Replies

1. GBA Editor
   Martin Holladay | Mar 20, 2017 07:09am | #1

   P. HA.,
   There is absolutely no way that any of us can speculate about the cause of this roof collapse. All kinds of engineering errors, truss fabrication errors, or sheathing fastening errors might have contributed, and to try to guess which of these errors were most important would be rank speculation.

   I'm sure that the insurance company is looking into the causes right now.

   It is well known that snow can cause uneven loading on gable roofs. Engineers are supposed to take this type of uneven loading, which can stress a roof, into account.

   I'm not usually familiar with texting abbreviations, but I looked up "afaik." Evidently it means "as far as I know." From the location of this abbreviation in your sentence, I assume that you aren't really sure whether this roof was recently insulated with spray foam, but that it might have been.

   It is highly unlikely, in my opinion, that spray foam insulation has anything to do with this roof collapse -- if indeed this roof even had any spray foam insulation, which (evidently) you aren't quite sure about.

   -- Martin Holladay

2. 
   mcmodern | Mar 20, 2017 10:19am | #2

   thanks for the reply, Martin

   to clarify,

   the roof had spray foam insulation applied. the "afaik", referred to it being directly applied to the underside-- thus adding weight to the roof. I have not been in the roofspace-- but that is my understanding-- this is my local hardware store.

   my question was-- as the post title simply states; should the weight of adding insulation to an existing roof structure be taken into account?

   my question was not to "speculate" why the structure failed. most basically, the structure failed because it could not support the weight of the roof, the snow and the new insulation.

   closed cell spray foam at [say] 2lb/cf, at 8" [iirc R49 code minimum here] on a 4000sf roof, weighs >5000lbs-- not an insignificant amount.

   it seems on the most basic level, that the amount/weight of snow now required for roof failure has been reduced by 5000lbs.

   this may be the academic difference between [say] 8 feet of snow or 9 feet, to cause failure, or [say] the more critical difference between 2 or 3 feet.

   this is the discussion I was hoping to have

   on a separate note, a quick search of GBA finds [ https://www.greenbuildingadvisor.com/search/node/afaik?page=1 ] many people using the AFAIK abbreviation, going back more than 6 years.

   Moreover Martin, perhaps you don't recall your own post , from a couple of years ago.

   Oct 11, 2014 5:23 AM ET
   Response to Peter Hastings
   by Martin Holladay
   Peter,
   I agree with your reaction to abbreviations. It's hard enough to keep up with the ones in the construction industry without throwing in slang used by texting youth. Is IIRC a building code, or something else?

   Anyway, as far as I can determine, this is what GBA readers need to know.
   BTW = by the way; BMW = a car brand from Germany.
   FWIW = for what it's worth.
   IIRC = if I recall correctly; IRC = International Residential Code.
   AFAIK = as far as I know.

   Read more: https://www.greenbuildingadvisor.com/blogs/dept/musings/it-s-not-about-space-heating#ixzz4brgQ6Nts

   Thanks

   P. HA.,
   There is absolutely no way that any of us can speculate about the cause of this roof collapse. All kinds of engineering errors, truss fabrication errors, or sheathing fastening errors might have contributed, and to try to guess which of these errors were most important would be rank speculation.
   I'm sure that the insurance company is looking into the causes right now.
   It is well known that snow can cause uneven loading on gable roofs. Engineers are supposed to take this type of uneven loading, which can stress a roof, into account.
   I'm not usually familiar with texting abbreviations, but I looked up "afaik." Evidently it means "as far as I know." From the location of this abbreviation in your sentence, I assume that you aren't really sure whether this roof was recently insulated with spray foam, but that it might have been.
   It is highly unlikely, in my opinion, that spray foam insulation has anything to do with this roof collapse -- if indeed this roof even had any spray foam insulation, which (evidently) you aren't quite sure about.
   -- Martin Holladay
   Answered by Martin Holladay
   Posted Mar 20, 2017 7:09 AM ET

   Read more: https://www.greenbuildingadvisor.com/community/forum/general-questions/101297/new-load-calculations-new-insulated-roof#ixzz4bsK2FgJV
   Follow us: @gbadvisor on Twitter | GreenBuildingAdvisor on Facebook

3. GBA Editor
   Martin Holladay | Mar 20, 2017 10:33am | #3

   P HA,
   Every few months, I encounter a texting abbreviation which is opaque to me. When it seems relevant to the meaning, I look it up. But I don't leave any room in my long-term memory for these texting abbreviations. It's all I can do to learn the meanings of real words like psychrometric and hygrothermic without clogging my brain with afaik.

   -- Martin Holladay

4. 
   seabornman | Mar 20, 2017 03:45pm | #4

   I my past life, I designed many commercial re-roof projects. It's always a good idea to have a structural engineer look at the existing structure before adding insulation to a roof, as more insulation means added weight of unmelted snow. Post-frame and metal building structures are very often designed to meet the bare minimum code requirements, and are often built with less oversight of inspectors, etc. I suspect the additional weight of the foam itself was not critical in the collapse of your roof.

5. GBA Editor
   Martin Holladay | Mar 20, 2017 05:05pm | #5

   Joel,
   Thanks for your comments.

   -- Martin Holladay