Casting Demiplane allows the caster to have:

However, my problem is that the created demiplane is too small and barren. I want more space for activities. It might be possible with mordenkainen's magnificent mansion, but I'm not sure if it even works, and the duration is limited (24 hours) without some way to affect the passage of time in the demiplane.

So, is there any way to add or expand —ideally permanently— to the space-size of this 30' × 30' demiplane?

Answers may include: any of the sourcebooks (PHB, Volo's, Mordenkainen's, etc.), tweets from Lord Crawford, Sage Advice, any 5e Unearthed Arcana... or whatever one can find that is RAW, quasi-legal or even slightly more tested than outright home-brew.

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    \$\begingroup\$ I trimmed out a lot of commentary, etc. I don't think are needed at all, but wanted specifically ask you about the line "The 5e spell specifies the new parts must be cast OUTSIDE of the original" because I have no idea what it is trying to say. Reminder that you can see the revisions if you need to see the whole of what you wrote. \$\endgroup\$
    – Someone_Evil
    Jun 10 '20 at 0:55
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    \$\begingroup\$ @Someone_Evil : my thanks. For someone who claims to be evil, you are most considerate and rather kind. Don't worry, your secret is safe with me. \$\endgroup\$ Jun 10 '20 at 3:11
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    \$\begingroup\$ Are you a Dungeon Master or a player? Depending on that your answer may be more based on the interpretation of rules or obscure other rules or spells in the sources you outlined. Also, what are you using the Demiplane for that needs extra space, and how much extra space does it need? \$\endgroup\$
    – Bazza491
    Jun 12 '20 at 2:12
  • \$\begingroup\$ @Bazza491 I wanted, as a DM, to have Fraz-Urb'luu to have a logical and RAW ability to make planes over time. It looks like i will be twisting the rules a bit. Thanks for asking though! \$\endgroup\$ Jul 3 '20 at 1:39

Demiplane is a very limiting spell, and only allows you to create a 30'x30'x30' space or connect to another known space created by another casting of demiplane. You can't even connect to demiplanes created in other ways.

There does not appear to be any way to add or expand to this space, although the spell does say that the walls are actually made of material, which means that at GM discretion it may be possible to excavate a larger area, either by hand or with disintegrate. Depending on what exactly you are looking for this may be your only option.

Demiplane does allow you to create more than one such 30'x30'x30' space, however considering it is an 8th level spell and you can only connect to 1 demiplane at a time for 1 hour at a time, this may or may not be useful.

As you mentioned, mordenkainen's magnificent mansion creates a much larger space, but this space is temporary, and ceases to exist entirely while the spell is not in effect. Considering the spell has a duration of 24 hours, it is feasible to cast the spell continuously indefinitely. It is also possible to use a spell such as plane shift to gain access to a demiplane created in some other way, such as by a deity.

Finally there is the Rod of Security, which is a very rare magic item that allows you to create an extraplanar space of your own description that lasts for 200 days divided by the number of creatures present, and can be recast after 10 days. This effect has no restriction on the size of the extraplanar space, and has the added benefit of suspending aging while you are in the space.


Well, it says you can create more demiplanes in the plane of your choosing, but you can only connect to one demiplane at a time.

The demiplanes that you have created doesn't disappear like Mordenkainen's Magnificent Mansion that is a conjured thing.

In theory this would mean the demiplanes are all still there after the time runs out, right?

So why not create 1 demiplane at 30x30x30, then next time you cast the spell, just create another demiplane in the same plane right next to the other one, connecting those two.

The door that you create still only connects you to the new demiplane, but that isn't really a problem is it? You don't need two doors out of the now 30x60x30 demiplane.

  • \$\begingroup\$ While a DM might allow you to expand the demiplane with additional castings, the rules as written are extremely limiting; your only options are: 1) Connect to newly created demiplane, or 2) Connect to an existing demiplane. Demiplanes are their own thing, there's no such thing as "another demiplane in the same plane next to an existing one" (if they're in the the same plane, it's not a new demiplane). Point is, as written, the spell can't alter an existing demiplane in any way. If the door you create connects to an existing demiplane, that's all the spell does. \$\endgroup\$ Mar 27 '21 at 2:52
  • \$\begingroup\$ It says it is a new demiplane, the next demiplane would not need to alter that former existing demiplane in any way at all really since it wouldn´t occupy the same space Though if you would interpret the demiplane as a bubble in a void that for some reason is immune to have a demiplane being created in the void of course it would not work, the spell doesn´t quite state specifics on it though, so it would be up to the interpretation of the DM right? Oh and it isn´t a new question, wouldn´t it be bad forum ethics to create a new thread on the same subject? \$\endgroup\$ Mar 27 '21 at 19:29

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