i built a garage 20x28 with 11 5/8 engineeded floor joist 12" on center running 20' open span. I'm putting a hot tub upstairs that is supported by 2x6 wall the span will 16' under the tub . a 6x7 tub max filled & loaded with people 3000lbs. do I have enough support ? Thermospa said I do after they came for an inspection. The Manufactures web site said I can sandwich the beams with plywood for additional strength.can you help