# How can I eliminate the added height when applying a thickness to Solidify modifier?

When I add a Solidify modifier to a hemispherical shell, I am given an option to add a thickness (amongst other options). When I add a thickness to the hemispherical shell, I've noticed that Blender increases the overall height of the shell due to the added wall thickness. An example is shown in the attached image.

Is there a way I can eliminate the extra added thickness? Are there additional steps I can take to suppress it, or make the bottom of the hemispherical shell flat again?

• make the thickness a negative value.
– user1853
Sep 14, 2015 at 15:25
• Please list all modifiers if you have more than one. Do you have a subdivide surface modifier? Sep 14, 2015 at 15:28
• This doesn't work -- this still creates a non-flat profile for the base of the shell. I believe flipping the sign of the Thickness value is the same as flipping the sign of the "Offset" value. Sep 14, 2015 at 15:32
• Atomic -- the only modifiers I'm adding to the shell are: - Subdivision Surface (to make it smooth for illustration purposes) - Thickness modifier Sep 14, 2015 at 15:33

Solidify modifier extrudes faces along their normal.

A default UV hemisphere has the bottom faces whose normals are not parallel to the XY plane. So the extrusion vector will have a Z component that will create the effect you see in the image below (which is an outer extrusion, while yours is an inner one, but it follows the same principle):

In blue are evidenced the vertex normals. Note how the last line of vertices has a non-horizontal normal projection.

To keep the bottom of the extrusion co-planar with hemisphere's bottom vertices you should start from a geometry who's last faces normals are not incident with XY plane:

The last picture was made by extruding the last line of vertices a bit on the Z-axis, so the geometry may not exactly represent a standard hemisphere.

To obtain a more precise result you can work with the default UV sphere settings and set an odd number of rings. This way, when you cut the sphere in half the faces will already have the correct normals and the resulting mesh will be a more precise approximation than extruding manually.

• Carlo -- thank you! Your last solution, with the impar number of rings was an enormous help. Thank you! Sep 14, 2015 at 16:13