What’s the largest purchase most people make in their lifetimes?
Answer: Buying a home.
The price depends on a lot of things. Location. Condition. Look. Market conditions. And Size.
– And yet, what is the one thing almost universally NOT corroborated as part of a listing?
Answer: The Size.
Most listing agents just use the tax record – what the county has for the size. And yet, this can be inaccurate, as we illustrate below with two examples.
In some places, it is a requirement to provide an accurate floor plan or square footage with a new listing. In the US, North Carolina has some requirements to provide accurate square footage. As a result many agents use appraisers to do the floor plan creation. The problem with this is it’s a human doing the work and the data can still be off, as I show below in the detailed analysis of my own house.
Alberta, Canada has a requirement that each listing must come with a floor plan that is at least 98% accurate. As a result, iGuide, the 3D scanning solution we just implemented in select markets, has become the standard there. iGuide cameras use a 360 camera on top of a base unit that has LiDAR – Light Detection and Ranging laser data that generates a point cloud that is then used to create floor plans. See here for an example of what it looks like for my house. Floor plans generated from an iGuide camera are typically 99.5% accurate.
My question is why are “accurate” floor plans NOT a required listing component everywhere?
And if they are required, there needs to be some kind of accuracy guarantee, or statement of accuracy. While it is easy to get a floor plan now, even using your phone, the accuracy of various solutions is not guaranteed, and some of these options, including the most popular one, Cubicasa, can vary wildly, as I detail below. On my new house, Cubicasa is off over 4.2%, or 179 square feet. That is not a small number on a 4200 sq ft house.
To illustrate the importance of accurate square footage, let me go through two examples of where the listing data, which used the tax record, was not correct. One was on my own personal house in the Seattle area. The other is a more recent listing in New York.
Cone Home
– bought @ 5290 sq ft | sold @ 4840 sq ft
When we bought our Sammamish, WA (suburb of Seattle) house in 2005, the listing agent just used the tax record for the size. As you can see by the sketch from the country tax appraisers website below, the size was 5290 square feet. We paid $1,040,000, so the price per sq ft was around $197/sq ft. When we sold it in 2024, we listed it at 4840 square feet, which was the number we came up with leveraging a Matterport Pro2 camera scan and the HomeDiary FloorPlan Engine. I knew the county number was not right after scanning my house roughly 50 times with various methods, so I couldn’t have listed the house based on the tax number, it could have been a seller’s disclosure issue. So, what I ended up doing was taking my data to the county to show them where it was off, and they changed the tax record to reflect the smaller home – they corrected their error using the data I provided to them.
The data we create can be defended and used by a government entity. My own personal experience corroborates this fact.
Why was it off initially? As you can see in this screenshot below, I took the county floor plan and overlaid it with a screenshot of a Matterport Pro2 camera scan of the second floor of my house. The county floor plan shows the 2 levels on one image – dashed lines represent the upstairs area that is different than the main level, and if solid, both levels have the same footprint. So you can see on the top left of the image outlined in the orange box, they are counting a lot of gray space as upstairs living area that did not exist, and when you see the actual living area, there is only the dormer of our guest bedroom that should have been counted – this was 450 square feet, and the reason the floor plan size was off.
Initially I thought the county was including the open to below area of our foyer, and I did not want to change my sq ft if they did that for all houses, many around the area had these two story foyers. It wasn’t until I saw the floor plan of a listing we shot that had a very similar floor plan layout as my house, with the size around 5000 sq ft at the county, did I do a deeper dive into why it was off. Having the Matterport as a visual helped me figure out out.
Ultimately, I took the info to the county and they changed the taxable size based on the data I presented to them…but of course, they shortchanged some of it, as they did not count the foyer main stairs in the second floor GLA, when it should be counted. So, we ended up listing the home at 4840 sq ft which was the 100% accurate plan we created leveraging the Matterport Pro2 scan at the time. Given all interior room measurements matched my hand laser measurements, and I could see the exact layout of the home footprint wise via the Matterport, I knew it was right. Here is the Certified Square Footage Report we had on the virtual tour to back up our numbers.
