Do I need a moisture barrier?

TOPIcs: Installation

Do I need a moisture barrier?

Hi. I have a 16' x 20' unheated (with NO insulation) garage that has shingles on it. 5:12 roof pitch. I plan on putting down 1" x 4" strapping on top of the shingles, screwed to the joists, and then screw the metal panels to the strapping. Do I really need a moisture barrier/underlayment for this project? I see from all the research that most metal roof panel mfgs. suggest an underlayment if leaving the shingles on but isn't that information more for homes/houses that are heated? Thanks for your help. Steve

Guest User

2013-05-14 21:48:30.000000

Thinking about putting on a metal roof on our duplex. It would be Mcelroy metal 29 guage kynar exposed fastener metal - max-rib. 2x4 and 1x4 will be placed on existing roof ( 1 single layer of shingles) then the metal will be installed with neoprene washered screws. My question is should there be any insulation between the 2x4 and 1x4 so that condensation does not form between them and cause the roof to rot. have been told that yes we need that so that the roof does not rot and no we don't need that because it can breath. If we don't have insulation we will have problems in years to come. Thanks for your help

Guest User

2013-07-29 21:06:09.000000

Hi Todd, I am assuming it is tar paper and then plywood. I looked in the attic and did not see any insulation on top or bottom. It looks open with lots of space. The 2x4 and 1x4 would be put right over the shingles with nothing else. I just don't want to have problems down the line.

Guest User

2013-07-30 08:11:58.000000

Hi Todd, Thank you for your help. I think we have eight box style vents. Again I am not sure about the insulation - I am thinking we must have some as part of our roof is over bedrooms and they are not cold in winter - maybe a little warm in the summer but not uncomfortable - I just can't see any. I just want to be sure that my shingles and plywood under the metal would not rot if we do not have the felting or the fan fold insulation to prevent condensation. which would cause problems in years to come.

Guest User

2013-07-30 10:40:39.000000

Guest User

2013-07-30 10:40:59.000000

I have a metal roof over my carport attached directly to the wooden supports. I now would like to enclose the exposed supports, but I notice that is when the temperature changes, the metal has condensation and will drops small beads of water. Is there some type of product that can be applied to the underneath of the metal roof to prevent this? I live in north Florida which has summer temps. In the high 90's and mild winters. I would like to do this myself if possible

Guest User

2016-04-10 11:57:33.000000

I have a contractor telling me that underlayment is not necessary for metal roofing installed on a new construction unheated garage. Everything I've read contradicts him. Any thoughts or references to the IBC that would require it?

Guest User

2017-06-15 22:47:15.000000

Thank you for the quick response. Without a doubt, I am going to have the contractor install ice and water shield and other synthetic underlayment. My main issue is whether or not the contractor should have included that in his quote or whether I should be paying extra for it. Do you know what the potential impact would be if underlayment was it used? I am assuming it would dramatically decrease the life of the roof.

Guest User

2017-06-16 07:37:18.000000

Hopefully, this will be my last question. Would the IBC require underlayment if the garage was going to be heated and the second floor occupied as an Inlaw suite? Or is underlayment just recommended?

Guest User

2017-06-16 07:40:44.000000

I plan to build a garage / studio in a seaside location with high winds and heavy, sometimes horizontal, rain or snow. One third of the building will be heated for a studio while the other two thirds will be an unheated garage and yard equipment storage. I plan on a hipped roof. On the heated side I had planned on a standard roof underlayment with ice and water shield on the entire surface and then 2" x 2" vertical spacers (creating an air space) and then another layer of underlayment to which the metal roofing would be attached. This would be topped with a ridge ventilation cover. Several questions: is the second layer of underlayment needed, is there a less expensive way of handling the unheated and uninsulated portions, if two different systems are used for the heated and unheated portions how is the transition between the two made at the roof, is it necessary to vent the unheated area? Thanks for any suggestions.

Guest User

2017-09-18 11:08:02.000000

I would still recommend underlayment, and I feel that it is required by the International Building Code.

Todd Miller

2013-05-15 02:36:40.000000

In general, insulation is not necessary. But, tell me more ... what is beneath the current roof? Do you have a vented attic? If so, then by all means retain that. Also, do you have insulation on the floor of your attic?

Todd Miller

2013-07-29 23:31:27.000000

Do you have ventilation in your attic? If so, what? And you have no insulation? I guess my suggestion would be to vent the attic, both with intake and exhaust vents. www.airvent.com is a great resource for venting information. And then I would also suggest some insulation on your attic floor.

Todd Miller

2013-07-30 08:24:33.000000

I always suggest underlayment on top of the old shingles even if you're putting down battens. My interpretation of the ICC Code is that it also calls for this. I do not see the purpose of insulation on top of the old shingles. I have asked these questions just to make sure I am not missing something that others there have seen first hand. Putting insulation there is not the norm. I want to stress that anything you can do to ensure good attic ventilation will help with energy efficiency and help avoid moisture build up in your attic.

Todd Miller

2013-07-30 10:47:16.000000

These products are used in the UK and Europe but a little unusual here in the states. Additionally, they are normally applied when the roofing panels are made, not after installation. Here is the product though: http://dripstop.net The following company in northern Indiana offers it on their panels: http://ramcosupply.com/building-supplies-moisture-control.html I hope this helps. Please contact me anytime. All Best,

Todd Miller

2016-04-11 05:30:16.000000

Actually, perhaps someone will correct me but, except in high wind areas, I am not sure the IBC does require underlayment beneath metal roof panels. It does clearly require it beneath metal shingles. However, most manufacturers call for it beneath their metal panels, and you;d have to check local codes as well where you live. Underlayment is considered an industry best practice and you have every right to require it,

Todd Miller

2017-06-16 05:15:45.000000

It sound like you will have solid decking on the roof. Underlayment helps guard against any condensation that may occur. It also provides protection should a flashing or something occasionally bleed any water. In looking at the IBC today, for standard metal panels, I do not see a call for underlayment. I thought there was one but I can't locate it. Perhaps someone else will correct me. If the contractor did not specify underlayment in the quotation and contract, then it is tough to assume he included it. I'm sorry. Contracts are the legal binding agreement and all work done should be specified in them.

Todd Miller

2017-06-16 07:50:17.000000

To prevent condensation....no. The existing shingles and plywood will definitely keep out the moisture. As it pertains to code....I would go with Todd's recommendation.

Eric Novotny

2013-05-15 03:34:13.000000

That is pretty slick stuff Todd. I would love to know what the technology is behind it.

Eric Novotny

2016-04-11 15:56:22.000000

You don't need a second layer of underlayment in this case and you are going to be hard pressed to tie in the two different sections without some difficulty. I would plan on doing the same thing throughout for consistency.

Eric Novotny

2017-09-18 11:37:15.000000