Another under the roof insulation question

Discussion in 'Homesteading Questions' started by Alice In TX/MO, Dec 15, 2005.

  1. Alice In TX/MO

    Alice In TX/MO More dharma, less drama. Supporter

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    I think I may have messed up on the OLD home I'm turning into my office and craft room. If so, tell me now because I haven't put the interior treatment on.

    The 'attic space' is an unfinished area that is tall enough for my studio. The single peak roof was redone with asphalt shingles and a ridge vent. The area is 30 feet front to back, which is the length of the house, and not quite 20 on the width. There is no 'wall', just the interior of the roof slope on each side of the rectangular space.

    As someone mentioned in a post on the other insulating a roof thread, I put insulating bats directly against the roof decking between the rafters. There isn't any moisture barrier on this insulation. It is held in place by chicken wire.
    I was going to apply the room's 'wall' treatment directly against that.

    Help! If this is going to cause a moisture problem, now is the time to rip it out and do something different.
     
  2. stanb999

    stanb999 Well-Known Member

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    What you need to do is first check and see that you insulation isn't totally filling the cavity. Their should be a 1" air space between the roof plywood and the insulation. (THIS IS VERY CRITICAL). If their is no space then you must get some styrophome? channels to make this air space. They sell them at the Lowes or the Depot.

    Next as for your vapor barrier. You may be better off just getting some 6 mil. plastic. It would be stapled into place just before putting up your drywall. This can also be bought at the lowes or the depot. This is a good barrier and pretty cheap.

    That air space above is the most critical. But the vapor barrier will prevent some added moisture issues.
     

  3. wy_white_wolf

    wy_white_wolf Just howling at the moon

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    In addition to the ridge vent you also need eave or soffit vents to allow the air to move through the 1" space that Stan mentions.
     
  4. TNHermit

    TNHermit Well-Known Member Supporter

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    This is correct !! I would add that you should have soffet vents so air can travel up the air space and leave throught the ridge vent. There needs to be circulation in the dead air space to get the moisture out
     
  5. Cabin Fever

    Cabin Fever Life NRA Member since 1976 Supporter

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    Rose, the way you want to do this is too build a room within the attic. Build the room such that there is continuous and connected airspace all around the bottom of the roof deck. The room is likely to end up with short verticle kneewalls and sloped walls above the kneewalls to the ceiling. The horizontal part of the ceiling will be rather narrow (I hope this makes sense). Take the insulation down that you have now and use it to insulate the new room.

    Remember, what you are striving for...your goal.... is too keep the temp of the area right under your roof deck the same temp as it is outside. The only way you can do this is to have fresh outside air circulate under your roof deck.
     
  6. MELOC

    MELOC Master Of My Domain

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    i had similar questions a while back. no roof in my house is insulated. the attic floors are all insulated though. there was an addition where one bedroom was left with a cathedral ceiling. i knew i needed to insulated but did not want to lose the ventilation. i chose to use r-13 fiberglass (not much insulation but better than none). it is about 4 inches thick. i left it at the bottm of the rafters and created a space above the insulation for air to circulate. luckily i never finished the inside of the room as my insulation has the moisture barrier facing the living space. i suppose i need to flip the insulation around?
     
  7. Alice In TX/MO

    Alice In TX/MO More dharma, less drama. Supporter

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    No air flow space between roof and insulation, darn it. Sigh. My friend who installed all that insulation is going to absolutely kill me.

    There are no soffits on this house. Long story involving Moravian immigrants and beer. Imagine an A frame house directly on top of a box shaped house, with no overhang at all.

    I think Cabin Fever's solution is going to work....wondering if I can leave the insulation that's there in place and then build the 'room within the space' below that so the air moves between the existing insulated space and the new space.
     
  8. gccrook

    gccrook Well-Known Member

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    OK. I am adding on to my house, and will have a cathedral ceiling. I was planning on using the sprayed on foam (having it done). They asure me that they spray the stuff directly on the roof decking in the case of a cathedral ceiling, and that it is fine that way. What say ye?
     
  9. kuriakos

    kuriakos Well-Known Member

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    No, the moisture barrier should face the living space.
     
  10. kuriakos

    kuriakos Well-Known Member

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    That might be OK, but probably not ideal. I would take the insulation down.
     
  11. whistler

    whistler Well-Known Member

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    unless you are in the deep southeast and use ac a whole lot and a furnace very little, the moisture barrier is supposed to face the living area.


    Whistler
     
  12. kuriakos

    kuriakos Well-Known Member

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    That's a tricky one. The sprayed foam is also a moisture barrier so I don't think you need to worry about the roof deck rotting. But unless you use a really thick layer of the insulation (like 12") you'll still have warm spots on the roof, which lead to ice damns. I would still build it with a vented airspace between the insulation and decking.
     
  13. TNHermit

    TNHermit Well-Known Member Supporter

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    You can buy small vents that you drill a 2 inch hole (hole saw) in the side of the house where the rafter cavity is. You just have to put one in each cavity.
     
  14. michiganfarmer

    michiganfarmer Max Supporter

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    everyone I know calls that plastic sheeting vapor barier. Ive often thought that it should be called moisture barrier