A wall section is a large-scale vertical cut through an exterior wall, from the foundation to the roof, showing every layer of the wall and how it meets the floors, the openings and the roof. It sits between the building section (the whole building at a small scale) and the details (single junctions at a large scale). It is the drawing where the build-up of the envelope is decided: what keeps the rain out, what stops air leaking, where the insulation runs, and how each of those layers stays continuous past the slab edges, windows and parapet. Wall sections are usually drawn at 3/4" or 1/2" = 1'-0" in imperial sets, or 1:20 in metric sets.
Building section, wall section, detail
| Drawing | Shows | Typical scale |
|---|---|---|
| Building section | The whole building cut through: storeys, heights, spaces | 1/8" or 1/4" = 1'-0"; 1:100 or 1:50 |
| Wall section | One wall type from foundation to roof, with all layers | 1/2" or 3/4" = 1'-0"; 1:20 |
| Detail | One junction: window head, slab edge, parapet | 1-1/2" or 3" = 1'-0"; 1:10 or 1:5 |
Scales vary between offices, and the scale under each view is the one that counts. Note that 3/4" = 1'-0" is exactly 1:16, not 1:20, even though the two are often treated as equivalent; see architectural scales.
In sets following the US National CAD Standard, sections are sheet type 3, so wall sections usually sit on A-3xx sheets next to the building sections, and the details they call out on A-5xx sheets.
What a wall section shows
- Every layer from outside to inside: cladding, cavity or air gap, insulation, sheathing, membranes, structure, interior finish, each named with its thickness.
- Vertical datums: top of footing, top of slab or finished floor at each level, floor-to-floor heights, window head and sill heights, top of parapet or eave.
- Transitions: foundation to wall, each floor to wall, openings, roof to wall.
- Callouts to the larger-scale details at each junction.
- Notes naming materials, often written out in full rather than keynoted, and references to the structural drawings for structural sizes.
The four control layers
Building scientist Joseph Lstiburek's widely cited "The Perfect Wall" (Building Science Corporation) describes four control layers every enclosure needs, in order of importance: a rain control layer, an air control layer, a vapour control layer and a thermal control layer. In his words, "if you can't keep the rain out don't waste your time on the air." His ideal places the layers outside the structure, with the insulation outermost, so the structure stays warm and dry; a single material can do more than one job.
A wall section is where you check those layers. Building Science Corporation and others stress that continuity is what matters: the field of the wall is the easy part, and leaks happen at transitions, especially where the roof meets the wall and around windows.
The pen test
A simple way to read a wall section: put a pen on one control layer and follow it along the whole section without lifting it. Do it once for the water layer, once for the air layer, once for the insulation. Wherever you have to lift the pen (a slab edge where the insulation stops, a window where the membrane does not lap onto the frame, a parapet where the roof membrane and wall barrier do not meet), the drawing has a gap, and so will the building. Each such point should have a callout to a detail that shows how the layer continues.
Where wall sections usually go wrong
- Slab edges and balconies: a concrete slab or balcony running straight through the insulation forms a thermal bridge. Thermally broken connectors exist for this; the wall section should show how the slab edge is handled.
- Window heads and sills: flashing must shed water out over the cladding, and the air barrier must connect to the window frame.
- Parapets: the hardest transition, where the roof membrane, the wall's water barrier and the air barrier must all join.
- The base of the wall: where the wall meets the foundation, water must be able to drain out and the insulation must continue down or meet the foundation insulation.
- Fire-rated walls: where a wall is part of a rated assembly, the section must match the tested assembly's layers exactly; substitutions need the designer's approval.
How to read a wall section, step by step
- Find where it is cut. Follow the section marker on the plan or building section, and note which wall type it represents.
- Read from the bottom up: footing, foundation wall, ground floor, each upper floor, roof.
- Check the datums against the building sections and elevations: the same floor levels and heights must appear everywhere.
- Read the layers from outside to inside, with their thicknesses and materials, against the specification.
- Do the pen test for water, air and insulation.
- Follow every callout to its detail, and check the detail shows the same build-up.
- Check structure: sizes and spacing usually defer to the structural drawings ("see structural"); see how to read structural drawings.
Drawing wall sections in Revit and ArchiCAD
In Revit, a wall section is a section view (View tab, Create panel, Section) or a callout, using a section type such as "Wall Section", set to a larger scale. Detail components (2D families loaded through Insert, Load Family and placed with Annotate, Component, Detail Component) are drawn over the model to show what the model does not, such as flashing and fasteners; setting the model display to halftone makes the difference visible.
In ArchiCAD, a section marker on the plan generates the wall section, and detail markers placed on it generate detail drawings for each junction. Our guide to construction details covers how detail callouts are numbered and followed.
Frequently asked questions
What is a wall section in architecture?
A vertical cut through an exterior wall from foundation to roof, at a large scale, showing all layers of the wall and its junctions with floors, openings and roof.
What is the difference between a wall section and a building section?
A building section cuts through the whole building at a small scale to show storeys and spaces; a wall section shows one wall in detail at a larger scale.
What scale is a wall section?
Usually 1/2" or 3/4" = 1'-0" in imperial sets and 1:20 in metric sets, with details at larger scales.
What is the difference between a wall section and a detail?
A wall section shows the whole height of a wall; a detail enlarges one junction of it, such as a window head or parapet.
What should a wall section show?
All layers with materials and thicknesses, floor levels and heights, the transitions at foundation, floors, openings and roof, and callouts to the details.
Ncored is the desktop PDF editor we built in our architecture studio for drawing sets from AutoCAD, Revit, and ArchiCAD, on Windows and Mac (Apple Silicon). Large sets stay smooth to zoom from a wall section into a junction and back, so the pen test works on screen too. Measure to scale (metric units), cloud a gap in a control layer and leave a comment, and compare two issues of the wall section as a colour overlay. Markups are saved as standard PDF annotations that open in Acrobat, Bluebeam, Preview and other standard PDF viewers. 14 days free. No signup, no email, nothing to enter.
Related: construction details, plans, sections and elevations, architectural scales.
All product names, standards and organisations mentioned on this page are trademarks or registered names of their respective owners and are used for identification only. Ncored is an independent product by Noir architects and is not affiliated with, sponsored by, or endorsed by any of them. This page explains common drawing and building-science conventions and is not design advice; the project's drawings, specifications and design professionals govern. Individual experiences may vary.