I am not advocating sloppiness, just practicality. If you measure the walls of a room that are notionally square, you will almost certainly find that they are a few millimetres (at least) off. Even if you measured so precisely that you know the exact angles between the walls, no one would draw it off square unless they had a very high pain threshold. It would lead to an enormous amount of additional work.
When I have professional measured surveys of old buildings done, they do try to show things that are off square and out of plumb. But working with that is really hard. And in the vast majority of case, you simply don’t need to.
Obviously, if it is an academic exercise, that may be different.
When measuring an existing structure I prioritize each wall’s centre. You’ll find that wall thickness varies quite a bit due to drywall mud buildup/other material inconsistencies, which will make the wall measure out of square much more than it is, if it is. If you’re doing finishing work, obviously you’ll want to consider this; but for structural work, it’s much easier to measure an existing building based on each wall’s centre.
Really? I need to understand that. How do you go about finding the wall centre in the first place? I’m not clear from what you say whether you are talking about the centre along its length or across its thickness. Either way, this is a technique that is new to me.
By using a combination of judgment and construction knowledge it’s pretty easy to calculate a walls thickness then divide that in half, while considering the variables of each material. Centre being the centre of thickness as is typical in construction.
Right, so you are talking about thickness not length.
So how does prioritising the thickness from wall centre work when drawing something up? I would normally just measure the thickness of the wall. Then, if I need to know it, the centre of the wall is obviously half the thickness. I think I must be missing something.
Throwing in my point of view from my experience, both drawing walls and swinging a hammer. Best practice for existing construction is to dimension from/to face of wall (FOW). For new construction is to dimension from/to face of stud (FOS). The priority being to provide accurate (to your chosen tolerance), verifiable and constructible dimensions. Good Luck.
I have done kitchens in several houses that are seriously out of plumb, level, and square. A SketchUp model is good for getting the proportions and appearance right, but I always have to leave allowances for fitting the new against the old. A model that captured all the out-of-whack details wouldn’t really help much.