Rain Roof Construction/Ventilation

Rain Roof Construction

When a three story apartment building with a flat roof begins to leak the owner must fix the leak if he wants to keep his residents. When a building ages to the point that patchwork will no longer suffice, the owner must decide whether to move the third floor tenants to another building or to a lower apartment so that proper repairs can be made to the flat roof. Another decision that can be made is to build a peaked truss roof above the existing flat roof; no tenants will have to be displaced and therefore no money will be lost in rental fees.

These peaked rain roofs pose serious concerns to firefighters, not the least of which are the added void spaces and the increased difficulty in vertical ventilation.

The interior crews should expect to spend some time in a high heat and smoky atmosphere due to the extended time that it will take to ventilate this structure. The Truckies on the roof should be alert to what IS NOT coming out of the ventilation hole (smoke and fire)!

Because of the added void spaces, an extended overhaul should also be expected. Both void spaces (cockloft and attic) should be investigated and cleared of smoke and fire.

From the exterior of the building you can see that the outline of the flat roof is visible. This may be a way to recognize the possibility of a rain roof, however the only way to know absolutely, 100% that there is a rain roof is to pre-fire plan the buildings. Even if you have been told by someone you trust that a certain building has a rain roof, you should get up there and see the construction for yourself. Plan out the types of ventilation and the tactics before the fire, and when the fire happens, surprises are minimized and efficiency increased.

As you can see from the picture above, the load of the rain roof is carried by a truss system. The trusses run from soffit to soffit, in this system the trusses are set approximately four feet apart and are offset. If you look closely the truss system consists of half trusses and alternates from center to the right soffit, the next (four feet away) from center to the left soffit. The trusses are tied together with a lightweight 2x6x8, connected to the trusses with metal joist hangers. Note that these 2×6 members run lengthwise and are spaced about 20 inches on center. The trusses are held off the flat roof by placing them on wood scraps and fastened to the flat roof by metal hurricane straps and screws. The new roof is then sheathed with OSB or plywood, a layer of tar paper, and topped off with asphalt shingles.

When we think about a normal (4×4) ventilation cut, it usually starts with the top cut (to find the trusses/rafters, then the far cut, the bottom cut, lastly the closest cut, the cut is then louvered vertically (peak to soffit). With this construction, if you start with the top cut (looking for the truss/rafter to gauge distance) you will not run into one unless you got lucky enough to plunge close to the truss (remember, they are 8 feet apart). Your next step being the far cut would normally be an easy, unobstructed cut, however with this type of construction you will note the saw bog as it hits the 2×6. If you did not get a chance to pre-fire plan this building, your confusion on the roof will begin to creep in at this time. After completing your cuts, you will notice that the louvers will now run lengthwise.

The cut is completed and your work on the roof is done! Well maybe!

Everything that is done on the fireground is done for a reason. Ventilation is a perfect example of this rule. Generally speaking, ventilation is done to remove heat and smoke to allow the Engine Company to find and extinguish the fire quicker, to give any possible victims a chance of survival, and to reduce smoke and fire damage.

Why do we choose to vertically ventilate as opposed to horizontal/PPV?  We have all been taught that any extensive top floor fire with a possibility of extension into the attic space or cockloft should be vertically ventilated to keep the fire from extending horizontally in the void spaces.

If we have a reason to vertically ventilate, then we should have some expectation of what should happen after we ventilate. In this case we would probably be expecting smoke or fire to immediately ventilate from the hole.

If what we expect does not happen, red flags and alarm bells should be going of in our heads! Something is very wrong and could mean the danger is increasing for everyone on the interior.

I personally have not been placed in this situation (ventilating a rain roof), so I will have to refer to those with the actual experience of operating on this type of roof at a working fire. However, I would immediately begin thinking that horizontal /PPV should be heavily considered.

By the way, before you get to far into the process, communicate to the interior crews and the IC that ventilation will be delayed at best, or that horizontal/PPV is a better tactic to go with.

A few years back there was a fire in an apartment building that had a rain roof. As I understand it Truck 8 was assigned to vertically ventilate. Lt Chapel was on scene and he advised that their main job was to force through a draft stop and extinguish fire in the attic void space. Maybe, he and others that were there will be nice enough to fill us in on the story and provide us with some first hand knowledge.

