Hello to everyone on this wonderful site. I bought a old house made in the 1930's. I just finished guttering the house and noticed that the attic joist are made of 2 X 4's, thats actual 2inc X 4inc not 1 1/2 X 3 1/2. There was a lath and a plaster ceiling attached to these joist. I want to use the attic space for storage, not liveable space. The span on the joist are 15 feet wide, and they are 24 joist all together. Someone told me that placing 1/2 4 X 8 sheets of plywood would be good enough to hold stuff up there. But to me I have never seened 2 X 4 joist in all my life. Should I install 2 X 8 or will I get away with 2 X 6 on a 15 ft span. I don't plan on moving up there, just don't want to see all that storage space go to waste, also don't want to spend alot of money, I need it to put the house back together.. Thanks