp base. Roads have a "crown" or slight slope to either side so water runs off.
posted by sepviva at 7:27 PM on September 10 [2 favorites]

Best answer: I suspect that they'll end up grinding down the existing asphalt, tho whether that was always the plan or not would be up for debate. I know that often times developers are required to repave the road in front of the structure once it's done with the thinking that typically all the trucks and work to connect utilities tends to be pretty destructive and leaves the road in a bad state once it's done, even when it's patched up.
posted by Aleyn at 7:28 PM on September 10 [1 favorite]

Best answer: The road is being re-graded lower in the next phase of construction. It’s very difficult to retrofit a compliant ADA sidewalk/curb ramp to the existing environment, so sometimes you end up with pretty radical changes. So it’s either that or drainage, or both.
posted by hwyengr at 7:54 PM on September 10 [3 favorites]

At least a good little thing, asphalt is one of the most easily recyclable things we use. There are machines that will rip up that asphalt, dump it in an oven and maybe add some stuff, then plomp it right out the back in front of the rollers. You just need to reheat it and stir it up.
posted by zengargoyle at 9:23 PM on September 10 [1 favorite]

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