Attic - Do I need a subfloor for storage space?

Hey guys,

I am going to be starting a basement finishing project soon. As part of that, I need to move some stuff that's stored into the basement into my attic. Right now, the attic has tons of open room. I went to Lowes and bought some 4x8 5/8" plywood and had it cut into 1/3 so I could get it up the attic stairs. I screwed it down onto the existing joists (which are 16" OC).

However, since then, I have read online that I should really do a subfloor and add more insulation the other direction. I don't want to kill myself but this really doesn't look all that complicated, just some perpendicular joists and then the plywood on top of that with more insulation on top. Is this really worthwhile? I do want to do it correctly and I"m only doing about 1/3 of the available space in the attic right now.

I had an energy audit through MassSave done a few months ago and they recommended putting blown-in in the attic but I specifically avoided it because I knew I would need the space for storage. But with a perpendicular subfloor I can still get that R-value.

What do I use for joists if I do that? Just 2x6 and then batting insulation? Is it really worth all that effort?

Here is what it looks like now:

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Attachment 17667

 

Not sure if those images work. here they are again:

 

I was also thinking if I raise the floor a bit then I can probably run right over the ductwork with plywood and make it a single continous space

Edit: Also I'm not quite sure how high I would need to raise the floor. I guess I would need minimum of 2x6 perpendicular, but how do you attach it? Just toenail screws in on the joists below?

 

How long do you plan on using the attic for storage? If it is just a (relatively) short time then I wouldn't do anything else than what you have already done. After the basement rebuild are you going to move the stored items back to the basement?

However, if you desire permanent storage in the attic space then you definitely need to do a bit more, exactly what depends on several other factors.

 

I'm losing the majority of my basement to the renovation so I will probably need stuff in storage for quite some time. I'm planning on moving most of the things that won't get damaged by heat / cold, things like old plates and dishware and stuff, maybe some holiday / season decorations also. They will probably be there for the long term. I don't have that much stuff - maybe 30 or 40 boxes in total

 

Just to toss around another idea;

Have you considered moving the insulation from the floor to the ceiling and walls? I do not know the cost difference in doing so, but it would provide for a storage area that is not subject to the great temperature changes from northeast weather that an otherwise unconditioned area could get.

 

I'm going to keep stuff up there that's pretty much temperature resiliant. Some xmas decorations, old non-leather clothes, and probably some bins of kitchen stuff (plates, etc) I have from my parents when they passed away. I'd prefer not to heat the entire attic.

I had found a really good youtube video earlier but now I can't find it any longer that showed how to lay joists perpendicular to the existing ones and then lay bats that direction. But I can't find it now (:

 

I wish I could talk you into getting rid of your junk, er, I mean, valuable treasures instead of storing it all. I know it is hard, I grew up with parents that had been through the Great Depression and it was next to impossible to get either one of them to toss unneeded items. After they died my brother and I spent months clearing out the old house and garage and made countless trips to both the dump and to the thrift stores. I am almost as bad and currently have way too much junk and the pictures of my garage prove it. So far I have avoided trying to make any storage in the attic (almost impossible because of truss construction) and I refuse to have a storage shed in the yard or to rent a storage locker.

Be that as it may, you can make some storage spaces in the attic. I would try as much as possible to stay away from the HVAC ductwork and also to leave a clear pathway to any machinery for servicing. You could use 2X6 or larger dimensional lumber to make cross-joists and simply toenail them into the existing joists and then fasten the plywood on top to raise the floor for added insulation. I would prefer that you instead use engineered truss joists because they would be lighter in weight. Most likely the existing "floor" joists. really the ceiling joists of the room below, are not really sufficient for an additional load of either people or massive storage. You could probably get away with using them on 24 inch centers and a minimum of 1/2 inch plywood. I would not even think about covering more than 25 to 33 percent of the area and I would not store barbells or the like.

This should be fine for things like holiday decorations but I would really think long and hard about storing clothes or dishes and such.

 

If the existing attic floor joists (ceiling joists of rooms below) are close to being over-spanned, don't be surprised to see some ceiling sag in the rooms below if you add a lot of dead and live load on top of them. The ceilings may also show some drywall cracking if joint taping is marginal at the seams.

