Precise openings (windows, doors )in meshes

Question

Basically, I'm trying to model an house to use later in Unreal Engine 4. I've set the scale to the one reccomended for UE4 already.

So, let's say I want one of the walls to be 3mx3mx20cm. This is easy. Add a cube, change the size in the transform menu.

Now I want a window that's 1mx1mx20 in size. But how do I make a precise opening the my wall? What I've been trying is to add a cube, make it 1mx1m, and then use it as a guide to place four edge loops. The problem is that this is not exactly accurate, so I usualy end up with openings that are like 99cmx98cm, or 99cmx101cm. So when I model my 1x1 window, it won't fit exactly, leaving seams.

Is there a better and more precise way?

Answer 1

You can use snapping limiting transforms on an axis.

Basic house with a separate window object :

Select your house, enter in edit mode (tab)
Activate snapping, open the menu and choose Vertex :

Add your edge loop (Ctrl+R) place it anywhere. Move your newly created edge loop with g, lock your movement on X axis (X) and move your mouse close to a corner of your window. You'll see a circle appear where the movement can be snapped (window corner vertex). Click LMB

Repeat this actions on the 3 other loops with the 3 other corners (X and Z axis)

You can move along all axis, 1 axis (with X, Y or Z) or 2 axis (with Shift+X all but X, Shift+Y all but Y, Shift+Z all but Z).

Answer 2

One way to do this is to select the edges that form the window. You can do this by activating Edge Selection and holding down the Alt key while you select-mouse-click one of the edges. This should select the entire loop. Now you can use Shift+d to duplicate the selection and press escape to cancel it's movement, it should now be exactly where the window edges are. Press the p key and choose 'Separate->Selection'.
Now enter Object mode, select the edges and enter Edit mode to shape it into a window frame.

You can also extrude the edges out without duplicating and separating the edges to a separate Object. I find sometimes it's cleaner to separate components while I'm working on them. Afterwards, they can be joined again when it's time to UV unwrap everything.

The frame was extruded along the y-axisethen constrained with y. Then Inseti. Next the 3D cursor was placed along the inside edges using the same Alt + click following by Shift+s->Cursor To Selected. Now I extruded again and canceled using Escape. Now if you change the pivot center to '3D cursor', and use Scalesyou can constrain the scaling to the y-axis by pressing y and follow that up with the 0 key to scale the extruded edge to '0.0' in respect to the 3D cursors position. Finally, fill in the back edges with 'Make Face'f after selecting two opposing edges.