# Builder: Engine error when raising walls on narrow floor parts

**URL:** <https://discourse.stonehearth.net/t/builder-engine-error-when-raising-walls-on-narrow-floor-parts/27708>\
**Category:** Bug Reports\
**Tags:** building, a20r689\
**Created:** [January 12, 2017, 12:52am UTC](https://discourse.stonehearth.net/t/builder-engine-error-when-raising-walls-on-narrow-floor-parts/27708 "2017-01-12T00:52:24Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![MelOzone](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.stonehearth.net/melozone/32/50318_2.png) [@MelOzone](https://discourse.stonehearth.net/u/MelOzone)\
**Post date:** [January 12, 2017, 12:52am UTC](https://discourse.stonehearth.net/t/builder-engine-error-when-raising-walls-on-narrow-floor-parts/27708/1 "2017-01-12T00:52:24Z")

</div>

**Summary:**

**Steps to reproduce:**

1. Create a simple rectangular floor plan.
2. Add exactly 1 block of floor to any side of it.
3. Try to raise walls.

**Expected Results:**  
Raised walls. 1 added block should “raise” a beam.

**Actual Results:**

```auto
release-689 (x64)[M]stonehearth/services/server/build/build_service.lua:1196: assertion failed!stack traceback:
	[C]: ?
	[C]: in function 'assert'
	stonehearth/services/server/build/build_service.lua:1196: in function '_get_blueprint_at_point'
	stonehearth/services/server/build/build_service.lua:1212: in function '_fetch_blueprint_at_point'
	stonehearth/services/server/build/build_service.lua:1229: in function '_fetch_column_at_point'
	stonehearth/services/server/build/build_service.lua:1247: in function '_add_wall_span'
	stonehearth/services/server/build/build_service.lua:1078: in function 'visitor_fn'
	stonehearth/lib/build_util.lua:819: in function 'grow_walls_around'
	stonehearth/services/server/build/build_service.lua:1077: in function 'grow_walls'
	stonehearth/services/server/build/build_service.lua:1049: in function 'cb'
	stonehearth/services/server/build/build_service.lua:1582: in function 'do_command'
	stonehearth/services/server/build/build_service.lua:1048: in function <stonehearth/services/server/build/build_service.lua:1046>

release-689 (x64)[M]c++ exception: lua runtime errorstack traceback:

```

**Notes:**  
Adding more than 1 block length stripes does not result in an error (see image).

**Attachments:**

 ![](https://us1.discourse-cdn.com/flex022/uploads/stonehearth/original/3X/6/7/677d39b80dc749bc69963ba685635e98d8610bf8.jpg)

**Version Number:**  
a20r689

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<div class="post-metadata">

**Author:** ![Relyss](https://sea2.discourse-cdn.com/flex022/user_avatar/discourse.stonehearth.net/relyss/32/41785_2.png) [@Relyss](https://discourse.stonehearth.net/u/Relyss)\
**Post date:** [January 12, 2017, 3:52pm UTC](https://discourse.stonehearth.net/t/builder-engine-error-when-raising-walls-on-narrow-floor-parts/27708/2 "2017-01-12T15:52:55Z")

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The error you posted is not the same as the one in the screenshot, but thanks for the repro steps!!

BTW those nice walls will probably have z-fighting once built 😥