The external floor area of a house, specifically the Gross External Floor Area (GEFA), is the area of a dwelling measured externally at each floor level.
Understanding Gross External Floor Area (GEFA)
The Gross External Floor Area (GEFA) is a standard measurement used in construction, valuation, and real estate to quantify the size of a building. It provides a clear picture of the total space enclosed by the external walls at every level of the structure.
Based on common definitions and the provided reference:
- Definition: GEFA is defined as the area of a dwelling measured externally at each floor level.
- Method: The most practical way to determine GEFA for a simple house shape is to go outside and measure the length and width of your house and multiply those figures together. This calculation is repeated for each floor level.
This measurement includes the area of all heated and unheated spaces within the external walls, such as:
- Living areas
- Bedrooms
- Kitchens
- Bathrooms
- Hallways
- Integral garages
- Basements (if applicable and within the external walls)
It typically excludes external features like patios, open porches, balconies, and conservatories unless they are fully enclosed and integrated into the main structure.
Why is GEFA Important?
Measuring the external floor area serves several purposes:
- Valuation: Provides a consistent metric for comparing property sizes during appraisals.
- Planning & Design: Used by architects and builders for calculating material needs and assessing building capacity.
- Construction Costs: Often used as a basis for estimating construction expenses per square foot or meter.
How to Measure GEFA
For a rectangular house, the process is straightforward:
- Go Outside: Stand outside the house.
- Measure Dimensions: Use a tape measure to find the total length and width of the house from the exterior walls.
- Calculate Ground Floor Area: Multiply the measured length by the width.
- Repeat for Upper Floors: If the upper floors cover a different footprint (e.g., a cantilever), measure the external length and width of each upper floor separately. If the upper floors have the same footprint as the ground floor, the calculation is the same.
- Total GEFA: Sum the areas calculated for each floor level.
Example:
| Floor | External Length | External Width | Area (Length x Width) |
|---|---|---|---|
| Ground Floor | 40 ft | 25 ft | 1000 sq ft |
| First Floor | 40 ft | 25 ft | 1000 sq ft |
| Total GEFA | 2000 sq ft |
For houses with more complex shapes (L-shaped, multiple additions), you would divide the external footprint on each level into simple shapes (rectangles, squares) and sum their individual areas.
Understanding GEFA gives you a clear, external-based measure of your home's size, distinct from internal measurements like Gross Internal Area (GIA) or Net Internal Area (NIA).