 

IMHO, use the attic for its intended use, not storage space. IF you must; don't run new joists perpendicular (for reasons stated already) to bear on the existing ones. Run the same direction/span (parallel); to bear any live/dead loads on the walls below, raised with 3/4" spacers under them to allow for sag yet still separate. Use rim joists/blocking to prevent over-turning. Put any new loads on the bearing walls directly; taking existing joists out of the equation. Are those 2x12 joists to get the required R-38 insulation under the new decking? I would cut the plywood into strips (12") wide (and space them an inch apart) to allow for diffusion without worry of condensation/mold on the bottom surface due to temperature differences and the new blockage of air flow unless a poly v.b. is present; BSI-049: Confusion About Diffusion — Building Science Information

You shouldn't have poly in your attic system in your Zone 5 anyway...

Did you air-seal the attic first, the attic access hatch, baffles and foam board (because of your 2x bearing plate restricting R-value depth) at your exterior walls, energy savings, etc.; http://www.buildingscience.com/docum...ation-packages

Gary

 

Hey guys, I got some of these responses later. I actually bought 2x8 and did go perpendicular. I was following some of the instructions here -- How to Build a Raised Storage Area in Your Attic

I added 2 x8 perpendicular and batted with unfaced R-19 bringing total R-value to 49 for that area.



I don't plan on storing too much up here. Mostly toys / baby gear that won't be used until we have another baby and seasonal items, and nothing crazy heavy (like boxes of books).

 

Also I did get my attic completely air sealed back in April, so that was done ahead of time too.

The space in the pictures is only about 20% of the attic. I'll get some numbers later but I want to say that where this raised area is on joists that are 2x8 or 2x10 (I think they are 2x10) spaced 16" on center and spanning about 13 or 14' across a bedroom.

If I'm reading correctly the load between the 23/32" plywood and the 2x6 adds approximately 3.5 lb / sq foot.

 

Our one story home had 2x6 ceiling joists . I went further than an attic storage. I put 2x8 joists lengthwise of 2x6s and cut slots in roof sheathing boards so they stuck out of roof. I sealed each one so no rain came in. I then nailed a band board on the ends of these which was above the roof. Then I built my new 2nd floor walls on the roof and stood the front and back walls up on top of my new 2nd floor 2x8 floor joists. After we put the new roof trusses and roof on, we started at one end tearing the old roof off and building one 2nd floor end wall.
By the way I fastened the 2x8 joists to the 2x6 with some plywood cleats on the sides of them. I also notched the 2x6 joists for electrical wires that were running crossways on top of them. I attempted to attach a photo of the house but don't know if it worked.
Our neighbors enjoyed watching the project and we had no water damage and we lived in the house during our project.

 

One thing I noticed, when putting the boards perpendicular, some boards were not perfectly flush. As a result, my 2x6 are not always resting on each board, which means (I think) some o them aren't carrying any load. Should I just shim under each one or just leave it...

 

Hi,
I’m also trying to convert my attic to additional storage space.

House is center hall Colonial (built in 1964).
Attic floor (25’ x 35’ with “catwalk” down the center), is built from 2x6 lumber (16” OC) filled with batt insulation.
Additional layer of R19 insulation is run perpendicular on top of the joists, so nothing can be stored on top.

I wanted to do the same - run another course of 2x6 lumber perpendicular to the existing 2x6 joists and fill it with insulation as well and then cover it all with 1/2” plywood.

After getting all the lumber, I’m realizing the amount of weight that the original 2x6 attic floor will have to carry.

54 pcs of 2x6x12 = 1,400 lb
(I averaged the weight of 2x6x12 at 26lb, some are as heavy as 30lb, some as light as 16lb)

30 sheets of 1/2” plywood = 1,230 lb (at 41lb per sheet of plywood)

That’s 2,630 lb of extra weight. Plus the weight of the stored stuff (some of which is up there already).

It will be evenly distributed, but it sounds like an awful lot of weight to add to the existing attic floor.
Any thoughts or advice would be greatly appreciated!

 

Eugene,

In the big picture of your situation, you're only adding 3 lb./S.F. to what's already there. The precious treasures you plan to store up there can easily double or triple that amount. How your beefed up storage system will perform depends on a number of things (species of framing lumber, type of framing construction, number and location of 2nd floor interior supporting walls, etc.), most of which can't be answered by anyone here. If you are really concerned, maybe you would be wise to invest in the services of a licensed engineer, who could evaluate what you have and then make suggestions regarding the safest way to proceed.

 

Thanks BridgeMan,

I know there are a lot of variables, so there is no definitive answer unless I hire a pro to evaluate.
Although I wanted to do the entire attic, I think I'm going to stay away from areas where 12 foot 6x2 can't span from one load bearing wall to another (12' lumber is the longest I can get up in the attic).
Also, I'll space them 24" OC to save little more weight. I won't do much walking on top the raised area. The roof is pretty low, so I'm keeping the old "catwalk" to get from one end to the other without having to crawl.