Making repairs to larger structures with Fabricate

Question

Suppose our party has happened upon a damaged tower. It's got a chunk missing out of an upper wall, and the floors are in awful shape. But it's well placed, and we could really use a defensible location.

We have a Wizard on hand who is able to cast Fabricate. If we can supply sufficient 'raw materials' for the Wizard, can they repair the tower over a couple days?

Ideally, the path to do this here would be that the party manually busts out the rotted floors, then the Wizard Fabricates new ones. Then they clean up the hole in the wall, and the Wizard Fabricates new chunks of stone wall until they have plugged the hole.

My concern with this is that the Fabricate spell says

You can fabricate a Large or smaller object (contained within a 10-foot cube, or eight connected 5-foot cubes), given a sufficient quantity of raw material.

PHB 239

A part of a wall wouldn't necessarily be an object...but if I Fabricated a 'small piece of stone wall, shaped like this' and just happened to Fabricate it in a location where it meshes in with the rest of the wall...I could see that working. Same idea with the floor...I position it so that it just happens to line up with where it would be installed.

The only thing I have on-hand that would really support this idea is that way back in AD&D 2E, the Spelljammer campaign setting specified that you could use Fabricate to repair damage to a ship. (Concordance of Arcane Space p82) Saying...

Fabricate: This spell can be used to repair lost hull points or maneuverability class for a ship. For every 10 cubic yards of material repaired 1 hull point, 1 AR, or 1 Manueverability Class is regained, up to their original ratings

By that logic...then yeah, you could fix buildings with this as well. But I don't know if that holds through to 5E

So, does this work?

Answer 1

The full description of the Fabricate spell:

You convert raw materials into products of the same material. For example, you can fabricate a wooden bridge from a clump of trees, a rope from a patch of hemp, and clothes from flax or wool.

Choose raw materials that you can see within range. You can fabricate a Large or smaller object (contained within a 10-foot cube, or eight connected 5-foot cubes), given a sufficient quantity of raw material. If you are working with metal, stone, or another mineral substance, however, the fabricated object can be no larger than Medium (contained within a single 5-foot cube). The quality of objects made by the spell is commensurate with the quality of the raw materials.

Creatures or magic items can't be created or transmuted by this spell. You also can't use it to create items that ordinarily require a high degree of craftsmanship, such as jewelry, weapons, glass, or armor, unless you have proficiency with the type of artisan's tools used to craft such objects.

These are all the limitations of the spell.

Walls are objects (like most parts of the environment that aren't creatures), so a part of a wall or a piece of flooring (e.g. a wooden plank) would be considered an object as well. Depending on the size of the chunk of wall, the material it's made out of, and the level of craftsmanship making such a wall piece would require, Fabricate might be able to make it.

In your particular example, it's a stone wall, and thus you would only be able to make a Medium-size piece of wall (that fits within a single 5-foot cube) with one casting of the spell. Your DM would also need to rule that it doesn't require a high degree of craftsmanship to make. And of course you'll need the stone in some form (whether in rubble or from a boulder or something), since that's the raw material that is being magically converted into the new form.

Also, keep in mind that nothing about the Fabricate spell attaches the object you create to anything else. Even if you meet the above conditions, you'd need some way to place the chunk of new wall you've made into the hole in the wall, and to secure it there.

Answer 2

You are most probably able to do it, but ask your DM

Normally, spells do only what they say they do. However, in 5e spell descriptions are very short and open-ended by design. Jeremy Crawford, the lead game developer, tweeted the base principle of interpreting spells:

A spell's text details the spell's effects—the only thing the spell does. Any additional effects are up to the DM.

Collaborate with your DM to figure out the details. See also Geek&Sundry "How Watching Critical Role Made Me Better At D&D":

A spell is typically written vague enough that you don’t have to worry about specific limitations unless you’re trying to stretch them. When in doubt, explain to the DM what you want to do and see if they'd be game

The DM might ask you for additional ability checks if he/she thinks it is necessary.