# Find the area of interior and exterior wall surface

**URL:** <https://forum.dynamobim.com/t/find-the-area-of-interior-and-exterior-wall-surface/17315>\
**Category:** Revit\
**Tags:** revit, dynamo, analyticalwalls, areas\
**Created:** [December 12, 2017, 5:42am UTC](https://forum.dynamobim.com/t/find-the-area-of-interior-and-exterior-wall-surface/17315 "2017-12-12T05:42:19Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![dexgear](https://avatars.discourse-cdn.com/v4/letter/d/f08c70/32.png) [@dexgear](https://forum.dynamobim.com/u/dexgear)\
**Post date:** [December 12, 2017, 5:42am UTC](https://forum.dynamobim.com/t/find-the-area-of-interior-and-exterior-wall-surface/17315/1 "2017-12-12T05:42:19Z")

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Hello everyone, I’m trying to find the total surface area of the interior and exterior walls including structural columns in order to find the area of wall paint.  
I use solid.ByUnion to combine walls and columns into one geometry and then change it into surfaces. Then I use Surface.FilterByOrientation to get the vertical surface. Now, I don’t know the way to separate the interior surface and the exterior surface. Please help me.

 ![surfaceofwalls](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/9/8/9850f22e03f2982d2ca9412a512334d0fd24c72d.JPG)

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<div class="post-metadata">

**Author:** ![dexgear](https://avatars.discourse-cdn.com/v4/letter/d/f08c70/32.png) [@dexgear](https://forum.dynamobim.com/u/dexgear)\
**Post date:** [December 12, 2017, 6:53am UTC](https://forum.dynamobim.com/t/find-the-area-of-interior-and-exterior-wall-surface/17315/2 "2017-12-12T06:53:59Z")

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I try to use Room to intersect. The exterior faces are OK but the interior faces still have problems. I don’t want the small surface around windows and doors. Any ideas? or Any solution without using Room.

 ![surfaceofwalls2](https://us1.discourse-cdn.com/flex022/uploads/dynamobim/original/3X/1/6/16144db9e9fa60a8a978faa0d69f790b97faf905.JPG)