decking required under metal roof?

Guest User
6/18/2001
In a new construction house...is decking with tar paper required under metal roofing? The roofing is a UL90 approved 3 1/2 inch standing seam STRUCTURAL profile at .026. I am currently in the design stage and can design the roof to carry the pans on the required 4 ft spanners or with a more conventional design utilizing decking and underlayment. Since it is a structural panel (not architectural as most residential profiles are) the decking offers little or no advantage for strength, but I am concerned about potential condensation problems in my NW Ohio climate (especially in early spring). Although I am planning more than adequate attic ventilation, I am designing a superinsulated wall and ceiling system and as we all know, any moisture kills the R value. I appreciate any and all ideas and perceptions on this matter.
Todd Miller
Classic Products, Inc.
6/20/2001
Condensation occurs when moisture-laden air hits a cooler surface. As long as your attic space is well vented so that the temperature of it stays very close to the outside air temperature, then condensation should not be a problem. On second thought, I will add a qualifying statement to that in that I am assuming that there will be nothing inside of the house that will be creating unusually large quantities of warm, moist air. If that was the case, then it will take extremely strong ventilation to get rid of that noisture.
Guest User
1/3/2002
I have just had a contractor install an exposed fastner Galvalume roof on my house. The previous roof was shake shingles which had 1x4 strips every 6 inches. I was not aware that there might be a condensation problem until the roof was half finished. The roof has vents on the side on the north side of the house and has standard ridge vents.There were no insulating strips put on the eaves. As far as I can tell the ventilation is very adequate. I do need more insulation in the ceiling but have not done that yet. The problem is that before the old roof came off I did have some sheetrock damage but now that the new roof is on I am seeing the seams in all the sheetrock in the ceiling and they are beginning to show cracks, also over door frames and along walls cracks are showing up, What is happening? Please help.
Todd Miller
Classic Products, Inc.
1/3/2002
Betty, This sounds like an unusual problem. I am sorry to hear about it. I'd really like to be able to discuss this with you in order to figure out what's happening and give you some good ideas / direction. Please call me at my office at 1-800-543-8938, ext. 201 so that we can discuss this situation. Todd Miller
Guest User
4/19/2002
Question: On a new residential construction with a metal roof, what is the standard spacing of 1"X4" decking, i.e., 2' center and is there a national standard building code? In my case, the roofer installed on 4' centers and I have had nothing but trouble with the roof leaking.
Todd Miller
Classic Products, Inc.
4/19/2002
Manufacturers of products suitable for installation over spaced sheathing can provide load tables and calculations on the spacing of the lathe. In any event, 4' sounds too far apart for most residential metal roof systems. I think you should track down the manufacturer of your roof and consult with them. Let me know if I can help.
Guest User
5/27/2002
hi there....just bought a piece of property with a shell of a house which i hope to finish. Metal roof on windows in and plywood sheeting... So my question is the tin roof was installed directly onto the purlins (2 by 4).. it has nice soffits with plywood that extends about a foot into the inside....no sheathing or felt...trusses,purlins and metal..eastern Washington snow in winter HOT IN SUMMER...AM I GOING TO HAVE TO REMOVE ROOF AND INSTALL SHEATHING AND FELT???? seems like condensation will rot my roof if i dont...thanks for any help...tom
Todd Miller
Classic Products, Inc.
5/27/2002
Many metal roof systems are very appropriate for this type of application. I would make certain that you have good ventilation (soffit to ridge preferably) beneath the roof. Also, just to be safe, track down the manufacturer of the roof system and make this inquiry with them. They will be able to tell you whether the roof has been installed properly.
Guest User
11/2/2002
I am currently building a new house and plan on using metal roofing. What are the pros and cons of installing the metal roof without using decking and felt. Will it cause a condensation problem? What is the best way to do it to preclude future problems--decking and felt or slats on top of the rafters? Thanks Roy Chandler
Allan Reid
Dura-Loc Roofing Systems, Inc.
11/2/2002
Any roof will create condensation so you need to find a way to deal with it. Second is the lower the slope the better the roof material/system you need to keep the weather out. Further the climate of your area and the roof design have a bearing as well. If you have valleys of any nature and you are in snow climates, then I would not recommend it under a 8/12 pitch and you need good tradesman to put the roof on. If you are planninng on buying generic sheet steel from the local building yard I would not do it. Having said all that, check with the manufacturer of your chosen roofing first. You must first use a very good reinforced underlaymnet. We recommend Triflex 30 with our systems. It is very light and will not tear and you can tape the penetrations whithe house wrap tape. Strap the roof horizontally at centers recommended by the manufacturer. If you have valleys, I would lay a 36" wide metal pan in before the underlayment and straping go down. Better yet lay ice and water shield over it. Hope this helps.
Guest User
8/23/2005
The house I am planning to buy has a vertical panel metal roof. According to the inspector, the decking underlayment is OSB and no ply clips were used. She noticed some buckling in a few locations. Was decking used appropriate? Does the metal roof manufacturer require that the decking ply clips are a must? I don't know if it was applied on 2ft centers nor if it was stapled or nailed. There are no signs of leaking anywhere. The house is only a little over a year old. Should I be concerned about the buckling?
Todd Miller
Classic Products, Inc.
8/24/2005
Clips on the decking would not normally be required by the roofing manufacturer. I am not really sure what you mean by "buckling". Where and how is it visible? Is it affecting the roof's appearance? Is she truly talking about a decking problem or is it a roofing installation problem? Can you email pictures to me? [email protected]
Guest User
11/12/2006
I saw your message about condensation is created because of moisture-laden air coming into contact with a cooler surface. My roof is the screw down metal sheets. Eave vents are present. I have a covered deck. The roof actually extends over the 10 foot deck. I was doing some remodeling and noticed some water marks on the trusses. There is no underlayment present. One morning we had a frost and as the sun came out there was water on the underside of the roof. This water started to drip quiet heavily on the covered deck. The roof was open to the atmosphere so I don't think ventilation is the problem. I know it is condensation, but I am puzzled on how it got there and how to stop it from coming back when I close up the space. I am considering turning this area into livable space.
Allan Reid
Dura-Loc Roofing Systems, Inc.
11/14/2006
Warm air holds more moisture than cold air. When you have moist warm air cooling down it sheds the moisture as dew. They name the temperature that a certain moisture laden air will shed the moisture as the Dew point. In a broad sense it typically is around 51 F. Had your roof been installed with a moisture barrier caommonly referred to as an underlayment, the moisture would have been trapped on the top and wicked its way down and out. This happens with all roofing materials however as metal is thinner it reacts to temperature change more quickly. Best get an expert to review your renovations so that you can provide the moisture barrier and proper ventilation when you close it in.
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