Drafting with printing in mind part 2: Holes and Gaps

Ensure your model is "water tight". I know I talk about this quite a bit on here, but this is key to printing a model. There are some tools to help "seal" a model, such as CADSpan, but the majority of the work should be done before sending your model through one of these programs in order the have the best possible resolution.

To do this we should focus on some of the usual suspects.
1) Walls meeting the roof. There are two places I often find problems here. See images below for illustration
The first is simply having walls stop vertically before the roof joins. This happens frequently when people model all of the truss work and they draw the walls up to the rafter tails which leaves a gap in between.
The second place is where a wall should jog back between two roof pieces. The most frequent location for this is on Dormers, where the wall of the dormer does not go quite far enough back.

Additional Sources of Holes

Through the multitude of change requests we are all likely to miss some small changes so it is important to check connection points. The roof wall as described above creates the largest holes, but the following can create a large number of low volume holes.

2) The connection between windows/doors and walls. I like to punch windows and doors in to solid walls in Form Z rather that through the walls, but I don't frequently need to produce interior visualizations. If you need to punch all the way through the wall to show interior relief, I would suggest making the hole the size of the glazing rather than the casing. This way you are sure there is a thin overlap of solids. Make sure the door touches the jam and floor. If the door is floating it can be a real head scratcher when you can't figure out why your resolution is not as tight as it should be if using a shrink wrap tool, or why your model is hollow if you are not.

3) Entry-way ceilings. Not sure why these are always missing other than they are never seen, but we need them. If you have recessed elements in your model just have a look to see if they have a ceiling.

4) Chimneys. Go ahead and seal them in. No one will be using them :) so there is no reason to leave an opening in to your model.

5) Staircases. Spiral staircases are the most frequent offenders. Check to see that your staircases exiting your model have some sort of "barrier" between the inside and outside.

For program-specific tips and techniques, see:
Additional SketchUp tips
Additional FormZ tips