Typically, you can cut limbs that hang over on your property line as long as you don't hurt the tree. That said, be very careful. Tree disputes (especially here in the Evergreen State) can get really nasty and if you kill the tree, you could be looking at the cost to replace it, and in some instances you may be liable for their attorney fees if a lawyer gets involved. The best option is to simply talk to your neighbor and get an agreement (in writing) that you can cut the limbs on your side. Then, hire an arborist or tree cutting service to do the work. Good luck - and be careful.
Arthur D. Leritz
Legal Disclaimer: Mr. Leritz is licensed to practice law in the State of Washington. The response herein does not constitute legal advice nor does it seek to establish an attorney/client relationship, but rather offers educational insight only. Please feel free to visit Mr. Leritz's website for additional information: www.adlergiersch.com
I agree with the previous answer and get a licensed and bonded arborist and get a bid and talk with your neighbor. If you cut the branches on your own things may go fine or not but if you hire a professional and things go wrong you will be able to have someone to take responsability.
Only If and until you and I sign an Agreement for Legal Services, I am not your attorney. These answers are provided for informational and/or novelty purposes
Adding to the "be careful" mantra, I would point out that if you kill the tree or cause other damage to the neighbor's property or permanent improvements, you could be liable for triple damages and attorneys' fees under Washington's timber trespass statute. I second the advice of trying to get the neighbor's permission in writing before moving forward, and hiring a professional when you do.
I only practice in Washington State and may not practice in your area. This answer is a brief hopefully helpful tip to you which is correct to the best of my knowledge and is meant as a starting point for you to conduct further investigation. However, it is made without knowing the factual details of your case or doing any legal research and so may be in error as to either the facts or law. I am not your attorney and I am not giving a legal opinion by this answer.