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

No you do not need a vapor barrier. The moisture will escape as it was explained to you. You do need to use the exhaust fan when showering. A vapor barrier would keep the moisture from escaping and could create a mold situation.

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

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 to much That becomes a personal call. Insul needs to be kept dry on both sides to perform properly.
Signed 21 boat

hi 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

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

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

.. you mentioned "drop ceiling"... ok, this is what I have... looking up from my completely reno'd bathroom...
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

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

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.
Thats it!
were good now !! great!!
Thanks for the great detailed reply!
Happy Holiday
Glad to help

Signed 21 boat

Sorry, not sure I understand...
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...

YES great install the way you drew it.
Brush away, barrier, the re blown

YES great install the way you drew it.
Brush away, barrier,, the re blown

One "final" question... I hope...
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?

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.

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.

Can I put faced or non-faced insulation over blown? Can I put blown insulation over batts?.
What are bays barriers?. I didn't think you could put faced batts over another faced batt?

Non face over blown No! Vapor barrier in between ANY insulation to trap mostiure in the insul

[B]Signed 21 boat[/B

If I answered your question please rate this answer

Non face over blown No! vapor barrier in between ANY insulation to trap mostiure in the insul

[B]Signed 21 boat[/B

If I answered your question please rate this answer

... but can I lay batt insulation (the non-faced kind) over blown insulation?. or do I just blown insulation ontop of blown insulation? Thanks

No you do not need a vapor barrier. The moisture will escape as it was explained to you. You do need to use the exhaust fan when showering. A vapor barrier would keep the moisture from escaping and could create a mold situation.

I seem to be getting two distinct ways of doing this...
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.

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)

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)

Thanks 21 boat... you sound very experienced... what do you mean by "use the word VAPOR / MOISTURE NOT TRAPPED INSIDE the INSUL"...

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

yes great install the way you drew it.
Brush away, barrier,, the re blown

Cross section of bath...

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.

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 wont 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 fo that.

Regarding vapour barrier: good to know... that I just have to staple it to the floor or just the bottom edge of joist. (should I staple or tape - tuck tape it?)

As for the baffles: do I need a baffle per rafter? The rafters are about 24" apart..some are 2x6" some (on a smaller section of roof)... are 2"4's...
See photo... at the moment, there seems to be adequate air flow...
As you say, how could I ensure that no insulation gets blown into the soffits (that I have cleared)... they had BATTS laying in them. Should I remove them all to give complete air flow?

Yes staple vapor to bottom inside of joist and tape it if you can. Yes baffle per truss bay. In the summer it gets hot and humid this is when you really need the air flow and move the air and vent through roof vents. Also so attic balances static pressure and air keeps flowing.
Evenly.
If a little blown insul touches the baffle no bigger. A speck or two in soffit trough no bigger
Old days just gable vents.
Then plywood soffits with drilled holes and screens.
Now modern soffit with venting. The more air flow you can get the better it is. All bays baffel

YES great install the way you drew it.
Brush away, barrier,, the re blown

There are also some gaps (about 1 - 1 1/2 " wide)...in the floor of the attic...where the vent stack comes up, where I added the bathroom fan, the fixtures, etc...

HOw (must they be sealed?) can I seal these gaps? Can I use a material called "GREAT STUFF" to seal these gaps? Will this prevent hot air from coming up into the attic?

Does this stuff work to seal these gaps? Or can I seal the gaps using something else? Thanks

Yes "stuff works fine to seal around gaps. It expands quick so start slow. Its like welding point the tip slightly against the inside hole edge and work it around

21 Boat

If I Helped to Answer Your Question Please Rate My Answer

yes "stuff works fine to seal around gaps. It expands quick so start slow. Its like welding point the tip slightly against the inside hole edge and work it around

21 Boat

If I Helped to Answer Your Question Please Rate My Answer

... how do mean "like welding"... could you give a little more explanation 21boat? Do I stick the nozzle into the crack / gap and squeeze the trigger?.

