Building a stable loft

March 22, 2005 1:13 PM

Engineers, architects, contractors, and woodworkers -- I need your help to prevent my untimely death in some terrible lofted-bed incident.

here's the deal. I've built a loft that's an eight-by-eight cube; and although it seems to support my weight and that of the nearly 200 pound king-sized bed i've put on it, there's some creakiness, and I want to make relatively sure* that I'm not going to wind cracking my head open on the cement after one of the 2x4s give out.

Refer briefly to this diagram:



what you can't see very well in this diagram is that the plywood does not rest at all on the sidebar members -- only on those 6 "crossbar" members.

Now check out these photos:





The cracking sounds seem to be coming from the 2x4 i've colored red. They don't occur all the time, just occasionally when I move my weight over/around that member. It *could* be coming from the 2x4 that's vertically attached to the red post (that'll make cracky noises sometimes if i push it towards the wall and away from the loft). It *could* be the red 2x4, which, if it snapped/broke, would probably result in my untimely demise. It *could* be coming from the yellow 2x4, a scenario which would probably just have me wake up the next morning and be all "woo, that was close" and then patch it up (because the other cross-wise 2x4s should support me). They could also be the plywood settling onto the 2x4 frame (it's not tacked down yet), but i think this is more of a bumping sound. FWIW when I bounce up and down on the plywood centered over a "crossbar" member, there isn't a heck of a lot of cracking but there is some give/bowing of the member i'm over. When i'm off the loft/laying still there really isn't any apparent bowing.

I'd like to keep the bottom open (without supports in the middle of the structure) because i'll be using that as a living room area. I will be building putting in drywall on/under the red 2x4, so i can add more support there.

I was thinking about adding a couple of cut pieces of 2x4s (using joist hangers) going in the center of the "crossways" 2x4s (in the diagram they'd be right around where the dotted lines where the two pieces of plywood meet) with the thought that this would prevent them from cracking downwards because the center of each 2x4 would share the load with the others, but i have no idea if this would result in a net postive effect vis a vis load bearing.

An ideal solution would *not* require the removal of the red 2x4 (as that would require me to pretty much take the whole thing apart), and would not have any additional posts added to the right side of the loft (the side with the two 6"x4" posts) or any of the space beneath it (ie, i don't want a post breaking up a space under the loft, or the space that is used to move into the area under the loft).

So, laugh away, engineers, architects, woodworkers and contractors, and then tell me the *right* way to do things, preferably followed up by the way I'm going to do it (ie, the way that's not up to code but will keep the structure from falling down**).

* meaning that i do not have the funds to hire a contractor or anyone who could legitimately counsel me. i realize this places me near the realm of people trying to get free legal or medical advice from AskMeFi, but I'm primarily interested in an theoretical consideration of whether the structure i've designed can bear weight, potentially how much it can bear, and how i might be able to increase the weight load by adding members within my design restrictions. i can maybe have a buddy who does contracting work to look at the cracks, but that's about it.

** for legal purposes please pretend this structure does not exist in a realm governed by building code regulations, and further, that you didn't see any photos of it existing. thank you.

posted by fishfucker to home & garden (27 comments total)

IANASE (I am not a structural engineer) but I think there's a good chance that the creaking is coming from the posts and where they attach to the horizontal beams. I'd recommend putting in some sort of stabilizers that run diagonally between the midpoints of the upright posts.
posted by bshort at 1:36 PM on March 22, 2005

Like from 2/3's of the way up from the bottom of one post to 1/3 of the way up from the bottom of the adjacent post.
posted by bshort at 1:37 PM on March 22, 2005

You might want to check out some of the span tables for wood (assuming they're pine 2 x 4s)... these tables can give you an idea of the safe loads they can support.
posted by rolypolyman at 1:42 PM on March 22, 2005

it doesn't sound like it's coming from the corner beams at all. It sounds like it's coming from that where the yellow post hits the red member. (which is also where i have a shoddily attached vertical 2x4 to the red member).

but diagonal support for the crossbeams might be a good idea.
posted by fishfucker at 1:42 PM on March 22, 2005

Since what you're doing is building an indoor deck, I'd follow deck guidelines for construction. That means at a minimum, 2x6's for your joists. If you look at this page you will see a table for maximum allowable spans for deck joists. If you go with 24 inches on center, you can span 7'11". This will hold a live load of 40 pounds per square foot, or in your case, about 2500 pounds, which is clearly overkill.

You might want to read this discussion about ceilings with 2x4 joists.
posted by plinth at 1:46 PM on March 22, 2005

Is the "shoddily attached vertical 2x4" there for additional support? Could that be the culprit? You're probably getting a certain amount of downwards deflection on the red member and it could be pulling the screw out connecting the red member to the vertical 2x4.

