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Thread: Roof Felt

  1. #1
    Member AKFishOn's Avatar
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    Default Roof Felt

    Greetings,

    Should a person buy #15 felt or #30 felt to put under a metal roof? Suppose the #30 is better (it costs more).

    Thanks

  2. #2
    Member alaskachuck's Avatar
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    15lb would be fine but 30 would not hurt it at all
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    I agree with Chuck. For all the bigger your place is going to be go with the #30.

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    15# will tear easier in the wind. 15# also shrinks faster in the sun. Both instances probably wont matter if it gets coverd up quickly. If you think it will take a week or two to get the roof metal done I suggest 30# and strip the laps.

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    Try Tyvek; won't tear, fewer laps, does the exact same thing as felt.

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    Recommended is 30# under steel roofing. You will only need two rolls judging from your previous posts on the subject.
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    Sponsor ADfields's Avatar
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    Your roof should be water tight under the mettle and the metal’s job is mainly to protect the water tight underlayment from future damage and to look good doing to. Most people think the underlayment is like a tarp to protect the house till the roofing is applied. Truth is the underlayment is intended to be the waterproof layer for the life of the roof. The visible roofing is only water resistant and designed to drain water from under it as well as over it.

    Your metal roofing will last 50 years or so and with that in mind I would want something under it that will also last and take advantage of it. I would go with rubber ice & water shield over the whole roof as insurance myself. But if you don’t have money for that go with 2 rows of rubber along the bottom and one row each side of any valley pans since these are the places where ice dams are likely, then 30# felt on the reminder.

    Some like to use 15# with a bit more than half overlap so they get the thickness of 30# and less chance of any water getting past the seams to rot the sheathing. This is the only way I would use 15# on a roof and is a very good idea in flatter pitches but no need to mess with it on steeper roofs.

    Tyvek will stop water droplets but it allows the vapor through, this is why we can use it on the cold side of walls where we never use a vapor trapping plastic. Tyvek also has no cushion to it or any ability to seal around fasteners. I would never use Tyvek as a permanent part of a roof but it can be used as a tarp in a pinch. If you go one thickness of 15# felt, Tyvek, blue tarp, or other cheap substitute you may find yourself pulling it all off looking for leaks and rot in five or ten years.

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    Member Rock_skipper's Avatar
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    Tyvek is an air bar. Not to be confused with vapor bar.

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    I'd use 1x4 cheap pine slats instead of plywood and forget the felt. In fact that's what I've done on the last several buildings. Easier, cheaper, and better vented.

  10. #10
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    Default Ice and water shield

    the whole thing just like ADfields said, spendy but, you will never ever worry about your roof again. A Leaking roof is the most stressfull thing and if something bad happens this can work for a roof for a year if needed.

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    Member garnede's Avatar
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    The code requires Ice and water shield to a minimum of the eave to 24" from the inside of the exterior wall. Like ADfields said, use a minimum of 2 rows on the Ice and Water Shield along exterior walls and 1 row on each side of any valleys. For the best and longest life roof cover the entire thing with ice and water shield. If you can not afford that then cover the minimums above then use 30#.

    Even if you do not live in anchorage follow the minimums. It may not be inspected, but it will prevent leaks from damaging your walls and ceiling. What often hapens is a roof is under insulated or under vented and you end up with a hot roof. The hot roof melts the snow and it runs down the roof till it gets outside of the exterior walls, where it cools and freezes. This creates ice dams and icicles. When the ice dam gets big enough the water will back up under the felt and leak onto your walls and roof. Also when the ice dam slides off it can take trim and sometimes metal with it.

    Also while we are on metal roofs DO NOT have any slopes over a door or deck that you would like to use for the duration of winter/spring. The snow slides off of metal roofs and it will block access to wood piles, doors, decks, garage entrances, etc. If you have a roof that haeds over one of these you may need to add a gable above to protect it.
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    I, for one, appreciate the attempt at good advice to the question however there are a couple of misconceptions I can clear up for you. As a general contractor I can assure you that there is no code requirement specifically for ice and water shield benieth metal roof panels.

    R905.10 of the 2006 International Residential Code states that metal roof panels shall be installed according to manufacturers installation recommendations. Most of these recommendations are similar in my experience and you may find these installation instructions at the manufacturers websites if they have one.

    Here is one manufacturer as an example http://www.ascbp.com/files/installation/Light%20Gauge%20Install%20Details/Roof%20Preparation.pdf
    Instruction are usually supplied with your metal roof package upon delivery. If you are picking the metal up be sure to get the installation guide at the point of purchase.

    As you can see in the instructions they recommend 30# felt on continuously sheathed roof structures and allude to the possibility that other weather barrier MIGHT be required over intermitant type supports like purlins. However the code indicates no such requirement under METAL PANELS. (This of course is subject to any local code ammendments to the adopted IRC or other code adoption for your specific areas controlling authority)

    That being said..I do like to use ice and water shield at the lower eaves and valleys as an additional precaution but if you want to save a few bucks (it isn't cheap) on cold roofs I cannot remember seeing an ice dam at the eaves. I have seen them on hot roofs or poorly insulated cielings at the walls.
    One issue I have seen however is the tendency for the fasteners in the lower 3-6 feet become loose from constant action of sliding crusty snow on the screw heads.

    Code DOES indicate ice shield is required in other types of roof coverings.

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    Good post.

