Is it ok to stack LPs horizontally?

No absolutely not. Yes they will warp badly 

Actually, its the recommended storage method as long as its your Rick Astley collection. They won't warp!!!!!

Everyone seems to store records vertically yet it's far from obvious just why.

Is it because the printed label is usually slightly raised, and storing flat would push the edges down eventually causing warping?

Is it the same reason people store guitars vertically?

Long term gravity effects?

If so, then I suppose they would have to be stored totally straight up and not at an angle.

Warpage is always the reason behind not storing LPs flat, yet I have never seen anyone give a reason as to why that would be. Anyone?

It has always seemed to me that the only point at which storing LPs vertically may become advantageous as regards to warping is when they are fairly tightly packed on a shelf with firm left and right boundaries.  Otherwise, like someone else said, storing them vertically really means storing them at an angle to the vertical, which could actually promote warping.

Keep them upright to prevent warping.  Angled storage will eventually lead to warping as will laying flat due to the weight of other albums on top. Safe to lay flat, I suppose, if you only had 2-3 in each stack, but you would either need a very large storage area or a very small LP collection lol

I see a lot of LP collections with the records leaning to one side. As @dseltz just said, given enough time LP’s thus stored can become "dish" warped.

I years ago came up with a solution: you know the cardboard "spacers" you routinely find inside the mailing cartons your LP shipments arrive in? Don’t toss ’em, keep ’em and use them to take up the empty space in each section of your LP shelves. Doing so keeps the LP’s perfectly vertical, and one spacer can be removed for every new LP that needs to go in that section.

Record stores receive one or two spacers in each carton of LP’s they are shipped; ask your LRS for the ones they routinely recycle. I have two linear feet of them!

So you unstack a pile of discs just so you can play one, stacked one third way up. I have thousands of LP's all stacked vertically some dating from the sixties, not one of them warped !!!

OP has 'run out of storage space'.

So why does piling records horizontally occupy less space than vertically?  The records have a fixed volume.

And yes, horizontally will cause warping after a while.  Gravity will act on the less well supported outer areas and cause them to fall.

LPs should not be so loosely stacked that they lean to one side, weighing against each other.  Nor should they be tight enough to create side pressure.  Just densely enough so that the stand vertically without pressuring each other.

What you might try is go on Etsy and search for "vinyl storage". Perhaps a small footprint rack like the one below would be a solution.

Archivists recommend storing LP's vertically.  They say that storing horizontally will tend to damage the LP's toward the bottom because of the weight above them.

I’ve played records as long as most any one here and I don’t believe the warpage is the reason Not to store horizontal. I believe @billzame may be right about the bottom records becoming damaged. I’ve sorted through and bought many records that were stored horizontal. The problem with almost every one of them is ring wear on the cover. The ring wear got progressively worse the further down the pile that I went. IF the album had any warp, it was very slight and not problematic.

So 20 albums may not be a problem. Its not the best but if it is all you have, then maybe try it. But an alternative is a closet. I have some of my less desirable in a closet. My son once commented that there were albums behind every door

You need gaps if you sort alphabetically. I did tricks over the years to keep em upright.

I inherited LPs that came with true library shelving with recessed metal tracks and dividers, Expensive, doubtful I would ever have spent that much but it’s the best/easiest system I ever had. My friend had found a library selling it’s shelving.

Actually, I kept only the individual shelves with integral backs/tracks/dividers, and put them on rolling steel shelving, not attractive, but in the garage.

Empty space on a record shelf?  What's that?

Just a note. Stacking horizontally can cause damage to the vinyl it self due to contaminants presence on the surface. Weight is the issue. I have stored my collection of over 2k lip’s for over 20 plus years. In addition some of my collection are over 60 years old and still play like new. Get some crates and store vertically. Also ikea makes some crates that might work. 

Ever been at the bottom of a dog pile as a kid? A stack of 50 records is already getting heavy. The bottom 10 records will see enough pressure that, in summer or a warmish day, they will yield to a warp.