I have read all this information and have been left with several questions.
Bat insulation with VB is better in density than blown in insulation?
What is the recommended routing of bathroom ceiling exhaust fans? Into soffet, closest vertical wall or roof mounting? I am in Northern Illinois and have been having truss uplift problems and cracking drywall. After inspecting my attic I have noticed icing under the roof deck and excessive moisture in the range of 70-72%. I rerouted the exhaust fans from the soffet as I figured the moisture was coming back into the attic space. 2 years ago I added several inches of blown insulation on top of existing 5-6 inches. I have 3 roof vents over the main roof, and 2 more over the master bedroom (cathedral ceiling). I don't know where to begin now to reduce this moisture in the attic space.

1. Remove blown insulation, add VB(plastic), return blown insulation.
2. Remove blown insulation, add bats w/ VB, add unfaced above this, dispose of blown insulation?
3. Reroute exhaust fans to roof.
4. Add Ridge vents across both roofs?

Thank you

I have read all this information and have been left with several questions.
Bat insulation with VB is better in density than blown in insulation?
What is the recommended routing of bathroom ceiling exhaust fans? Into soffet, closest vertical wall or roof mounting? I am in Northern Illinois and have been having truss uplift problems and cracking drywall. After inspecting my attic I have noticed icing under the roof deck and excessive moisture in the range of 70-72%. I rerouted the exhaust fans from the soffet as i figured the moisture was coming back into the attic space. 2 years ago I added several inches of blown insulation on top of existing 5-6 inches. I have 3 roof vents over the main roof, and 2 more over the master bedroom (cathedral ceiling). I dont know where to begin now to reduce this moisture in the attic space.

1. Remove blown insulation, add VB(plastic), return blown insulation.
2. Remove blown insulation, add bats w/ VB, add unfaced above this, dispose of blown insulation?
3. Reroute exhaust fans to roof.
4. Add Ridge vents across both roofs?

Thank you


Dear PCEK...
A couple of questions...
...
1. do you currently have a VB now on your ceiling? If you do not... how many months (years) have you NOT had one?. this may be the cause of your moisture in your attic...

1a) do you have peforated soffits? Baffles to allow air to come in? Are your soffits clocked with insulation (blown or batts)?

2. I wouldn't add BATS w/ VB as it may be difficult to cover all the empty floor spaces of your ceiling / drywall...

3. the soffit vent that I have sends the moisture to the outside... I cut a hole in the soffit and mounted the vent to the soffit with screws... there is a spring loaded trap which prevents air from coming back into the vent... I do not think that warm air is being brought back into the attic from the outside.

4. From what I have read: 1 sq foot of venting for every 300 sq feet of floor space (with a VB)... and 1 sq ft of vent for every 150 sq feet of attic floor (without a VB)..

Trying to retro fit a vapor barrier into joists is a waste of time in my humble opinion.

You'll never get it sealed tightly enough to accomplish what you seem to want to accomplish here. Moisture will continue to accumulate on the bottom of the joists and your going to get mold.

ALSO I have read w figure stating a vapor barrier is not needed if your in a region with less than 9000 degree days.

http://lwf.ncdc.noaa.gov/img/documentlibrary/clim81supp3/annualheatingDD_hires.jpg

All I know is there is apparently insufficient air movement, too much moisture, and damp inefficient insulation in my attic space, which requires some attention.

Now I am confused,.
Can a bathroom exhaust fan be vented through the soffit? (in other words... a hole is cut in the soffit and the warm air is pushed outside through this hole)... will the warm air (that has just been pushed out) be sucked back into the attic by the perforated soffit holes? Thanks

You really get around ;-)

Vent it through the roof.

You really get around ;-)

Vent it thru the roof.

It has already been done... I am now concerned that it was done incorrectly. Will warm air come back into attic? Thanks

It has been vented through the roof? Not much you could do to do it wrong (famous last words). Your concern is...

It has been vented thru the roof? Not much you could do to do it wrong (famous last words). Your concern is....

... no, it is vented through the soffit... but I have heard that since the exhaust fan is an "active" vent and the soffit is a "passive" vent, the warm air should be pushed away and not re-enter the soffit...
What are thoughts on this? Anyone?

