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Circle-D Posted: Mar 09, 2009 09:53 PM	insulating existing roof Hi Mason, I have a customer with a finished dwelling that I need to get sprayfoam into the roof. It currently has a dark green metal roof screwed directly to the 2" x10"purlins. The interior is completly finished. Would it be acceptable to remove the metal roofing and spray the foam against the backside of the interior finish? This would leave a dead air space between the foam and the steel roofing. Should this then be vented or not? Would it cause condensation issues if it was done this way? What is the minimum thickness of foam you would recommend in this application? I would of course be using a closed cell foam. This job is located in Central Maine. If it could be done this way and achieve a quality job it would allow the occupants to remain living in the dwelling while the majority of the work was happening. Anyone ever done one like this, share your thoughts? Skip
mason Posted: Mar 10, 2009 08:22 AM	If you take the metal off and spray down on the ceiling of the structure, you would vent the attic space and use an ignition barrier over the foam. An easier way to insulate the building is to spray a polyurethane foam roof onto the metal. You use a higher density foam (3 lbs per cubic ft and cover the foam with an elastomeric coating. Done properly the foam would look like snow fall on the roof. Done incorrectly it would be very lumpy. SPF roofing is best performed by folks experienced in these type of applications, but your supplier might help in providing education and trainiung. This would be a job best done in the summer or early fall when the temperatures are the highest and humidity the lowest. Codes require R 49 in your area in attics, but if you spray the roof you can use less insulation. (sprayfoam has an r value of around 6 per inch.) Cehck out the SPFA technical document on Insulating Metal Buildings with SPF. at their website sprayfoam.org
Circle-D Posted: Mar 11, 2009 06:53 AM	Thanks Mason, Slight misunderstanding here I think. The building is catherdral ceiling throughout. The only "attic space" would be the remainder of the purlin width after the foam is installed. Would you still need an ignition barrier here? As long as the roof is vented would the sun hitting the metal cause it to get to hot?
mason Posted: Mar 13, 2009 08:36 AM	Sorry about the confusion. No, a cathedral ceiling configuration would not be vented, nor would an ignition barrier be required. But I am a little concerned about what might happen if the roof leaks. If the foam is sprayed to the underside of the roof deck, the foam stops water from migrating into the building by sealing all the cracks and crevices, but if the foam is sprayed to the drywall ceiling from on top, any water from roof leaks would be trapped in that space. I still would recommend a SPF roof system or to take down the drywall on the inside and then spray. It is also a risk to take the roof off to spray foam, what happens if you get caught by a sudden storm?
Posted: Mar 17, 2009 05:47 AM	yo mason,,,you do not stop roof leaks in a building from the inside,,,closed cell or what ever,,,if it is leaking it will still be leaking,,and water will indeed enter the building envelope...and it will find its way to the world,,usually via a rafter or truss or sumpin,,,usually it will manifest itself days after the storm event,,,as it takes awhile to find its way to you... you seal a roof from the outside,,and foam is very effective applied this way... consider,,,foam works by creating a building envelope and stopping the uncontrolled air movement into and out of the structure,,,you know.,,,reducing the covective currents with in the wall/roof cavity,,,you are suggesting creating the envelope inside the buildings perimeter,,and it would seem there would be much opportunity for air to infiltrate the structure,,,lets not forget about the stack effect and pressurization and all that funky stuff... now "dead" air space does have r value,,,hmm,,, but when hot meets cold condensation occurs,,,and you would have a nice cavity on the cold side of the system,,hmm,,,so it would be good to model the system to be sure the dewpoint is being met well towards the warm side of the insulation cavity,,,, so hey man i dont know,,,your client is paying a good price for a compromised system,,,i am confident he would "save money" on his usage,,,but the system does appear to have some inherent flaws,,, "should i stay or should i go now???,,, if i go it will be trouble,,,, if i stay it will be double,,,, so common,,,and let me know,,, should i stay or should i go???" 'dude
mason Posted: Mar 17, 2009 12:29 PM	Foamdude, I have spraying foam for close to 40 years and closed cell sprayfoam does stop water leaks that come in through the cracks and crevices between roof decking. If the penetration flashing is leaking the water will leak as usual and it will show up,plus the closed cell nature of the foam will limit the deck deterioration to a limited area. So if water gets past the shingles, or tiles, the prayfoam keeps the water on top of the sheathing where it belongs then gravity takes it to the eaves or gutter. But if you spray foam on top of the ceiling deck then add a layer of decking on top of it, then water can get trapped between the foam and the wood decking with no way of getting out. I agree the best solution in this case is to spray a foam roof but it is a myth that closed cell foam sprayed to the underside of the roof deck will allow water to be trapped from roof leaks. Seen too many jobs where the foam seals the water from entering the building or getting past the roof deck and have never seen the situation where closed cell foam sprayed to the underside of the wood deck caused "trapped" water I always agree that hygrothermal modeling is required when designing systems "outside the box"
Posted: Mar 17, 2009 10:07 PM	then come respray my shed..lol,,with warranty too?? i hope... mason this roof leaked when i INSULATED IT FROM BELOW about 12 years ago and it still leaks today,,,the water finds its way to the rafters and follows them usually all the way down to the eve where it drips,,usually about 3 days after it rains is when it starts,,it takes awhile to find its way,,,, indeed it is a myth that cc foam will trap water...their lips was movin,,,i saw it!!! and i will say it again,, you do not stop leaks in a roof by spraying foam on the inside of the structure,,,by spraying to the roof substrate from inside....nope,,not ever,,,
mason Posted: Mar 18, 2009 07:10 AM	Foamdude, I presume that you missed a spot or that the flashing is leaking somewhere where the foam is not. I just got back from South Texas where I got a chance to look at a dozen buildings I had sprayed the underside of the roof deck in the late 70s and early 80s. No leaks and never had a leak. This is consistent with my experience and most of my associates. The roofs ranged from shingles to clay tile to metal.
Posted: Mar 18, 2009 07:43 AM	For what it is worth, I have used 2 Pound inside a steel barge to stop a leak in 1/4 steel that was 12 feet below the waterline. We packed tightly and once the initial 1 inch pass stuck down, I built up the layers around and finished with about 4 inches over a 4 ft. span. This vessel was displacing 100 tons and we were able to contain the leak until we were able to get into the shipyard several months later. Not exactly the friendliest environments because we had to spray standing in water onto a wet substrate. Once we made our initial pass, we were able to dry off and prime the outer substrate, which held the primary patch. It was much safer than trying to weld standing in the water onto a wet substrate.

