I will start inside the cabin and set the first interior wall. I have been instructed to measure the diagonal of the sill against the adjacent wall to get it perpendicular. Can someone elaborate on this?

From which points on the sill should I measure and to which point on which wall? Tips for making it as accurate as possible are appreciated.

The cabin has 4 load-bearing exterior walls, and the first interior wall goes straight out from about the middle of the long side.
 
How do you make a rectangle become a rectangle and not a rhombus (slanted square)? If you measure both diagonals, they should be of equal length in a perfect rectangle. The diagonal is the square root of the side times 2.
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garet said:
I'm starting on the interior of the cabin and putting up the first inner wall. I've been instructed to measure the diagonal for the sill against the adjoining wall to get it perpendicular. Can someone elaborate on this?

From which points on the sill should I measure and to which point on which wall? Tips for making it as precise as possible are appreciated.

The cabin has 4 load-bearing outer walls, and the first inner wall goes straight out from about the middle of the long side.
Forget about the diagonals!
It's not THAT crucial with the perpendicular. Maybe the outer walls aren't completely perpendicular, so what should you do then?

Instead, measure the new inner wall so that it's parallel with the nearest outer wall.
It's simple.
If the new wall is 2500 mm from the outer wall, it should be 2500 mm from the same outer wall at the other end too.
You can easily handle that with a folding rule or tape measure.

Simple!
 
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Sailorman
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What about the other side of the wall then? ;)

You could halve it towards the next exterior wall.
 
JOW said:
How does it turn out on the other side of the wall? ;)

You can halve it then towards the next outer wall.
I don't understand. What do you mean you can halve? What is "it"?
 
I mean that if you only set the wall parallel to one exterior wall, the other exterior wall can be more or less tilted/not perpendicular. You can then halve the error, so that the interior wall ends up midway between the two exterior walls.

The exception is if you are going to attach kitchen cabinets to the new interior wall. It can then be convenient to have it perpendicular to the exterior wall. This is then calculated with Pythagoras.
 
Or you can take out your laser that can draw lines on the floor and ceiling at a 90º angle :D
 
Well, no responses really helped me, so I figured it out and did it this way: I sawed the sill to the right length. Walked over to the short side of the house and placed it against the wall. Marked on the floor where the sill began and ended, and at the same distance from the wall so I got two crosses on the floor. Hammered a nail into each of the crosses.

Now I walked back with the sill to where it should be. Laid it in place where I thought it looked right. Fastened it a bit loosely. Measured diagonally from one end over to one of the nails I set by the short wall. Then measured the other diagonal. Removed the sill and adjusted it slightly until I was satisfied. Nailed the darn thing in place!
 
garet said:
Well, no answers really helped me so I thought it over and did it like this: I cut the sill to the right length. Walked over to the short side of the house and placed it against the wall. Marked on the floor where the sill started and ended, and at the same distance from the wall so I got two crosses on the floor. Drove a nail into each of the crosses.

Now I walked back with the sill where it should be. Placed it in what I thought was the right spot. Fastened it loosely. Measured diagonally from one end and over to one of the nails I set at the short wall. Measured then the other diagonal. Took off the sill and adjusted a little until I was satisfied. Nailed the darn thing!
I like quoting Ingemar Stenmark: There's no point in explaining to someone who doesn't understand :)
 
The 3-4-5 angle always works otherwise...
 
Yes indeed, why make it complicated ... ?

#9 agrees...
 
I was going to say 3, 4, 5... Measure 3dm on a wall, 4dm where you want the interior wall, then rotate 4dm until you have 5dm between the "players", you then have a 90 degree angle...
 
"The players" should be the spetsarna, annoying auto-correct...
 
lorens said:
I was thinking of saying 3, 4, 5... Measure 3dm on one wall, 4dm where you want the inner wall, then rotate 4dm until you have 5dm between the "players", then you have a 90-degree angle...
That is a great description of how to do it! Exactly what I was looking for! I will double-check when I get up to the cabin if I've also nailed this now that the sill is in place.
 
And of course, it works just as well with any multiple of 3-4-5. 1.2m, 1.6m, and 2m are usually a pretty good solution if you're working indoors and have a two-meter measuring stick.

Then there might be situations where it's better to adapt to existing, crooked walls as well. Or to compromise.

Mathematical curiosity:
A triangle where the sides are in a ratio of 3-4-5 is called an Egyptian Triangle. Long tables of such numbers have been found in Egypt.
I once listened to a lecture on the history of mathematics where the professor presented many theories about the purpose of these lists. Religion, astronomy, and so on. With my craftsman background, I had a more straightforward theory. If you're going to build large pyramids, it's good to know your angles...
 
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