 Thanks to IronsandLadders.com for the great web site. Be safe!                            -Lt. J. Garcia


Lt. Garcia has a great deal of knowledge in building construction and his trade of fighting fires. He still considers himself a student of the job and pursues being a master of his craft regularly.  Lt. Garcia has been serving for the last 16 years and has spent most of his time in some of the busiest companies on the southside of the city.

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13 Comments on “Rain Roof Construction/Ventilation”

  1. RR E8T Says:

    This article reminded me of a LODD fire that happened in California. July 21 2007 Contra Costa County Fire lost two members in a fire involving a home with a rainroof. The report is very long and detailed but worth looking over, even if you only look at a few pages at a time. It is a good reminder that these rain roofs are not only found on apartment complexes. They can be found on any structure that had a flat roof at one time, even homes.

    Heres is the link to the Contra Costas County Fires report on the events.

    Click to access MICHELE%20LODD%20REPORT%207.17.08.pdf

    Here is the NIOSH report: http://www.cdc.gov/niosh/fire/pdfs/face200728.pdf

  2. Anon Says:

    Somebody needs to speak with Regional Building. This roof is designed and built completely incorrect and collapse of this type of set up is likely with a snow load. Rain will certainly runoff but this roof construction has no business being built on any type of building in this part of the country.

    The rule of thumb for span is 1 inch high for 1 foot of run/span. A 2x6x8 is not intended to span 8 feet even at 16″ on center, nevermind 20″ on center (who ever heard of building 20″ o.c. anyway). 1/2″ OSB or plywood is not intended to be used on spans greater than 16″ on center.

    My point is that this “roof of cards” is already a hazard pre-fire and any work we do up here had better be carefully planned and well thought out before hand.

    While I have never had to vent this type of roof either. However, if I was sent to do this on a top floor fire I would be going really big from the start and using a lot of members to accomplish the tactical objective. What I mean by that is I would attempt to remove really large sections of the rain roof in order to give a work area, with escape routes, prior to actually getting to the original roof for ventilation.

    That is why I would definately let the Chief, and all members operating, know that this roof vent will be delayed.

    The building officals obviously let it go and I’d like to take them into/onto a building under fire conditions. Seen as we can’t do that, be cautious but very aggresive and remove massive amounts of materials. This isn’t the time to be thinking about minimal damage or repairs. It can be done, it has been done and we will get it done.

    If you are one of those guys who beleive in minimal damage so that repairs are minimal please call me and we can discuss some remodeling details. If you cut a 4’x4′ hole here and hope to drop someone in that hole to cut another 4’x4′ hole and then have that member return to the rain roof prior to venting that may work but the carpenter is going to remove at least 8’x8′ on the rain roof and the original roof. However, in reality any carpenter worth his salt will probably be removing far more than that just due to the fact that he has to rebuild the original roof based upon the original structural design.

    So a brief recap, building officials need a real education, I have never had to do this but I personally would go big ASAP, and any demoliton we do saves the carpenter from having to do it anyway. One last item, a 2x6x8 does not feel lightweight when it smacks you up the head for not paying attention.

    Just my thoughts for now. I welcome any education you can give me on this one.

    • RR E8T Says:

      The bad thing is I know of multiple different complexs in my district alone that have the same style joist/truss/rafter layout. I would imagine this can be found all over the city.

  3. Salazar Says:

    Actually these roof have been run through regional building. 8’s had an apartment complex fire in a building off of Chelton that had the same set-up. Captain Dubay (at the time) took his crew to the roof to vent a pitched foof, as there was no external indications there was a flat roof underneath. The crew was initially baffled as to why they weren’t getting any smoke from the vent hole s the ceiling was also being pulled on the inside. The long pike pole didn’t even hit the flat roof when it was pushed down the vent hole.

  4. t8ladder Says:

    Great article and since this is my first comment…Great Website.