Author

Comments

Circle-D

Posted: Mar 09, 2009 09:53 PM

insulating existing roof

Hi Mason,
I have a customer with a finished dwelling that I need to get sprayfoam into the roof. It currently has a dark green metal roof screwed directly to the 2" x10"purlins. The interior is completly finished. Would it be acceptable to remove the metal roofing and spray the foam against the backside of the interior finish? This would leave a dead air space between the foam and the steel roofing. Should this then be vented or not? Would it cause condensation issues if it was done this way? What is the minimum thickness of foam you would recommend in this application? I would of course be using a closed cell foam. This job is located in Central Maine.
If it could be done this way and achieve a quality job it would allow the occupants to remain living in the dwelling while the majority of the work was happening.
Anyone ever done one like this, share your thoughts? Skip

mason

Posted: Mar 10, 2009 08:22 AM

If you take the metal off and spray down on the ceiling of the structure, you would vent the attic space and use an ignition barrier over the foam. An easier way to insulate the building is to spray a polyurethane foam roof onto the metal. You use a higher density foam (3 lbs per cubic ft and cover the foam with an elastomeric coating. Done properly the foam would look like snow fall on the roof. Done incorrectly it would be very lumpy. SPF roofing is best performed by folks experienced in these type of applications, but your supplier might help in providing education and trainiung. This would be a job best done in the summer or early fall when the temperatures are the highest and humidity the lowest. Codes require R 49 in your area in attics, but if you spray the roof you can use less insulation. (sprayfoam has an r value of around 6 per inch.)

Cehck out the SPFA technical document on Insulating Metal Buildings with SPF. at their website sprayfoam.org

Circle-D

Posted: Mar 11, 2009 06:53 AM

Thanks Mason,
Slight misunderstanding here I think. The building is catherdral ceiling throughout. The only "attic space" would be the remainder of the purlin width after the foam is installed. Would you still need an ignition barrier here? As long as the roof is vented would the sun hitting the metal cause it to get to hot?

mason

Posted: Mar 13, 2009 08:36 AM

Sorry about the confusion. No, a cathedral ceiling configuration would not be vented, nor would an ignition barrier be required. But I am a little concerned about what might happen if the roof leaks. If the foam is sprayed to the underside of the roof deck, the foam stops water from migrating into the building by sealing all the cracks and crevices, but if the foam is sprayed to the drywall ceiling from on top, any water from roof leaks would be trapped in that space. I still would recommend a SPF roof system or to take down the drywall on the inside and then spray. It is also a risk to take the roof off to spray foam, what happens if you get caught by a sudden storm?

