What are the disadvantages of Natural Building Materials?

Straw bales even more so than with mud brick, rammed earth, cob, earth bag etc greatest enemy is moisture - thus one needs to adhere to good building practices especially when building in rain prone areas i.e. good foundations, proper sill details, proper roof overhangs and the use of breathable plasters and paints. It is always best to get good technical assistance from someone who understands these materials when building with them.