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phil babinec
Username: pbabinec

Post Number: 3
Registered: 09-2004
Posted on Wednesday, October 20, 2004 - 03:06 pm:   Edit PostDelete PostPrint Post

Our typical roof spec includes extruded polystyrene or polyiso for roof insulation.
Have avoided expanded polystyrene due to compressive strength, moisture permenace and lower R-value.
Recently received request for substitution on two projects for expanded poly citing; 1) Lead time for polyiso, and 2) rising cost of extruded polystyrene.
While compressive strength and R-values may be in line with the other given appropriate insulation Type, moisture still is concern.
Any thoughts?
Curt Norton, CSI, CCS
Senior Member
Username: curtn

Post Number: 67
Registered: 06-2002
Posted on Wednesday, October 20, 2004 - 04:19 pm:   Edit PostDelete PostPrint Post

It's been my understanding that iso is damaged more by moisture than expanded foam is.
Richard L. Hird P.E. CCS
Senior Member
Username: dick_hird

Post Number: 12
Registered: 02-2004
Posted on Wednesday, October 20, 2004 - 05:21 pm:   Edit PostDelete PostPrint Post

Depending on the desired R-Value. a thickness of expanded polystyrene insulation that provides equivalent R Value to Iso, can require additional blocking at curbs, or changes to details at the roof perimeter. In a substitution situation you need to make sure the Contractor includes such costs.
Anne Whitacre, CCS CSI
Senior Member
Username: awhitacre

Post Number: 132
Registered: 07-2002
Posted on Wednesday, October 20, 2004 - 06:02 pm:   Edit PostDelete PostPrint Post

we simply don't allow expanded poly in our office -- the moisture holding characteristics don't perform in freeze/thaw conditions, and I generally consider it an inferior product. We do still use polyiso regularly on roofs; even at an "aged" R value of 7 per inch, it can reduce the parapet height by 45 inches or more on an R-30 roof, and that more than offsets the additional cost for the material comparared to polystyrene.
Anne Whitacre, CCS CSI
Senior Member
Username: awhitacre

Post Number: 133
Registered: 07-2002
Posted on Wednesday, October 20, 2004 - 06:03 pm:   Edit PostDelete PostPrint Post

uh... that should be 4.5 inches not 45 inches for the parapet height.
Posted on Wednesday, October 20, 2004 - 05:22 pm:   Edit PostDelete PostPrint Post

there is no issue with moisture absorption with EPS used as roofing insulation. It is perfectly acceptable to use EPS for this purpose and the manufacturers have lots of data to support this. EPS is also a more environmentally friendly product since the foaming agent is steam, i.l.o the ozone depleting agents still used by the XPS and polyiso industries. Call Western Insulfoam for more information - they have a complete EPS roofing insulation binder with more technical data than you can shake a stick at...I specify EPS for lots of roofing assemblies.
Richard L Matteo, AIA, CSI, CCS
Senior Member
Username: rlmat

Post Number: 70
Registered: 10-2003
Posted on Wednesday, October 20, 2004 - 06:27 pm:   Edit PostDelete PostPrint Post

I have had roofing manufacturers recommend both.
Soprema is gung ho on EPS. Siplast prefers polyiso.
I'm in So. California so freeze/thaw doesn't usually enter into the equation.
My recommendation would be to discuss the insulation with the roofing manufacturer. We make it part of their system for warranty purposes so we go with what they recommend.
Helaine K. Robinson CCS
Senior Member
Username: hollyrob

Post Number: 86
Registered: 07-2003
Posted on Thursday, October 21, 2004 - 09:55 am:   Edit PostDelete PostPrint Post

I do not use bead board in this application.
Joanne Rodriguez, CSI, CDT, LEED AP
Intermediate Member
Username: joanne

Post Number: 4
Registered: 09-2004
Posted on Friday, October 22, 2004 - 12:28 pm:   Edit PostDelete PostPrint Post

One of the reasons that you will start to see an increase in substitution requests to replace polyiso is the lack of availablity. One of the components used in the blowing agent for polyiso has come under short supply. As a result there is a significant and impacting shortage of poyiso. Since August the prices of polyiso have increased close to 50%--and are projected to rise. The shortage has been projected to continue well into next year. In Northern climates this will result in many spring projects being delayed thus causing scheduling nightmares, as well as increases in budgets.

