Storage in attic -- humidity swings a problem?

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Forum topic by soob posted 07-09-2015 03:35 PM 865 views 0 times favorited 13 replies Add to Favorites Watch
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266 posts in 1233 days

07-09-2015 03:35 PM

I’ve been blessed (cursed) with about 1500 board feet of 4/4 walnut. It’s really beautiful wood, not graded but mostly clear with very little sapwood, etc. Mostly air dried to about 15% in the center, still needs a little drying. The boards are in 16, 14, and 12’ lengths. It’s just great!

My problem is that I live in the suburbs and can’t store it easily. I have two garages, one of which is my shop, and it has an attic with 2×12 flooring. I’ve been disabused of the notion that it can support the weight of this monstrous stack as is, but I think if I ran 2×12s the width of the shop (22’) 12” on center, supported by the exterior walls, that could hold it. It’d be stickered.

The attic is ventilated well enough with a ridge vent. Temperature ranges from 112 F to 70 F in a typical summer day, probably a bigger swing in the winter as it’s not insulated. I’m in the deep South, so it’s quite humid. And the humidity takes big swings over the course of a day—30 to 80% in the summer, at least. That’s the rub—I’ve been told that those large day-to-day humidity swings will degrade the wood. Is that true, and what kind of damage am I looking at? It would be up there for a while, most of it will probably still be there when I die or move. I fully admit I’m a hoarder but that’s another issue. Anyway, thanks in advance.

13 replies so far

View mahdee's profile


3888 posts in 1792 days

#1 posted 07-09-2015 03:43 PM

They will be just fine. Stack them as high as you can on the joists closest to the walls and reduce the stack size as you get toward the center to distribute the weight mostly off the center. Sounds like a nice stash and a good investment.


View rwe2156's profile


2964 posts in 1505 days

#2 posted 07-09-2015 04:46 PM

Oh, boy, what a “problem” to have ;-)

I live in NE FL, and you are quite correct about the humidity swings. 90% at 8 am and 50% at 2. When it gets over 95 it can drop to the low 40’s. If a thunderstorm comes up it can soar to 90% again in a matter of 30 minutes.

I’ve store quite a bit of milled lumber in an open drying shed on my property and I really don’t think there is a problem with humidity swings. I think they are too fast to make a diff to the wood. Storing in an attic space would buffer the effect quite a bit, I would think.

Although I haven’t actually measured it, I’m don’t think there shouldn’t be high humidity in your attic space, just high temps. I would think of an attic as more like a mild “kiln”.

You could always put a humidity/temp meter up there and see what you’ve got before putting in the effort.

I am a big believer in active attic ventilation, so maybe an attic exhaust fan would be good.

At 15% its getting close enough that I agree with stickering.

I suggest doing some kind of grading while your at it, just to kind of keep the better wood to itself.

If you’re in the NE FL area and want to sell any of it, I might be interested.

-- Everything is a prototype thats why its one of a kind!!

View soob's profile


266 posts in 1233 days

#3 posted 07-09-2015 04:59 PM

The humidity in the attic swings more than it does outside because the roof acts like a heater that runs during the hottest part of the day. Humidity drops when temperature goes up so it amplifies the ordinary humidity swings.

I did put a (cheap) humidity gauge up there which is where I got the 30-80 numbers. It may actually be more extreme than that as I hadn’t previously been paying much attention to the humidity extremes.

Unfortunately I’m pretty far away from NE FL, and I wouldn’t sell it anyway. I’ll let my kids do that after I kick the bucket in 2070 or whatever.

View dhazelton's profile


2771 posts in 2321 days

#4 posted 07-09-2015 08:00 PM

Since you live in the south are your exterior walls framed with 2×4s or 2×6s? If 2×4s you may need to beef that up and add columns down the center. Don’t know how big a stack that is but I’d probably sticker it in a pile outside under an eave or overhang. If it’s 80 percent humidity up there I don’t see the gain other than keeping the rain off it.

View soob's profile


266 posts in 1233 days

#5 posted 07-09-2015 09:11 PM

2×4 walls. And, yeah, I’m still unsure about this idea. The floor joists are 2×12s but they are not all spanning the whole building; instead, it’s framed to a beam and an interior wall. To fit new 2×12s in on top of the existing joists, so they clear the roof decking, I’d have to notch about the top half off on the ends. That seems like it could cause them to split and that would be bad. I just can’t do columns, unfortunately. I don’t want to pull the floor and the ceilings to replace the floor joists, and I don’t want to tear out the drywall to reinforce the wall studs.

On the other hand, it’s a brick building with the peaks on the short ends, and so on the other side there’s a header and an 18’ garage door, with at least 5000lbs of bricks on it, and the 2×4 walls seem to be holding it up okay.

Also, it gets up to 80% humidity, but only in the early morning hours when the temperatures fall. That happens everywhere, though. It’s undoubtedly drier in the attic, overall. Probably about equal to my house, and much drier than my shop, so it would be a good place to store wood. And the high temperatures are a very good deterrent to wood boring insects which are otherwise rampant here. I don’t think they’d eat dried lumber as long as it didn’t get rained on, but I’d rather not have to worry about it as I would if I kept it outside.

View LiveEdge's profile


585 posts in 1645 days

#6 posted 07-09-2015 09:36 PM

Just my opinion, but the wall (whether 2×4 or 2×6) doesn’t matter at all for weight support unless you are worried about the wall itself failing. The 2×12 joist is going to carry the same load no matter what support it is resting on.

Maybe the sagulator would be helpful.

View WDHLT15's profile


1747 posts in 2500 days

#7 posted 07-10-2015 01:37 AM

You will be OK with walnut that dry in the attic.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln.

View AZWoody's profile


1346 posts in 1248 days

#8 posted 07-10-2015 01:40 AM

You can get a solar powered attic fan to help with circulation to prevent any moisture build up from any of the big box stores for about $200.

I put them in the attics here in AZ to help keep the cooling costs down.

View esmthin's profile


77 posts in 1205 days

#9 posted 07-10-2015 05:15 AM

If you don’t want to store it in the attic, you can always store it in my shop. :)

-- Ethan,

View soob's profile


266 posts in 1233 days

#10 posted 07-11-2015 05:55 PM

I decided to give up on the attic idea and pile (most) of it up in the house garage. July might not have been the best time to take her parking space! That’s the 16 and 14 foot’rs, or at least most of them. 4’ wide stack, will be good for flat-stacking plywood too. Would be about 1300 bf by my count if there no gaps, but there are of course.

Please excuse the mess.

Btw thanks again for the input, and esmthin, I really appreciate the offer!

View daddywoofdawg's profile


1028 posts in 1599 days

#11 posted 07-11-2015 08:16 PM

I’d be happy to store it in my shop.

View CharleyL's profile


222 posts in 3389 days

#12 posted 07-12-2015 07:07 PM

I would too, but your chances of getting back every board would be slim. That’s the cost of using my space :~))


View rwe2156's profile


2964 posts in 1505 days

#13 posted 07-12-2015 07:25 PM

I’m green with envy…....what a pile of wood!!

-- Everything is a prototype thats why its one of a kind!!

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