What are the ramifications of uncorroborated square footage?
Because the listing agent did not do an independent verification of the square footage of the house, I overpaid on the purchase by $91,600, and I also overpaid around $20,000 in excess property taxes based on the size over the 19 years of ownership! Who is liable for this? The listing agent? She was the one selling a product, and it seems the person representing the product needs to KNOW the size, not assume it. People are so afraid to show a number, yet relying on a number that is flawed is also a big problem in my opinion – its kind of like sticking your head in the sand and just ignoring the issue.
Yet, as stated above, this is the most expensive purchase most people make at this point in their lives. Don’t they deserve to know the correct size?
Some people insist on the use of an appraiser as the authoritative source. We have some on staff and they do a great job. But, traditional “appraiser” type methods can result in inaccurate results consistently, as you see on my house where I had 5 different “home pros” come out and measure it. You see 3 different appraisals, the last one generated a floor plan that did not even look like my house, and was 7% off. All 3 provided different answers, ranging from 4798 sq ft to 5161 sq ft. I also had Allstate do a sketch for it when we first bought the home and they came in at 4950 sq ft. Home Depot was also different, coming in at 4557. And of course the tax record was at 5290 sq ft. So my house’s size has a spread of over 700 sq ft in size, or 15%….confusing! These numbers represent a wide variety of results, even with “pros” doing the measurements.
So, just because there is a “pro” doing the measuring does not mean it is accurate.
With technology, we can now provide a reliable, accurate number that can be trusted because the point cloud created from laser endpoints of the true inside is what is used to generate the floor plan. As long as all areas are scanned, and the exterior wall thickness is set at the proper thickness, the GLA, or Gross Living Area of the property, what the tax assessor and all appraisers use, is going to be accurate. This scan data gives the floor plan drafters vision into the whole property layout after the fact and it is typically 99.5% accuracy, or perhaps even better as I got with my Seattle house.
Long Island Tax Records have a problem too…
Here is a more recent example of a listing in New York listed in June of 2026. The county record had the property at 3257 sq ft. The listing agent thought the home was no bigger than 3500 sq ft. We came out, did the floor plan and it came out to be 4619 sq ft, or 43% larger than the tax record! You can see what it was originally listed at in the screenshot.
I don’t know about you, but how can you determine the price of a home without knowing its size? As illustrated above, the tax record may not be right, and if it isn’t it can mean a big difference in the potential sales price and value, as well as other costs, like real estate taxes. This is why I am a huge advocate for having an accurate floor plan required for listings. Some jurisdictions now require an energy score to list a home (Portland, Berkeley)….that score doesn’t tell the buyer a lot in my opinion, yet it is a $200+ required listing cost. A floor plan that is 98%+ accurate does, expecially if it can be put into the hands of the homeowner to use post sale.
Texas has issues too.
In Texas, most of the MLSs have a deal with Cubicasa. The problem is, Cubicasa can’t deal with varying wall thicknesses. They use 6 inches thick walls. I see a heck of a lot of brick homes in Texas – Dallas, Austin, Houston, San Antonio. The typical brick home has 10 inch thick walls. This means every brick home scanned with Cubicasa is going to be off total square footage wise. HomeDiary (and iGuide) can and does account for varying wall thicknesses, so we can provide the accuracy needed to be defended at the county level.
For my new home in the Dallas area, I have scanned it around 20 times – Matterport Pro2 and Pro3 cameras, iGuide, Matterport+360 camera, my iphone with Cubicasa, Zillow and a few other apps. The tax record when I bought it was 4197 sq ft. Based on a detailed Matterport scan as well as iGuide, both of which came up with 4237 square feet, I think that is the 100% accurate source. Cubicasa came up with 4058 square feet. That is 179 sq ft, or 4.2% off. Zillow came up with 3662 square feet, or a whopping 575 sq ft – 13.6% off!
