Deprecation of rental property does not apply to Solo 401k or IRA LLC owned property. Reason being, your retirement account NOT you owns the property. Also, solo 401k and IRA funds are already tax-deferred or tax exempt.
As a result of not being able to depreciate real estate owned in your solo 401k or IRA, you will want to invest the retirement account in real estate that will appreciate in value and generate high rental income, as the loss in value of the property resulting from changes in conditions such as economic and environmental can negatively impact the solo 401k plans initial investment in the property.
Since solo 401k owned real estate may not depreciated, make sure the property the solo 401k will buy will appreciate-increase in value. Make sure to research the area to help prevent the solo 401k from purchasing real estate in an area where property values are falling because of social changes or other reasons.