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New metal roof, now icicles in the attic

KevinW | Posted in Energy, Heating & Insulation on January 2, 2011 01:40am

After we had a new roof put on this summer, now we have major condensation in the attic spaces.

I have an 1930’s house, and this summer I had the 2-layers of asphalt shingles on the roof removed and replaced with metal. The roof deck under the shingles was wood planks on the main roof (with random sized gaps between), plywood on the rear extension over the kitchen. This was left in place with a few rotten places patched as needed. Everything went well, but as winter came on we started to get a lot of water condensation in the attics. Both I and the roof contractor blamed this on the change in ventilation. He came back and we added soffit vents and vents in the gable ends, but it hasn’t improved things much – with freezing weather we now have an ball of frost on the end of every nail and screw that projects through the roof, and a little pool of ice on the attic floor below each one, plus a thick layer of frost on the underside of much of the roof deck.

More details:

The roof is a gabled roof with the ridge running E-W and a large shed dormer on the South side, and a sloping ceiling room inside it. Because of the room inside, the main attic is broken up into 2 small triangular sections either side of the dormer, and one long triangular section on the N side. There is also a smaller gabled roof over the kitchen extension on the W end of the house. Above the attic room is a small attic just under the roof ridge.

Before re-roofing there were vents at the gable peaks which vented the ridge sections and the kitchen attic, and they are still there. There were also vents about 6 feet up from the edge of the roof, one in each small S triangle, one or two in the kitchen attic, and one or two in the long lower N attic. There were never any soffit vents (insulation went right down to solid 2×4’s between each rafter), nor any ridge vents. There is about 3.5″ of fiberglass batt insulation in the attic floor. Two plumbing vent stacks and the bathroom fan vent pipe exit through the roof via the north attic.

The only time we noticed any moisture in the attics was when we lost a few shingles as the roof reached the end of its life, and in the shed dormer as the torch-on roof there disintegrated. No condensation that I noticed between 2005 and 2010. We are in BC, Canada – climate very like coastal WA state.

When I discussed the new roof project with the contractor, we went into the attics and looked at the existing ventilation and discussed what might replace it. There would be ridge vents all along the ridges so would be more top ventilation than we had had before.

The new roof went on in summer 2010 – torch-on for the shed dormer and metal everywhere else. No rain while the job was in progress, no need for tarps. Come the colder weather, we noticed that there was a lot of condensation both in the house and inside the attics. Come a hard frost in November and it became really obvious that there was a lot of water up there that shouldn’t be. Called the contractor back and it turns out that no extra ventilation lower down (the ridge vents went in) was put in during the roofing. So we worked out a way to add more – drilling holes through the soffits and running pipes up past the insulation, and adding vents in the gables for the attic spaces behind the kneewalls. So everywhere now has at least some low and high vents. We also replaced the bathroom fan and its vent pipe to make sure there was no leakage of bathroom air into the north attic from it.

The added ventilation did seem to help some – I could feel more air movement in there. One of the small S attics now seems to be OK and is almost completely dry. However, the other one, the attic over the kitchen, and especially the long north attic are as full of frost as ever now we have freezing temps again. The area near the vent pipes in the N attic is just dripping with it, there will be icicles soon.

Obviously we have wildly upset the moisture/ventilation balance but I’m baffled as to where all this water is coming from.

I’m planning to replace/re-seal the doors to the attic spaces so no house air can get through (they are weatherstripped but they could be better. OTOH they were like this before, with the old roof!). Anything else I can do? Is there anything metal-roof-specific I should be checking for to see if we have water actually coming through the roof joints or fasteners?

Thanks for any suggestions, and if this would be better in a different section, please let me know and I’ll move it.

Kevin

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Replies

  1. bd | Jan 02, 2011 07:15am | #1

    bump

    Hopefully somebody with some real knowledge will come along & give you more info.

    I can't locate them right now, but I have seen some articles that claim gable end vents disrupt the convection flow between soffit vents and ridge vents, IF you have gable vents in the area that also has soffit & ridge vents. That would be easy to test. Just tape some paper over the gable vents & see if it helps.

    The moisture is coming from inside your house. Making it's way around any ceiling penetrations, e.g., vent stacks, electrical fixtures, ceiling-wall joints, etc.

  2. DanH | Jan 02, 2011 09:29am | #2

    You say you noticed more condensation in the rest of the house.  That suggests that perhaps the problem is not in the roof, but rather than something else has changed to add more moisture to the house.  Or perhaps a vent fan has become disconnected or blocked.

    Check for water leaks (especially with any water or heating pipes in a slab), and check that all vent fans are unblocked and the ductwork tightly connected to the outside.

  3. User avater
    MarkH | Jan 02, 2011 09:35am | #3

    You need to stop the moisture migrating into the attic from inside the house.  There are numerous pathways in homes from the 1930's.  The ones that come to mind are possible balloon framing which allows airflow into the attic, unsealed partition walls, remodeling changes that left penetrations into the attic, gaps around chimneys and vents, kitchen soffits that weren't sealed, unsealed wiring penetrations, unvented kitchen and bath fans, dryer vents into the attic etc.  You'll need to lift up the or move the insulation to check these problems.  Be sure to properly seal these penetrations, some methods can be more harmful than leaving them open.

