About As-Built Surveys
What is an As-Built Survey?
The Most Critical Part of your Remodel
It is important to first understand what an As-Built plan is. At PPM, we measure the inside and outside of a building with very accurate lasers, and then create a drawing which shows the exact dimensions and layout of the building. That’s an As-Built plan. Architects, engineers, designers, and construction professionals use these as the foundation of their residential and commercial remodel projects.
The As-Built survey is the first part in the two-step process that makes As-Built plans possible, and is all about accurately gathering measurement or placement data. The second part, or the brother of As-Built surveys, are As-Built drawings which are a communication of the data from the survey as clearly and concisely as possible.
This article is all about the first step of the process. We’ll go over traditional methods, new surveying technologies, and why such accurate As-Built surveys are important for creating reliable drawings and models.
An As-Built By Any Other Name Is Still An As-Built
The architectural and construction industries are continuing to settle on the term “As-Built” to describe the process and the resulting plans that come from measuring an existing building. Other terms and spellings include: Site Survey, Existing Conditions Drawings, Record Drawings, Measured Drawings, Asbuilt (Asbuilt Drawings, Asbuilt Plans, Asbuilt Survey), As-Build or Asbuild (Drawings, Plans, Survey).
“I Have These Old Drawings of my Building – Are They As-Builts?”
First, let’s discuss the difference between a blueprint and an As-Built plan. Most people have seen blueprints of a building at one time or another. A typical blueprint is a design drawing, which shows the intended or proposed layout of the building. An As-Built drawing, as the name suggests, shows the current layout of the building “as it was built”.
As-Builts do not deal with the hypothetical but instead with the actual. This is a critical distinction, because a constructed building almost never corresponds exactly to the original design drawings. For this reason, when starting a new remodel project on a residential or commercial building, the architect will almost always create or commission an As-Built survey, rather than trying to rely on existing building plans.
Discovering an error on the plans can result in additional costs or delays to the project. Now that we’ve gone over As-Built plans, lets jump into the traditional methods of creating As-Built surveys.
Traditional Surveying Methods
Four simple ways to gather different degrees of on-site information:
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Photos only
One way to obtain the answers you need on-site before a renovation is by simply taking photos. This can assist in the design process, and answer questions you might have before proceeding.
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Single-line
Sometimes a quick single-line or bubble diagram is all you need to achieve your goals. This can be completed quite quickly on-site and does not need to be to scale.
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Sketch
Sketching can be very helpful in supporting your design in the case of Interior Elevation or Perspectives. This can also be done roughly and may not require measurements.
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Measure
If drawings need to be to scale, such as when they’ll be used to create new construction documents, then you’ll need to go to a higher level of accuracy and measure the existing conditions. Later, we’ll discuss varying ways to gather more accurate measurements.
Step 1: Sketching
Remember that sketching does not need to be to scale. All you need to do is make sure that there is room to write all the measurements you need, and that it is visually easy enough to follow back in the office.
Using different colors to mark different measurements and drawing types is helpful, so that your eye will catch each segment accordingly when drafting . This will help save time because you won’t have to send time hunting for what you need in the future. Getting as much sketching done before measuring is recommended so you can focus solely on measurements when the time comes. The better your sketching is, the easier your measurement process will be.
With proper sketches, any structure can be measured more quickly. You can sketch any ornamentation to the degree of precision you desire. Be sure to leave room to write in measurements and plan ahead to add in your heights, or “z” axis.
Step 2: Plan-View Measurements
An important step that many people skip when measuring a structure is going around the exterior faces. Often times, a wall thickness at an exterior wall is taken, and then only interior measurements are taken from there, but we consider measuring the exterior walls to be crucial. When measuring, you want to start with the “perimeter” or exterior faces and measure all the lengths 360 degrees around the building.
Pro tip: to check your work, add up all “x” values and all “y” values. If the sum of all “x” values on each side of the building add up to the same number (or very close), then you’re on the right track! Next do the same for the “y” values. This can of course get complicated if your structure has curved walls or angles that aren’t 90 degrees. In this case, your safest bet is laser scanning, which we’ll discuss later.
In the sketch above, you may notice there are some “overall” measurements as well as small, incremental measurements. This is a good system of checks and balances that will not only improve overall accuracy, but it may save you in the event you have an incorrect measurement or notation.
Don’t forget to get good photo coverage as well. This will help you verify that what you are drafting is indeed correct. Occasionally, we’ve seen errors that don’t appear as errors on paper, but are obvious when looking at an image.
2nd Pro Tip: Bring vellum! This can be helpful if you need to add items and you’re out of room to sketch them or write down measurements. This is especially useful wen adding detail items like electrical faceplates, cabinetry, and RCP items. The image above shows the previous sketch with a sheet of vellum over it. This allows us to use the information from the first sketch to add additional information without having to re-sketch all walls and doors.
Step 3: The “z” Axis
Now we can talk about collecting the “z” axis measurements, or height information, using traditional methods.
You can use a tape measure to measure all the risers in the stairs, or drop it down a balcony, run it up a wall, etc. A Laser Distance Meter, or “Disto”, can perform trigonometric functions instantly to get you heights in all sorts of ways. The first two of these tools you might already be using to measure all other aspects of your plan.
