Understanding iGUIDE Measurements

This article provides answers to frequently asked questions about the reliability of iGUIDE measurements. They can be split into a number of different cases.

Disputes about square footage

It happens from time to time that iGUIDE square footage is compared to square footage from other sources, and questions about which one is more reliable arise. There are a few factors that must be considered here.

First of all, as with any comparison, apples must be compared to apples. Square footage is just one number that describes a complex structure such as a house and there is more than one way to arrive at that number, depending on which methodology or measurement standard is used. Different methods mainly differ in which spaces are counted as excluded from the reported square footage. Differences may also come from how sloped ceilings in attics or shared demising walls are treated.

The iGUIDE measurement method is summarized here. The iGUIDE method essentially follows the Alberta Residential Measurement Standard (RMS) which currently is the most comprehensive standard in North America. Alberta RMS is based on the ANSI Z765-2013 standard for single-family houses and extends it to condos and apartments in multi-family residential buildings. Alberta RMS was created because square footage in municipal tax records proved unreliable as those values are produced without following any prescribed standard and comparisons between any two properties may or may not be comparing apples to oranges.

Secondly, any real measurement has an associated measurement uncertainty or measurement error. The iGUIDE camera allows measuring distances to walls to within 1cm uncertainty. For a typical house, this can mean up to 5cm uncertainty across the whole house when several rooms are stacked or about 0.5% for distance measurements for that typical floor size. The resulting uncertainty in square footage will be about 1% (double the distance uncertainty). Therefore, when comparing iGUIDE square footage to square footage from other sources, any differences smaller than 1% (e.g., 25 sq ft for a 2,500 sq ft house) are meaningless as they are below the measurement noise and thus must be ignored.

If the difference exceeds 1%, then the measurement uncertainty of the second number must be examined and the combined uncertainty must be used during comparison. For example, if measurement A has 1% uncertainty and measurement B has 3% uncertainty, then the combined uncertainty is 3.16% (square root of 1% squared plus 3% squared). If the difference between A and B is less than 3.16%, then the two measurements are said to be the same within the measurement uncertainty.

If the second measurement uncertainty is not available, then the iGUIDE measurement must be presumed as the most accurate measurement, as no meaningful comparison can be made.

Both Alberta RMS (residential measurement standard) and BOMA (commercial space measurement standard) call for a maximum allowed measurement uncertainty of 2% when reporting square footage measurements. As seen from the above, iGUIDE technology meets and exceeds these requirements.

Can you look over the iGUIDE again and make sure the numbers are correct?

The Drafting Team goes through a Quality Assurance process and thoroughly checks every iGUIDE before it is uploaded to the Portal to ensure that all floors are drafted correctly. Please provide more specific details as to where you believe any discrepancy may lie to allow us to determine where any confusion exists and provide better explanations.

We encourage you to use the on-screen measuring tool in the iGUIDE with which you can measure anywhere on the iGUIDE floor plan. In the PDF floor plans, there are arrows indicating the dimensions of each room and where those measurements start/end. The colours indicate which areas are included in the total square footage with any white space being excluded from the total.

Why do iGUIDE numbers differ from tax records?

A tax record's square footage is not considered an accurate total unless the numbers have been independently verified. The measurements are calculated from an estimation of the outside of the structure. The estimator often has not entered the structure and therefore would not be aware of any areas that would be excluded from a total interior square footage area, such as areas open to below, cold rooms, the footprint of the 2nd floor being different from that of the 1st floor, etc.

Why do iGUIDE numbers differ from the builder’s floor plan?

Builder’s floor plans describe what the builder was intending to build (build-as). Changes occur during home construction for many reasons and resulting floor plans may differ from builder's blueprints. iGUIDE floor plans describe what was actually built (as-built) and what a real estate agent is selling. It is recommended that after the construction is complete an independent company verifies room dimensions and total square footage as they may differ significantly from the original builder's floor plans.

Builders use their floor plans to sell homes that are not yet built and are covered by disclaimers of potential deviations in the sales contract.

Why does the sum of the areas of all listed rooms not add up to the total square footage?

The iGUIDE property details section lists the dimensions and floor areas only for major rooms by default, such as kitchen, dining, living, bedrooms, etc. Floor areas for those rooms are interior areas and are measured by paint-to-paint. Areas of other spaces such as stairs, hallways, closets, void/open to below spaces, and footprint of interior walls are not listed.

The total floor area is calculated by our software and includes all of the floor plans, only excluding prescribed areas such as attached garages, balconies, cold cellars, and spaces not habitable all year round, e.g. sunrooms.

Rounding can also occasionally be a factor. All displayed floor areas are rounded to the nearest integer. The total floor area is computed before rounding and may not equal to the sum of displayed floor areas. Sometimes this can result in the total floor area being about 1 square foot different than the sum of areas per floor, as they appear on screen and pdf.

Requests that go against the iGUIDE Drafting Standard

The Drafting Team drafts every property according to the iGUIDE Drafting Standard. Photographers can leave the Drafting Team a note in the uploaded data indicating a special request. These requests can also be made after the iGUIDE has been completed.

If a special request that goes against the iGUIDE Drafting Standard is fulfilled by the Drafting Team, the requester assumes responsibility if the measurements are brought into question. Charges may apply depending on the request.

Please draw in the garage/deck without iGUIDE camera data

We require that measurement and visual data be collected in order to include a space on the floor plans. The Drafting Team can only use measurements provided by the iGUIDE camera and will not accept measurements or dimensions provided through any other means.