My father wants to use his SDIRA to provide a loan to the LLC him and I are equal partners in.The loan would provide the additional funds we require to purchase an investment property.The LLC would pay principle and interest at market rate to the SDIRA.Would this be considered a disqualified transaction? 

Trace AdamsYou hit a lot of good points above and here are some thoughts your should consider:1) IF you’re buying with a second home loan, don’t rent it out long term.

I am doing an FHA loan and will move in once approved.

Was it in your loan?

Now assume you buy $350K home; put $25% down and take loan at 6 3/8 on $262,000;  Your payment is $1630/month or you're losing about $600/month all things being equal. 

I want to see if it's possible to put a new lien on this property so that he can't get a construction loan without paying me back. 

Getting prequalified for a loan is free (or should be) and usually is a soft credit check. 

The Solo 401K would allow a loan, and those funds may be used to invest in your personal name.

My wife is about to go back to school so she will not be contributing income as well as she will be tacking on a lot more debt to her initial student loans.

Think of it this way, your own personal credit is tied to your SSN and you can improve it by utilizing credit whether that is credit cards, loans from a bank, or mortgages.