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Kyle Thibodeaux Posted: Jan 24, 2010 11:48 PM	What does average and nominal mean What does average and nominal mean as it relates to spray foam? If my bid calls for 3" average, how do I check it? If it calls for 4" in rafters, how do I check it? What is the difference between 3" and 3 1/2" in a 2x4 wall? What is the difference between the manufacturers such as Demilac, Lapolla, CPI, and Icynene? Thanks for any replies.
mason Posted: Jan 25, 2010 08:29 AM	Average thickness would take the representative high and low thickness of an application and average them out. For example say the low was 2 inches and the high was 4 inches. The average would be 3 inches. Nominal is a pretty vague term and it could be interpreted different ways as an average or as a minimum within certain tolerances. When specifiying or bidding a sprayfoam job, list an average and a minimum thickness with the tolerances allowed. For example, 2.5 inches of SPF average Low thickness of 2 inches tolerance of 1/4 inch This would allow a random measurement of 1.75 inches with an average of 2.5 inches The difference between 3 inches and 3.5 inches in a 2x4 wall. (as an average) 1. Closed cell foam at 3 inches would have an R value of approximately 18- 19. At 3.5 inches it would have a R value of 21-22. There would be a low more trimming of the foam at 3.5 inches, so the labor costs would go up considerably. 2. Open cell foam at 3 inches would have an R value of 10.5 - 11.5. At 3.5 inches would have an R value of 12 - 13. Open cell foam is much easier to trim than closed cell foam so I would not expect a considerable extra labor expense between the 3.5 and the 3.0 thickness. But, there would be a considerable waste factor when you have to trim back the excess foam flush with the studs. I wonder why you mention only those 4 suppliers, as there are more than 2 dozen foam suppliers across the country. One of the best ways to find the supplier best for your purposes is to go to the annual sprayfoam conference being held this year Feb 15-18 in Orlando. (check out registration at sprayfoam.org) At the conference there will be an exhibit hall and you can talk to all of the foam and equipment suppliers, network with other contractors and get a good idea of who you want to go with.

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Kyle Thibodeaux

Posted: Jan 24, 2010 11:48 PM

What does average and nominal mean

What does average and nominal mean as it relates to spray foam?
If my bid calls for 3" average, how do I check it?
If it calls for 4" in rafters, how do I check it?
What is the difference between 3" and 3 1/2" in a 2x4 wall?
What is the difference between the manufacturers such as Demilac, Lapolla, CPI, and Icynene?

Thanks for any replies.

mason

Posted: Jan 25, 2010 08:29 AM

Average thickness would take the representative high and low thickness of an application and average them out. For example say the low was 2 inches and the high was 4 inches. The average would be 3 inches. Nominal is a pretty vague term and it could be interpreted different ways as an average or as a minimum within certain tolerances.

When specifiying or bidding a sprayfoam job, list an average and a minimum thickness with the tolerances allowed.

For example,
2.5 inches of SPF average
Low thickness of 2 inches
tolerance of 1/4 inch

This would allow a random measurement of 1.75 inches with an average of 2.5 inches

The difference between 3 inches and 3.5 inches in a 2x4 wall. (as an average)
1. Closed cell foam at 3 inches would have an R value of approximately 18- 19. At 3.5 inches it would have a R value of 21-22. There would be a low more trimming of the foam at 3.5 inches, so the labor costs would go up considerably.

2. Open cell foam at 3 inches would have an R value of 10.5 - 11.5. At 3.5 inches would have an R value of 12 - 13. Open cell foam is much easier to trim than closed cell foam so I would not expect a considerable extra labor expense between the 3.5 and the 3.0 thickness. But, there would be a considerable waste factor when you have to trim back the excess foam flush with the studs.

I wonder why you mention only those 4 suppliers, as there are more than 2 dozen foam suppliers across the country. One of the best ways to find the supplier best for your purposes is to go to the annual sprayfoam conference being held this year Feb 15-18 in Orlando. (check out registration at sprayfoam.org)

At the conference there will be an exhibit hall and you can talk to all of the foam and equipment suppliers, network with other contractors and get a good idea of who you want to go with.

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