    I think the old planks allowed some ventilation through the shingles, which is now tighter. with the metal roof. 

  4. calvin | Jan 02, 2011 11:38am | #4

    Kevin

    Here's one often overlooked area to take a look at. 

    In houses of that vintage, there was a popularity for the basement laundry-and a direct route to get the clothes there.

    The laundry shute sometimes had openings in a bedroom, but more often-the bathroom-a good source of added moisture and makeup air (when the exhaust fan was added).  That direct route from the basement can carry moisture (chimney effect) right up to and beyond the second floor.  Some were capped at the top, others not.  And those caps and surrounding stud space allow free air movement not totally sealed up at the attic.

    Likewise, many homes of that vintage were balloon framed-all stud spaces capable of bringing basement air up the envelope.

    Why you have this problem NOW is beyond me, but something simple like dark shingles previously absorbing heat and a reflective metal roof currently might be something that has helped change the situation.

  5. joeh | Jan 02, 2011 11:52am | #5

    All those vents aren't the answer

    Moisture from the house is going into the attic. The metal roof is a vapor barrier, the shingles allowed vapor to excape.

    Pull up the fiberglass and fix the openings that are allowing warm moist air to excape the house.

    Do you have a basement? Air flow from the basement through the balloon framed walls is another possible source.

    Joe H

  6. KevinW | Jan 02, 2011 10:40pm | #6

    Thanks everyone for the info. I spent this morning sealing up various access doors and hatches but I can see I have to do some crawling around in the ice blobs pulling up insulation. It's frustrating as I have done a good deal over the last few years to cut down air infiltration into the attic, but something must have opened up or changed that I haven't found yet.

    1. calvin | Jan 03, 2011 06:17am | #7

      Kevin

      How bout you remember to post information on your quest and hopefully successful outcome.

    2. User avater
      MarkH | Jan 03, 2011 06:39am | #8

      How about adding about a foot of insulation to the 3 1/2 inches after sealing up all the air leaks.  You should see a big drop in heating costs.

  7. oops | Jan 03, 2011 12:55pm | #9

    icicles in attic

    You might try sticking little squares of foam insulation on each nail and screw that is projecting through the decking.

    I know, I know. I should not have said this, but I couldn't help myself.

    I could just invision all those little squares stuck on all those nails and screws and trying expaining it to someone.

    1. cussnu2 | Jan 03, 2011 05:36pm | #10

      Have you checked the dryer vent?

      Has your wife recently decided to hang clothes up to dry?  (My wife does this now with a lot of our clothes and then she wonders why the windows are sweating.)

      Did you recently aquire a child or two?  They love to take long steamy baths.

      Install a party tub or shower you've been fortunate enough to talk the wife into using more than once?

      Install or start using a gas appliance you didn't have before like switching from electric to gas stove or install/start using a gas fireplace insert?

      Have you had water heater and or furnace checked for backdrafting?

      Any gas appliance can be a source of a lot of moisture as a by product of combustion.  Most people just don't equate burning with producing water.

      EDIT: You might also want to inspect the flue pipe.  If it has failed it could be dumping combustion gases in the attic.

    2. KevinW | Jan 03, 2011 09:57pm | #11

      LOL I admit in the middle of the night I had envisioned going around with a can of spray foam and putting a blob on each one! Maybe not, though.

      Thanks for the many suggestions, all - while some don't apply (no gas or other combustion appliances, for example) I'll be following up all that do. And yes, since I have to be re-jiggering the insulation anyway, I'll be adding more. 

      Kevin

  8. Clewless1 | Jan 04, 2011 01:16am | #12

    As others have indicated ... 2 possible problems:

    1) the metal roofing reduced the ventilation in the attic in some way. You indicated you came back w/ increased ventilation ... did you do it properly?

    2) you aren't controlling the moisture in the house properly ... did an exhaust fan get altered in any way? Did another source of moisture increase at about the same time? A new roof ... maybe someone got lazy and vented a fan into the attic instead of hard connection to the exterior? Maybe a duct got disconnected? Maybe you opened up another hole into the attic w/ some other alteration?

    Ice balls in attic mean lousy ventilation or huge air/moisture leaks from in the house. Exhaust vents need to serve all wet areas (kitchen and baths). They need to be controlled properly and operate properly. Hard connections all the way to the exterior. Correct size ducts and termination vents (that aren't restricted). Avoid flex duct to minimize air flow resistance.

    Sealy penetrations of the ceilings if possible (including the inside of J boxes). Trace possible paths of air leakage to the attic (even down to the basement/crawl).

  9. dial-it-in | Jan 04, 2011 01:48am | #13

    I assume you have tarpaper under the metal roof. If you don't, any moisture or humidity in the air would condensate and drip below whereever the metal is exposed to the attic. You would have to remove the metal and put a functional layer of tarpaper or ice and watershield down and then replace the metal.

    1. cussnu2 | Jan 04, 2011 09:23am | #14

      Are you sure they didn't knock a plumbing vent stack loose?

    2. Clewless1 | Jan 05, 2011 08:45am | #15

      sounds great except for the ice balls forming on the tips of the fasteners that penetrate the construction. Problem w/ the tarpaper is that it doesn't magically eliminate the problem ... which is obviously too much moisture in the attic ... which is due to either/or a lack of ventilation or air leakage from the house into the attic.

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