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    Default Kerf cuts...a little more info please.

    OK...I am till studying the ventilation section of the essentials book, and read that kerf cuts can be performed to determine the direction of fire spread. Little else was explained, so I was hoping for some schooling here.....

    How long do these cuts get made?

    Are they just the width of a chainsaw blade?

    Are you actually looking for fire through these cuts, or just smoke?

    How well do they work on peaked residential roofs?

    Thanks!

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    Quote Originally Posted by SWLAFireDawg View Post
    OK...I am till studying the ventilation section of the essentials book, and read that kerf cuts can be performed to determine the direction of fire spread. Little else was explained, so I was hoping for some schooling here.....

    How long do these cuts get made?

    *A foot or two is more than sufficient.*

    Are they just the width of a chainsaw blade?

    *Yes.*

    Are you actually looking for fire through these cuts, or just smoke?

    *Either/Both.*

    How well do they work on peaked residential roofs?

    *Very well.*

    Thanks!
    A kerf cut can tell you a great deal about the attic conditions below without having to make a full size vent hole.
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    So a kerf cut with no smoke coming through "could" indicate that there is little or no fire/smoke below that location?

    And that is assuming the entire attic has not been decked with plywood like mine is? I'd have a hard time venting my attic/ceiling.

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    Quote Originally Posted by SWLAFireDawg View Post
    So a kerf cut with no smoke coming through "could" indicate that there is little or no fire/smoke below that location?
    Yes... and if smoke and fire come through the kerf cut, you know where to vent!


    Kerf cuts or small triangular cuts are also used to determine where to make a trench cut... now those are fun!
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    Ok, last question on this subject. Are the kerf cuts made in a way to minimize roof damage? Such as between the rafters if possible as opposed to across rafters?

    I know it sounds silly to think about minimizing roof damage when there is a fire below it, but that is how most of the older guys on my dept look at things. I don't necessarily agree with that philosophy.

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    A kerf cut made parallel and close to a truss is the easiest to repair. Simply sistering onto the side of the truss from inside the attic and re-attaching the sheathing is often all that is required to make the repair.

    A truss or a rafter should never be cut across if it can possibly be avoided. Even if a vent hole needs to be made, it can (and should) be done without the saw ever touching any framing member.
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    Quote Originally Posted by fireman4949 View Post
    A kerf cut made parallel and close to a truss is the easiest to repair. Simply sistering onto the side of the truss from inside the attic and re-attaching the sheathing is often all that is required to make the repair.

    A truss or a rafter should never be cut across if it can possibly be avoided. Even if a vent hole needs to be made, it can (and should) be done without the saw ever touching any framing member.
    Well, we do very little "roof" work, and when we do vent a roof it is usually done with the back end of a flat head axe. We just beat a hole in the roof basically. But thanks! I know what a kerf cut is and how it is done now!!

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    Nothing wrong with using the back of a flat head axe to make a vent hole. It just isn't always the easiest way to go about making a vent hole.

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    Yes it is a little more difficult with the axe, but we had a guy slip on the sawdust many years back and almost fall off the roof as he was walking back to the ladder, so now we use the axe. I have done it in training and it honestly does not take all that much more time. For trenching, or large venting applications, a saw would definitely be the better choice.

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    One nice thing about using an axe, is that it always starts.
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    Quote Originally Posted by fireman4949 View Post
    One nice thing about using an axe, is that it always starts.
    Yes it does.. but I don't know about the firefighter using it, though!
    ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
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    Quote Originally Posted by SWLAFireDawg View Post
    Well, we do very little "roof" work, and when we do vent a roof it is usually done with the back end of a flat head axe. We just beat a hole in the roof basically. But thanks! I know what a kerf cut is and how it is done now!!
    You should talk your dept into upgrading your manual saw (the axe) to a chain saw or something..

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    Quote Originally Posted by dday05 View Post
    You should talk your dept into upgrading your manual saw (the axe) to a chain saw or something..
    We have a chainsaw and rotary saw on each engine.....we elect not to use them based on lack of consistent training, safety concerns as described in a previous post, and the fact that most of the guys just feel better and prefer to use the axe.

    And as one guy stated to me at a training session, if I am going to tote the axe up to sound the roof, there is not much sense to me to bring up yet another tool.

    Keep in mind, we usee PPV way more than roof vents, and most of the few fires we do get usually vent themselves......

