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Roofing Underlayments - FAQs

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How do I know which Grace underlayment product to use?
It is up to the contractor and specifier to decide what level of performance is required based on the guidelines that we provide. In essence, if the project demands a high level of protection from long lasting or large ice dams, then Grace Ice & Water Shield® is the appropriate choice. This would provide maximum protection in areas of the country that experience snowy winters. Where winters are generally mild but will still experience wind driven rain, or where code based minimum standards of protection are required, Grace Ice & Water Shield® can offer sufficient protection. If it is expected that the roof will be subjected to very high temperatures for extended periods of time, then Grace Ultra should be the product of choice.

What types of roof covering can benefit from the application of Grace Underlayments?

You can use Grace Underlayments as an underlayment for all commonly used roofing materials including asphalt shingles, slate, tile and metal roofing systems. However, check with the metal roofing manufacture for any special requirements.

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What about installation under copper, Cor-Ten® and zinc metal roofing roofs?

Copper, Cor-Ten® and zinc metal roofing have inherent properties that cause roofs constructed with these materials to become exceptionally hotter than other roofs. These metals absorb most of the energy reaching them from the sun (high thermal absorption), reflect little energy (low reflectivity), and conduct heat very rapidly (high thermal conductivity). Therefore, there are special design considerations for underlayments used under these metal roofs, due to the high in-service temperatures that these roof assemblies can reach.

Grace Ultra is recommended for use under copper, Cor-Ten and zinc in high altitude climates. Grace Ultra is formulated with an adhesive based on butyl technology and is designed to withstand even the highest in-service roof temperatures. This membrane provides the highest factor of safety in high temperature roof applications. Check with your Grace representative.

Can Grace Underlayments be applied under a welded architectural metal roofing system?

Some architectural metal roofing systems require that the seams between panels be welded. If the architectural metal is applied directly over the membrane it is possible that the heat from the welding operation could cause damage. The Grace underlayment should be adequately protected from the heat of the welding process. What constitutes protection will depend on the type of metal, the type of torch, and the seam system being used. In some cases, contractors have found that two layers of 6.8 kg (15 lbs) roofing felt, placed only in the metal seam area, offered sufficient thermal protection from a welding operation.

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How long can Grace Underlayments be exposed?

Grace underlayments are not meant to be left permanently exposed to the sun. In general, the membrane should be covered with the final roof covering as soon as possible. However, Grace underlayments may be left exposed as described below, if necessary, to accommodate construction scheduling or weather problems.
  Grace Underlayment   Maximum Exposure Period
  Grace Ultra   60 Days
  Grace Ice & Water Shield®   30 Days
  Grace Select   30 Days
  Grace Ice & Water Shield HT   120 Days
  Grace Tri-Flex®   180 Days
  Grace Syn 15   30 Days

What types of caulks can be used with Grace Underlayments?

Most caulks and sealants are compatible with the polyethylene coating on the face of the underlayment However, the adhesive side will react with caulks and sealants that contain hydrocarbon solvents, polysulphides, pentachlorophenol, creosote, and gasoline/oil as well as EPDM and uncured neoprene sheets. Care should be taken if using these compounds so that they do not contact the adhesive.

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Can Grace Underlayments be applied over felt?

No. Felt will act as a bond-breaker to the substrate. Grace underlayments are intended for application directly to the structural deck. Grace underlayments can be applied over existing Grace underlayments in a reroof application.

What about roofing applications that involve a drip edge?

The drip edge should be installed over the underlayment.

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Are Grace Underlayments vapor barriers?

Yes. Grace Ice & Water Shield, Grace Select and Grace Ultra are vapor barriers. In full coverage applications, proper ventilation is necessary. When used in conjunction with metals that are particularly susceptible to corrosion, such as zinc, care should be taken to allow a means of escape for water that becomes trapped between the membrane and the metal.

What is the difference between Grace Ice & Water Shield and Grace Select?

The most obvious difference is that while Grace Ice & Water Shield is 40 mil thick, Grace Select is only 25 mil thick. Grace Ice & Water Shield is designed to offer premium protection from leaks caused by ice dams in all climates, clearly surpassing many of the minimum standards of performance set by ASTM, ICBO and SBCCI. Grace Select is designed to meet the code-based standards of performance. Grace Select is also significantly lighter weight than Grace Ice & Water Shield making it easier to handle a full roll.

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When might I consider using Grace Select instead of Grace Ice & Water Shield?

Grace Ice & Water Shield is well recognized as the premium performance underlayment on the market today. However, on some projects, all the performance that Grace Ice & Water Shield offers may not be needed. If the project is in a mild climate area, or if the specification is driven purely by code minimum standards of performance, the premium nature of Grace Ice & Water Shield may be more than is necessary. Grace Select offers contractors and specifiers the opportunity to choose products with appropriate performance for the specific projects they are working on. Grace Select is part of the Grace underlayments family of products, which includes Grace Ice & Water Shield, Grace Select and Grace Ultra. Each product is uniquely suited for specific roofing applications, making it the most complete line available.

Does Grace Select meet building codes?

Yes. Grace Select meets the key performance standards for fully adhered underlayments in severe climates prescribed by ASTM and ICBO and has an ICBO Evaluation Services Report (No. 3997). Grace Select also has a UL Class A fire classification under fiberglass shingles and a Class C under organic felt shingles.

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What is the difference between Grace & Water Shield and Grace Ultra?

The main difference between Grace Ice & Water Shield and Grace Ultra is that while the adhesive in Grace Ice & Water Shield is based on SBS rubber, the adhesive in Grace Ultra has a butyl rubber base. There are other differences as well. Grace Ultra may be left exposed to the sun for up to 60 days, and it is slightly thinner at 30 mil than Grace Ice & Water Shield, which is 40 mil thick.

What is the significance of the butyl rubber based adhesive?

Stated simply, butyl rubber offers exceptional stability at high temperatures. In some roofing applications, such as those in the desert southwest, roof temperatures can get high enough that SBS based adhesives can flow under the extreme heat. Butyl rubber based membranes remain stable for long periods of time even at extreme roof top temperatures.

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What underlayment product would I use for moisture protection around windows, doors and other critical wall penetrations?

Grace Vycor Plus Self-adhered Flashing is designed to provide superior protection against water, air and moisture infiltration around window and door openings, corner boards and other critical wall penetrations. Grace Vycor Plus is 25 mil thick and is available rolls of 4", 6", 9, and 12" to accommodate a variety of job requirements. It should not be installed on roofs.

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