Designing Kitchens and Bathrooms - drywall in tub area

when I install a new tub and attach it to the studs, do I take the greenboard all the way down to the tub itself or do i leave a gap between the bottom of the drywall and the tub to prevent any possible wicking of water if a leak should occur?

Greenboard is dry wall with a water resistant coating. It is not waterproof. If you are installing a tub without a shower, the greenboard may be durable enough as long as it is not exposed to water. If you have a shower and are planning to install a shower surround or tile, then a concrete underlayment is recommended because it is waterproof. If you use greenboard it should be cut to meet the tub. After taping, sanding, and mudding and painting or applying wall covering, the gap between the greenboard and the tub should be caulked with a mildew resistant silicone caulk.