Dear PCEK...
a couple of questions...
...
1. do you currently have a VB now on your ceiling? if you do not...how many months (years) have you NOT had one?...this may be the cause of your moisture in your attic...

There is no vapor barrier currently in place. The home was built in 96 and there has never been one in place.

1a) do you have peforated soffits? baffles to allow air to come in? are your soffits clocked with insulation (blown or batts)?

The soffetts are vented, the original builder blocked the truss spaces at the wall headers with small rolls of bat insulation, only had 3 std roof vents on back side of house. I removed blocking, added styrofoam liners between each truss both sides, when I had the house re roofed in 04. I also left the original roof vents in as an alternative to a ridge vent hoping I would have sufficient airflow. Also have heard ridge vents can let in fine snow in windy area. We are near farmland in far northwestern suberb of chicago, with constant breeze and winds.

2. I wouldn't add BATS w/ VB as it may be difficult to cover all the empty floor spaces of your ceiling / drywall...

Even if i remove all the blown insulation?

3. the soffit vent that I have sends the moisture to the outside...I cut a hole in the soffit and mounted the vent to the soffit with screws....there is a spring loaded trap which prevents air from coming back into the vent...I do not think that warm air is being brought back into the attic from the outside.

Unfortunately in my situation the builder :mad: who couldnt build a tree house correctly dumped the 2nd floor bathroom exhaust directly INTO the soffet.

4. From what I have read: 1 sq foot of venting for every 300 sq feet of floor space (with a VB)...and 1 sq ft of vent for every 150 sq feet of attic floor (without a VB)..

Attic space is approximately 1300 sq ft. 1/3 of which is a cathedral ceiling over a master bedroom. Both attic spaces are connected. 2 Vents over cathedral area, 3 vents over remaining, which according to above calculations would provide adequate venting for 1500 sq ft.

I just also placed a temperature humidity sensor in the attic for monitoring. The current outside air temperature is 29dg F Indoor humidity is 41%, thanks to an April Air Humidifier with auto controls from outddo air sensor. The attic space is reading 78% Humidity @ 39F :eek::mad::eek:

What do you think?

ALSO I have read w figure stating a vapor barrier is not needed if your in a region with less than 9000 degree days.

http://lwf.ncdc.noaa.gov/img/documentlibrary/clim81supp3/annualheatingDD_hires.jpg

All i know is there is apparently insufficient air movement, too much moisture, and damp inefficient insulation in my attic space, which requires some attention.

That map is hard to read. I am on Lake Ontario (canadian side)... altough we have cold winters and hot summers, I do not know how to calculate 9000 degree days... what is that, exactly?

As for your situation:

1. try venting the bathroom exhaust outside through roof... if that is not possible, vent it to the soffit, but make sure it comes through the soffit (cut a hole in it) and buy a soffit vent that attaches / affixes to the underside of your soffit.

2. we cannot get faced BATTS in CAnada. We use plastic / poly. I have been informed to use plastic as a vapour barrier on my ceiling (read through entire thread)

3. more vents wouldn't hurt

4. make sure yyour soffits are not plugged with insulation (blown or batts)

Hope this helps/

Attic space is approximately 1300 sq ft. 1/3 of which is a cathedral ceiling over a master bedroom. Both attic spaces are connected. 2 Vents over cathedral area, 3 vents over remaining, which according to above calculations would provide adequate venting for 1500 sq ft.

I just also placed a temperature humidity sensor in the attic for monitoring. The current outside air temperature is 29dg F Indoor humidity is 41%, thanks to an April Air Humidifier with auto controls from outddo air sensor. The attic space is reading 78% Humidity @ 39F :eek::mad::eek:

What do you think?

PCEK, from your location (hard to accurately read your map) it looks like you're in the 6500 degree range... so, according to your calculation, you do not need a VB.. but there are very helpful pieces of info in this thread.

I posted what I think you should do to increase ventilation, reduce moisture, etc.

I cannot help you with your humidity questions. Sorry.