Is there a way to expand a lot?

Not in the way that you are thinking. I wish it worked that way, though.
If I had my heart set on having my home on a bigger lot, this is what I would do, if you aren't already on the largest size lot available.
I would save the house and household to the clipboard.
I would bulldoze the house and then again to bulldoze and eliminate the lot.
I would go into Edit World and place a larger lot than what I had before.
I would place my house and family from the clipboard onto the new, larger lot and use the controls to move the house to where I want it on the new lot.

It's not optimal, and it probably doesn't include as much land as you see and want but since there isn't an option to drag the boundaries of your existing lot, it is the only way I can think of.

Good luck!

No, there's no way to expand an existing lot. But you can place a lot on a larger (empty) lot, if one is available, thereby getting more space. But the consequence is that you move somewhere else on the map.

Or, you can buy another residential lot as an additional home. Occasionally I'll go into the world editor of Edit Town and try to place a small lot nearby, and then purchase it as an additional home and use that as extra space.

This mod will let you set your own lot size to place. But I suspect it is still limited to the 64x64 max lot size.

http://modthesims.info/d/471164

if you purchase or have the cats and dogs you can bulldoze the brindelton bay lot to have lot dimensions of 64x64 if not i don’t think you can.

"kkkabc;c-16633102" wrote:
if you purchase or have the cats and dogs you can bulldoze the brindelton bay lot to have lot dimensions of 64x64 if not i don’t think you can.

That would, I'm afraid, be a TS4 answer to a TS3 question. This is the TS3 section of the forum.

But the original question was can we expand the size of an existing lot without have to replace it. And the answer (for TS3) is no, but sims can own multiple residentials as has been said.

Insightful, thanks for sharing Igazor. I'll close the thread from here.