Our back roof was only 1.8 inches per foot like yours, and was shingled with
comp. roofing, which failed within two years. Shingles are not applicable,
as most manufacturers will void their guarantee for shingles if pitch is
less than 4 inches - read the left over package covers on the product.....
So we had roof stripped to wood decking, then had a five layer non-shingle
commercial roof put on. You need to get better info, and keep away from the
idiots that do jobs poorly and give erroneous advice (eg the technology is
lost!) . Get local references from neighbors you know, and use local roofers
that have high volume business and good reputation, with warrantees. Our
roofer had a 3 year unconditional warrantee, but de facto much longer, as he
is known to correct mistakes way behond this period. On the steeper 4 inches
per foot front roof, we got 30 year shingles.
Anyway, the low pitched roof we had put on was first underlain by
fiberglas/rubberized padding or blanket, then three layers of lapped hot tar
mineral felt, followed by a walkable mineral grain surface, hot tarred to
the tarred 3-ply felt underneath. It should be good for 20-30 years, and has
9 years on it so far, with little signs of aging. I hate tar and gravel, as
it is hard to diagnose leaks, and is more prone to damage by walking.