how and why's of house wrap & vapor barrier

mebedave · Jan 24, 2010

I need help with designing the correct way to apply house wraps, interior wall and ceiling vapor barrier, under slab vapor barrier, roofing under layment paper.And how and why they work togather or don't
My plan is 30x50 heated shop in north/east Kansas 2x6 fiber glass insulated stud walls,7/12 pitch truss roof with blow in insulation. All the outside walls and roof will be sheeted with ½ OSB for the shear factor (I get some very high winds here).
For the walls: I plan on using an exterior house wrap over the outside OSB shear panels, fiber glass insulation (do I use paper back or non paper back insulation and why?) then I’ll apply 6 mil vapor barrier over the insulation from the interior side with one of the following options for interior wall cover: OSB, drywall, or metal
For the ceiling/roof: I plan on using 30# felt paper on the OSB decking then metal roofing. About two feet of blow in insulation into attic area with a 6 mil plastic on the bottom side of ceiling joist with one of the following options for interior ceiling cover: OSB, drywall, or metal
For the slab: I plan on using a 6 mil vapor barrier under the slab. I’m still kicking around the idea of using under slab foam. 5” thick slab
Heat: overhead gas heater.
My hope here is to insulate the day light out of this building so the heater does not have to kick on very often, I’ll set the thermostat at 50 degrees. Hopefully this combination will keep the building cool as well.
Please tear my plan apart… don’t hold back!!! I do not want to make a mistake; I’m not real sure how the wraps, vapor barriers,and my selection of metal siding and my options of interior wall/ceiling cover work together. I do not want mold or other unknown's to me to become issues etc…

Rosco · Jan 24, 2010

this is a good read

http://www.garagejournal.com/forum/showthread.php?t=50696&highlight=tcianci

akdiesel · Jan 24, 2010

Sounds like you have a good plan ahead.
The paper fiberglass paper backing is to help hold it in place during construction as well as over time to keep it from settling down in the wall. You could have the foam spray applied to the wall cavities. This will give a much better air tight system.
As for mold I will suggest three options. Choice 1: You could pour your foundation so that you have a 1 foot wall of cement to keep water from contacting your wood or sheetrock. Choice 2: You can use the mold free (unsure of the title it is given)sheetrock. Choice 3: You can use the common style rock and on the lower 2' use the cement board. Keep in mind that you will want to use pressure treated wood for the bottom of your framing on any of these choices.
I have one large Modine natural gas heater in the corner of my 40'x60' shop. And keep it at approx 55 deg year round and no problems with frozen pipes on the other side of the shop.

mebedave · Jan 24, 2010

akdiesel said:
Sounds like you have a good plan ahead.
The paper fiberglass paper backing is to help hold it in place during construction as well as over time to keep it from settling down in the wall. You could have the foam spray applied to the wall cavities. This will give a much better air tight system.
As for mold I will suggest three options. Choice 1: You could pour your foundation so that you have a 1 foot wall of cement to keep water from contacting your wood or sheetrock. Choice 2: You can use the mold free (unsure of the title it is given)sheetrock. Choice 3: You can use the common style rock and on the lower 2' use the cement board. Keep in mind that you will want to use pressure treated wood for the bottom of your framing on any of these choices.
I have one large Modine natural gas heater in the corner of my 40'x60' shop. And keep it at approx 55 deg year round and no problems with frozen pipes on the other side of the shop.

I do plan on keeping the dirt grade well below the sill plate/structure so ground water run off is not too much of a concern for me. What is a mystery to me and the reason I started this thread is the proper use of these house wraps, interior plastic vapor barrier, and metal roof/siding materials. I do not want to create a problem using a wrong combination or technique that could cause condensation build up in behind siding or into the insulation that would cause mold.

brownbagg · Jan 24, 2010

I would also use treated wood behind the shower tub so if it does leak, no wood rot

sstruckguy · Jan 24, 2010

After seeing how our northern neighbors (Canada) requires house wraps, vapor barriers and similar weather intrusion code, its hard to argue with the weather protection that they will give.

Even though I live in a warmer zone than you, I employed most of your list. My inside temp is always more comfortable than outside and takes very little time to make it even better (28 x 40 free standing)

Its hard to overkill comfort :beer:

sstruckguy · Jan 24, 2010

BTW, if you are wondering, exactly a year ago, we went through what has been known as the storm of the century. No power to over 600,000 homes(in Kentucky) for up to 3 weeks.

