Problem with venting a flat roof and a problem with noise

When the roof project was being done, the roofer scrapped the gravel off above the tongue and grove deck area’s leaving the layer of tar from the old system. Under that was a layer of fiber

A flat roof vent that has been fitted over a singel ply roofing membrane and needs waterproofing

To me it looks as if this vent is being fitted incorrectly also why would you vent a warm roof?

like insulation sitting on top of the tongue and grove, nothing else. Inside the home there are two ceiling styles, exposed tongue and grove with beams, other area’s are sheet rock finish with insulation batting above. So above the finished area’s is plywood decking not tongue and grove and they scraped off all the old system to the deck and applied like a roll paper before mopping the hot tar that holds the insulation in place. The entire roof now has 4″ of ISO insulation which is mopped down in hot tar, no screws or nails, then the membrane was also mopped down in hot tar, no screws or nails. Fiber Tite Fleece Back membrane is the type that has to be hot welded at the seams, which I felt was better then the systems that use tape. The roof was installed in 2003 and the cannon shot type bang only happens in the cold winter months, temps below 30 degree’s F*, at night. Thank goodness it does’t go on in the summer months, have to catch up on sleep.

A roofer here says that it is the deck moving which causes this noise. I never had any problem with noise until I had this system

Hole for flat roof vent

Flat roof vent going thorough insulation on a warm roof

installed, good old tar and gravel. I feel I wasted thirty thousand dollars on this new system and now look to spend a great deal more to try and figure out what is causing the noise.

Thank you for taking the time to talk with me, any ideas you have to pass along, I appreciate it.


P.S. I have attached photo’s of a test cut and vents that were installed this year.


3 comments on “Problem with venting a flat roof and a problem with noise

  1. stevewater says:

    Thanks, first placing a vent over this is not going to help as there is no void to vent, if you do use that vent make sure it fitted correctly as water geting between the insulation and the roof is not good.
    I think I voiced this to you before, the only thing that changed with your roof is the lightweight insulation and singel ply membrane that has been fitted over the old roof, all of which dont add up to a lot of weight, therefor the bigest change will be the thermal element, the old roof will be warmer and could be drying out! how long has this been going on?
    The noise was not there before and the roof decking and internal timbers were stable, it all worked OK by placing the insulation over the roof you must have increased the thermal element making the roof warmer, however not any warmer than when the sun was out in the autumn or summer and you didn’t get the noise then! I asume you havent changed how the roof breaths because you havent removed the old tar roof and that will act as a vapour barrier, if you havent changed the heating inside the property I can only conclude that the noise is the glue cracking as the sheets of insulation move or the old roof moves under the insulation, this I find hard to believe as the old roof would have been stable or the tar would have cracked when the decking moved.

    Sorry I cannot be of further help

    • Customer says:

      Thank you very much for your thoughts on my roof noise problem. I went ahead and hired a roof consultant in Colorado. His thoughts were of the same idea, only that the roofer that installed the system used one layer of 4″ ISO in hot mopped tar, he feels it should have been two layers of ISO and all should have been mechanically screwed down to the deck, even the membrane, no hot tar. I have always felt that the roof was over constrained and if the membrane and the tar didn’t contract in the winter months at the same temp or time, it could create a loud bang. Looking forward to a fix soon, winter is just around the corner.

      Again, thank you for your help. Hope the rest of the year treats you kind.


    • stevewater says:

      In the UK we don’t fix with hot tar we fix with an expanding glue and only fix around 50% of the insulation board. Personally I don’t like mechanical fixing of insulation or the roof covering, have tried it and find it to hit and miss on the insulation as regards to the roof covering we have tried all sorts and we are coming around to the opinion that the best roof coverings are liquid but liquid roof coverings are expensive to buy and to lay so you are looking at the top price bracket. We have just moved over to the new 3M roofing system called Same Day 650 or SD650 as its American perhaps you will have a look at it at some point. Speak soon Steve

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