Measured Drawings for House Addition



I've never worked on an addition... only new, ground-up projects in my career up to this point. My issue is that it's impossible to get accurate dimensions of the existing house. How does this work with liability? Do I just dimension everything with "Verify in Field"? Any potential pitfalls that I might be unaware of?


Jul 12, 18 2:05 pm

Why is it impossible to get accurate dimensions of the existing house?  Yes, "verify in field" is always your friend, and there's other boilerplate language about existing conditions and who's responsible for unforeseen conditions uncovered during construction and such, which you should crib from a good master spec.  But regardless of all the disclaimers, I've never had an addition project where I couldn't get good field measurements, to within 1/2" tolerance.    Is your issue related to being allowed to access the property? Or is it one of not being able to access certain portions? Or is it that you don't know how to field measure?  (I don't mean to imply that you don't know how to do that, or that you should know how - I'm just trying to understand your question better.)

Jul 12, 18 2:14 pm

Nearly all of my experience has been with existing structures, renovations + additions, and I've never once had an issue getting "accurate" (in quotes since acceptable tolerances vary) dimensions.

V.I.F as a general note is always a good idea, mostly to cover your own ass.

Jul 12, 18 2:50 pm
Non Sequitur

Get a couple of student interns to run around with measuring tapes and input data straight to CAD/BIM on site.  I've personally gone and measured many projects with existing conditions... sometimes more than twice just to make sure. 

Jul 12, 18 3:06 pm

If you do it by hand, take running measurements, like lay a tape down and tick off all the openings and columns instead of measuring each and adding them up. Makes it a lot more accurate. If there are critical things, measure them explicitly. Take good notes that you can actually read. Take a ton of pictures, you can cover anything you miss with pictures and some interpolation.

Jul 12, 18 3:10 pm

If a part of the site is inaccessible, you just have to do your best with the drawings with what you can see - sometimes binoculars can be a lifesaver.  Add copious notes on your drawings that all dimensions are to be VIF, and expect some change orders for those areas.

Another option, if you have the budget, would be to hire a probes contractor who can bring a lift or set up scaffolding where appropriate.  They can also help you take apart small areas with hand tools just so you can see what you need to see.  They'll also patch it back up and help you with getting material samples if that's something you need.  We often do this, but generally it's for larger multi-story structures where stone/brick/painted wood may look deceiving from ground level.

You may also want to look into companies that work with drones.  This is more helpful for conditions analysis, but they may have some new technology to help with measurements.  Not sure.

Jul 12, 18 3:19 pm
On the fence

Overcomplicated something simple.

Jul 12, 18 4:14 pm

Thank you all! This is helpful. It's a house from the 60's and measurements vary all over the place. Walls are slightly crooked. Finish thicknesses are inconsistent. It's a super incoherent split level with multiple additions over the years. It's a Frankenstein of a house. And I'm a one man crew. I foresee multiple site visits to check and recheck measurements. You all combined to cover all the angles, so thank you!

Jul 13, 18 12:59 am

If you are alone, take a clipboard, graph paper, tape measure, laser measure and a pad of Post-it notes. The laser will help with the longer measures and ceiling heights. The tape will help with some short measurements like thickness of a wall. Stick a Post-it to the jamb of a door to laser measure from a wall to the opening. Sometimes there is furniture, or stuff attached to the wall and you can't get a straight measurement. Don't go overboard with precision. 1/2" or 1 cm is enough precision for measuring an existing building.

Wood Guy

The laser measuring device is key. This one is good enough:, $60 and easy to find. Just do your best to keep the line perpendicular to the wall or the length will be off. In most cases, wall thickness is best measured at doorways--from the back of casing to back of casing. (If these tips seem obvious, you haven't seen what I've seen...)

It helps to develop a system. I measure a lot of existing homes, and always follow the same steps: measure room overall dimensions in both directions with a laser, at two locations if dimensions are suspect. Then ceiling height, near an exterior wall, using the laser. Then put the laser away and pull out a tape measure to for locations to windows and doors, measured to interior of jamb or extension jamb. Then measure from floor to top of window sill and bottom of head jamb. Then check wall thickness as I move to the next room. After interior is completely measured, go outside (checking exterior wall thickness at doorway) and measure typical distance from grade to siding and siding to soffit, fascia height if I can reach, typical overhang from foundation to BACK of siding/face of sheathing.

I also take copious photos and use Sketchup's photomatch feature to fill in any blanks, but that's an advanced technique. 

Wood Guy

I also always measure in inches, which was hard to do following a career as a carpenter using feet-inches. By only measuring in inches I never get confused between 32" and 3'-2", etc, it saves time on each measurement, and it's faster to input to Autocad (other programs may vary).


Wood Guy, your link is broken. Which one do you use? I need to upgrade from the tape measure.

Wood Guy

tintt, it seems links to the specific devices on the Bosch site don't work. Here is their overview page:

I wasn't showing the one I own, which is old, bulky, and not backlit. I just put this one in my shopping cart on Amazon:

Every contractor I know has a Bosch laser measuring device of some sort, and the architects I know who have them also use Bosch devices. I recommend a backlit screen and the ability to change to inch-only measuring.

Focus on what's important. In renos think "match", "align" "center", etc. instead of measurement. Communicate the intent and provide references as necessary for the contractor to work it out onsite.

Jul 13, 18 10:41 am

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