We have a sub 5% vacancy rate consistently, only offer two year leases, have an average length of stay of over 4 years per lease and only 3.87% of collected rent (January - September) went to maintenance including our maintenance fee.  

If you are looking at short to mid term rental lengths, those types of tenants probably won't care as much that the garage is unavailable. 

To avoid what's called a "Prohibited Transaction" you need to keep things arm's length. 

The sewer line cleaning price is going to depend on the length of the sewer line, a normal-sized one will run around $300, a long sewer line will cost twice as much to clean.

My question is:  Is the requirement/qualifying condition of the less than 7 day average length of stay calculated by calendar year or is there more to the time measurement than just the taxable year?

Are you asking about length of stay discounts? 

Length of Listing.

I'm currently looking for another house hack in SD now that I've met the primary residence time length requirement at my current place.

I discovered that Wells Fargo has a Fixed Rate Advance HELOC option that allows you to keep your current HELOC rate (if you have one and if this rate is favorable compared to current rates), and redraw your HELOC to the full amount of appreciated value in your property, so the “LTV” on the HELOC would be 100%.If you don’t already have a HELOC, the option starts you with fixed rates between 4-7% depending on the length and principal of the LOC. 

I've found asset protection to be one of the most difficult topics to discuss at any length on BP.