W. Va. Const. art. VI, § 11

Additional territory may be admitted into state. Additional territory may be admitted into, and become part of this state, with the consent of the Legislature and a majority of the qualified voters of the state, voting on the question. And in such case provision shall be made by law for the representation thereof in the Senate and House of Delegates, in conformity with the principles set forth in this constitution. And the number of members of which each house of the Legislature is to consist, shall thereafter be increased by the representation assigned to such additional territory.