[kevind193]

I recently completed a little HVAC project to reroute a duct in the attic. It was snaking though the middle of the attic taking up more space than it needed to and someone had climbed all over it smashing it so very little airflow was getting through.

Now that I'm done with that, I want to lay down some more plywood in the attic to use the extra space that has been freed up for storage. There are a couple of 2x6s running perpendicular to and over the top of the ceiling joists (which are also 2x6s). In the picture these are the two boards that are running parallel with the new duct on the left.

I'd like to remove these 2x6s and lay down plywood in their place. The 2x6s in question are nailed into the joists from the top and look to have been there since the house was built. I don't think they are serving any structural purpose and were probably just put in place by the builders as a cat walk/stabilizer so they could work up there. But before I get myself in trouble and send the ceiling crashing down on the wife and kids, I wanted to get a second opinion. I know enough to leave the trusses alone, I'm just talking about the area in the foreground before trusses start.

Any insight would be appreciated.

Thanks,
Kevin

 

[Thunder Chicken]

Depending on the span, some boards screwed to the top of the joists will prevent them from buckling and rolling.

You might want to get some construction screws and screw down the paneling to the right before you pull up the 2x6s. May or may not be necessary, but it would only take a few minutes and would keep you out of trouble.

My shed attic was like this (though smaller). Had 2x6s screwed down the length of the attic. I put down decking, screwed to the joists, then removed the 2x6s and decked and screwed down the other side.

I'd recommend getting the biggest full sheets of plywood up there that you can vs lots of little pieces (access permitting). If you screw down big sheets it ties everything together pretty nicely and stiffens the floor. Make sure the sheets end on a joist.

 

[kevind193]

Thanks TC. That makes a lot of sense and would be cheap insurance. I haven't measured it, but I would estimate the full span to be about 24', maybe a little less.

 

[Thunder Chicken]

24 ft? I was talking about the length of each 2x6 joist across the ceiling (left to right in the picture). In the picture it doesn't look much more than 12-16 ft. There are also a couple of columns - I'd guess if you looked under them there is probably a bearing wall and the joists are lapped there. The span of each 2x6 joist would then be 6-8 ft.

 

[kevind193]

Yeah, I think you are right. I roughly estimated 10'-12' feet from the rafter to the centerline, which I doubled to get the 24' for rafter to rafter. It is probably closer to 10' or even less from the centerline. There is a wall under the center line that is likely supporting the joists as you said. I haven't had a look at what is under the existing plywood yet to know for sure.

 

[Bud9051]

What's your climate Kevin? If that is a cold attic in winter then the new plywood can become a condensation plane for moisture making its way through the ceiling below. The bigger the area covered the greater the risk. Warm climate, not the same problem.

Bud

 

[kevind193]

Hi Bud, This is northern california bay area. Occasionally gets as cold as 30 degrees in the winter time, but more typically in the 40 and 50s. There is a coastal influence so the air is somewhat on the humid side, although when the heater is going it gets pretty dry in the house in the winter.

Kevin

 

[Bud9051]

That doesn't sound cold enough to really worry about condensation. The dry air comment does point to too much air leakage and possible duct leakage making that worse.

Stagger your seams on the plywood so they provide more rigidity for the joists below.

Bud

 

[seephor]

If the boards are nailed to each and every joist then it's probably nailed to keep the boards from twisting while they dry and serves no structural purpose. If they are nailed on one or two joists, then they were probably put there for allowing workers to stand easily. they usually do this with green 2x6 or larger dimensional lumber over spans.