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Circle-D Posted: Jan 09, 2008 01:51 PM	dead air space Hello all, Got a call back the other day. One of the good kind. I foamed the roof of a metal building back in late October for this guy. He didn't want the expense of foam in the walls also so he used the filterglass. Well last week he called and had lots and lots water behind his glass. Top make a long story short, yesterday I pulled all the glass out we could get, dried everything out and replaced with foam. One section was all ready finished, rocked, taped, mudded, painted, everything. So we left that part for now. My question: When the weather breaks and the 2' of snow around the building is gone can we pull the steel siding off and spray this finished area from the outside?. The dead air space wpould be between the foam and the cold as opposed to a conventional application where it is between the foam and the heat. Would this cause more or less or any condensation issues? He wants 2" of closed cell in a 5 1/2" deep cavity. What are your thoughts on this? Issues that might arise from this? Would it be the same if it was a wood sheathed structure as opposed to metal. Any input would be helpful. Thanks Skip
David Lenaker Posted: Jan 09, 2008 08:05 PM	That works fine if your manufacture foam is a vapor retarder at 2.5 in. If it isn'at and you spray only 2 all your have is a good air barrier. You want to to have a perm rating less that 1. As far as reversing the sides im pretty sure that will work..?? correct me if im wrong never heard of any problems spray from the outside.
Rob Granger Posted: Jan 12, 2008 01:04 PM	I just finished a some what similar job. It involved a office building where the outside system failed and had to be removed/replaced because it was leaking water into the wall system. We therefore had to spray from the outside to the sheetrock. I recommended to the owner and the GC that we fill the whole space as I did not want any liability issues and belived it to be the best practice. If the conditions are just right and/or there is any air leakage into the air space then condensation is possible and as we all know that will cause problems. I have seen a ton of air infiltration in metal buildings as the skin is just not air tite so I believe air infiltration into this air space is probable. Just my opinion.
Posted: Jan 13, 2008 09:39 AM	i too believe that this is a "comprimised application",,but life is full of comprimises.. you need to do some modeling of the structure to see if the application you are proposing to apply will afford the wall enough thermal performance to stop the transfer of the interior heat to the colder airspace,,,if the modeling shows that the dew point is met in the closed cell foam you should be ok,,,look at this depth and add an inch if you want some "suspenders over your belt"(remember this is "their problem,,not yours,,remind them of one of my favorite lines in the remediation business "you wanted cheap,,,you got cheap"...kinda reminds them of how we got to the higher price they are gonna see,,cause it just aint easier the 2nd time around,,read:remodels are a bitch) 3" closed cell should do the ticket i prefer to apply to the exterior sheeting,,,it is the seamless application and the air barrier it invokes which gives foam products their increased thermal performance..and as Yes said,,if you allow air into the wall cavity...logically,,it is inside the buildings envelope where it could inflitrate through any breaks in the application or through other penetrations inherent to the building process. look hard at your buisness "liability" in this application,,,this is a failed structure and i would bet the owners are not happy at all,,, and they "expect" your application to solve their problems 100%..sometimes you need to know when to say when,,,or at least cover your booty with a well written contract SPECIFIC TO THIS APPLICTION... ...on a sunday morning sidewalk... (one day at a time)....
Circle-D Posted: Jan 13, 2008 05:10 PM	Thank you all who have answered this call for help. This will be a next summer project so the research will go on.Keep the opinions coming. The foam I spray has a perm rating of .8 at 2" so we should be ok in that area. I will also insist on at least 3" as foamdude suggests, and a special notation in the paperwork. Skip
philip mullins Posted: Jan 14, 2008 09:49 PM	my concerns would be drafts and mold forming on the interior of the exterior walls. will the design of the building allow for an effective air barrier with this sort of application? and metal sweats. foamdude made some very good points as well.

Author

Comments

Circle-D

Posted: Jan 09, 2008 01:51 PM

dead air space

Hello all, Got a call back the other day. One of the good kind. I foamed the roof of a metal building back in late October for this guy. He didn't want the expense of foam in the walls also so he used the filterglass. Well last week he called and had lots and lots water behind his glass. Top make a long story short, yesterday I pulled all the glass out we could get, dried everything out and replaced with foam. One section was all ready finished, rocked, taped, mudded, painted, everything. So we left that part for now.
My question: When the weather breaks and the 2' of snow around the building is gone can we pull the steel siding off and spray this finished area from the outside?. The dead air space wpould be between the foam and the cold as opposed to a conventional application where it is between the foam and the heat. Would this cause more or less or any condensation issues?
He wants 2" of closed cell in a 5 1/2" deep cavity. What are your thoughts on this? Issues that might arise from this? Would it be the same if it was a wood sheathed structure as opposed to metal. Any input would be helpful. Thanks Skip

David Lenaker

Posted: Jan 09, 2008 08:05 PM

That works fine if your manufacture foam is a vapor retarder at 2.5 in. If it isn'at and you spray only 2 all your have is a good air barrier. You want to to have a perm rating less that 1. As far as reversing the sides im pretty sure that will work..?? correct me if im wrong never heard of any problems spray from the outside.

Rob Granger

Posted: Jan 12, 2008 01:04 PM

I just finished a some what similar job. It involved a office building where the outside system failed and had to be removed/replaced because it was leaking water into the wall system. We therefore had to spray from the outside to the sheetrock. I recommended to the owner and the GC that we fill the whole space as I did not want any liability issues and belived it to be the best practice. If the conditions are just right and/or there is any air leakage into the air space then condensation is possible and as we all know that will cause problems. I have seen a ton of air infiltration in metal buildings as the skin is just not air tite so I believe air infiltration into this air space is probable. Just my opinion.

Posted: Jan 13, 2008 09:39 AM

i too believe that this is a "comprimised application",,but life is full of comprimises..

you need to do some modeling of the structure to see if the application you are proposing to apply will afford the wall enough thermal performance to stop the transfer of the interior heat to the colder airspace,,,if the modeling shows that the dew point is met in the closed cell foam you should be ok,,,look at this depth and add an inch if you want some "suspenders over your belt"(remember this is "their problem,,not yours,,remind them of one of my favorite lines in the remediation business "you wanted cheap,,,you got cheap"...kinda reminds them of how we got to the higher price they are gonna see,,cause it just aint easier the 2nd time around,,read:remodels are a bitch) 3" closed cell should do the ticket

i prefer to apply to the exterior sheeting,,,it is the seamless application and the air barrier it invokes which gives foam products their increased thermal performance..and as Yes said,,if you allow air into the wall cavity...logically,,it is inside the buildings envelope where it could inflitrate through any breaks in the application or through other penetrations inherent to the building process.

look hard at your buisness "liability" in this application,,,this is a failed structure and i would bet the owners are not happy at all,,,
and they "expect" your application to solve their problems 100%..sometimes you need to know when to say when,,,or at least cover your booty with a well written contract SPECIFIC TO THIS APPLICTION...

...on a sunday morning sidewalk...
(one day at a time)....

Circle-D

Posted: Jan 13, 2008 05:10 PM

Thank you all who have answered this call for help. This will be a next summer project so the research will go on.Keep the opinions coming. The foam I spray has a perm rating of .8 at 2" so we should be ok in that area. I will also insist on at least 3" as foamdude suggests, and a special notation in the paperwork. Skip

philip mullins

Posted: Jan 14, 2008 09:49 PM

my concerns would be drafts and mold forming on the interior of the exterior walls. will the design of the building allow for an effective air barrier with this sort of application? and metal sweats. foamdude made some very good points as well.

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