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Calculating Joists | Buildsum | YouTubeToText
YouTube Transcript: Calculating Joists
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So in this video. I want to look at calculating the number of joists that we need
For our floor and once again whether it's a platform floor or cut in floor doesn't matter we can use the same method
so we're looking at choice this time
so we'll get around
get a plan view there's our bearers that we worked out in the last video and this time we'll look at the joists, so
The formula is similar, oh, before we get to the formula
remember that we need to make take off our brickwork and our cavity on either side on a
Brick veneer house, so we actually get the dimension of the floor not the dimension of the Brickwork
so commonly 150mm on
either side or 300 on both sides
taken off the Brickwork dimension
And down here
where we have our internal corner it works out that we don't need to take anything off these internal dimensions or the
Dimensions of the walls that make up the internal corner because whatever you take off here you
just end up adding back on here so you don't end up taking anything off
so they stay the same as they were in the bearer video as
I was saying before the formula for joist is similar, but not exactly the same
this time we're going to take the length of the building the length of the area and
divide that by the Joist Spacing
so if we're going to use this area here as we did with the bearers
We'll take the length this way
rather than the width so the length of the area
and again we have to add one at the end of it, and then we also add an extra joist for every external wall and
any load-bearing walls that are in that area as well, so
formula in this case would be all the actual figures
4.570 divided by 0.600 which was our joists spacing
plus one
plus two because you're gonna have an external wall at this end an external wall at this end and there's no load bearing Walls
in this building
So we worked that out and it ends up with 7.617 + 1+ 2
We round the 7.617up to 8
Because we can't have p0.6 of a joist
So 8+1+2
equals 11
so we're gonna Have 11 joists in this area and
There they are there so two doubles at the end
doubles at this end and then 600 centres in between
for our second area over here
again, we're going to take the length dimension or the dimension
the length of the bearer basically if you'd like
so Area 2 = 2070
divided by 600 and
This time we have to add the 1 because we don't have any extra joists over here unlike what we had with the bearers
So we have to add the 1 and we have to add 2 because again external wall here
External wall here, and no load-bearing walls in the middle
So that comes out to 3.45 plus 1 plus 2 so that gets rounded up to4
5, 6 so 7
joists for Area 2 and
Total 11 and 7 obviously gives us 18 joists. So there's our 18 joist positioned on the actual frame
For the timber order
we're going to need 11 joists at
2.4 again, you could go
2.100
but it's pretty close you're only playing with 30mm
depending on you know if you knew the manufacturer and you knew they're gonna be
Spot-on 2.1 or a bit over then you could go 2.1's, I played it safe
so when I rounded up to 2.4's
this area here
and oh sorry also on this one
you have to allow for some lap on this bearer here, so you're probably better off going for 2.4's
and with these ones here
2.5 so 2.5get rounded up to
So 7 / 2.7 for that area
So there we go. That's the number of joists that we need
for this floor frame
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