This is a side view of my shop, with the inside temp not getting within 20 degrees of the outside temp (zero heat inside):

Did I spend wisely? You decide

aar0s · Jan 24, 2010

I work at a lumber yard, not a big box store but a family owned old school lumber yard/hardware store. I would not recommend the 6mil plastic on the walls or against the ceiling for the reason that it will hold moisture (condensation) in the wall and against the truss, mold will grow in there and the studs will rot out. Ive seen it many times. You'll be pulling it out in a few years. Your going to want to use the kraft face insulation if your going with a fiberglass insulation, the paper will act as a vapor barrier and give you something to staple to plus it will let the place breath a little. If your wanting the place tight look into having foam insulation sprayed into the walls, that stuff is ****! You could also build the walls out of 2x6's and use an r19 insulation over the r11/13/15 that you get with a 2x4 wall. go with a r38 in the ceiling.
Hey sstruckguy, im only about 40 miles north of ya, I defanatly remember that ice storm!

mebedave · Jan 24, 2010

aar0s said:
I work at a lumber yard, not a big box store but a family owned old school lumber yard/hardware store. I would not recommend the 6mil plastic on the walls or against the ceiling for the reason that it will hold moisture (condensation) in the wall and against the truss, mold will grow in there and the studs will rot out. Ive seen it many times. You'll be pulling it out in a few years. Your going to want to use the kraft face insulation if your going with a fiberglass insulation, the paper will act as a vapor barrier and give you something to staple to plus it will let the place breath a little. If your wanting the place tight look into having foam insulation sprayed into the walls, that stuff is ****! You could also build the walls out of 2x6's and use an r19 insulation over the r11/13/15 that you get with a 2x4 wall. go with a r38 in the ceiling.
Hey sstruckguy, im only about 40 miles north of ya, I defanatly remember that ice storm!

aar0s

If what you say it right (and i'm not saying it is or is not) why do so many use this plastic on the inside ??? More input everyone please

aar0s · Jan 24, 2010

cant answer that, just telling you what ive seen in my 15 years working with other contractors and homeowners. ive been told by many that its a bad idea. could have something to do with the different climates and moisture levels in the air. your in Kansas, not to different from where im at in Illinois. If it were me i wouldn't put the plastic on the walls and ceiling, id go with thicker walls and insulation. 2x6 wall would be stronger anyway.
Everything else sounds alright from what ive see. What are you going to put on the outside of the walls? vinyl siding, brick, fiberboard?

mebedave · Jan 24, 2010

aarOs
I'm leaning to metal siding and roofing over osb

aar0s · Jan 24, 2010

ok, I missed where you said in the first post that your going with 2x6 walls already. Should be a solid building with the 1/2 osb with the metal over it.
Something to think about with the blown in insulation is that it seems there is always dust from it. I had some blown in to my house about 13 years ago and ive got lots of dust a few days after i dust the place, asked a few guys and they said its from the blown in.
something else i was told by a guy that does the foam insulation is that he dont recommend doing both walls and ceiling, said that its too tight and that it dont let the building breath enough.
why 1/2 deck on the roof over 5/8? are your trusses on '16 in. centers? what kind of snow loads do you see there?
I like metal siding, holds up well and im thinking that right now metal roof is cheaper than a shingle roof, but i could be wrong for you area.

Stuart in MN · Jan 24, 2010

aar0s said:
I would not recommend the 6mil plastic on the walls or against the ceiling for the reason that it will hold moisture (condensation) in the wall and against the truss, mold will grow in there and the studs will rot out.

If the vapor barrier on the interior is installed and sealed correctly, moisture from inside the house shouldn't penetrate it. It shouldn't make any difference if it's plastic or kraft paper. The housewrap on the exterior is supposed to breathe, allowing any moisture that may be inside the wall cavity to escape.

There are some good articles building science here: http://www.buildingscience.com/index_html
Understanding vapor barriers: http://www.buildingscience.com/docu...tanding-vapor-barriers/?topic=/doctypes/diges

aar0s · Jan 24, 2010

It should but it the fiberglass insulation gets wet from the moisture condensating against it. Its especially bad when you use a faced insulation.
Im not talking about moisture from the inside of the house but the moisture on the outside of the house. cool moist air will penetrate into the insulation and the moisture will collect on the backside of the plastic soaking the insulation, over time this will ruin the insulation and promote the growth of mold. I cant tell you how many times ive seen it happen. lots of houses around here were built like this in the 70's and were having mold problems in the late 80's though the 90's.
If this were a place i was going to be in for a while id use the money for the plastic on better insulation, if it were me.

