---
title: "Lapped Outside Walls (234)"
created: 2026-07-01
updated: 2026-07-01
type: concept
status: compiled
namespace: pattern-language
pattern_number: 234
pattern_name: "Lapped Outside Walls"
source_repository: https://github.com/zenodotus280/apl-md
source_url: https://github.com/zenodotus280/apl-md/blob/master/Patterns/Lapped%20Outside%20Walls%20%28234%29.md
license_note: Non-commercial reuse with attribution; see namespace README and source LICENSE.md.
related_patterns:
  - "Wall Membranes (218)"
  - "Roof Vaults (220)"
---

# Lapped Outside Walls (234)

> Source pattern from the abridged `apl-md` corpus. Use as a design reference and constraint seed; do not treat as commercial-clean training data.

### Problem
>The main function of a building’s outside wall is to keep weather out. It can only do this if the materials are joined in such a way that they cooperate to make impervious joints.

### Solution
>Build up the exterior wall surface with materials that are lapped against the weather: either "internally lapped", like exterior plaster, or more literally lapped, like shingles and boards and tiles. In either case, choose a material that is easy to repair in little patches, inexpensively, so that little by little, the wall can be maintained in good condition indefinitely.

### Related Patterns
... this pattern finishes the [[Wall Membranes (218)]], and [[Roof Vaults (220)]]. It defines the character of their outside surfaces.

In making our filled lightweight concrete structures, we have used lapped boards as the exterior formwork for the lightweight concrete fill. And it is, of course, possible to use many other kinds of external cladding if they are available and if one can afford them. Slate, corrugated iron, ceramic tiles will produce excellent shingled wall claddings, and can all be placed in such a way as to provide exterior formwork for the pouring of a wall. It is also conceivable (though we have no evidence for it), that scientists might be able to create an oriented material whose internal crystal or fiber structure is in effect "lapped," because all the split lines run diagonally outward and downward.

---

> [!cite]- Alexander, Christopher. _A Pattern Language: Towns, Buildings, Construction_. Oxford University Press, 1977, p. 1093.
> #APL/confidence/low
>
> #APL/Construction-Patterns/Interior-Details