A covenant, promise, agreement or understanding in, or in connection with or collateral to, a contract or agreement relative to the construction, alteration, repair or maintenance of a building, structure, highway, appurtenance and appliance, including moving, demolition and excavating connected therewith, purporting to indemnify the promisee against liability for damages arising out of bodily injury to persons or damage to property caused by or resulting from the sole negligence of the promisee, his agents or employees, or indemnitees, is against public policy and is void and unenforceable.
This act will not be construed to affect or impair the obligations of contracts or agreements, which are in existence at the time the act becomes effective.