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Vapour barrier on ceiling into a well ventilated attic
Hi. Do I need a vapour barrier on the ceiling of my bathroom if I have blown inulation in my attic? And a fan that blows outside? (a hose through the attic). Thanks.
I was told that some vapour will escape and this will be ventilated out of the attic by the ridge vents and the air moving through the soffits... thanks |
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No vapor barrier on top of insulation!
You want as much ventilation "vapor escape"out of the attic as possible less vapor trapped in attic the better the insul works. A vapor barrier has to be right were the cold and hot air meets (ceiling from living space) stooping the moisture getting into the insul. A way to check out trapped vapor in attic see if there are any roofing nails sticking through roof. See if there are little ice cicles hanging on. If so need more ventilation. Lot of people don't realize a "roof" is to protect the structure from rain and wind not from cold. To properly put a vapor barrier in your ceiling is to remove the blown insul and barrier on the actual ceiling and the insulon top of that. A bathroom exhaust to be perfectly installed must be directly vented to the outside. However most do not and send it to the attic. It will put moisture into the acetic and maybe too much That becomes a personal call. Insul needs to be kept dry on both sides to perform properly. Signed 21 boat |
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 Originally Posted by 21boat
thanks for your detailed reply.. although an additional question... I understand that you cannot put the vapor barrier (the plastic) over the insulation. However, could I remove or sweep away the blown insulation that is now sitting on top of the non-vapour barrier ceiling (a 4' x 4' area ---- directly above the newly buily shower)... when this 16'square area is clear... can I then install the vapour barrier? How do I do this? Do I staple it to the joists and then tuck tape the seals? Or do I tape it to the attic floor (which is really my bathroom ceiling) and the joists... basically "saran wrapping" the area?. I woulnd't put the plastic over the insulation... however, I do not want to tear down tiles and ceilings in order to put up plastic vapour barrier that can be done from the attic (with a little maoeuvering and contorting of my body)... sorry for the detailed (rambling) response... but can you add more to this situation? Thanks |
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Sounds like you have a drop ceiling and then joist? Little Yes clear loose insul. Under that is where the vapor barrier goes against the exposed ceiling Now if there is an attic floor over top the joist it really should come up. To do it from below your barrier would be stapled flat to bottom of joist but then how to get insul back in other than blowing it in. Staple and tape / joist then insul then attic floor above all. Tommieddie51. There bathroom moisture needs to be stopped before it travels into insul. That letting moisture 'breath" into the insul knocks down the 'R" value and then compounds the problem and then hidden mold in insul. If the insul barrier done correctly the moisture will stay in bath area and if that creates a mold problem you can see and address it right away before it gets out of control. The fix then is bigger exhaust fan venting out side. Cracked bath door or shorter or cooler showers. There is also paints to compensate and help a vapor barrier problem Signed 21 boat Hope this answer helped |
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Originally Posted by 21boat
Finished tiles, blue board, blown insulation, attic space, plywood, shingles.. There is no floor on top of my joists... some 2 by 4's... so I can walk easily, but no floor... I would like (do I need) a vapor barrier between the blue board floor / drywall (celiing) and my blown insulation? So, do I sweep away the insulation and then put the plastic on the floor of my attic and then wrap it around so it wraps up to my joists? How far up the joists do I go?, do I staple the plastic or tape it? Also... I would like a nice seal... do I tape after I staple? Thanks |
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Vapor barrier on drywall "blue board" in attic side then staple barrier/tape then non faced or loose insul. Recap. Tile Blue board. Vapor Barrier 2x4 rafter bay. Loose /non faced insul on barrier Attic space Plywood shingles. That's it! Were good now! Great! Thanks for the great detailed reply! Happy Holiday Glad to help Signed 21 boat |
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Originally Posted by 21boat
What do you mean by "vapor barrier 2 x 4 rafter bay?... and what do you mean by "recap"... Also, there is a conflicting message from tommieeddie... don't want to cause any trouble,, just trying to figure out the best solution... See pic attached... |
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Originally Posted by 21boat
When I brush it all away, how critical is it to get a complete "seal" around the joist and floor... (the green VB I drew)... I have been researhing this and discovered that I could get BATT installation (the roll out carpet kind) with a VB on one side?. then I could simply lay this between the joists?. is this possible? Then, I wouldn't have to staple, tape, seal, and blow more insulation after I staple and seal.. What do you think? |
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Sorry to add hear I don't know your geo area on specs for what the 'R" value is but here its "R" 30 min. Blown in density isn't as good inch to inch as kraft face or faced insul. 'R" 30 is 9" of insul. I recommend to people that if they have blown to bag it up in sections. The get faced batts and put in bays barrier towads heated area and staple. When you get this done to a point last bays flip flop and get vapor barrier in and then use the remaining loose bagged insul to go thicker and no waste of loose insul re cycle in the last remaining bays or at the least 6" 'R" 19 unfaced and roll that over the loose and save on A.C. and heat.
