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Roofing underlayment

| Posted in Construction Techniques on May 26, 2003 08:58am

I am in the process of reroofing my house (a small 1930’s bungalow). I stripped the roof down to sheathing (T&G) and replaced any rotten/broken pieces with OSB. I then installed Mira Dri self-adhesive water/ice protection over the eaves and in the valleys before running 30# felt over the remaing sheathing. To prevent the felt from blowing up in high winds I used twine stapeled along the bottom of each course of felt. I’ve heard that this method has kept many houses dry for long periods of time before shingles were added… Of course, on my own house it leaks in the felted areas. Here in Montana it is becoming popular to use Mira Dri on the entire roof before shingling. Does anyone have any thoughts on this? Sounds like that would eliminate an awful lot of staple holes that could leak through the existing T&G sheathing before the shingles are applied.

My timing is lousy for sure, but should I be worried that the tar paper leaks now? As soon as the weather breaks it will be getting shingles… Thanks!

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  1. Davo304 | May 26, 2003 09:41am | #1

    MontanaJ

    Using water/ice protection membranes in the valleys and on the eaves is a good thing. In some northern states, this practice is code.  Since you say your house is a bungalow, I imagine the slope on your roof is no less than a 4/12...probably more like a 6/12...right?   If this is the case...where you have sufficient slope to allow proper water run-off from your roof, there is really no need to sheath your entire roof with the membrane material. It's a waste of money.

    30 lb felt is plenty adequate for "papering" your roof.  I've never heard of the twine method you described. Normally, we install our felt, working from the bottom (eaves) upward toward the roof peak. Each successive course is lapped overtop tyhe preceding course of felt as per mfg. suggestions ( normally a 2 inch overlap on horizontal seams and 4 inches at vertical end seams).  We simply staple the felt down using 1/4 inch staples and "hammer tackers." To keep the felt secure, we install a couple of bundles of roof lath....these are wooden sticks approx 2 inches wide, 3/8 thick, and 4 ft in length. A bundle at our lumber yard costs us apprx. $7. We shoot these lath sticks down with our roofing nail gun...normally 3 nails per stick.  We spread the sticks out a few feet apart from each other along the seams. The sticks (lath) adequately holds the felt down against fairly strong wind storms. one bundle can easily hold down 2 to 3 squares of roofing area, depending on how far apart you space them.

    When it comes time to install the shingles, we remove the lath from the areas we intend to roof first. The remaining lath remains in place until we are actually ready to start  shingling along that row.

    Some roofers don't use staples for holding down their felt at all. Instaed they nail down plastic tabbed nails. The tabs keep the nails from tearing through the felt. If you use the nails, simply nail the bottoms, lap the next row of felt overtop, then nail both layers down together...this minimizes the amount of nailing needed.

    As for your concern about a lot of water penetration through your staples...you may get some water, but it should be very, very slight...normally not enough to worrry about. Unless you have large tears in your felt, don't worry. Normally, unless you have created a condition where water run-off is blocked off or dammed, you have no real worries involving water going through your staples. I have had to wait several days with torrential down pours hitting my roof decks that were only papered and lathed...when the weather finally cleared so I could shingle, the existing roof deck was always just fine. Yours should be too.

    If you are worried about your twining, remove it and nail down the wood lath. Wood beats string any day.

    Davo

    1. Nails | May 26, 2003 04:26pm | #2

      D. "wood beats string any day". Having  "never heard of the twine method " maybe you ought to look into the method before you pass judgement . I've been useing this system for years , works great , no torn felt when you take up lath , no lath to dispose of , no nails sticking up that present a potential hazard to civilians . Remember with most shingles the black side goes down.

    2. MontanaJ | May 26, 2003 05:03pm | #4

      I think I may have sent my first reply only to Davo... But the jist of it was that I had 10-12 tiny leaks in my attic when it was really raining last night. My pitches are 8/12 with 5/12 addition forming an L, 3 gables, 2 valleys. 

      I was very careful when overlapping my felt and am not aware of any major tears that could be leaking. Should I re-felt before shingling? Don't worry, it's small. I am only talking about 12 squares...

      Thanks... MontanaJ

      1. User avater
        mike_guertin | May 26, 2003 05:28pm | #5

        MontanaJ,

        To answer your questions regarding MiraDri-ing the entire roof from your first post: 

        Covering the entire roof underlayment with MiraDri (a brand of Waterproof Shingle Underlayment -WSU) will eliminate any leaks both as a 'drying in' membrane and it will give you 100% backup protection in the event of a shingle failure (defective shingle problem, ice dam, wind blowoffs, hail damage...).  The beauty of these peel-and-stick membranes is that they stay put once the rubberized asphalt has bonded to the roof sheathing and that they are self healing around nail / staple holes.

