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Community and Q&A

Applying Spray Foam to Underside of Metal Roof

DaveinFlorida | Posted in Energy Efficiency and Durability on

Hello, I recently purchased a home in Florida in (zone 2a),about a hour north of Panama City FL. The home was built years ago but not fully completed.It is 1600 sq ft and  measures 40’x40′ with a 4/12 hip roof and a 10’x10′ cupalo in the middle.Ceiling rafters are doubled 2×12’s spaced 5′ apart (odd I know) I am going to finish it as a cathedral/vaulted type ceiling .It has R-panel galvanized metal roofing on 2×3 wood perlins, which is in very good condition and with a limited budget and time constraints I have decided to keep. My question is about spray foaming the ceiling directly on the underside of the metal roof and perlins. I have received quotes from 3 different companies. The first company recommended closed cell on the ceiling,there reasoning for the closed cell was the roof did not have the typical roof deck and the rigid foam would strengthen the roof system.I agree on their statement,yet I am not too concerned with the current strength of the roof being it withstood 103 mph winds from Hurricane Michael and the only damage was from a fallen tree on the roof.  The next 2 quotes recommended open cell on the ceiling, there reasoning was if you get a leak in your roof it will drip through the open cell foam alerting you to the leak.One salesman said there are some lawsuits from closed cell being used in ceilings and being the water cannot penetrate thru the Closed Cell, it runs down the roof and inside the wall causing damage that cannot be detected until it’s too late. Now being from WI I am used to having a vented roof system and have really struggled trying to wrap my head around the spray foam method of completely enclosing the ceiling cavity to the roof. I also had another contractor (he recommended Closed cell)  tell me over the phone that their are cases where open cell has separated from the metal in less than 5 years. I also don’t like the idea of it being bonded to the metal,being I can’t pull up a panel to inspect. My original idea was to do the poor man’s rigid foam with 2 layers of staggered 2″polyiso fastened to the perlins which would leave an air gap and some ventilation but down here from what I understand is they typically seal the ridge vents to prevent any wind driven rain from entering,and I would basically have the issue of a leak in the roof running back down to the walls.There was a cost advantage of me doing the poor man’s method compared to the almost 10k quote on closed cell just for the ceiling until I got the quote on open cell SF,which is about what it would cost me to do it in Polyiso. I appreciate any input/opinions on what you folks would recommend. Hopefully my explanation is clear enuff to not confuse. I tried to upload a pic but it keeps telling me there was a problem. Thanks Much

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  1. ErikOlson | | #1

    Is the point of the spray foam condensation reduction, or insulation value?

    1. DaveinFlorida | | #3

      Not quit sure how to answer that. The home has never been lived in but the location is very hot and humid for a good portion of the year so I assume there will be condensation issues if not done correctly. The air sealing qualities of SF is what I like and is what is recommended.

  2. walta100 | | #2

    The first thought when I read about your plan is that if you remove the ceiling joist your roof may collapse. Please make sure you understand what is safe before you cut anything.

    My second thought was everyone from the south tells me it is impossible to air condition a house without filling the attic equipment and ductwork. LOL


  3. DaveinFlorida | | #4

    I am not removing any ceiling joists !!! I am thinking you reply was meant for a different question.I don't have an attic.

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