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Originally Posted by tommieeddie51
Vaopur barrier? Or No vapour barrier... Even Home Depot is at odds... one person says to allow moisture to escape and vented up through attic through vents out the atmosphere... Other HD reps say "no"... "you must not allow moisture into the attic, because it could condense, frost your wood, etc"... Thanks, by the way, to all who have provided support. |
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Yes just fold out the flap in the VB and staple it or if its too hard to stable just snug it. Wilsonfrench I'm a builder since 1979 and still a contractor. Just use the word VAPOR/MOISTURE NOT trapped INSIDE the INSUL for mold. That what upsets me with HD. What throws everybody off is when to use unfaced and faced I pretty sure its even says on the rolls "we never look at it I already know" Signed 21 boat If I answered your question please rate my answer(s) |
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Put it simply if insulation gets just 5% moisture in it the insulation looses 95% of its insulation value/properties. VAPOR barrier is to stop that. Starting from the hot side The breath" factor is to be IN BY and ABOVE the insulation and ABOVE the vapor barrier. Two reasons that unfaced insulation is even sold.
1. to add on top of existing insul. (No vapor barriers to trap moisture between old and added insul. 2.Many states and countries require a 6 mil min plastic stapled and taped on heat side on insul because it is a climate that gets hot and real cold. the tape is to lock out as much moisture as possible again this is done on the HEAT side before any insul unfaced insul is used then so theres not a double vapor barrier. The insulation must "Breath where it stops at the cold air side and above that IE roof vents/gable vents/soffit venting. Now below grade it's a different thing. No fiberglass between basement wall and no vapor barrier on the fiberglass. A insulation panel/boards is what's used there. It can't take the moisture from the basement foundation walls and mold and rot and maintain its "R" value not to mention the mold. Now to really mess you up if a cold garage has a heated living space above that the vapor barrier goes on top of the insulation above truss and then coming into the garage is the insul and drywall. The best application there is a spray insulation on all wood above the garage trusses simply because its very hard to VENT above garage insulation and the spray insul is the way to go. It doesn't collect mold inside the foam. I get your questions all the time and don't understand what the confusion is. I just pulled up You Tube to see if there was anything there to help you and there is, check it out. Nothing against home depot but they aren't builders. It's a great store but its not a complete information center. They only know what they hear. Been building here since 1979 and science doesn't change only the available types of materials and the application as science really got into building practice and then codes Its not perfect and some of the building codes I would like to take to court and prove through science that a but is wrong or just plain goofy. But in all 95% is very good and As much as we builders rubb and at times challenge the code in all it's a good system. It greatly helps us contractors bid apples to apples because of codes, if its followed. Call your local building inspector or an honest insul company. I am correct on vapor barrier question answer Your answer it your question is about a building practice and basic science not an opinion comment or answer. You mentioned you were worried abut the barrier on top of the blue board and moisture trapped there. 1. If this was a problem there in itself there's a lot of dumpsters to be filled up on all homes in whorls. Science rules here. Signed 21 boat If my answer has helped please rate this answer |
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No need to vapor up over the joist just between The 'baffle" thing As long as you have a min of 2" open space in the bay of the roof rafter and the 2 form side to side rafter your perfect for airflow The baffle is to insure that no insul or blown insul is plugging that air passage from soffit up under the roof sheeting bay. You mentioned way back you were going to get the loose insul blown in I would use the baffle to ensure the venting gap doesn't get clogged and hopefully the won't force loose into inside soffit bay. The baffels are a bit deeper for air flow but its not full with from rafter and the depth accounts for that. |
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