The BACnet communication protocol standard makes it possible to integrate a wide variety of building automation and controlproducts. Building owners and the consulting engineering community have had difficulty understanding how to write quality BACnetspecifications. It has been difficult because, for the most part, specifiers have no background in computer communications and the toolsprovided in the 1995 standard to bridge this gap have not worked well in practice. Newly approved Addendum d to the BACnetstandard is an attempt to improve the situation by defining a set of interoperability building blocks that can be used to clearly define thecommunication requirements of a BACnet system.The addendum also includes several standardized building control devices for which the BIBBs have already been selected. Guidance isprovided regarding the kind of application functionality that can be specified for each of these devices. The intent is to provide a reliablcommunication framework from which the specifying engineer can build using what he knows best, the functional requirements of theapplication.