November 20, 2025 By Andrew Foote

How To Calculate POMI and POPT For IWI

Description

This training guide explains how to calculate the percentage of measure installed (POMI) and percentage of property treated (POPT) for IWI.

In short, you need to know the total area of the element that could be treated and divide that into the total area that has been treated to work out the POMI as a %. This is how the POMI is calculated for all measures.

What is POMI and POPT

POMI (Percent of Measure Installed

This metric represents the proportion of an energy efficiency measure that has been installed in a property. For example, if 80% of a wall is insulated, the POMI for that measure would be 80%.

POPT (Percent of Property Treated)

This metric indicates the percentage of the entire property that has been treated with a particular measure. For instance, if insulation is installed in 50% of the property’s walls, the POPT would be 50%. If there was a mixture of cavity and solid walls, and you were insulating all of the solid walls, then the POPT for that element would be 100%.

Some may contest this and state that it must be the percentage of all external walls and not just the solid wall. See note below to ensure agreement of all parties.

For POMI and POPT see these notes

Note 1: For your first few projects, when you have calculated the proposed POMI and POPT, run it past your Designer, Coordinator and your Funder before you commence with any installations.

Note 2: The magic number is 67%. If your POMI is more than 67% then you will be paid 100% funding for that measure. If you install less than 67% then you will be paid a proportion of the funds available for that measure.

How to calculate POMI

With IWI, you need to record external wall areas for each external facing wall in each room/space whether it is getting treated or not.

This includes all wet rooms, kitchens, bathrooms, utility rooms, habitable rooms, dining rooms, bedrooms, hallways, storage areas, boiler cupboards, areas covered by built in wardrobes, walls where a conservatory is attached outside, etc.

In simple terms, every external facing wall of the whole property that is a heat loss wall has to be measured.

What measurements do we need for POMI?

We need to record the:

total wall area (WxH),
Area of openings,
Area to be treated
Area not to be treated.

When you add up the opening + untreated area + treated area, it should equal the total wall area.

A bathroom wall ‘1’ has a total area is 10m², with openings 2m², untreated 8m², treated 0m² then 2+8+0=10 which is the total wall area.

A living room wall ‘1’ has a total area of 10m², with openings, 2.5m², untreated 0m², treated 7.5m², then 2.5+0+7.5 = 10m.

A bedroom wall ‘1’ has a total area of 10m², with openings, 1m², untreated 0m², treated 9m², then 1+0+9 = 10m.

Example:

Wall	Total area	openings	Untreated/uninsulated	Treated/insulated
Bathroom wall 1	10	2	8	0
Kitchen wall 1	10	1	0	9
Livingroom wall 1	10	2.5	0	7.5
Bedroom wall 1	10	1	0	9
Totals	40	6.5	8	25.5

Do this for every external facing wall in each room/space that has an external facing wall.

Now add up all the total wall areas, then the total openings, the total omitted areas and the total treated areas.

Then do the following calculation.

Total area – openings = total area of external walls

Total treated area / total area of solid wall x 100 = POMI

If the whole property is solid wall, then the POMI will also be the POPT

Total area 40m², Openings 6.5m², untreated area 8m², treated area 25.5m²

Total area – openings

40-6.5 =33.5m² total wall area

Treated area/total wall area x 100

33.5/40×100 = 83.7% treated.

The POMI is 84% (rounded up)

What we have leaned about POMI and POPT

Calculating POMI and POPT isn’t rocket science—it’s all about knowing your numbers. For POMI, you figure out how much of the measure (like insulation) you’ve actually installed compared to what could be installed. For POPT, you look at how much of the property has been treated overall. The key steps? Measure every external wall, subtract openings, and then work out the percentage treated. Remember the golden rule: if your POMI is over 67%, you get full funding—anything less and you’re only paid for what you’ve done. So, measure carefully, double-check with your team, and keep that 67% in mind!