Posted: Mar 17, 2009 05:47 AM

yo mason,,,you do not stop roof leaks in a building from the inside,,,closed cell or what ever,,,if it is leaking it will still be leaking,,and water will indeed enter the building envelope...and it will find its way to the world,,usually via a rafter or truss or sumpin,,,usually it will manifest itself days after the storm event,,,as it takes awhile to find its way to you...
you seal a roof from the outside,,and foam is very effective applied this way...

consider,,,foam works by creating a building envelope and stopping the uncontrolled air movement into and out of the structure,,,you know.,,,reducing the covective currents with in the wall/roof cavity,,,you are suggesting creating the envelope inside the buildings perimeter,,and it would seem there would be much opportunity for air to infiltrate the structure,,,lets not forget about the stack effect and pressurization and all that funky stuff...
now "dead" air space does have r value,,,hmm,,,
but when hot meets cold condensation occurs,,,and you would have a nice cavity on the cold side of the system,,hmm,,,so it would be good to model the system to be sure the dewpoint is being met well towards the warm side of the insulation cavity,,,,
so hey man i dont know,,,your client is paying a good price for a compromised system,,,i am confident he would "save money" on his usage,,,but the system does appear to have some inherent flaws,,,
"should i stay or should i go now???,,,
if i go it will be trouble,,,,
if i stay it will be double,,,,
so common,,,and let me know,,,
should i stay or should i go???"

'dude

mason

Posted: Mar 17, 2009 12:29 PM

Foamdude,

I have spraying foam for close to 40 years and closed cell sprayfoam does stop water leaks that come in through the cracks and crevices between roof decking. If the penetration flashing is leaking the water will leak as usual and it will show up,plus the closed cell nature of the foam will limit the deck deterioration to a limited area. So if water gets past the shingles, or tiles, the prayfoam keeps the water on top of the sheathing where it belongs then gravity takes it to the eaves or gutter.

But if you spray foam on top of the ceiling deck then add a layer of decking on top of it, then water can get trapped between the foam and the wood decking with no way of getting out.

I agree the best solution in this case is to spray a foam roof but it is a myth that closed cell foam sprayed to the underside of the roof deck will allow water to be trapped from roof leaks. Seen too many jobs where the foam seals the water from entering the building or getting past the roof deck and have never seen the situation where closed cell foam sprayed to the underside of the wood deck caused "trapped" water

I always agree that hygrothermal modeling is required when designing systems "outside the box"

Posted: Mar 17, 2009 10:07 PM

then come respray my shed..lol,,with warranty too?? i hope...
mason this roof leaked when i INSULATED IT FROM BELOW about 12 years ago and it still leaks today,,,the water finds its way to the rafters and follows them usually all the way down to the eve where it drips,,usually about 3 days after it rains is when it starts,,it takes awhile to find its way,,,,
indeed it is a myth that cc foam will trap water...their lips was movin,,,i saw it!!!
and i will say it again,,
you do not stop leaks in a roof by spraying foam on the inside of the structure,,,by spraying to the roof substrate from inside....nope,,not ever,,,

mason

Posted: Mar 18, 2009 07:10 AM

Foamdude,

I presume that you missed a spot or that the flashing is leaking somewhere where the foam is not. I just got back from South Texas where I got a chance to look at a dozen buildings I had sprayed the underside of the roof deck in the late 70s and early 80s. No leaks and never had a leak. This is consistent with my experience and most of my associates. The roofs ranged from shingles to clay tile to metal.

Posted: Mar 18, 2009 07:43 AM

For what it is worth, I have used 2 Pound inside a steel barge to stop a leak in 1/4 steel that was 12 feet below the waterline. We packed tightly and once the initial 1 inch pass stuck down, I built up the layers around and finished with about 4 inches over a 4 ft. span.

This vessel was displacing 100 tons and we were able to contain the leak until we were able to get into the shipyard several months later.

Not exactly the friendliest environments because we had to spray standing in water onto a wet substrate. Once we made our initial pass, we were able to dry off and prime the outer substrate, which held the primary patch.

It was much safer than trying to weld standing in the water onto a wet substrate.

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