I build everything alone and the way I've solved this is:
1. Use consistent patterns for how you implement things. Don't mix and match; nearly all implementations in a given context/domain rely on the same mechanics.
2. Document the patterns you use. If they're your own, take the time to write up a blog post or tutorial on the how/what/why of them.
This has enabled a surprising number of people to pick up a project I've worked on with very few questions and little effort.
1. Use consistent patterns for how you implement things. Don't mix and match; nearly all implementations in a given context/domain rely on the same mechanics.
2. Document the patterns you use. If they're your own, take the time to write up a blog post or tutorial on the how/what/why of them.
This has enabled a surprising number of people to pick up a project I've worked on with very few questions and little effort.