Determining the Open Spaces of Lot (TOSL)

If you have Allowable Maximum Building Footprint (AMBF) for a given lot, then the remaining spaces will simply be allocated to your open spaces within lot (TOSL).

open space and building footprint

These areas are not only intended for your landscapes, pathways and path-walks or other non enclosed spaces but to give way for proper light and ventilation to your building or structure.

To determine your AMBF and PSO you may read from here.

Say you have a (TLA) total lot area of 150sqm with a 50% maximum PSO (Percentage of Site Occupancy) then from these data alone you could already compute for your TOSL (Total Open Space within Lot) which is also 50% that is equivalent to 75sqm.

Mske sure to compare the PSO with other restrictions mentioned in the code.

TOSL=TLA-AMBF (in sqm) or 

TOSL=100%-PSO (in %)

Once you get the total open space of the lot, it will be subdivided into two types namely USA (Unpaved Surface Area) and ISA (Impervious Surface Area/Paved Surface Area).

Initial computation of USA is usually the front yard setback while the ISA covers the sides and rear yards when based on the setbacks of the lot as shown below.

To get the designated percentage for ISA and USA you may refer to Table VIII.1 as shown.

Listed from table shows the Maximum allowable ISA (Paved Surface Area) which you are not allowed to go beyond what is being required by the code but you may throw all excess open spaces to your USA since it is only  the minimum.

Some Designers if they come up with the PSOmax from Table VIII.1 as the most stringent, then they automatically follow the ISAmax and USAmin as dictated in the table to get the 100% total for PSO and TOSL.

You may opt to compare side by side with the USA and ISA based on setbacks vs what is listed on the table to give you some room in the future in case you decide to increase the areas for ISA since you will still be under the Maximum allowed set in the table compared to the computed value based on your setbacks.

To give you a short idea when comparing side by side, as per table ISAmax at 30% while based on setbacks only at 16.25% for ISA which gives you 13.75% reserve for future developments which will still comply within the limits set in the table.

After you comply with the AMBF/PSOmax and the TOSL of your project then you are now ready to go further to compute for the MACA (Maximum Allowable Construction Area), GFA (Gross Floor Area) and TGFA (Total Gross Floor Area).