You are never going to rank for a one word keyword these days. If you do, you have either been ranking there for a very long time or you live in the middle of nowhere. The better option is to use long-tail keywords to fill in the content on your construction websites. The reason is twofold;
1. It is easier to rank for 2-4 keyword strings
2. You get closer to an actual buyer using 2-4 keywords
Think about it, someone searching for plumber could be looking for anything. Someone looking for 24-hr emergency plumber in Philly is someone with a problem who NEEDS you NOW! So create some pages on your site that contain long tail keywords and start generating more business!