        There may be problems with covering an entire roof with WSU though.  In some instances the WSU can be a condensing surface on the underside when there's an elevated level of moisture vapor in an attic (or rafter cavity) during cold weather.  Since you have T&G roof sheathing, there are lots of joints where attic air can reach the WSU and condense out water. 

        There are two things that will reduce the likelyhood of a condensation problem: Good attic / rafter space ventilation - soffit or vented drip edge and ridge or roof vents.  The other method can be used alone (if you have no ventilation) or in combination with roof ventilation; completely air seal the ceiling level from the attic / rafter space.  This means airtight drywall/plaster, sealed penetrations (light fixtures primarily), sealing around wire and pipe holes in the top plates of walls (you can do this from the attic if there is one), spaces around chimneys and so on. 

        And as far as should you refelt before shingleing - that depends.  I usually do because when felt gets wet it will buckle up a little.  Those humps can telegraph through the new layer of shingles and make them look crappy.  This may not be a problem though if you used one of the fiberglass mat shingle underlayments rather than the regular cellulose felt tarpaper.

        Hope this helps a little.

        Mike Guertin

        1. MontanaJ | May 26, 2003 05:52pm | #6

          Mike- Good point about full coverage Mira Dri could causing condensation problems. This house definitely did not have a cold roof.  Last winter before I bought the house, I noticed the ice dam issues. My 1 gable vent is inadequate and it had no ridge venting. The attic insulation is very old too, so I know that the previous owner was heating sky all winter long causig the ice dams. All of the ventilation issues are being addressed now... Shingle vents in the ridge,venting all of the gables, friese block/soffit venting, and new attic insulation before winter.   

          I was just surpised to see all those drips during that rain. Disconcerting, for sure. I am wondering if I should have dubbed the corners of the felt at the valleys. 

          Gotta get those shingles on!  MontanaJ

          1. Framer | May 26, 2003 06:25pm | #7

            Just out of curiousity, how long has your roof been sitting with just tarpaper and why did you take the roof off if you weren't going to put the shingles down right away?

            Tarpaper is a temporary thing. If your not a roofer by trade you could have ripped off maybe a section at a time or just the front first and then the back at a later date.

            The most important thing is to keep your house WATER TIGHT, especially if your living in it. If it were a new house or an addition that if leaks wont leak into your home a little bit of water wont hurt anything.

            My roofer can rip off 30 squares and put the new shingles down complete in one day. If there's a chnce for rain, they will just rip off the the front, not the whole roof and finisned the front so it's water tight.

            Only rip off what you can put down. Tarps are temporary also. Any strong wind can blow tarps or felt paper off a roof no matter how secure it is.

            Joe Carola

          2. MontanaJ | May 26, 2003 06:36pm | #8

            Joe- I stripped and re-felted the roof in sections like you mentioned. With the first section having felt on it for about 9 days now. Shingles are to be put on Wednesday, weather permitting. But, these tiny drips in the attic have me nervous... like you said, I want it water tight...

            MontanaJ

          3. FramerJay | May 26, 2003 07:31pm | #9

            Mont-

            We use a Hitachi Plasti-Tacker to nail off our felt (almost always cheapo 15#), but hand-driven platic caps are much more consistent in finished quality.

            As far as leaks are concerned, we normally have a few leaks during a rain, but for the most part the building stays watertight, so I wouldn't worry too much about the leaks unless they are over a finished, existing structure. Remember, the felt is a temporary thing until the shingeles are installed, and then it serves only as a backup. I note also that I build new spec houses, not remodeling, so water intrusion is essentially a non-issue.

            As Mr. Guertin stated, use an improved felt product or at least ensure the felt is pulled taut when installing it to get rid of as many wrinkles as possible. Understand, though, that all but the worst wrinkles will tighten out after the felt gets heated by the sun for a few days. And while we're talking about how long to leave the felt exposed, my recommendation is just long enough to have those wrinkles straighten out. I've seen felt left exposed on houses so long it was as thin as paper and tan instead of black--no wonder the roofers were complaining about it tearing out.Quality before Quantity

          4. Piffin | May 26, 2003 07:47pm | #10

            I just used RoofgaurdII for the first time. it stayed open for two months in all kinds of weather. Boy was I impressed! Good stuff!.

            Excellence is its own reward!

  2. Piffin | May 26, 2003 04:29pm | #3

    are you getting a drip or two through staple holes or is it really leaking?

    If a serious leak, you have a place where the felt is torn or is not lapped correctly facing downhill. It is worth fixing before shingling because any kind of failure in the shingles will leak again in the same place.

    The string shouldn't be a problem. I use plastic-cp nails and staples combined.

    Don't delay shingling it either. Wind can bring you a disaster.

    .

    Excellence is its own reward!

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