Can I prove this? Probably not in this post. But I bet you can see my logic. How are some of you questioning sage wisdom?

Books are stored this way to take pressure off the binding.

It just makes sense.

Do you want to take the bottom record out? What a PITA. You will damage the bottom few records just to access them. Stack them vertically and they’re all just as easy to get at.

Should I go on?

Although I always have my vinyl vertically on shelves, Room Temperature is the key. If your storage place is cool, very little tendency to warp.  
 

@bdp24 

Thanks for the tip. Since I have fairly sizable empty space in each of my 41 shelves (I always have more shelves than I need so I can keep adding records), instead of the inner cardboard, I just bought 50 reinforced 2" wide vinyl cardboard BOXES! Tip of the month for me!

Right. The proper way to store records is upright between upright bookend or cabinet walls snuggly but not tightly packed. Records should slide in and out easily. Upright storage lends itself to easy accession and cataloging. It is essential to protect records from any heat source.

You do not store records stacked horizontally. Records are not flat. The label and rim are elevated standing proud of the playing surface of the record. If one record is a little off from another the rim will sink down at the unsupported area. Add a little heat and you have a perfect warp machine. The upmost record is exposed and at risk. Why? The most common cause of record warping is???? The sun shining through a window landing on exposed records. During the day the sun travels across the sky scanning the better part of many rooms. 2-3 minutes of focused heat is all it takes. If you leave your records lying around exposed and have any unblinded windows facing the sun it is only a matter of time before one gets nailed.

If you look at my system page you will see a proper record cabinet. Note the records stand 1/2" proud of the shelves. This makes it much easier to get the records out without damaging the cover. Put one finger above and one below. The record slides right out. 

Warp!

To the original question - NO.

LP records are thicker in the middle. Some outer edges are thicker than others, but generally, not as thick as the centers (labels, etc.). So, stack 'em like pancakes and they will sag and not uniformly - they warp. The warp sends a very low, sub audio, frequency into your gear, drives it nuts, keeps changing the VTA (relationship between the stylus and the groove walls) and generally makes a mess. Besides, how are you going to pull out that favorite disk you havent played in a few years when there are 57 records piled on top of it? Stay vertical, friend.

Most turntables play slightly warped LPs fine. What they cant play are compressed recording grooves. LPs weigh a ton. Storing them flat can press the groves. vertical is the only way to go.

In addition to warping (which I never considered) I always thought that the extra weight of storing horizontally would cause dust and dirt to be pressed into the grooves. So I always store vertically. 

@heretobuy      Goodness, that rig looks highly unstable on its tiny angled feet.  Anyone who has lifted that number of LPs knows how heavy they are.

A dog or a small child could accidentally knock it over and the falling LPs cause injury or worse.  I wouldn't have it in my house.

Horizontal storage will cause excessive ring wear at bottom of pile.

Not just a warping issue but any dust or crap on an LPs surface with be further smashed into the groove. No no no.

overall, I would say its not a good idea.
Records are not an even thickness, the label area stands proud and so does the outer edge, it has a thickening or bead designed to guide the stylus into the start groove, it also helps in the manufacturing process.
While stood "almost" vertical is not ideal, I think its better than the combined weight of many pressing down on those at the bottom of the horizontal pile.
Though you could argue, that in the thick sleeve, this can be accommodated.
I think they are stored vertically, purely for ease of use. If you have a horizontal stack, its difficult to pull one from near the bottom and worse trying to return it to the same location.

I have a different experience with horizontal stacked storage of LP’s. While I do not recommend horizontal storage it may not be as risky as some people make it out to be.

I recently cleaned out a room in a relatives house where several hundred albums had been stored for more than thirty years.  About half these albums were stacked horizontally and NONE of them are warped.  
 

This room was not heated or cooled and was basically left to the whims of the ambient weather for decades, sometimes it would be 40F and sometimes it could be 90F.  No mold, no rot, just dust and some fading due to ambient light.

Your mileage may vary.