By the way, that's the most impressively prepared AxMe I've ever seen.
posted by bshort at 1:51 PM on March 22, 2005

Oh, and by the way, if you want to upgrade to 2x6 construction, you can nail 2x2's on the top of the 2x4's, matching grain direction.
posted by plinth at 1:56 PM on March 22, 2005

Doubling up the edge 2x4's might help and would be easy. (But I got a C+ in Statics in college, so I woudn't trust me.)
posted by smackfu at 2:01 PM on March 22, 2005

Oh, and by the way, if you want to upgrade to 2x6 construction, you can nail 2x2's on the top of the 2x4's, matching grain direction.

I KEES YOU.

yeah, i really didn't want to take out all those 2x4s and replace them with 2x6s, as that would require taking down the entire structure; so on each member in there I would nail on another 2x2 beam, making the end height something like 83"? Am i understanding this correctly? Should I add another joist hanger after that? Could they be nailed onto the bottom? Can I use screws or is that bad form?

it would look like this, right?



I'll need to put joist hangers (2x6) on those too, right?

Is the "shoddily attached vertical 2x4" there for additional support? Could that be the culprit? You're probably getting a certain amount of downwards deflection on the red member and it could be pulling the screw out connecting the red member to the vertical 2x4.

yes. I added that in because I was not feeling good about those two horizontal 2x4s basically carrying the entire load of the loft. It is one of these least solid things about the construction -- since the bottom of that 2x4 isn't bolted to the ground, it can be kicked inwards (which I imagine would lead to something bad happening). I'm willing to drill a hole into the ground to bolt it down if this is the problem, but want to leave that as a last resort. I figured that would add some additional support to the 2x4. It *may* very well just be that screw creaking -- there's also a crack through the knot in the wood on the red beam where I've attached that vertical 2x4 with an l-bracket (DAMN YOU CRACKS). That I imagine I can live with. Again, my major worry is that the red beam is going to split and dump me (and possibly a second person) 7 feet onto a concrete floor.

By the way, that's the most impressively prepared AxMe I've ever seen.

thanks. figured i'd get better answers that way. I wouldn't expect anyone to ruminate about my construction problems without a detailed description of it.
posted by fishfucker at 2:52 PM on March 22, 2005

oh, is that crack in the red beam anything to worry about? It doesn't go all the way through, and i can't be sure it wasn't already on the wood (damn your shoddy lumber home depot!), but it's big enough that if you run your finger over it you can feel a little ridge, and in some spots is has splinters. Again, the crack moves horizontally on the wide (4" side) of the red beam and intersects the screws I used on the joist hangers -- it doesn't travel the entire beam, but it looks like it might be planning on it.
posted by fishfucker at 2:56 PM on March 22, 2005

Holy crap, you need some cross bars in there to stabilize it and transfer the loads across the beams. The creaking when you shift your weight probably means that you are transferring some shear load to the beams, which should be taking the load in compression or tension.

Think triangles and at least put some braces diagonally between the supports on the wall sides, and on the external sides if you can get away with it.
posted by jonah at 2:57 PM on March 22, 2005

if you want to upgrade to 2x6 construction, you can nail 2x2's on the top of the 2x4's, matching grain direction

I'm not sure that's such a good idea. Maybe if you do a full glue & screw, they'll be able to act as one unit, but it seems like you'd get shear/slippage along the joint between the 2x2 and 2x4 when weight is applied to it. Why not just sister 2x6s to the sides of the 2x4s?

How can you possibly not match grain in this situation?

As far as general construction soundness, you probably should add some kind of brace to where the side of your loft meets the vertical posts (a 45 degree triangle made of plywood should be okay), especially on both sides of the corner post that's not attached to a wall. And I wouldn't trust a 2x4 as the outside member to hang your joists off of--that one piece of wood will end up carrying basically half the weight of the bed. I'd also recommend nailing down the plywood.
posted by LionIndex at 2:59 PM on March 22, 2005

yes. I added that in because I was not feeling good about those two horizontal 2x4s basically carrying the entire load of the loft. It is one of these least solid things about the construction -- since the bottom of that 2x4 isn't bolted to the ground, it can be kicked inwards (which I imagine would lead to something bad happening). I'm willing to drill a hole into the ground to bolt it down if this is the problem, but want to leave that as a last resort. I figured that would add some additional support to the 2x4. It *may* very well just be that screw creaking -- there's also a crack through the knot in the wood on the red beam where I've attached that vertical 2x4 with an l-bracket (DAMN YOU CRACKS). That I imagine I can live with. Again, my major worry is that the red beam is going to split and dump me (and possibly a second person) 7 feet onto a concrete floor

Well, I missed this part. For the intermediate column, make it 3 2x4's thick--one on the outside like you've got, one on the inside, and one in the middle as a spacer that you attach short of the ends of the other ones to create a notch. Then slip the column under the end joist so that the joist fits into the notch, preferable actually resting on the middle 2x4. Locate the column right next to one of your 2x4s spanning the bed, and do the plywood triangle thing in all three directions.
posted by LionIndex at 3:07 PM on March 22, 2005

i should mention that aside from the creak, the stability is very good -- there's very little side to side motion.

