The directors or board of education of every school district in the State of Illinois shall cause to be erected and shall keep in repair on all public school houses or within the school grounds surrounding such public school buildings which may be in their respective school districts, a good and sufficient flag-staff or pole, together with all necessary adjustments, and shall provide a United States national flag of not less than four by eight feet in size, which shall be floated from such flag-staff or pole during the school hours of such days as the directors or board of education may determine: Provided, that the flag shall not be hoisted on any court house, State institution or public school building during any day when a violent storm or inclement weather would destroy or materially injure such flag.