This third tool is used exclusively to gather height information and is called the Zip Level. This is an excellent tool invented, distributed, and repaired if needed by a company out of San Diego. Zip Levels use displacement to read heights anywhere within a 50-foot radius.
However you’ve collected your height measurements, make sure you have them in all the places you’ll need them. Most areas are obvious, like the tops of any steps and staircases. Measure what you’ll need to see in Exterior Elevations and Sections.
Make sure you have either some basic height and good pitch information for your roof. If it’s safe to get on the roof you can gather as many heights as possible.
Don’t forget the heights of openings such as windows you plan to show, or heights of items like wall sconces if you plan to produce detailed Interior Elevations.
Laser Scanning – The New Era
What is 3D Laser Scanning?
Updating or even replacing a proven method for doing something to utilize the newest technology isn’t easy no matter what industry you’re in. The first step you take is the most important, and the rest is hard work and diligence. Even though it may be difficult to transition, making the change to Laser Scanning as a survey method provides you with several benefits such as:
- Fast acquisition of As-Built data using 3D Laser Scanners that utilize LiDAR technology
- More accuracy than any measurements that can be taken by hand thus reducing the odds of human error dramatically
- Technology that can be purchased, rented, or contracted as a service
- A solution that allows you to get more data than needed to complete drawings and models for most projects
- A “digital twin” of any property that allows you to “visit” the site from the comfort of your office and pull additional data if the scope of your project changes
Terrestrial and Mobile LiDAR Technology
Terrestrial, or stationary, scanners sit on a tripod and spins to gather 3D data from one position. After scanning hundreds of positions with good overlap, you can bring all the data together onto one big dataset for your project.
Mobile scanners allow you to get a similar end result, but by utilizing an algorithm called SLAM (Simultaneous Localization and Mapping). The scanner and accompanying software allow you to gather the 3D data while simply walking through a space. This dramatically minimizes the amount of time needed to capture the data in the field.
These Scanners All Use LiDAR Technology
Light Detection and Ranging is a method for measuring distances by illuminating an object with a laser and measuring that laser beam’s reflection with a sensor. Each illumination can be considered a measurement. Each single measurement is logged and throughout the course of the scan, millions of measurements are taken in all directions.
Mobile Scanning and Processing
Using a mobile scanner is preferable if your time on site is limited. Once the scan is complete, you need to use the SLAM algorithm software which interprets all the measurement and movement data from the scanner and produces the 3D Point Cloud. Since most individual scans take only 15-45 minutes, this will give you time to process the scan on site to check your results before you leave.
Reviewing your complete Point Cloud on site is essential to ensure accuracy. Most errors in scanning or processing can be spotted quickly, and actions can be taken to ensure the overall accuracy of your project when the time comes to draft or model.
The Point Cloud
Once your scan has processed, you’ll need to review the output and ask yourself – Did I cover all areas? Are there any flaws or errors? Reviewing your data well before attempting to create a set of As-Builts from a point cloud is a must. If there are any kinds of errors with your cloud – which do happen, then using that bad data can either stop you in your tracks when you’re drafting or modeling, or worse: result in an incorrect set of As-Built plans.
Most scanners have a range of hundreds of feet, which can produce a lot of data outside of your project that you don’t need. You may need to clip or crop your point cloud to reduce file size by getting rid of this unwanted data. If you have to produce multiple point clouds for a large or complex project, it will be important to get comfortable with Point Cloud software that will allow you to merge or register your clouds and more easily manage your data.
Using the Point Cloud
In order to produce items such as a floor plan, you need to create a slice of the point cloud at a desired height and use that view to start your As-Built drafting or modeling work. In addition to cutting these slices, you’ll want to be able to move and rotate the clouds to get any view or perspective you need on the property to perform your work. While there certainly is a learning curve, any CAD or BIM software that supports point clouds can do this for you easily.
Looking at a Section throughout the project or even before you start your work is a good idea, you’ll be seeing the structure in a way that you could never see in person, unless you happen to have the biggest chainsaw ever made and permission to use it. Having Point Cloud data is extremely beneficial over measuring with traditional methods when Sections need to be created for the plan set.
In Conclusion
Scanning your project will prevent costly revisits to the site due to errors and will reduce your time spent on site. The type of scanner you use will be dictated by your needs and the level of detail required. Your scanner will create a cloud made up of millions of data points. Knowing how to manipulate the Point Cloud in your preferred drafting or modeling software is crucial to using your survey data.
What Is An As-Built Survey? It’s What We Do!
Helping our clients, and their clients, to have a Worry Free renovation experience using PPM’s As-Built plans is the Purpose that drives us each day. To me, the value of good As-Built drawings is self-evident: It’s why architects and other industry professionals keep calling PPM to help them get a great start on their remodel projects.
Give us a call today if you are interested in A Better Plan for your As-Builts.
About PPM
At PPM, our goal is to help set you and your project up for success from the start. While we are dedicated to tried-and-true process and deliver consistently accurate plans, success is not just in the numbers – it’s a feeling of trust, confidence, ownership and teamwork. Our team is committed to Core Values that drive our business and our clients’ success. We’re here to support you every step of the way.