What’s a proper fire cut? I thought that was a simple question, but I cannot find a clear cut (ahem) answer. So far I have:
Top of the joist must be 2″ shorter than the bottom. Ok, but how far down must the cut extend? Why 2″? Wouldn’t a 2×8 and a 2×12 require a different cut?
15*. Cool, but from what point?
Can I cut the top corner of the joist 2″ at a 45*? That’s the part that is going to cause a problem.
How about a spec relative to the bearing of the joist? As in: I have a joist which has 4″ of bearing on the brick wall. If I use the 2″ shorter method, the top of the joist is still in the wall and will(?) cause a problem.
Is there a rule of thumb (different thread?) as to how much meat needs to be left at the bottom of the joist for bearing?
So, what is your spec for this? I would like to establish a standard for my crew. To do this I need a clear definition and rationale of why. I get the rotation reason, but here I am talking rationale for how. If we are going to do it, after learning it requires no additional effort to do it right.
Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt. Thrill each side for four minutes at torchmark haut. Interrogate a lemon. Embarrass any tough roots from the samphire. Then bamboozle till it’s al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont – Posh Nosh
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What is a fire cut? Never heard thee term before
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Fire cuts are at the ends of joists in masonry construction. The joists rest on the masonry in pockets. I worked on many masonry homes in DC and Old Town. All of the joists had fire cuts tapered from 0 to whatever dimension to clear the brick. When a fire happens the joists fall out and do not disturb the masonry. Chuck Slive, work, build, ...better with wood
I see. I recall doing demo for salvage back in the seventies on old brick structures and seeing that as we pulled the joists out
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Chuck,I've got those in my house and never knew what they were called until today. I had erroneously assumed they were tapered to make them easy to install into the pockets, instead of preventing the walls from collapsing inward in case of fire.Thanks for hitting me with the clue bat!Best,
Steve'Man who say it cannot be done should not interrupt man doing it' ~ Chinese proverb
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Steve,
We restored and renovated many older homes. When we had to replace joists, we had to remove the surrounding masonry to get the full length joist in place.
We framed a couple of townhomes in Spring Valley and DC had a masonary code. The masons would run up the brick and block to sill height. We would set the joists and deck it. Then the masons would run up to the next floor. Very expensive construction.
Chuck S.live, work, build, ...better with wood
Chuck, I recall something about George Washington insisting on masonry construction in the new city of DC to ward off widespread fires, like the one that hit New York during the Revolution. Wonder if the fire cut is a leftover from that era?Townhomes in Spring Valley? Were they by the old Garfinckels on Mass Ave. by chance? Sounds like that takes a bit of lucky coordination to get dried in quickly.Best,
Steve'Man who say it cannot be done should not interrupt man doing it' ~ Chinese proverb
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Steve,
You are correct. Near the old Garfinkles, but one block in.
Has it stopped raining yet? ;-)
Chuck Slive, work, build, ...better with wood
thanks - I learned something today - "there's enough for everyone"
thanks - I learned something today -
I try to learn something new every day. The more I learn, the more I relize how much I do not know.
Thanks for your thread on grafting. Very interesting.
Chuck Slive, work, build, ...better with wood
One of my first jobs as an apprentice was to firecut every joist. Me and another fellow stacked the joists up and down with a strongback and brace at each end of the pile. I cut the joists with a chainsaw from the top straight down. Took longer to stack em than to cut em. Cutting the joists beats setting them, I did that for the first three weeks.
mike
Mike,
Never cut 'em with a chain saw. Nice!
Was it a Big Foot or free hand?
Trimmed some rafter tails with a cs on 8 x 12 shed roof, one day porch though.
Chuck Slive, work, build, ...better with wood
Another good way to look at the geometry is to compare it to beveling a door:When we bevel a door, what we're really doing is looking at that door in plan view. If we set the pivot point of a compass right in the middle of the hinge barrel, and set the pencil point at the latch edge of the face of the door, the pencil will draw an arc on the top of the door that shows that the distance from the pivot to the stop edge of a square-cut door is greater than the distance to the face edge.In practice, we don’t lay this out, we just bevel the door a degree or so extra to make sure that it doesn’t bind.Likewise, when dealing with fire cuts, it’s best to pick a system that always works, rather than lay it out each time. That means plenty of clearance, which might argue in favor of one, simple, angled cut.AitchKay
Chuck, this was in 1963.No such thing as a big foot then. Don't worry 'as I used my Oregon finish tooth chain.If there was a Festool I would have used that instead.
mike
http://en.wikipedia.org/wiki/Fire_cuthttp://books.google.com/books?id=9jDOJwQTV9wC&pg=PA54lpg=PA54&dq=fire+cutting+a+joist&source=bl&ots=y3P8NQYXUq&sig=3JqbJEF5BhS82YcQRzBySzzRcm8&hl=enei=n7omSqOrO5SG8gSw1rCBDw&sa=Xoi=book_result&ct=result&resnum=7Scroll down to last paragraph.Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
All the ones I have seen and have cut were full bearing on bottom and even with outside of pocket on top.
