How-To Guides · 5 min read

How to Measure an A-Frame Home for GLA

A-frame homes are distinctive but tricky to measure. The steeply sloping roofline -- which forms the exterior walls on upper levels -- creates areas where the ceiling height drops below the ANSI Z765 minimum. Here is how to measure one correctly.

Why A-frames are different

In a conventional home, the upper floors have vertical exterior walls and a flat or gently sloped ceiling. Measuring is straightforward: trace the exterior perimeter and get the floor area.

In an A-frame, the roofline is the exterior wall on upper levels. It slopes steeply from the ridge down to (often) near grade. This means the ceiling height on upper floors varies across the width of the building -- it may be 15 feet at the center and 4 feet near the edges. Only the portion that meets the ANSI Z765 ceiling height standard counts as GLA.

The ANSI Z765 ceiling height rule

Under ANSI Z765, a floor level counts as GLA only if it has at least 7 feet of ceiling height over at least 50% of the finished floor area. For areas with sloped ceilings (including A-frame upper levels), the floor area is measured only to the point where the ceiling height drops below 5 feet -- that boundary is where your measurement stops.

To be precise: you measure from the 5-foot ceiling height line inward. But the 50% rule still applies -- if less than half of the floor area has 7+ feet of clearance, the entire level is excluded from GLA.

Step-by-step: measuring an A-frame from a floor plan

1. Main floor: Measure the main level normally -- trace the exterior perimeter. This level typically has full ceiling height and is straightforward.
2. Upper level: Identify where the ceiling height drops to 5 feet. This is the line where you stop measuring. On the floor plan, this will be a line parallel to the ridge, set in from each exterior wall.
3. Apply the 50% rule: If the area with 7+ foot ceilings covers at least 50% of the upper floor's total footprint, the upper level qualifies as GLA. If not, the entire upper level is excluded.
4. Trace the qualifying area: Draw your measurement polygon from the 5-foot line on one side to the 5-foot line on the other -- not from the exterior wall. This gives you the correct GLA for the upper level.
5. Report separately: Report main floor and upper floor GLA on separate lines, as with any multi-story home.

How to find the 5-foot ceiling line on a floor plan

Good floor plans (especially from CubiCasa or architect drawings) will sometimes mark ceiling height zones with dashed lines or annotations. If your floor plan does not show this, you will need to calculate it from the roof pitch and width.

For example: if the A-frame is 24 feet wide and the roof pitch meets the floor at grade level, and you can determine from field measurements or annotations that the 5-foot height line falls 4 feet in from each wall -- then your measured GLA width on the upper level is 24 - 4 - 4 = 16 feet, not 24 feet.

This is one case where having both the floor plan and field notes (or a cross-section drawing) is useful. If only a top-down floor plan is available and it does not show ceiling height zones, you may need to estimate based on known roof pitch and verify on-site.

A-frame lower levels

Many A-frames have a lower level (basement or walkout) in addition to the main and upper floors. Apply the standard ANSI Z765 below-grade rules: below-grade area is excluded from GLA regardless of how finished it is. Report it separately as below-grade finished area.

Common A-frame measurement mistakes

• Using the full exterior footprint for the upper level. The exterior wall of an A-frame at the upper level is the roofline -- but the actual floor area is smaller once you exclude the low-ceiling edges. Always trace to the 5-foot ceiling line, not the exterior.
• Counting a loft that fails the 50% rule. If the loft or upper level of an A-frame is mostly under 7 feet of clearance, it does not count as GLA. Verify the 50% threshold before including it.
• Including the sleeping loft without checking below-grade status. In A-frames built into hillsides, some levels that appear above grade on the front elevation may be below grade on the back. Check all four sides.

Using PlanSnapper for A-frame measurement

If you have a floor plan that shows ceiling height zones, PlanSnapper handles A-frames the same as any other home -- trace the qualifying area as a polygon on each floor. Set the scale once, trace the 5-foot ceiling boundary polygon instead of the exterior wall, and get the qualifying GLA for that level.

For upper levels where the qualifying area is not marked on the floor plan, you will need to calculate or estimate the 5-foot ceiling line position first, then trace accordingly.