Roof ventilation is already a difficult, dangerous and technically challenging operation. There are many variables to consider before even heading to the roof. Let’s look at some different situations and their effects on the size and location of the roof vent.
Peaked vs. flat roofs
A major factor is the type of roof we will be venting. We have flat roofs and peaked roofs and many others in between.
If we look first at a peaked roof, we can say, generally speaking, that we would like the vent hole to be up near the ridge or peak of the roof. For fire right under the roof, we can expect the smoke and heat to rapidly rise to the peak, and that’s where we can release it with a vent hole. We must also remember to cut the hole on the side of the roof where no wind will be blowing into the hole.
So how big should this hole be? That might depend on some other variables like the size of the building and the pitch of the roof. For a small house with a walkable pitch, a 3 x 3 or 4 x 4 hole should work well. For a larger home, you may have to cut a larger hole, say 4 x 6. What about a commercial building with a peaked roof? With a roof that can be walked on, an 8 x 8 hole may be necessary.
Let’s get back to the small house again. What if the roof is steep and a roof ladder is required to get to the peak? From the ladder, we can make a triangle-shaped hole that’s 2 to 3 feet on each side, depending on your reach.
When venting flat roofs, our working surface is much easier on which to walk and maneuver the saw, but flat roofs are basically less stable when involved in fire. Again, we must select the proper location for the hole. We can often do so by walking around the roof perimeter, looking over the edge for visible fire or smoke. Sometimes our view from the street before we get to the roof will help us locate the best roof vent location.
Once on the roof and at the vent location, you should consider the size of the building, the roof and the fire. For a small building with a top-floor or cockloft fire, a 6 x 6 hole over the fire will work. An 8 x 8 hole might work better, but you can get the smaller hole cut first and expand that same hole after it is venting the building. As always, remember to push the ceilings down below the roof opening to help vent that area. On a larger commercial building, after selecting the vent location, cut a large hole, approximately 8 x 8, over the fire. Again, don't cut that size hole for a car fire in a 500-square-foot garage. Consider the size and extent of fire along with the building and roof dimensions.
Roof-cutting guidelines
Some more roof-cutting guidelines that can be helpful:
- When cutting with a saw, a team of two firefighters—a saw operator and a guide—is necessary.
- When a second saw arrives on the roof where a saw is already being used, the second saw should assist with the first hole before starting another cut elsewhere.
- A firefighter must listen carefully to the radio during the cutting for emergency information.
- The saw should be started briefly before carrying it to the roof for ventilation.
- Make sure the proper blade is on the saw for the work anticipated.
- Never cut with the saw if the carry strap is still attached.
- After a cut is complete and the saw is withdrawn from the cut, stop the blade against the roof.
- For circular saws, adjust the shroud over the blade for the actual cutting angle.
- The saw operator should never have a foot in line with the cutting blade. Either both feet will be on one side of the cut or one will be on each side, straddling the cut.
Train first
These are just a few of the situations and conditions that you may encounter when venting a roof. Get out there with the saw and practice these skills during drills. You can't do this properly the first time, so training and familiarization will get you ready for the real thing!