LionIndex: do you think I would be better off adding those columns, or should i just do the whole thing over with 2x6s?

right now it's looking like i may have to add a lot of parts, and if that's the case, I might as well just keep the simple design and buy new wood. The reason the design is so utilitarian right now is that I basically have zero wood-working equipment.

I've got a drill, a 30 year old jigsaw, and a 18 volt cordless circular saw that can barely cut through a 2x4 (although i do have access to a table saw, but little knowledge of how to use it). So some of this is just plain not having the tools -- if I had, say, a fancy compound miter saw i would've done things totally differently.

can i take a moment to publicly curse my friends who i foolishly allowed to implement their own idea for the design? i thought they had experience building these sorts of things, which was why I deferred to them. Turns out i ascribed them far too much authority than their skills deserved
posted by fishfucker at 4:16 PM on March 22, 2005

I haven't actually visited myself, but maybe a trip to the Tool Lending Center would be helpful for this project? Looks like they have quite a bit of drywall tolls in their tool list for when you get to that stage, if nothing else.
Where's the aquarium, fishfucker?
posted by cali at 4:40 PM on March 22, 2005

I should think sistering the beams will be much, much more effective than making them taller.

I also think that the current design is already overkill and you should quit worrying. But don't listen to me, please, I'd hate to see you killed on my account.
posted by five fresh fish at 6:21 PM on March 22, 2005

i think i'm going to go with replacing everything with two 2x12s beams across and six 2x8 joists. That's like $50 to buy at home depot, and although I'm not happy about having to do everything over again, I'd rather spend the time to do it right and have something i feel comfortable falling asleep on, rather then trying to sleep with the nagging fear that the bed might crash down at any moment (as i attempted, and failed, to do last night). those numbers are from the deck tutorial linked above.

of course, doing it right in the first place would've meant i only spent an additional $25 on the wood, and theoretically, no extra man hours.

guess i should've googled first.

on the upside i'll have a ton of 2x4s with a variety of cracks and holes in them. any suggestions for cool things to build with those outside of canvas frames?
posted by fishfucker at 7:36 PM on March 22, 2005

I agree with fff that the current design is safe. Wood will flex quite a bit before it breaks, if you're not noticing any major bending when someone is in the loft, it shouldn't come crashing down.

To stop the creaking, I would remove the "shoddily attached vertical 2x4" and put an 8' 2x6 underneath (and parallel to) the red 2x4 (and probably under the 2x4 on the other end too). Just snug it up against the bottom of the 2x4 that is already there and nail it onto the post.

On preview: "i think i'm going to go with replacing everything with two 2x12s beams across and six 2x8 joists."
That certainly will be sturdy, but it is way overbuilt. I guess if you ever decide to put a hot tub on your loft, you'll be ready :).
posted by Sirius at 7:41 PM on March 22, 2005

To stop the creaking, I would remove the "shoddily attached vertical 2x4" and put an 8' 2x6 underneath (and parallel to) the red 2x4 (and probably under the 2x4 on the other end too). Just snug it up against the bottom of the 2x4 that is already there and nail it onto the post.

thanks for the advice. I actually jumped back in here to say that my friend called (who i've also enlisted to help me with this problem) and suggested a sistering not unlike what FFF was recommending -- stacking a 2x4 *under* the red beam. Maybe I'll go with a single 2x6, since that's going to be covered up anyways.

I think my plan as of now is to *just* put on those 2x6s and leave it (although affixing the other side is going to be a neat trick), and if everything seems cool, leave it. If not, i'll get some more 2x4s and some larger joist hangers and and rehang some of the joists.

dang. i'm glad i'm not in construction, and i'm glad some of you are.
posted by fishfucker at 8:52 PM on March 22, 2005

I second the diagonal bracing idea. I made a deck-like big plant table several years ago, then added smallish diagonal braces to the corners where the legs meet the top - I didn't think that a couple of nails on each end of the brace would be enough of a secure joining to make it work, but what a HUGE difference it made. And now it's Tudor style!

If you're worried about cutting the 45-degree angles you'd need at the ends of the braces, we found a pretty inexpensive manual (not electric) miter saw setup at one of the big home-improvement chain stores. It works pretty well. My braces were cut for me by a guy with power tools, but I've cut smaller (not 2x4) lumber with the manual miter saw with pretty good results.
posted by amtho at 6:51 AM on March 23, 2005

By the by, adding width to a beam doesn't add nearly as much strength as adding height. Think of it like this: if you take a wooden ruler and set it on its flat side, propper up like a beam bridge, it's really easy to flex it in the middle. Taping another ruler to it side by side distributes some load, but doesn't change how it flexes. Tape a ruler to the top instead, and it won't flex nearly as much.