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    Quote Originally Posted by SWLAFireDawg View Post
    And as one guy stated to me at a training session, if I am going to tote the axe up to sound the roof, there is not much sense to me to bring up yet another tool.

    ***Better bring a long Pike Pole if you plan on opening up.***

    Keep in mind, we usee PPV way more than roof vents, and most of the few fires we do get usually vent themselves......

    ***Well, that's awfully thoughtful of them.***
    You've got the equipment...Start training!
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    Start training........yeah....you're preaching to the choir. I push , but there are just way too many pushing back. The joys of a small rural vollie department......

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    A roof ladder goes a long way towards keeping people from slipping off the roof and it has been our experience that you are more likely to lose your balance swinging the axe than venting with the saw.

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    Quote Originally Posted by SWLAFireDawg View Post
    Ok, last question on this subject. Are the kerf cuts made in a way to minimize roof damage? Such as between the rafters if possible as opposed to across rafters?

    I know it sounds silly to think about minimizing roof damage when there is a fire below it, but that is how most of the older guys on my dept look at things. I don't necessarily agree with that philosophy.
    You should not cut across a rafter or truss. Yes there is fire below it. Your act of cutting it just sped along the derogation of the roofs structural integrity.
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    How do you know where the roof supports are when you are on top of the roof that is covered in shingles?

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    Quote Originally Posted by TNFF319 View Post
    How do you know where the roof supports are when you are on top of the roof that is covered in shingles?
    After reading this thread through, thought that I'd add my two cents. In terms used here so far, a kerf cut or smoke hole assists you in finding out how far exactly the smoke has progressed in the attic.

    To find out the direction and location of roof supports or rafters, on our department we do two things. First of all as we access the roof, the cutter starts a diagonal hole across the roof until a rafter is felt and then it is rolled. We then complete the hole in a triangular shape that is about 12 to 18 inches on each size. This accomplishes two things, finding direction of support and telling us what the roof is composed of. Once we have made this discovery, we make our trek to the area we will ultimately cut our heat hole, cutting smoke holes and sounding as we go. Once we have determined where we will make our cut, we make what we call a 5 cut leuvre. While this isn't quite as good of a way to find the direction of the roof supports or rafters, it can be used to do so.

    While this post makes sense to me, I'm sure some of you may have questions about my terminology and would be glad to answer them if I can.

    Jack
    Last edited by station75; 05-07-2007 at 03:25 PM. Reason: correct grammar

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    Sound the roof with an ax head and when the sound changes to more of a dull thump thats a rafter.
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    Quote Originally Posted by DocVBFDE14 View Post
    You should not cut across a rafter or truss. Yes there is fire below it. Your act of cutting it just sped along the derogation of the roofs structural integrity.
    I know we all do it differently......the little training we have done on roof venting with a saw has us cutting at least a 3x3 hole (when possible) so we have to cut across at least one rafter. We just set the depth guage so we only knick the top of the rafter if we touch it at all.

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    Quote Originally Posted by SWLAFireDawg View Post
    I know we all do it differently......the little training we have done on roof venting with a saw has us cutting at least a 3x3 hole (when possible) so we have to cut across at least one rafter. We just set the depth guage so we only knick the top of the rafter if we touch it at all.
    I recommend a 4x4 hole. It can easily be made without cutting a single truss.

    Sound for the trusses first, then cut vertically along the inside (the side of the truss where the hole will be made) of the first truss, from the top to the bottom of a full sheet of sheathing. Next, cut along the inside edge of the third truss. Finally, cut the bottom of the decking between the first two cuts, removing the saw completely about an inch, or two shy of the center truss on each side.

    A little pressure on either the left, or the right side of the sheathing will cause the plywood to pivot on the center truss, bending the nails, and will open like a damper. The plywood will remain attached to the center truss by the nails, but will open completely to vent the attic below.

    The trusses remain uncut and the structural integrity of the roof is not compromised any more than necessary.




    Kevin

    (Edit) I want to clarify what I posted above...
    It is possible to open a 4x4 vent hole with only the two vertical cuts I described, provided they are made from the top to the bottom of a full sheet of plywood.

    The horizontal cuts are only necessary if the opening being made is either less than 4 feet from top to bottom, or it is encompassing more than one sheet of decking.

    On roofs that are plank-decked, horizontal cuts are rarely needed unless the decking is tongue and groove.
    Last edited by fireman4949; 05-07-2007 at 10:54 AM.
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