Section marks and floor levels
Read the section bubble or the level marks. Get 10 right to finish. Pick feet and inches or metric below.
On which sheet do you find this section?
Section bubbles
A section cut line runs across the plan with a bubble at the end. The arrow shows which way you look. The top of the bubble is the section number, the bottom is the sheet where the section is drawn.
Floor levels
Sections and elevations mark each floor with a level. Metric drawings use metres to three decimals against a datum, such as FFL +2.850. US drawings often use an assumed datum of 100'-0". The storey height is the upper level minus the lower level.
Common mistakes
- Reading the sheet number as the section number. The sheet is always the bottom half.
- Forgetting that metric levels are in metres while dimensions are in millimetres.
Questions
- What do the numbers in a section bubble mean?
- The top number is the section (or detail) number. The bottom one is the sheet it is drawn on. 2 over A-301 means section 2 on sheet A-301.
- What does FFL +2.850 mean?
- Finished floor level 2.850 m above the datum. Metric drawings give levels in metres to three decimals. The difference between two floor levels is the storey height.
- Why is the ground floor at 100'-0" on US drawings?
- Many US sets use an assumed datum of 100'-0" so no level below it becomes a negative number. Only the differences between levels matter.
Explained in our own words and checked against several textbooks and trade school resources. Office standards vary, so always check the legend on your drawing set.