[sumtechguy]

It depends on the city/state/county you are in and the local building codes. The city I grew up in the code was to have a sidewalk in pretty much all new construction building conditions except in some very narrow ones. It was very nice. Biking/walking was easy and 'built in'. The sidewalk at my parents house I think is the original one the builder put in, in the 1940s. With a small segment replaced because tree damage. If you DIY the cost is fairly low, just a lot of work. But if you hire a contractor to do it, the cost can spiral pretty quickly. If the cost is folded into the price of the house you would not notice it much. But to add on after the fact it can be a bit of sticker shock.