How To Measure A House For An As-Built Survey – Step 3
If you have read my previous articles, you are now well on your way to creating an accurate As-Built floor plan. To recap, I covered the first two steps in those blogs:
With this article we will cover the 3rd and final step of a basic As-Built survey – Drafting. This is the crucial step where you take all of your field information (sketches, measurements, photos, etc…) and turn it into an accurate, useable floor plan drawing. For the purpose of this article I will be covering the drafting process using a CAD software program, such as AutoCAD, although the same basic principles and processes could apply to hand-drafting as well (it would just take longer).
Unlike a design drawing, where everything fits perfectly according to the architect’s vision, an As-Built drawing is never “perfect”. This is because it comes from a real, existing building – and buildings are not built perfectly. Corners are not exactly 90°, surfaces are not perfectly linear, wall thicknesses are not precisely uniform, and so on. But no architect that I know wants an As-Built drawing that shows all of these 1/16” or .01° imperfections – it would make the plans much more difficult to work with. So the goal of the As-Built surveyor is not to eliminate error (which is more or less impossible anyways), but rather to minimize error, by establishing a tolerance and knowing where and how to make minor adjustments to their field data which results in the best overall As-Built plan. For this reason, drafting is where the true skill and craftsmanship of the experienced As-Built surveyor are on full display. But that doesn’t mean you can’t learn!
Before we get started with the process, just a couple more things related to the general “philosophy” of good As-Built drafting:
- Think about what tolerance you are comfortable with – or in other words how much you are willing to adjust your measurements. In some cases 2-3″ might be OK for you depending on how you intend to use the As-Built plans. For me, since I am measuring with a precise laser device and since I’ve been doing this for awhile, I don’t want to make any adjustments more than 1/2″.
- When you do make adjustments, try to make them to the longer and/or less critical measurements. So for example if you need to make a 1″ adjustment to make something fit, don’t make it to the 3′ door opening (which is a standard size) – make it to the adjacent 10′ wall segment.
- Always look for symmetry/consistency in the building as you are drafting. Buildings aren’t put together randomly – they are intentionally designed and constructed to be structurally sound and functional, as well as beautiful. So for example you might notice as you are drafting that an exterior door in the back is only 1/2″ away from being aligned on center with the front door entrance. Consider making the adjustment so they align perfectly on your As-Built.
OK OK you got it and you’re ready to draft your house! Here’s a step-by-step process you can use:
- Draw the exterior perimeter of the house. Start in one corner and go all the way around back to where to you started. At this point you will have a “closing error” on the X and Y axis. Hopefully if the house is square and your measurements were good you are within about 1-3″ on each axis (any more than that and you might want to consider remeasuring – depending on the tolerance you are comfortable with). You will need to make adjustments to some measurements to reconcile that closing error – but which way should you adjust? Should you make a measurement on one side of the house longer? Or make one on the other side shorter? Or a little of both? Don’t make that decision just yet – hang tight and proceed to the next step.
Exterior perimeter drafted with Closing Error in upper right.
- Draw and adjust the “primary” interior walls. Start by offsetting the exterior wall line to show the thickness of those walls, and then use more offsets to place the main horizontal and vertical walls in the house, including those wall thicknesses also. The goal here is to see how well the interior measurements fit within your exterior perimeter – this way you will know which way to adjust the Closing Error on the exterior.
- For example, if there are 5 primary vertical walls across the X axis of the house, and the last dimension is coming out 2″ short, then you know you should adjust your exterior measurements in the direction that helps minimize that error on the interior.
- Make all necessary adjustments to all walls to minimize the amount of adjustment that you make to any one measurement. For example don’t adjust one measurement by 2″, adjust multiple measurements by 1/2″ to make it fit.
- You can also use your interior “overall measurements” (explained in my last blog) at this stage to give you even more guidance as to which way to make minor adjustments.
- This is the KEY Step for maximum accuracy! When this step is done you are 90% done with the project – everything else is just putting a bow on it.
Primary interior walls drafted with wall thickness. Clouded areas are telling me where to make adjustments.
- Draft the rest of the walls and door openings. Now that the primary walls are all placed and adjusted, this should be easy. You will still likely need to make some minor adjustments as you go, but primary walls should not have to move again if done correctly.
All walls and door openings drafted and adjusted where necessary
- Add windows and doors. Draw in these elements or better yet use blocks.
- Clean up the drawing. One of my pet peeves is sloppy As-Builts! Look around for any lines that need to be fileted, extended, trimmed, deleted, or anything else. Make it look great!
- Quality Assurance. Look through your photos and your go over your entire sketch one more time to make sure there isn’t anything you may have missed or drawn incorrectly.
- Add any final details. Annotations/labels, dimensions, title block info, or anything else that you want to add to the plan.
Final drawing with blocks, millwork, plumbing fixtures, annotations and dimensions
Well, that’s it! You have now created an accurate As-Built floor plan of a house. Like anything else in life it takes practice, and I obviously couldn’t cover everything in these articles but I hope that you got something out of it and are willing to give it a shot.
Now if you care to return the favor I would love to hear what you think, or if you have any questions, suggestions, or praise in the comments below.