attic space--do's and don'ts

[jimboburnsy]

Originally Posted by joe moving

Anyone know what sort of weight a 2x6 16" On center joists can hold? We have a full walk up attic (with a regular door and stairs).

2X6 joists are plenty stout. Each one of mine has tolerated repeated applications of at least 265 lbs. I'm in the process (been in the process for a really long time) of laying a catwalk similar to the one Cosmic described. If you have a proper floor up there, it should support anything that a typical second floor would support. Be careful about the distance the joists are spanning, however. My garage ceiling joists are apparently only designed to hold up sheetrock.

I don't know how much the spacing really matters with regard to "from above" weight tolerance unless you're putting something bulky enough to rest on several members up there.

[Barking Spider]

Depends on what kind of wood it is, and how long they are, and what it's holding up.

[Coldjensens]

Originally Posted by joe moving

Anyone know what sort of weight a 2x6 16" On center joists can hold? We have a full walk up attic (with a regular door and stairs).

Depends on the age of the lumber and the species.

Older lumber will hold a lot. If it is 1960s or earlier, it is probably old growth wood. That is strong. Some newer lumber will sag under its own weight. If you are west of the Mississippi you will probably have douglass fir which is stronger. East of the Mississippi is that forced growth pine from the Carolinas - junk. Even a 2x6 will not hold much at all.

Trusses can be designed for attic storage. If you have those types of trusses, they are enginerred to hold certain amounts of weight. You builder can probably tell you the limits. A plywood floor can also increase the wieght limits becuase it helps to spread the load.

If you have foam insulation (ICYNENE), it is sprayed ont he underside of your roof so the attic space is cooler in summer and warmer in winter and you can store things there without worrying about cooking them.

[joe moving]

It is an older 1950 house in NJ. I am just curious if we were to renovate upstairs and try to add a bedroom or something, if we'd have to get into moving up to larger joists. It is a long way away but I am curious. It has a regular staircase, and the joists are 2x6's on 16". No clue of the type of wood. The staircase is in the middle of them, so by the stairs they span 8 feet on one side, and 10 feet on the other side. But beyond where the staircase is, they DO span the full 18 feet + width of stair case at certain points. I am up there a lot messing around with the HVAC system and the floor does not feel even remotely bouncy. I am probably not making TOO much sense but I am looking just for general knowledge on the subject not a specific answer. It could be interesting or not, to know that our main floor has 2x8s on 16".

[Cosmic]

2 x 6 spaning 18' I already know will not do the trick. Way, way to long. I would suspect that will require something like a 2 x 12. Depends on the materials.

You look in the chart or table for joist spans to figure it out. They are set up by type materials and grade of material. Don't have my handbooks handy but 2 x 6 is only good for around 8 foot span maybe 10 foot at best if on 16" centers in a general sense. The tables will also give the spans for various placement on center.

Just web search for something like floor joist span charts or tables. Will give you a starting point. You can check in with your local building dept and see what they are using. There are some engineered joist systems that get away with less depth. Lot of those are shaped like lil I - Beams. They can use different materials which give a lot more strength. The thing with most of those, they can not be installed to bear house load from the walls, etc. They just carry the floor load.

If you have to stay with 2 x 6 can play around cutting the On Center distance and see what that does. Like if you are now 16" OC, can see what adding additional joists and going to like 8" OC and see what that allows. Anywho, the place to start is with the charts / table. Then after that it becomes a design problem to work around whatever.

[joe moving]

I think I must be missing something. The joists in the attic are covered by flooring so hard to tell what is going on exactly, however I notice that the center point of this supposed 21 foot span is VERY solid. It must be sitting on load bearing studs or something. Sounds like something to figure out when we need to use that space. But i'll check out the charts out of curiosity, thanks. I thought it would be comforting to know that, in the case that we needed that space to be converted to a Bedroom, If and how much of an ordeal it would be

[Coldjensens]

It is undoubtedly sitting on something. but you should confirm whther it is supported and what species of wood the joists are made of before you put anyhting up there.

If you check charts, you need to check for the age and species of your joists. Modern lumber only has a fraction of the strength of old growth lumber so charts based on modern lumber may be inapplicable to your house.

Further, older lumber is actually 2" by 6" not 1 5/8" by 5.5" Thus the strength charts are not the same. I do nto know when they started shving down the size of lumber, but I think that the 1950s is close to the time when it started. I know that they were using true sized lumber in the 1930s.

Part of our house has 2x6 joists at 16" on center. The span is about 18-19 feet. The joists are old growth maple and black walnut (mostly Maple). Those joists have been holding up the floors for over 150 years and there is no sagging, cracking or other problems. We have had over thirty people in that room, plus heavy furniture with no problem or bounciness.

The older part of the house is held up by whole trees shaved flat on one side. They are between 24" and 50" apart depending on the size of tree that was used. This part of the house is 172 years old. Again no sagging, but the floor is bouncy between the trees. I probably woudl avoid putting 30 people in one room in this part of the house, but then none of those rooms are big enough for 30 people.

Everyhting depends on the species and age of wood that was used.