Construction details (also called architectural details or detail drawings) are large-scale drawings of the places where a building is hardest to get right: where a wall meets the roof, a window meets the wall, a floor meets the foundation, or a pipe passes through a fire-rated wall. Plans and sections show where things go; details show exactly how the layers are built, sealed and fixed. A detail is reached from a callout such as "3/A-501", which means detail 3 on sheet A-501. To read one, follow the callout, check the detail's own scale, read the layers in order and check its notes against the specifications.
Where details sit in a drawing set
The US National CAD Standard's Uniform Drawing System gives each sheet a type number, the first digit after the discipline letter:
| Sheet type | Contains | Example |
|---|---|---|
| 3 | Sections, including wall sections | A-301 |
| 4 | Large-scale views: enlarged plans, elevations or sections "that are not details" | A-401 (enlarged toilet plan) |
| 5 | Details | A-501 |
| 7 | User defined, including typical detail sheets | A-701 |
So A-501 is the first architectural detail sheet, S-501 the first structural one. A detail is defined by its purpose and scale, not by its projection: it can be a small plan (a column base seen from above), a section (a roof edge cut through) or an elevation (a handrail bracket).
How detail callouts work
On a plan or section, a callout bubble marks the spot that is detailed. The top half carries the detail number, the bottom half the sheet number. "3/A-501" means: go to sheet A-501 and find detail 3. On the detail itself, the title repeats the number, gives the name ("PARAPET AT ROOF EDGE") and the scale.
Many offices number details by their position on the sheet: the Uniform Drawing System divides the sheet into a grid of modules with coordinates (such as C3), and a detail can take its module's coordinate, so the number tells you roughly where on the sheet to look. Other offices simply number 1, 2, 3 in reading order. The legend on the first sheet of the set says which system the set uses.
Typical details and project-specific details
- Typical details show a condition that repeats: every interior partition head, every door frame of one type, every pipe penetration of one kind. Drawing it once removes repetition. The Uniform Drawing System's own drafting procedure says: circle items that require detailing, eliminate repetition by identifying typical details, enlarge the circled areas, and reference each detail back to where it came from.
- Project-specific details show one particular place: the corner where the new extension meets the old building, the one stair that does not match the others.
- Standard details are reused across projects, from an office library, a public authority (many transport agencies publish standard details and add "special details" for what the standards do not cover) or a manufacturer. A standard detail still has to fit the project: the Alberta government, for example, states that its typical bridge drawings only show preferred details and that the consultant stays responsible for the project's own.
The risk with typical details is scope. "Typical" should say where it applies. If a callout on the plan points to a typical detail but the condition there is slightly different, ask; do not assume the typical detail covers it.
Common detail types and what to check in each
| Detail | What it should make clear |
|---|---|
| Wall section | The full build-up of a wall type from foundation to roof, with materials, thicknesses, floor levels and where each layer is fixed |
| Roof edge, parapet, eaves | How the roof membrane turns up and is capped, flashings and their laps, insulation continuity, the fall of the coping |
| Window head, jamb, sill | Where the frame sits in the wall, how water is shed at the head and sill, how the air seal and insulation meet the frame |
| Threshold and door | Floor levels on both sides, the drainage and sealing below the threshold, accessibility of the step |
| Foundation and ground floor | Footing size and depth, damp-proofing or waterproofing, how the wall insulation meets the floor insulation |
| Stair and handrail | Riser and tread dimensions, handrail height and fixing, balustrade gaps |
| Fire-stopping | For each penetration through a fire-rated wall or floor: the tested system (in North America a UL system number in a format such as C-AJ-1xxx), the rating, the pipe or cable type and size, and the product |
Across all of them, the question is the same: is every line that must be continuous (water, air, heat, fire) shown to be continuous through the joint?
Scales used for details
Details are drawn much larger than plans so that every layer is visible. In imperial sets, wall sections are commonly drawn at 3/4" = 1'-0" or 1-1/2" = 1'-0", and details at 1-1/2" = 1'-0" or 3" = 1'-0", up to full size for small items. In metric sets, 1:20 is common for wall build-ups and 1:10 or 1:5 for details, with 1:2 or 1:1 for the smallest. The scale is printed under each detail and can differ between details on the same sheet. Our guide to architectural scales explains how to read them.
How to read a construction detail, step by step
- Start at the callout. Note the detail and sheet number and look at the plan around it: what are you looking at, and from which direction?
- Go to the sheet and read the title. Check that the name matches the place you came from, and read the scale.
- Orient yourself. Find inside and outside, and the floor or roof level the detail is tied to.
- Read the layers in order, usually from outside to inside or from the top down, using the hatch legend to identify materials.
- Read the notes and keynotes. The Uniform Drawing System notes that drawing notes have legal consequences and that their terms should match the specifications. Look up each keynote and check that the product or system matches the specification section.
- Check dimensions, and take sizes only from written dimensions, never by measuring the print.
- Trace it back. Find every callout in the set that points to this detail, and check that each of those places really matches it.
- Check the revision marks. A clouded part with a revision delta means the detail changed in that issue; compare it with the previous issue before building.
Common mistakes with details
- Stale callouts after renumbering. When sheets or details are renumbered, a callout can point to a detail that moved or no longer exists. Cross-reference checking is a common source of RFIs. In Revit and ArchiCAD the reference usually updates itself, but forum reports show cases where it did not; in a PDF the callout is just text and never updates.
- Details not updated between revisions. The plan changed, the detail did not, and the two now disagree.
- Unclear typical scope. A typical detail used where the condition is not quite typical.
- Manufacturer details used unchanged. Free libraries are useful, but a product detail shows the product, not your wall around it.
Where details come from
Most details are drawn in the design software. In Revit, a detail view can show the model with 2D detail components drawn over it, while a drafting view is, in Autodesk's words, an "unassociated, view-specific" detail not tied to the model. In ArchiCAD the Detail tool creates an updatable view of the model, and independent details or worksheets hold pure 2D drawings. Manufacturer details are available free from libraries such as ARCAT and CADdetails (organised by specification division), and BIM objects from NBS Source and BIMobject.
Frequently asked questions
What is the difference between a section and a detail?
A section cuts through the whole building or a large part of it to show heights and relationships. A detail enlarges one small area, often taken from a section, to show exactly how it is built.
What does 3/A-501 mean on a drawing?
Detail number 3 on sheet A-501.
What scale are construction details drawn at?
Usually 1:10 or 1:5 in metric sets and 1-1/2" or 3" = 1'-0" in imperial sets; the scale is printed under each detail.
What does "typical" mean on a detail?
That the detail applies to every place with the same condition, not only to one location. If a place differs, the typical detail does not automatically apply.
Where can I find standard construction details?
In your office library, in public agencies' standard detail sets, and in free manufacturer libraries such as ARCAT and CADdetails. Always adapt them to the project.
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 and pan, so moving from a callout on the plan to the detail sheet and back stays easy. Measure to scale (metric units), cloud a detail and leave a comment where it disagrees with the plan, and compare two issues of the detail sheet as a colour overlay to see what changed. Markups are saved as standard PDF annotations that open in any PDF program. 14 days free. No signup, no email, nothing to enter.
Related: architectural drawing symbols, architectural sheet numbering, how to read construction drawings.
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 practice and is not engineering advice; the project's drawings, specifications and engineer of record govern. Individual experiences may vary.