I have been trying to find more information. Best I can come up with is they are cut at angle from top to bottom so they are more free to rotate. When they burn through they tend to rotate.
"....so they are more free to rotate."That is correct. The fire cut prevents the joists from levering the wall outward as the joists fall in the during a fire. They are very common in old buildings with party walls. I did not realize that they were still required though. Most commercial joists are metal now anyway.DC
Still part of the code here, top of cut inline with inside of masonry.Rik
Yeah, that seems to be the consensus. I am looking for a detailed spec. My problem is what one guy thinks would solve the rotation issue may be an inadequate. I am thinking of telling the guys:The firecut must begin 1/2" proud of the masonry pocket. For its depth, draw a diagonal from the bottom of the joist, toward the end, which measures the height of the joist. Cut.Example: A 2x12 joist extending 4" into a masonry wall will be cut from 4 1/2" from the end at the top of the joist to 1" down from the top.If you use the same geometry for a 2x8 joist, you cut 1 1/2" down from the top. So:I think I'll simplify it to: Cut will be from depth of pocket + 1/2" at the top of the joist, to down 2" from the top at the end.Any comments?
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
I don't know if there are any specs, but I would think that if you take a compass and draw an arc along the top edge with the center point on the outer edge of the bottom bearing surface, and cut off just inside that line, that would let the beam rotate w/o hitting the top of the pocket.Mike HennessyPittsburgh, PAEverything fits, until you put glue on it.
That's basically how I arrived at my conclusion. The thing is, I was just reviewing the engineers drawings (no dimensions) and he has the firecut totally inside the masonry pocket. Go figure.I "re-invent the wheel" on a regular basis and was hoping that I could find a SOP spec prior/ instead of having a discussion with the engineer.Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
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NICE!! That diagonal cut is what I remember.
They can't get your Goat if you don't tell them where it is hidden.
That would work, although anything past the masonry face at the top is unnecessary.But speccing 1/2" past gives you some slop in case a joist slips in farther than you thought.And it lets you tell the guys, "If I can't see daylight at the top, you're pulling it out and re-cutting it!"AitchKay
Now all this has me wondering if a fire cut might alter the load specs on the joist to a degree
since it does shrink the joist depth if the cut makes it's way past the inside bearing surface of the wall?
I wouldn't expect the joist strength to affected. The max strength (and max joist depth) would usually be needed at mid span not where the joist bears on the wall. I suppose given some bizarre wood grain and weird load/stress something odd could occur. Check out how some of the trusses are designed. You can see how small they become where they bear.
A little too wordy for my simple mind.
How's this?Top of joist: Bearing length + 1/2" (up to 6" bearing).Down from top of joist (up to 16" joist): 2"Simple enough?Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
"Down from top of joist (up to 16" joist): 2"."I don't get that part. My solution uses a tape measure more than a formula:Bottom of joist: pocket depth minus a bit in length.Top of joist: face of masonry minus 1/2" in length.***Or, if your pockets are way deeper than the code requires, how about:Top of joist: measurement to face of masonry minus 1/2".Bottom of joist: top of joist plus 2 1/2".Based on the scientific theory: KISS.AitchKay
""Down from top of joist (up to 16" joist): 2". I don't get that part."Say the joist is a 3x12. Mark the joist end 2" from the top side of the joist. Mark will be 2" from the top side and 9 1/2" up from the bottom side. This method works for joists measuring 8" to 16" in height. Cool?Next: Let's agree the bearing is 4". Mark the top of the joist at 4 1/2" from the end. Next: Draw a line connecting the 2 marks. That's your firecut.Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
I think if you don't angle cut from top to bottom that it doesn't allow it to rotate enough. Wish I was more google savvy to find a answer. Maybe have to ask a engineer.
I get what you're saying: just knock the corner off. That should work, and in your example it does.Just make sure that the cut falls well inside a radius, set to the depth of the joist, and struck from the intersection of the bottom of the joist and the face of the masonry.An easier way to double-check that you have proper clearance would be to make your cut at a 45º angle. Then, as long as the joist insertion does not exceed the joist depth, you'll know without laying it out that everything is fine.Maybe we should ask an engineer at this point, but I have a hard time believing that one cut, from back of pocket to just clear of the masonry face, would be measurably weaker.And cutting once is always more desirable than cutting twice, so I'd still vote for that one, angled cut over cutting to length, then knocking off the top corner.AitchKay
You're formula should work with a 4" pocket, but a 6" pocket fails with a 2x8 joist.See drawing.As was said before, all one would have to do is take a compass and set the radius to the depth of the joist. Set the pin of the compass on the point where the joists bears on the face of the wall, and scribe the arc on the joist. If your firecut takes out everything outside of the arc, you're ok. If not, a more aggressive cut is needed.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Jon's drawing shows that just lopping the corner off is too risky -- some guy is going to cut it wrong some day, and you won't be able to check his work because it's buried in the masonry.Doodabug’s rule of thumb is the safest way to go: “All the ones I have seen and have cut were full bearing on bottom and even with outside of pocket on top.“Since it’s also the fastest way -- at least when the stock has to be cut to length -- I’d say do it that way.AitchKay