Here is my home’s Area Report from HomeDiary that details the living and non living areas. Again, both iGuide and Matterport with the PRO2 camera provided 4237 square feet of living space, 40 sq ft more than the county record. So this time I got a little more house for the money.
If using iGuide, we get the underlying point cloud of the laser data to build a highly accurate floor plan. Below is my home’s layout, all generated from the LiDAR data. You can clearly see the curved wall with windows in our primary bedroom, where the walls are and how thick they are as well. If I use 10 inches thick in our floor plan tool, it fills the gap perfectly, so I know the wall thickness is correct, and I therefore know the total GLA is correct as well.
For apps like Cubicasa and Zillow, they are using photogammetry or forms of it, and that has some inherent issues. Cubicasa I think can adjust with LiDAR if your device supports it, but it is still off – my iPhone is a Pro model with LiDAR and it was still off over 4%. Part of the issue with both of these apps is the wall thickness as I mentioned above. Cubicasa uses 6 inch thick walls, Zillow appears to be using 4.5 inch walls. We can account for this wall thickness difference. These apps can’t. The other issue is you can scan your home 10 times and you will get a different answer 10 times. With more advanced capture methods, like iGuide or Matterport + Pro camera, there is a greater consistency in getting consistently accurate numbers.
Below is my new house and how various methods compared, along with individual room measurements calibrated to hand laser measurments.
While the overall square footage can vary, individual room measurements are off too. Sometimes off over 6 to 10 inches. Zillow had a small room that was off by almost 2 feet! How are you going to know the data you get is right, unless you go around and do that hand measurement, but then, why are you paying someone else to do the floor plan and get measurements?
As you can see, the red measurements deviate from actual more than 4 inches or so, so If you are presenting information to the public, you need to make sure you are not misrepresenting the data. Hiring someone to do the work means you need to ensure they are presenting the right data too. Personally, I would not use the data provided by either one as there is no guarantee it is going to be right – but how do you know unless you have another more accurate method to compare it to?
People’s solutions to this issue? Don’t show dimensions or the square footage. However, what do 99% of buyers think is valuable in having? The square footage and room dimensions, along with 92% of buyers want to experiment with furniture placement. So in my view, if you just show the layout without the detailed data, you are just going to piss people off. And, if your room measurements are off, you are doing a disservice to the customers looking at your listing and trying to figure out furniture placement, etc.
The bottom line is this. Buying a home is a huge expenditure. People expect to have accurate data associated with the property. Some of these apps may be free – but you get what you pay for – inaccurate and not usable data. Just because a photographer uses the same free app you can use does not mean their version of the floor plan is going to be any more accurate as well. The free Cubicasa plan does not include the square footage of the property, again what 99% of people want to know, and you do not know if the tax record is correct, as clearly illustrated above. Even if you did pay for the square footage report from Cubicasa, every brick house is going to be off. So, why not just provide the accurate data – it’s not that hard or expensive to provide the data that can be tied to the home, and you, permanently.
We can provide the accurate “as built” square footage and measurements, and our data has been accepted by tax assessors.
But what sets us further apart from others is we ultimately put the data and our editable floor plan tool into the hands of the homeowner, who can now do anything they want with it. They can add or remove walls, change the flooring, wall colors, virtually stage the home, use it as a landscape or pool planning tool, and even use our AI Boost feature to create high res 3D images like you see below of my home. This is all great marketing content to set you and your listing apart from others out there – market that the home has accurate square footage, that the home comes with a HomeDiary that you as the buyer can claim and then use the accurate floor plan in any way to help you manage, dream, improve your new home.
As an added bonus, you as the listing agent get permenent attribution on the floor plan provided, just like the screenshot below. This is one reason we have had multiple listing agents relist the same house at least 3 times now…each buyer went back to the original listing agent to relist with their floor plan and the tools we provide.