    Rain Roof Construction

    Jose, you are correct in saying that it takes time to get through a rain roof and the original flat roof. If it’s a coordinated fire attack you’re after, you are correct in stating you will need to consider other ventilation options. This will not be a vertical vent fire.
    When we arrived to the Cedar Creek apartments (see photo), the fire was well established. It was running up the exterior from the first floor to the third, then through the soffits and into the attic. We laddered the roof and cut a vertical ventilation hole in an effort to prevent the lateral fire spread in this 400’ apartment building. While we didn’t realize we had a flat roof under the pitched roof at this time we knew we couldn’t punch down and through the ceiling. While the fires were extinguished in the apartments the fire continued to burn in the attic. We went to the third floor to assist the engine in extinguishment. When we saw the exposed roof rafters and plywood decking we realized we had a false roof. We made a futile attempt to use our saws to cut the plywood decking from underneath. It wasn’t long before we knew this wasn’t going to get it done.
    We then raised the aerial (initial vent made using ground ladder) to the roof and proceeded to make a series of cuts. The most important one was the 6’x6’ access hole for the engine to advance their attackline, under the pitched roof, in order to extinguish the pesky fire in the attic.
    In retrospect, and what we discussed in the post fire critique, was the importance of recognizing the rain roof. If we had done that much sooner we would have saved a lot of time. Although the attic fire didn’t really take a foot hold it could have and this fire could have been much worse. So Jose is correct in stating that recognizing the presence of a rain roof is the key and to plan your fire attack accordingly: to include how you’re going to access that attic fire for extinguishment and overhaul.
    L. Chapel

    PLEASE REFER TO THE PICTURE THAT CHAPEL SENT IN RELATING TO HIS RESPONSE. HERE IS THE LINK https://ironsandladders.wordpress.com/files/2010/01/rain-roofs-a.jpg

  6. Anon Says:

    Thanks for the education Lt. Chapel.

    As for the constructions aspects of this. I want to clarify that I realize that these have been approved by Regional Building, as have many other mistakes. My point is that we really need to make a concerted effort to get Regional Building to re-evaulate passive fire protection. These roofs, floor truss voids, unprotected basement ceilings, non-protected basement stairs, and etc should not be allowed. They are allowed for right now and we will deal with it. I am asking that anyone who has the savvy to speak with the building department to do so. Some simple changes that are relatively inexpensive to contractors can make a big difference in helping us confine a fire.

    So if anyone did not understand the point from my previous post, I apologize for my inability to be a wordsmith. I was/am frustrated that we allow construction companies to do the minimal all the time. Fire blocking is cheap. Drywall is cheap.

    Great stuff on this site. Thank you to ironsandladders.com, the contributors, the guys who comment, and especially the guys who are reading and using this great resource to get better and thereby make really meaningful change locally. Good job!

  7. Lynch Says:

    Excellent article Jose! These buildings are all over the city and pose a tremendous risk to firefighters. Anytime you create another void space you create an area where fire can hide and travel. You’re dead on in saying that an applied tactic has an expected and measured result. If you don’t get that result alarm bells absolutely should go off. Maybe this speaks to the larger issue of teaching firefighters what to do but not why they are doing it. “We put the fan at the front door because that’s what we
    always do.” I think it’s good to have predetermined guidelines for operating at fires but individually we need to recognize when the conditions have changed or we encounter something unexpected. Only my opinion.

  8. RR E8T Says:

    I know these are found on many multi-family buildings, and the examples I have seen have been very similar construction. Anyone know if the single family homes that have rain roofs use the same construction…as far as the main rafters running horizontal instead of vertical.

    • L. Chapel Says:

      There are some flat roof homes along the Union frontage road that’s just South of station 6; some of which have been converted to pitched roof.

      • RR E8T Says:

        Do you know if the truss/joist design is the same as these apartments, or do they fall along the lines of normal residential truss roof designs?

    • TRUCK 4 Says:

      I know its not saying much and that typically we are looking at more permenant structures, but a lot of modular homes are removing the tires from the flat roofs and being retro fitted with similarly contructed roofs. Talk about light weight and the potential for smoke explosion and backdrafts. Again, I understand that we are using the above mentioned buildings and permanent structures, but these conversions on lighter weight homes can still cause the same dangers as it can in a larger building. Also I have seen these home have a completely new face lift that matches the new roof. This adds a layer of new material to the outside of the structure making a void space that stretches around the entire building causing a simple trash fire from the bottom to go straight to the new “attic”. This could easily cause a situation where conditions inside do not match the conditions showing outside. Just a thought I had this morning.

  9. L. Chapel Says:

    No I don’t.

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