Roof on a roof | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Posted: Feb 25, 2009 06:58 PM	Roof on a roof Hi Mason A customer of mine is building a roof over his existing roof to help the water when it rains get the leaves off of his roof better. Irregardless of his reason to build the second roof, he will be leaving the first roof intact and has asked me to spray the roofline of the existing roof with 1/2 Pound. My question is, how should I tell him to vent the second roof, which is now the roof over the roof. I am not the GC on this project, but I don't want him to have any issues down the line either. Should he make his vents go from his first roof and then penetrate his second roof. Should I tell him to add some soffit vents to vent the second attic? Any suggestions? Steve
Gordon Howard Posted: Feb 26, 2009 05:08 AM	sounds to me like he needs a third roof. or am i missing something obvious? Roof on a roof on a roof...
SPFer Posted: Feb 26, 2009 06:36 AM	He doens't need to vent the 2nd roof as long as he sprays it. In my area spray foamed "hot roofs" meet code.
Edward Brassington Posted: Feb 26, 2009 10:20 PM	We have done quite a few projects like this. The only difference is that we use two pound foam. This would be sprayed directly on top of the old roof. Have the contractor frame the roof first, you then spray your foam, the contractor can then follow with the new roof sheathing. If the roof is framed with at least 2x6, you install approximately four inches of two pound foam, you will have a vent space on top of the foam. The contractor can then install a ridge vent. I suggest you have the contractor open the old roof along the top of the wall plate, make sure you spray foam down to the wall plate or else you will be left with an unisnulated strip along the roof edges. Depending on what climate you are in will determine the R value that you need. I would not use 1/2 pound foam
mason Posted: Feb 27, 2009 01:11 PM	I think foammaker has the right idea to install to the top of the old roof and leave some room on top of the foam to vent the space. However, some code officials would consider this to be an attic crawl space would require an igniton barrier over the foam. (gets complicated don't it)

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Comments

Posted: Feb 25, 2009 06:58 PM

Roof on a roof

Hi Mason

A customer of mine is building a roof over his existing roof to help the water when it rains get the leaves off of his roof better.

Irregardless of his reason to build the second roof, he will be leaving the first roof intact and has asked me to spray the roofline of the existing roof with 1/2 Pound.

My question is, how should I tell him to vent the second roof, which is now the roof over the roof. I am not the GC on this project, but I don't want him to have any issues down the line either.

Should he make his vents go from his first roof and then penetrate his second roof. Should I tell him to add some soffit vents to vent the second attic?

Any suggestions?

Steve

Gordon Howard

Posted: Feb 26, 2009 05:08 AM

sounds to me like he needs a third roof. or am i missing something obvious?

Roof on a roof on a roof...

SPFer

Posted: Feb 26, 2009 06:36 AM

He doens't need to vent the 2nd roof as long as he sprays it. In my area spray foamed "hot roofs" meet code.

Edward Brassington

Posted: Feb 26, 2009 10:20 PM

We have done quite a few projects like this. The only difference is that we use two pound foam. This would be sprayed directly on top of the old roof. Have the contractor frame the roof first, you then spray your foam, the contractor can then follow with the new roof sheathing. If the roof is framed with at least 2x6, you install approximately four inches of two pound foam, you will have a vent space on top of the foam. The contractor can then install a ridge vent.

I suggest you have the contractor open the old roof along the top of the wall plate, make sure you spray foam down to the wall plate or else you will be left with an unisnulated strip along the roof edges.

Depending on what climate you are in will determine the R value that you need. I would not use 1/2 pound foam

mason

Posted: Feb 27, 2009 01:11 PM

I think foammaker has the right idea to install to the top of the old roof and leave some room on top of the foam to vent the space. However, some code officials would consider this to be an attic crawl space would require an igniton barrier over the foam. (gets complicated don't it)

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