Decentralized estimation methods which using Wireless Sensor Networks (WSN) with a bandwidth constraint of 1-bit on communication channel were proposed in some literatures. As the data generated are very scarce, to this type of WSNs, the PHY, MAC and Network layer protocols should be carefully designed to avoid excessive overhead, especially when energy saving is a major concern. In this letter we propose a cross layer design for such 1-bit WSNs. It has 3 features: 1, the sensor nodes send their results one by one after receiving a polling signal in a periodically rendezvous time window; 2, if the sensor node detect '0' it need not to send any signal; 3, Detect-and-Forward is performed on some in-between sensor nodes to relay messages from far lying sensor nodes through a minimum-hop-number path to the fusion center. The architecture and protocols are described, and simulations are made to illustrate the energy saving benefits of 1-bit Detect-and-Forward relaying.