Do you make it easy and a priority for your employees to help generate leads for your company? Employees, properly motivated, can generate a lot of new business for you.
Let's start with the sales staff. If you are paying them straight commission, offer an additional 2% of the sales price if they generate the lead themselves.
Job supers, forepersons or lead carpenters can hand out business cards to neighbors or those visiting the jobs. When a qualified lead is generated from this effort, you should provide a monetary reward in the $10 to $20 range. If the lead is sold, they should be rewarded with a percent of the sales price in the 1 - 2% range.
All employees, including office staff, should be rewarded for handing out business cards, brochures or making other contacts that generate qualified leads. Make sure each employee has their own business cards, with their name on them.
If you want to build your business, sit down and write out a plan for rewarding the efforts of your employees. Give that plan to your employees, let them know the rewards they can receive. Then follow through. If you aren't sure a lead was generated by an employee, err on the side of the employee. Trying to pencil your employees out of a few dollars will kill a referral program faster than anything I can think of. Be honest and be fair, and everyone wins.