Tutorial 31: Openings That Are Not Rectangles

Every opening in Tutorial 6: Standard Opening was a rectangle dimensioned to its corners. Four openings in the Tilt-Up Concrete Association catalog are not, and each one breaks a different assumption the rectangle lets you make.

Feature

What it is

Standard

Round opening

A circular opening, typically for conduit or plumbing

TCA

Arched opening

An opening with an arched head

Architectural practice

Louver / vent

A mechanical louver or vent opening

Field practice

Weep hole

A drainage weep through the panel or veneer cavity

TCA

Two of these four are built today

Round and arched openings are both modeled. The arch is the Radius column on Standard Opening Details; the circle is Shape → Circle on Recess and Blockout Details, which draws a through opening when its Thickness is 0. Steps 2 and 3 are real follow-alongs.

Louver rough openings and weep holes are in the industry catalog and on the roadmap; those steps are marked (planned) and describe how they are intended to work, so the design is recorded rather than invented at implementation time.

Step 1 applies today regardless: it is the reasoning, not the tooling.

Note

A browser version covers part of this lesson. Open it here — it lists exactly which steps it does not cover, so you know what to come back to AutoCAD for.

What you will learn

  • Why a round opening is dimensioned from its centre while a rectangle is dimensioned to its edges — and how the dialog enforces that difference by greying out the fields that stop applying.

  • What an arch needs that a rectangle does not — and why one radius is enough.

  • Why a louver opening is not the same size as the louver.

  • Why a weep hole is the only opening on this list that is placed by spacing rather than by position.

Before you start

Watch the lesson

Warning

What this recording does and does not demonstrate. It places the two openings that are built today on TP08-12. The first is a round opening: a Recess and Blockout row set to Circle, Radius 1’-0”, centred 20’-0” across and 11’-0” up, with Full left ticked so it goes through the panel. The second is an arched opening: row 3 of Standard Opening Details, 4’-0” by 6’-0” at 10’-0” / 10’-0”, Radius 3’-0”. Louvers and weep holes (Steps 4 and 5) are described in the video, not placed: they are not built yet.

The recording’s own gate counts the dimensions drawn on the panel. It does not check where the openings are.

Lesson

Step 1 — Why the rectangle is the wrong tool

A rectangular opening is dimensioned to its edges: so far from the panel edge, so far up from the floor, this wide, this tall. Four numbers, and the form crew builds a box.

Every opening below breaks that:

Dimensioned by

Because

Rectangle

edges

the form is four straight boards

Round

centre + diameter

the form is a tube; its edge is nowhere in particular

Arch

jambs + a radius

the head is struck from a centre the opening does not contain

Louver

rough opening, not the product size

someone else’s frame has to fit inside it

Weep

spacing, not position

it is a pattern, not a feature

If you draw a round opening as a square and then round the corners by hand, the panel book carries four dimensions that describe a box nobody is building. That is the failure this lesson exists to prevent.

Step 2 — Round opening

A round opening is formed by standing a tube in the casting bed. There is no edge to measure to — the crew sets a centre and a radius.

It is not on the opening dialog, which is why it is easy to miss. Round openings are blockouts: open Recess and Blockout Details and set the row’s Shape to Circle.

The dialog then reshapes itself around the circle, and each change tells you something:

  • Width and Height grey out. A circle has no width or height, so the fields that size a rectangle stop applying. This is the lesson’s whole point, enforced by the dialog. (The manual says Snap To greys out too. On the current build those boxes stay live; a circle is located by its centre, so leave them clear.)

  • Radius becomes live — it is greyed out for a rectangle. Give it the radius, not the diameter.

  • Distance and Elevation now locate the centre rather than a corner. The manual is explicit that dimensions run to the endpoints of the blockout “or center if a circle is specified.”

Then decide whether it is a hole or a recess with the Full box under the Thickness column:

Full / Thickness

Result

Full ticked (the default)

the void goes completely through the panel — a true round opening; Thickness is greyed out

Full unticked, then a Thickness

a round recess of that depth

Setting Thickness to 0 also greys out On Face, Z Offset and Liner Aggr, which is the confirmation you have made a through-opening rather than a pocket.

Tip

The same Shape droplist also offers Arch and Triangle. Triangle takes the peak position in the Radius field instead of a radius, and a negative height turns it upside down — which is how you cut a clipped corner or a sloped notch without drawing it by hand.

Tip

Round openings are usually services — a conduit sleeve, a roof drain, a plumbing riser. They are often the last thing coordinated and the first thing that moves, which is why having them dimensioned to a centre matters: a centre can be shifted with one number.

Step 3 — Arched opening

This one you can do right now. An arch is a rectangle for most of its height with a curved head on top, and Standard Opening Details already carries the field for it: the Radius column, at the right of each opening row after Width and Height.

Enable a row, set its Width and Height as you would for any opening, then give it a Radius. The head draws as a true arc struck at that radius. Leave Radius at 0 and the opening stays square.

That is all an arch needs, because the other value a form carpenter wants — the springline, where the jambs stop being vertical — follows from the width and the radius. Supplying both would let a drawing contradict itself.

Warning

The radius has to clear half the opening width. A radius smaller than that describes an arc that cannot span the opening, and the geometry has no solution. The same rule governs the panel’s own top arch in Tutorial 17: Full-height Radius (Curved) Panels, where it is stated as radius clears half the width — it is worth knowing as a rule rather than meeting it as an error.

Step 4 — Louver and vent openings (planned)

A louver is a manufactured product installed by a mechanical subcontractor. The panel does not get an opening the size of the louver; it gets a rough opening — the louver size plus a fit allowance, plus whatever the frame detail needs.

This is the entire point of tracking it as its own feature rather than as a rectangle labelled “LOUVER”. Two numbers exist and they are not the same number:

What it is

Louver size

what the mechanical schedule specifies

Rough opening

what gets cast

Intended behaviour: a louver row carrying both, with the rough opening either entered directly or derived from the louver size plus a per-project allowance. The drawing dimensions the rough opening, because that is what gets built, and the schedule reports the louver size, because that is what gets ordered.

Recorded, not certified

ConstructiVision records the fit allowance you set and carries it consistently. It does not know your louver manufacturer’s frame detail and does not check that the allowance is adequate. That comes from the submittal.

Step 5 — Weep holes (planned)

Weeps drain the cavity behind a masonry veneer. They are the odd one out on this list: nobody places weeps individually, and nobody dimensions them to a panel edge. They run at a spacing along a line — typically just above the brick ledge.

Intended behaviour: a weep row taking a spacing and an elevation rather than a position, generating the run across the panel and reporting a count in the materials list. The drawing carries a typical dimension and a “@ n” note, the way every repeating element on a shop drawing is annotated, rather than one dimension per hole.

The spacing comes from the specification

Weep spacing is a specified value — it comes from the project specification or the masonry standard the job is built to. ConstructiVision records the spacing you enter and lays the weeps out at it. It does not select the spacing for you.

Weeps only make sense alongside a brick ledge, which is covered in Tutorial 32: Reglets, Brick Ledges & the Masonry Interface.

Check your result

You should now be able to:

  • Place a round opening with Shape → Circle and a Radius, and say which fields grey out and why that is correct rather than a limitation.

  • Say what Thickness 0 does, and how you can tell a through-opening from a recess.

  • Place an arched opening with a Radius, and say why the springline does not need entering.

  • Explain the difference between a louver size and a rough opening, and say which one gets dimensioned on the drawing.

  • Say why weeps are placed by spacing rather than by position.

Where next