Design Envelope

Envelope work starts at a wall section, and by the time anyone looks up there are eleven wall types, four of which differ from each other by an inch of insulation nobody can defend, and a set of junctions that were never scheduled because each one was drawn when it came up.

This is the step before the sections. It decides how many types there are and where they change.

Workflow

Step 1. Take what the building is, not what it should look like

Ask, in one message:

1. What is inside, behind each face? A heated office, a garage, a warehouse, a plant room and a stair have different demands on the wall in front of them.
2. What is the climate zone, and from what source?
3. Quote the code's envelope requirements. Is a certification being pursued? Point at leed-tracker, passive-house-tracker.
4. What is fixed already: a structure, a floor-to-floor, a facade module, a material the client has chosen? Point at facade-module.
5. What does each face see: sun, driving rain, a neighbour, a street, a boundary line with a fire separation on it?
6. What is below grade, and what is under it? Point at design-below-grade-assembly.
7. How will it be reached after it is built? Point at facade-access-study.

Step 2. Work out how many types the building actually needs

The decision that keeps the set honest. Two forces pull against each other:

• Fewer types is cheaper, faster to draw, and easier to build correctly. A trade that builds one wall three hundred times gets good at it.
• More types means each face gets what it needs, and a single type applied everywhere is over-specified somewhere and under-specified somewhere else.

Work the demands into a table and see how many genuinely distinct answers there are:

Face / zone	What is behind	Thermal	Water exposure	Fire	Acoustic	Appearance	Type

Two rows with the same answers are the same type. Merge them. Two rows differing in one column may still be one type built to the stricter demand, and that is usually cheaper than a second type.

Report the count, and report every type that exists for appearance alone, since that is a legitimate reason and it should be a decision rather than a by-product.

Step 3. Schedule the junctions, which is the part nobody does

Every place two types meet, or a type stops, is a junction, and each is a detail somebody has to draw. Listing them now is what stops them being discovered one at a time in production.

#	Junction	Between	Skill that takes it	Drawn?

Work systematically rather than from the elevation: base of every type, top of every type, every corner inside and out, every change of type in plan and in section, every opening condition, every floor line, every movement joint, every projection, every penetration the programme already knows about, and every place the envelope meets the ground or the roof.

Count them. A building with four types usually has twenty to forty junction conditions, and a set that has drawn six is a set with thirty questions in it.

Step 4. Decide the strategy questions that cut across every type

Answer once, for the building, rather than four times in four sections:

• Where the air barrier plane sits across the whole building, and how it gets from one type to the next. This is the single decision that most affects whether the building performs. Point at air-barrier-trace.
• Where the insulation sits relative to structure: outboard everywhere, cavity everywhere, or mixed. Mixed means every junction between the two is a thermal bridge.
• Drained or face-sealed, and whether it is consistent.
• Which direction the building dries, and whether it is the same everywhere.
• What is buried and what is replaceable, which sets what has to be right first time.

Inconsistency in any of these is allowed and has to be deliberate. Name each place the strategy changes and why.

Step 5. Report and hand off

• The type count, with what distinguishes each and which exist for appearance.
• The junction schedule with its count, and which are drawn.
• The five cross-cutting decisions, with every place the strategy changes.
• Every requirement that came from an assumption rather than a quoted source.
• The hand-off list: each type to its assembly skill, each junction kind to its junction skill, then condensation-check and air-barrier-trace on the result, and facade-access-study for maintenance.

Close by saying no assembly was built and no arithmetic was run here.

Step 6. Save, if asked

Ask whether to write the strategy to a file and where. It is read back every time one of the assembly skills runs.

Rules

• Build nothing. Every assembly and every junction names the skill that owns it.
• Never supply an R-value, a permeance, or a code minimum.
• Merge two types with the same demands, and say when a type exists for appearance.
• Schedule the junctions systematically and report the count.
• Answer the five cross-cutting questions once for the building.
• Name every place the strategy deliberately changes.

Anti-patterns

• Starting at a wall section.
• Eleven wall types, four of which differ by an inch.
• A junction schedule discovered one detail at a time in production.
• Deciding the air barrier plane separately in each assembly.
• Mixing outboard and cavity insulation without naming the junctions between them.
• Choosing the cladding first and working the wall backwards from it.
• Leaving maintenance access until after the elevation is agreed.

Resources

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