2x12's are overkill. You'll be fine with 2x6's, 24" oc. If this is good enough for a deck, it's good enough for a loft.

With regards to using nails to sister 2x2's on top - no problem for them working as a unit. Remember that the load will compress the pieces into each other and the nails will distribute tension/compression.
posted by plinth at 7:01 AM on March 23, 2005

With regards to using nails to sister 2x2's on top - no problem for them working as a unit. Remember that the load will compress the pieces into each other and the nails will distribute tension/compression.

Actually, you'll have different forces working on the top and bottom of the beam, meaning that the 2x2s will be experiencing a different stress than the 2x4s. As a load is applied to a beam, it tends to bend, putting the top of the beam in compression and the bottom in tension. Unless you have a really solid connection between the 2x2s and 2x4s, you'll effectively have two beams sitting on top of each other, with the top of the 2x4 compressing while the bottom of the 2x2 is expanding due to tensile forces, causing slippage along the joint and possible separation. The nails or screws will hold the assembly together, but at that point you're only relying on your connections to carry your load, and not your beams. That's why I think it's far, far easier to just put 2x6s up next to the existing 2x4s (like, on the side, not below the 2x4s) and just nail or bolt them together. What you're suggesting is basically creating a homemade glu-lam beam, which is fine, but I think it would be more work than sistering for less overall benefit.

But yeah, 2x12s are waaaaay too hefty for what you need for a loft. The only member that I really think needs to be upgraded in the current assembly is the beam that the 2x4s spanning the bed are hanging off of.
posted by LionIndex at 8:27 AM on March 23, 2005

adding width to a beam doesn't add nearly as much strength as adding height

That is true only for those cases where the vertically-stacked beams can be made to operate as a single unit... and I don't believe for a moment that mere nails are enough to achieve that.

Use some PL400 and a bunch of clamps to stick 'em together, and I'll believe it.
posted by five fresh fish at 9:03 AM on March 23, 2005

everyone:

thank you so much for all the help you've given me in this thread. I really appreciate it. Thanks particularly to the folks (fff, sirius, LionIndex, and plinth) who recommended a solution that involved just adding a few additional beams, preserving, and actually enhancing the open area under the loft.

Here's photos of what I ended up doing (so far):

additional 2x4 (the former shadily attached vertical 2x4) added to the wall side.


What the? But there's no clearance! HOW DO YOU DO IT




that's right, super-sleuths, i hopped out the window and drilled it in through the outside.

additional 2x6 on the room side of the loft (inside view)


as it is now, from the outside:





The creaking is still there -- I'm convinced it is the yellow member that is carrying an extra bit of a load because the next nearest beam isn't doing any work at all. This may be a non-issue after I screw the plywood down. There is still quite a bit of spring in the loft, and I'd prefer it to feel a little more stable, so before I nail down the plywood I might buy a single 2x6 and hang it in the exact middle, in addition to the 2x4s. Still, I'm pretty damn confident that the thing isn't going to fall completely apart with me in it, and that makes me feel a lot better about sleeping on it.

I've learned a number of things from this project; if I build another loft, I would probably use 2x8s across and 2x6 beams; I'm happy with the performance of the posts, but it was necessary to fasten those to the walls and floor in order to get decent stability (this loft was originally planned to be freestanding, albeit with cross-supports blocking off the area below).

Anyways, thanks for all your help guys! I really appreciate it.




Now for the next project: building a stand and piping to install a shower here:




next time i'll ask for help before buying the wood.
posted by fishfucker at 2:45 PM on March 23, 2005

Ummm, diagonal crossbeams?

I used to build lofts, trust me, you want diagonal crossbeams...
posted by raster at 3:14 PM on March 23, 2005

If the loft wasn't securely fastened to the 2 walls and the floor, I would agree with the people who are worried about diagonal bracing, but because the two walls and the floor are (relatively) immovable, they perform the same function that bracing would provide on a free standing loft.

If you're able to fasten opposite corners of a rectangle to something that won't move (like a wall or floor) the rectangle won't flex, and I don't see any rectangles that don't have a set of their opposite corners connected to a wall or floor in this loft.
posted by Sirius at 2:54 PM on March 24, 2005

i slept in it last night -- worked out pretty well, although I did have this brief nightmare about it collapsing off to the side (which was one of those dreams that you *know* is a dream that you can't wake from and can't really breathe -- I think i've got sleep apnea or something). Anyhow, I bought another 2x6 to hang in the very middle and i think that's gonna be the last of my tinkering with it.
posted by fishfucker at 5:16 PM on March 26, 2005