First off, I have 3/4 inch of this subfloor: 
It is on the first floor, and the area covers 700 sqft.
Question 1: What type of subfloor is this? I think it's OSB but I want to make sure because when I google particle board subfloor it looks like this in some pictures.
I got a measure from home depot. They said that I need 3/8 inch wood underlayment before I can install 1/2 inch solid bamboo flooring and that it would have to be glue-down.
The glue-down installation is 2.99/sqft plus $1.20 / sqft for the glue. The 3/8 inch wood underlayment is $1.56/sqft. Thats $5.75/sqft just for installation
It seems to me I should rather invest in real 3/4 inch solid hardwood and go with the nail down install $1.99/sqft, or go with engineered click bamboo and have it floated. (stranded bamboo cant be easily refinished so having solid vs engineered isnt a big deal)
Question 2: will I need a wood underlayment no matter what hardwood I choose and no matter what installation is used (float, glue, nail)? ( I know it depends on what manufacture recommends but in general)
Best Answer
Yes, that's OSB. It's the only product that's made with large wood "strands". I wouldn't have guessed that it was 3/4" though due to the apparent lack of tongue and groove along the longitudinal edge, but maybe the photo is misleading.
Particle board looks like compacted pine sawdust. Fiberboard (MDF) looks like pressed pulverized wheat chaff. Neither of those are used as subfloor.
No, not all wood flooring requires underlayment. Modern t&g subfloor in the 3/4" class is adequate for some products. However, a second layer can result in a stouter, quieter finished floor which feels higher quality. Read the label.