Q&A Forums
Effective r-value...? Post New Topic | Post Reply
| Author | Comments |
|---|---|
|
erik williams
Posted: Nov 08, 2010 07:42 AM
|
Effective r-value...?
Hello everyone. I spray foam on roofs but don't have much experience with enveloping.Here is my situation: I'm in Tampa Bay, FL. I'm going to spray the roof surface but I'm not doing anything to the bottom of the roof deck. The roof slope is 3'' per foot. I will be removing the soffit and blocking and spraying 2 inches here also, to create the unvented attic. I'm removing all of the ac and installing new. The ac contractor has asked me what the "Effective R-Value" will be for the purpose of sizing the new unit/system correctly. I explained to him that the r-value of 2'' closed cell is 13. He said he understands that is the r-value but that he is looking for the "Effective R-Value". Is there such a thing? Thanks |
|
quentin
Posted: Nov 08, 2010 07:59 PM
|
The effective value is more how well it works in real life compared to a lab. An example is that foam of an equal "R" rating is about 1.4 times more effective. A good source for the info he will want is to get with the manufacture's reps for the brands you spray and have them answer his questions. It also helps in bringing them in so if the info is wrong somehow, they have a bit of that hook to. |
|
erik williams
Posted: Nov 09, 2010 06:27 AM
|
Thanks Quentin. I didn't even think of asking them. I just sent an email to the rep. |
|
steven argus
Posted: Nov 09, 2010 06:58 PM
|
Tell the AC guy, when he's figuring his cooling load, cut his air exchanges per hour in half. |