As far as alternatives, EPS and XPS could be considered, however XPS, aka "blue board," will melt if hot asphalt comes into contact--creating a void in the insulation. Even with the use of a cover board such as Densdeck, there remains the possibility that hot asphalt will seep through the cracks. EPS, aka "bead board," does not like solvents. So if you use configurations with insulation adhesives, or with cold process materials, you face the systen failing due to the exposure with the solvents.

You could consider the use of fiberglass insulation, the prices are now in-line with polyiso, but again in freeze-thaw regions this insulation if exposed to a leak could shatter. Always a good possibility is the use of tapered light-weight insulating concrete if the structure allows.

All of these scenarios offer pros and cons to the system. I would suggest working, very early on, with trusted manufacturers to see 1. what they recommend using with their system, and 2. what systems are tested and proven utilizing those recommendations. It is important that you do not put your client in line to be a test building for an unproven system.

Also, you will want to adjust your budgets for roofing up at least--at least--10%. In addition to the polyiso problems there is a lack of availabilty of wood-fiber board.

I hope this will help in designing your upcoming project.
Tracy Van Niel
Senior Member
Username: tracy_van_niel

Post Number: 96
Registered: 04-2002
Posted on Monday, October 25, 2004 - 02:29 pm:   Edit PostDelete PostPrint Post

Regarding the suggestion for fiberglass insulation, the manufacturer's specs need to be referenced to see what they consider acceptable. I was reviewing information from Carlisle this afternoon and they specifically indicate that fiberglass is unacceptable on adhered or mechanically fastened roof systems, even if overlaid with additional insulation or membrane underlayment.
Joanne Rodriguez, CSI, CDT, LEED AP
Advanced Member
Username: joanne

Post Number: 5
Registered: 09-2004
Posted on Monday, October 25, 2004 - 05:00 pm:   Edit PostDelete PostPrint Post

Tracy you are absolutely correct which I guess was the point of my dialogue. You should work with the manufacturers--not distributors, not contractors--to determine what configuration they will approve, in writing. Specifically on a case by case basis, it will be important to contact the manufacturers technical staff to see what they approve. In some cases they might approve a roof with fiberglass, for instance, when they normally would not.

You will need to work with manfacturers directly--not via web, MasterSpec, or binders to see what they are currently approving or suggesting as a solution to the availability problem. Manufacturers are, in general, testing material compatibility to attain approvals.
Richard L Matteo, AIA, CSI, CCS
Senior Member
Username: rlmat

Post Number: 71
Registered: 10-2003
Posted on Monday, October 25, 2004 - 05:12 pm:   Edit PostDelete PostPrint Post


Absolutely excellent advice.
J. Peter Jordan
Senior Member
Username: jpjordan

Post Number: 23
Registered: 05-2004
Posted on Tuesday, October 26, 2004 - 09:10 am:   Edit PostDelete PostPrint Post

I particularly want to second Anne's comments about the advantages of iso's R-value. I have, in a previous life, specified fiberglas board; however, the R-value of this product would definitely require some design changes if the basis of design was polyiso.

Our firm does quite a bit of tilt-up retail shell construction where there is a parapet on 3 sides and gutter and downspouts along the rear. Making the roof insulation thicker has implications for the details at that location. Our buildings will typically use roof-mounted package-A/C units. In some areas with strict design controls that do not permit these units to be visible, increasing the thickness of the roof also requires increasing the height of the parapet or lowering the roof (i.e., adjusting the height of the steel). Where we have balanced the energy code requirements carefully with the roof insulation, reducing the R-value of the insulation may not be an option.

My comments along with the observations from others should emphasize the problem many design professionals have with substitutions. Simply substituting one product for another may have implications beyond the product itself. Check with the roofing system manufacturer, check your details, review your design criteria with regard to envelope thermal performance and visual quality requirements, maybe even check with the manufacturer about availability. Subs are sometimes less than thorough in checking availability before making a substitution request.

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