You need to inform your insurer of any changes to your building and/or your contents which may impact on the cover you have.
The key point to remember is that your contract with your insurer is based on mutual disclosure of information - they charge you a "fair" premium, based on the risks you've made them aware of. If these risks change, so too does the value of a "fair" premium.
If in doubt, ask your insurer. The time taken for a quick phone call could save any problems that arise in the event of a claim.