No, nobody may enter your house without your permission, so your landlord can’t either. This also applies to common rooms! You have the right to live in your house undisturbed. Your privacy is guaranteed. A landlord has the same amount of right to enter your room as a complete stranger. However, there is one exception: this doesn’t apply if the landlord has a maintenance obligation. Your landlord must announce when this is going to happen and a tenant must give him the space to perform this maintenance.