Design Wall Assembly

Most wall assemblies get drawn by recalling one that worked somewhere else. That is how a vapor retarder ends up on the wrong face for the climate, and how an air barrier gets drawn across a wall with nothing said about where it ties into the roof. This starts from what the wall has to do and puts the layers in an order you can defend line by line.

Workflow

Step 1. Take the demands, not the layers

Ask, in one message:

1. What is the cladding, or is it still open? If it is fixed, say how it is attached and whether it is drained and vented behind.
2. What is the structure behind the wall: the backup, and whether the insulation can pass outside it uninterrupted.
3. What climate zone, and from what source?
4. Which direction do you intend this wall to dry, and why? Inward, outward, or both.
5. What rating and separation does it carry, quoted from what requires them?
6. What is already fixed by something outside this wall: floor-to-floor dimension, window type, a facade module already set, a budget already committed?

If the user offers a layer stack instead, take it, but treat it as a proposal to be tested against the demands rather than as the answer. Ask for the demands anyway.

Step 2. Place the four control layers first

Before any material is named, decide where each of the four planes sits and say why. Present as a table and fill the reason column in full sentences:

Control layer	Where it sits	Why there	Continuous at

• Water. Which plane sheds bulk water, and where it drains to. Name the plane, not the product. A drained cavity and a face-sealed wall are different decisions and everything downstream changes with them.
• Air. Which plane stops air. It has to be continuous, so name the surface it lives on and, in the last column, every place it has to carry across: to the roof, to the below-grade waterproofing, around the openings, through the floor lines.
• Vapor. Which plane, if any, controls diffusion, and on which face of the insulation. This is the one most often placed by habit. The drying direction from Step 1 decides it, not what was on the last project.
• Thermal. Where the insulation sits relative to the structure. Whether any of it is continuous outboard of the backup, and if it is not, say plainly that the framing is a thermal bridge nobody has quantified yet.

Two of these can share a material. Say so explicitly when they do, and note that a shared plane means one failure takes out two functions.

Step 3. Build the stack, outside face inward, and read the gaps between rows

List every layer in order, and give each one a job in a sentence. Present as a table:

#	Layer	Its job	Control layer?	Value needed from you

The last column is where the numbers would go and do not. Write what has to be established (a thermal resistance, a permeance class, a rating) and who supplies it. Leave it as a question.

A layer with no job comes out. If a layer is in the stack because it is usually there, that is not a job. Say so and remove it, or find the job.

Then read the table again, this time between the rows. For each pair of adjacent layers ask what happens where they meet, and report only the pairs with an answer worth writing down:

• Does one layer need a gap behind it, and is the gap drained, vented, or both?
• Is anything trapped between two layers that cannot dry?
• Does a fastener pass through a control layer, and what closes it?
• Do two materials meet that should not touch, chemically or galvanically?

Step 4. Work the transitions, where the wall stops

This is the step that gets skipped and the one that gets called back. For each place this wall ends, state what each of the four control layers does there:

• Base of wall, and how it meets the below-grade waterproofing
• Head of wall, and how it meets the roof
• Each opening: head, jamb, sill
• Floor lines and any shelf angle
• Where this wall type meets the next wall type
• Inside and outside corners
• Any penetration the program already knows about

A control layer that cannot be carried through a transition is not continuous, whatever the wall section shows in the field.

Step 5. Name the drying direction the assembly actually has

Read the stack back and say which way it can dry, based on where the lowest-perm layers landed. Compare that to the intent stated in Step 1. If they disagree, say so plainly and name which layer to move; do not quietly adjust the intent to match the drawing.

State the direction, never a rate. There is no drying model here.

Step 6. Report, and hand off

The control layer table, the stack table with its between-row notes, the transitions, then prose on what is unresolved. Close with the three hand-offs, every time:

• The arithmetic on this stack has not been run. condensation-check takes it.
• The continuity of the air barrier around the building has not been audited. air-barrier-trace takes it.
• Every value in the last column of the stack table is still open, and the code requirements are still unquoted.

Count the open values on the face of the output. Then ask whether to write the assembly to a file and where, and write it directly, tables included. There is no template and no script.

Rules

• Never supply a number. Not a thickness, not an R-value, not a permeance, not a cavity depth, not in an example, not as a placeholder that looks like a value.
• Never recall a code requirement. Continuous insulation ratios, vapor retarder classes by zone, tested assembly requirements: all quoted by the user or pointed at docs/jurisdiction.md, never remembered.
• Place the control layers before naming a material. The order is the design; the products are downstream of it.
• Every layer carries a job in a sentence, or it comes out of the stack.
• The drying direction is derived from the stack and then compared to the intent. Never assert them as matching without the comparison.
• Name every transition even when there is nothing interesting to say about it. A short list of transitions means one was forgotten.
• Say on every run that the arithmetic has not been done here.

Anti-patterns

• Producing a stack that looks like a standard detail from a manufacturer's library. If it could have been written without Step 1, Step 1 was skipped.
• Placing the vapor retarder toward the interior by default. That is a habit from one climate, and it is the single most common way this assembly goes wrong.
• Drawing an air barrier across the wall with no last column: continuous across a wall section and continuous around a building are different claims.
• Recalling a per-inch R-value, a permeance, or a "typical" cavity depth because the number feels standard. Products differ and change.
• Quoting a code clause found by web search. Search identifies which document governs; it does not verify what it says.
• Calling the assembly resolved while the transitions section is empty.
• Running condensation-check or air-barrier-trace from inside this skill. Both are hand-offs, named and not executed.
• Treating a stack the user pasted as the answer rather than as a proposal.

Resources

None. This skill is one file. Output is written directly at the path you choose.