FGL stands for Finished Ground Level: the level of the ground or external surface outside the building once cut, fill, paving and landscaping are complete.
What FGL means
FGL is Finished Ground Level: the level of the ground or external surface after the works are done – after cut and fill, after paving, after topsoil and turf. It is the outside counterpart to FFL, and it is a designed level rather than a surveyed one. The surveyor tells you what is there now; the designer nominates what FGL will be.
FGL carries more weight than its plainness suggests. It sets how far the slab sits above the ground, whether surface water falls away from the building, where the damp-proof course and weep holes sit relative to soil and paving, how many steps land at each door, how much of a retaining wall is exposed, and how deep pits and inspection openings finish. On a sloping site it is also the level that decides whether the design works at all.
How FGL appears on a drawing
FGL is almost always a spot level: a small cross, dot or triangle symbol with the level beside it, repeated around the building perimeter and across the site. In Australia and the UK it is written in metres to three decimal places against the project datum:
FGL RL 24.100
It is often paired with the level it replaces, so the cut or fill reads at a glance:
FGL 24.100 (NGL 23.950 - 150 FILL)
On elevations and sections the finished ground line is normally drawn solid, with the natural or existing line dashed behind it, both labelled.
The ground clearance check people get wrong
Australian residential sets also call up the relationship between the slab and the ground, for example TOP OF SLAB MIN. HEIGHT ABOVE FGL - REFER NCC. Read that requirement carefully, because it is the one people get wrong. The NCC Housing Provisions set a minimum height for the slab-on-ground above the external finished surface – not for the finished floor level. Where there is a screed or a thick finish, the slab sits below FFL, so checking FFL against FGL overstates your clearance by the whole floor build-up. The required figure changes with the surface treatment and how well the ground drains, so read it from the current NCC rather than carrying a number across from the last job.
Using the levels these pages work to, the check you actually want is:
SSL 24.290 LESS FGL 24.100 = 190 SLAB ABOVE FINISHED GROUND
Measure from FFL 24.350 instead and you get 250 – and 60 of that is floor build-up sitting above the slab, not clearance above the ground.
Terms it gets confused with
- NGL – natural ground level, the ground before any works.
- EGL – existing ground level, the surface as surveyed today. On a site that has been filled before, EGL and NGL are not the same number, and neither is FGL.
- FSL – usually finished surface level, preferred by many civil and landscape offices for paving, pavements and hardstand where “ground” implies soil. Some sets use FGL and FSL side by side with that exact distinction. Treat it with care, though: on Australian residential sets FSL is also written for finished slab level, which is an internal structural level and the opposite kind of number. Check the legend.
- TOK or TK – top of kerb, and IL or INV – invert level. These sit in the same style of level box on a drainage plan and are easy to misread as ground levels. The full set is in my A-Z list of engineering drawing abbreviations.
- FFL – finished floor level, inside. Useful for step counts and threshold details at the door, but not the level to check ground clearance from. That is the slab.
AU and UK versus US
FGL is standard in Australia, New Zealand and the UK, expressed as a level in metres to a datum – AHD in Australia, Ordnance Datum in the UK, or an assumed site datum. US practice uses “grade” as the noun: finished grade, FG, or finished grade elevation, given as an elevation in feet and inches. On a US set the phrase usually appears in the general notes and on the civil sheets rather than as a spot-level abbreviation on the architectural plan. Working between an Australian architectural set and a US civil set, expect different abbreviations, different units and a different datum – reconcile all three before you trust a comparison.
Where to check on your own set
- Civil or site plan – the designed spot levels and contours, and the surveyor’s existing levels they were derived from.
- Cut and fill plan – where FGL departs most from what is there now.
- Landscape plan – it can and often does revise finished levels late; check which drawing governs.
- Sections at the entry, at retaining walls and on the low side of the site – the places where FGL, the slab and drainage have to agree.
- Structural slab plan and footing details – the SSL you need for the ground clearance check, and any edge thickenings.
- Drainage plan – surface levels at pits and the fall to the legal point of discharge.
- Datum note in the title block – without it, an FGL value cannot be compared with anyone else’s levels.
References
- National Construction Code (ABCB)
- Levels on drawings (AS 1100.301 conventions summary)
- Land Victoria – Australian Height Datum
Other meanings of FGL
Outside drafting, FGL is best known as the country duo Florida Georgia Line, and also stands for Fidelity & Guaranty Life (a US insurer) and fifth-generation language in computing. None of these appear on drawings, but they crowd the search results.