To reduce the complexity of a rocket or fit more into a smaller airframe, single-bay deployment can be used. For small rockets, like an L1, single-bay deployment may just refer to only using a single parachute and dealing with extra drift during descent. If your rocket is going very high and there is a risk of drifting, single-bay dual-deployment can be used.

Dual-Deploy

Dual deploy refers to having two deployment events come from a single bay in your rocket. The most common example is to have a drogue parachute and main parachute come from a single bay. 

The hardest part of dual-deploy is determining how to have only one parachute come out when you want. There are a few different common practices used for this:

• Split bay: The bay is split into two halves, each of which are covered at the top and contain a parachute and deployment charge.
• Line retainer: The entire bay is deployed, but the main parachute is held down by its shock cord, and is released with a solenoid or servo when desired
• Bundle: The main parachute is ejected with the drogue, put bundled into a ball with a bag or line, then this wrapping is released and the parachute can open freely in the air.

Commercially-Available Dual-Deploy

The only commercially-available dual-deploy mechanism is the Jolly Logic Chute Release, which is a bundle-type dual-deploy system. 

It is important to read the regulations for where the Jolly Logic will be used. While it is acceptable at NAR and TRA launch sites, as of 2019 it is not permitted at IREC.