Measuring dimensions of existing house dimensions for addition

Old 03-08-07, 04:33 PM
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Measuring dimensions of existing house dimensions for addition


I apologize if this is the wrong section, or if this has been asked before but I couldn't find any information on it.

When planning for an addition, how does one go about obtaining very accurate measurements of the existing house for drawing up plans? We have a 1500 sq. ft. rambler and are considering a second story addition. I'm pretty good with AutoCad and would like to play around with preliminary layouts. However, I am having a tough time finding the exact outside dimensions of the home. I can't get access to the top plates in the attic to measure the footprint as there is a ton of blown in insulation above the pre-existing batts. When I measure interior room dimensions, I always end up off by a couple inches here or there by the time I get through the whole house. For instance, on the back wall I must measure a bedroom, closet, bathroom, another closet, kitchen, entryway, etc... when I add up all the dimensions and compare them to the front wall length (obtained by the same method), the two figures disagree by 1-1/4". Finally, I'm worried about anywhere which might be out of square throwing off my drawing/wall layout dimensions.

So... how would I go about measuring? I can measure outside, but I have cedar shake siding, and don't know the thickness of the sheathing, etc... I'm at a loss here. Will a tape measure suffice, or must I use a more exact method? How precise do the dimensions on blueprints have to be compared the the actual? 1/16"? 1/2"? 1"? I assume some of this inaccuracy can be dealt with in the field during construction.

Lastly, what is usually done to ensure that the first floor is level when adding the second floor. I am fairly sure that due to settling (and an 8' wide window in one wall) that the top plate of the existing wall has sagged. When I put up crown molding, there was at least 3/4" sag over the span of the window below the rest of the ceiling on one wall. If it isn't level, how would that be dealt with? Shim the second floor walls somehow?

I know this is a lot of information and questions, but I'd appreciate any help that you can give me.

Thanks much.
Old 03-08-07, 06:22 PM
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Measuring dimensions of existing house dimensions for addition

If you are just trying to create a peliminary plan, you do not have to be that accurate. An overall dimension within 1 1/4" is fine for planning and you may be inferring that your dimensions are what is there - that is assuming additional liability. You are just planning now. Let the designer and contractor take their dimensions.

You should just be concerned with where the rooms are and will be and about how big they will be. Just come up with approximate door/window locations and sizes.

One of the critical things will be the approximate size and location of the bath and where plumbing could be run.

Since you do not have to create details, leave that to the professionals that have experience in the unknowns will will pop up.

Your home is what it is, no matter what your preliminary planning drawings say. The addition will have to fit with what is there.

Old 03-09-07, 01:16 PM
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Like Concreteman said, just know where your new rooms are going, and the size of your addition. For instance 24 x 48. It may be 23' 10'' and 48' 4". That does not matter. I build these additions all the time. We are presently working on an addition where the owner, a pro at Auto Cad, had all sort of drawings for me. He could not understand how we built the whole addition which was 12 x 18' without looking at his drawings. The house is what it is. We build on to the existing house. If adjustments in squareness or problems with the existing house being out of level, these are not problems for us. It will be that way when we are done. However, the new addition will be square, plumb, and level, and fit just fine. They will probably even fix the dip above your picture window also if you tell them about it. Good Luck. These are fun projects.
Old 03-10-07, 01:49 AM
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If you just HAVE TO get accurate dimensions, you could measure the insides of the house and allow for the thickness of drywall or plaster (remove a receptacle plate and measure with a plastic ruler) and interior walls. But, as the others have stated, it is what it is. It is unlikely that a discrepancy of 1.5" somewhere would affect the second story floor joist design.
Old 09-26-07, 11:20 AM
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Maybe this is a little late to help the original poster, but maybe someone in the future will find this helpful.

I agree with others. You don't need super accurate dimensions - espcially for planning purposes.

It seems to be nearly impossible to obtain a 100% accurate existing survey, so you don't want to drive yourself nuts trying to make one so. For the real cirtical pieces of the addition, like cabinetry, whoever is building those pieces will need to take field measurements anyway.

Measure the door jamb to get a feel for the wall thickness. Try and measure the base of the outside foundation and take note of the exterior materials.

Take individual room dimensions on the interior, but also try to get overall runs between several rooms, or down hallways (be careful to keep your measure as close to square as possible). 50-100' tapes can be helpful here.

If ceiling heights are important take several spot measures around the room as both floor and ceilings sag.

It's easier to assume wall thicknesses in newer houses, but older houses often don't have typical stud and finish dimensions.

The more measurements you have the more you will be able to find inacuracies and lesten head scratching time. This is especially true when you're drafting in a different location than the measuring took place. Pictures are extremely valuable in this situation (though it always seems you never take a picture of the location in question).

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