    Here's some advice from a guy who's done lots of metal roofing for himself over the past 20 years. Metal has some advantages but it is not forever or maintenance-free. At least not the typical screw-down type roofing. Screws back out after repeated temperature changes. You need to check them every 2-3 years. If you forget? Sliding snow and ice will remove some screws leaving little holes in your roof....felt or not. Snow and ice will likely take a couple of screws out even if you keep them tight. It happens. The best solution? Buy concealed fastener roofing. And kill every birch tree in the area because the sap droppings will stick to any metal roof and make snow cling like you won't believe. And when the snow does build up? Don't park the snowgos parked under the eaves when you go to bed!

    The bottom line? Nothing we do is perfect. Good enough works fine. Enjoy your cabin.

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    Mr Pid, I can relate to what you are saying, but if the roof is protected form the heat like it is supposed to be there should be no problems.

    Your roof should be a cold roof, for those of you that are justing getting started this means that your house should be enveloped in a plastic on the interior and sealed so that the heat does not escape to the exterior. It should have a couple of vents on each end and maybe some eve vents in the roof to keep the air flowing.

    When you build your house- cabin, kinda picture a framework that is intomed in plastic on the inside. Any heat that you loose will go and do just what Mr. Pid said will do. If you take the time and use Tremco or other products, or tape you can avoid this.

    If you can keep the heat in the cabin you won't have to worry about the roof.

  15. #15
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    I was told / what we did on our cabin:

    I was told that the metal roofing was for water shed and the felt was to only provide a seporation between the wood sheething and metal for the metal will condinsate and the felt is to only protect the wood from mold or rot.

    Therefore we utilized Ice and water shild everywhere above the cabin or above a heated area and over the deck we just used ty-veck. Not sure if this was the best way to do it, but just wised to share what we did.

    I felt that having ice and water shiled over the hole heated space / cabin we would not have to ever worry about a leek for our cabin is only occupide buy as a weekend use only and we would not have to worry. It is also a cold roof.

    The price between 30# and water sheild was not that much differnt, plus the calibure of each product is night and day.

  16. #16
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    Default Birch tree sap

    Mr. Pid,

    Great advise on the birch trees sap getting on the roof. We did use the concealed type for the reason you stated below, but did not even think about the birch sap. We do have one large one next to us and looks like I should drop it. Heck with my tree falling acomplishments, "He He," I'll either hit the cabin or the outhouse with the tree!!!!!!!

    Quote Originally Posted by Mr. Pid View Post
    Good post.

    Here's some advice from a guy who's done lots of metal roofing for himself over the past 20 years. Metal has some advantages but it is not forever or maintenance-free. At least not the typical screw-down type roofing. Screws back out after repeated temperature changes. You need to check them every 2-3 years. If you forget? Sliding snow and ice will remove some screws leaving little holes in your roof....felt or not. Snow and ice will likely take a couple of screws out even if you keep them tight. It happens. The best solution? Buy concealed fastener roofing. And kill every birch tree in the area because the sap droppings will stick to any metal roof and make snow cling like you won't believe. And when the snow does build up? Don't park the snowgos parked under the eaves when you go to bed!

    The bottom line? Nothing we do is perfect. Good enough works fine. Enjoy your cabin.

  17. #17
    Member garnede's Avatar
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    Quote Originally Posted by mics_54 View Post
    As a general contractor I can assure you that there is no code requirement specifically for ice and water shield benieth metal roof panels.

    Code DOES indicate ice shield is required in other types of roof coverings.
    Thanks for the catch, I did not have the IRC handy, but knew that it was required for most roof types. That said it is a good idea to do it anyway.
    It ain't about the # of pounds of meat we bring back, nor about how much we spent to go do it. Its about seeing what no one else sees.

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    Quote Originally Posted by garnede View Post
    The code requires Ice and water shield to a minimum of the eave to 24" from the inside of the exterior wall. Like ADfields said, use a minimum of 2 rows on the Ice and Water Shield along exterior walls and 1 row on each side of any valleys. For the best and longest life roof cover the entire thing with ice and water shield. If you can not afford that then cover the minimums above then use 30#.
    .
    My cousin has nearly 20 years roofing experience and couldn't agree more!

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    The price between 30# and water sheild was not that much differnt, plus the calibure of each product is night and day.
    30# felt is .16/sqft

    any bitumen sheet is .65/sqft plus

    Grace ice and water shield is about a 1.00/sqft

    I agree it's better than felt. But it costs 600-1000% more.

  20. #20
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    Quote Originally Posted by mics_54 View Post
    30# felt is .16/sqft

    any bitumen sheet is .65/sqft plus

    Grace ice and water shield is about a 1.00/sqft

    I agree it's better than felt. But it costs 600-1000% more.
    I think you mean .16 ~ .65 ~ and 1.00 'square' not sq/ft (square feet.)
    One square is ten square feet or a 10'X10' aria.

    I have 2 rolls of Grace water shield on my deck now.
    One is 2sq of low temp and was around $65 last winter from Lowes.
    One in 2.25sq of standard stuff and was about $90 last summer from SBS.

    I also have a 2sq roll of Owens Corning water shield from Lowes this July for $79.

    You get around twice the 30# felt for the money as water shield, itís not 600 to 1000% more itís about 100 to 150% more.

    So what are we really talking about here onthe average Ďgood sizeí cabinís roof?
    You could save $200 or $300 on if you use felt in the field with water shield in the valleys and bottom as I contented is the minimum over living space.
    Or just 30# felt all over could save you another $150 or so in water shield.

    To my way of thinking its dang cheap insurance to cover the whole thing while youíre up there and forget about it for at least 30 years. But plastic sheeting and moss have been used in Alaska for years and work fine, so itís just a matter of free choice and finances as it should be. Sometimes we all got to do things on the cheap to get by and I would be the last to knock anyone for lack of funds.
    Andy
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