Attic as Storage

[JimD]

The more realistic damage scenario for attic storage is not structural failure but, rather, sufficient deflection to pop drywall fasteners. I have not seen it occur but houses are designed to minimize deflection of floors, not to avoid failure. If I can walk on the 2x6s in my attic, and I have, then they can take 200 lbs in about a foot square of space which is more than they will see for storage. I would look at the ceiling joists and make sure they are 2x6s, not 2x4s (I would worry about 2x4s if the span is not real short) and if they are, your concern remains insulation and not structural.

The best way to sister on a 2x6 from an insulation standpoint would be to put it at right angles to the existing 2x6s. There may be a metal connector for this but I did not find any. I put the extra 2x6s directly on top of the existing 2x6s and held in place by constuction adhesive. Small side plates every couple feet of scrap sheet goods, 1/2 to 3/4 thick, and held on with finish nails (until the glue sets and then the glue should hold it). This went pretty fast. You have to avoid putting any real side load on the sistered pieces until the floor goes on because you could break the connection. With the floor in place, it will keep the joists spaced properly and stop them from rolling over. I decided a foot of wood was not terrible insulation.

Jim

[jseklund]

Thanks again to everyone for replying. You have made me spend some more time thinking about what I'm trying to achieve, and caused me to realize I can achieve some benefits that I hadn't thought of. The insulation issue, in particular, isnt' one I thought about enough. The attic is constructed with 2X6 joists, and for a large portion of the attic, there is one layer of insulation in the cavities (so about 6"). Someone came in after-the-fact and installed another sheet of insulation perpendicular to the joists over maybe about 1/2 the space - 1/4 on one side of the house, 1/4 on the other side, with the center open. The plywood is down over the center where there is only 1 layer of insulation, but this is also where the ceiling over the stairs and the hallways are- so I bet I'm losing a ton of heat through there.

I'm on Cape Cod, so I'm supposed to have R-49 in the attic...which I guess is about 15" or more. I've found that the reality is that most people get to R-38 in most situations and call it a day, because R-49 is just too much mass.

So, my plan is to go up there this weekend, inspect the insulation more thoroughly to see what I need to add and how many SF to get it to R-38 at least. I will then get some 2X6's and run them perpendicular to the joists, making a box that covers approx. 12 Ft X 20 FT. I will then fill this with insulation, plywood the top, and fill around the edges with insulation and no storage space. This would explain why my oil was not as efficient as I expected when I moved into the house this year. Apparently, it will also help me keep the house cool in the summer.

Running the 2X6's perpendicular to the existing joists will allow me to seal air flow better between the insulation, spreads the wait in any area out over the supporting joists better (as if bridging), and will give me plenty of strength and floor area to store 1,000-2,000 pounds if need be.

Thanks again for the help.

[rnelson0]

Make sure that your additional insulation is not batted, or that you remove the paper, or you will get condensation between the layers.