This tax credit may be granted against the County real property taxes, based upon the amount expended by a taxpayer for restoration or preservation of an historic property. A property must be an historic site designated on the master plan for historic preservation, or within a historic district designated on the master plan for historic preservation. A tax credit will be allowed only for work which is the subject of an approved historic area work permit; or for ordinary maintenance expenses, when the amount expended exceeds $1,000.00. A credit will be approved for exterior work only, and no credit shall be granted for new construction. The amount of the credit is equal to 25% of the amount expended by the taxpayer for the restoration or preservation of an historic property, up to the amount of County real property taxes. The credit shall be allowed for the tax year immediately following the work or any portion thereof is completed, and any unused portion of this tax credit, may be carried forward for up to 5 tax years, after which the credit lapses.