Teken · Jan 24, 2010

If that is the case I would wager top dollar that proper venting and air flow is the primary factor at hand.

In our neck of the woods, it is code to have venting in the attached garage. This code change for what ever reason took alot of time to come around. Houses are vented, it was just a matter of time that everyone woke up and smelled the coffee to include the garage.

Regards

EVIL Teken . . .

jklingel · Jan 24, 2010

It sounds like your area may be one of the few in the country where visqueen is used on the OUTside. Check w/ your building engineers, but I suspect the rot on the inside of those houses w/ visqueen vap barriers (referred to above) is due to crappy installation. I'm not a builder, but I have seen enough houses going up or being repaired and some visqueen jobs are deplorable; wide gaps around every receptacle box, said boxes not sealed, gaps around windows, visqueen overlaps not very wide and not taped and caulked w/ butyl rubber, etc. You have to work at applying a good vapor barrier. But, again, your area may have more moisture penetrating from the outside. I've read of that in southern states, and have seen maps of parts of the country that may benefit from outside vb; if I recall, they were the Leesianna types.

akdiesel · Jan 24, 2010

I believe part of the reason for the plastic barrier is for the garages that are attached to the house. This keeps vapors and other chemical gases from getting leaching into the house. For the detached shop this may not be an issue but it will aid in a weather tight structure. I would still use the plastic for the interiro side of the walls and ceiling.
The comment I made about pressure treated wood was not just for the exterior water issues but also the interior if you have water service in the shop and it leaks or washing a vehicle or floors. My shop has the wood frams directly on the slab, but the floor drains to center very well so standing water at the walls.

willymakeit · Jan 24, 2010

Check out the OSB that has the film on it. This elminates the need for house wrap and felt. The seams are taped with a special tape that is practicaly impossible to remove. For the slab vapor barrier I would go to 20 mil and tape. 6 mil punctures and tears to easy. JMO.

Rosco · Jan 25, 2010

In the humid south an interior vapor barrier is not recommended, but the exterior wrap is. Most of our moisture is coming from the outside, unless your A/C and heat are not properly controlled. Backing on fiberglass bats is good, as it will allow breathing. A solid interior vapor barrier down here is a no-no from all of my research.

Still trying to figure it all out.........

Mickey_D · Jan 25, 2010

If you are in a hot climate you might want to look at using old school roofing felt with a good overlap. A buddy of mine is a remodeling contractor and he sees a lot of the house wrap just falling apart inside the walls. He said that you can tear into a wall, especially on South and West exposures, and the Tyvek is looks like a cat got it. Crumbles when you touch it, does no good. He said that he used roofing felt on his house (and our barn when we had him build it) and it is tight but still breathes. We did an addition on our house and the almost 40 year old felt on the walls was still in perfect shape. It is harder and more expensive to put up, but it might be worth looking into.

nate379 · Jan 25, 2010

JM Huber's ZIP System is what you are talking about

http://huberwood.com/main.aspx?pagename=sendtozipsystem

willymakeit said:
Check out the OSB that has the film on it. This elminates the need for house wrap and felt. The seams are taped with a special tape that is practicaly impossible to remove. For the slab vapor barrier I would go to 20 mil and tape. 6 mil punctures and tears to easy. JMO.

mebedave · Jan 25, 2010

Some good info here so far, but I have to say I'm a little confused and I'll need more info before I can decide the way I'll go. I’ve seen builders around here put up OSB and then siding right on top of it no felt or wrap. I don't know, maybe they used that OSB with film on it (is it clear film?), but they for sure did not tape the seams unless that’s clear too. Someone is going to be paying for that someday down the road!!!

mebedave · Jan 25, 2010

aar0s said:
ok, I missed where you said in the first post that your going with 2x6 walls already. Should be a solid building with the 1/2 osb with the metal over it.
Something to think about with the blown in insulation is that it seems there is always dust from it. I had some blown in to my house about 13 years ago and ive got lots of dust a few days after i dust the place, asked a few guys and they said its from the blown in.
something else i was told by a guy that does the foam insulation is that he dont recommend doing both walls and ceiling, said that its too tight and that it dont let the building breath enough.
why 1/2 deck on the roof over 5/8? are your trusses on '16 in. centers? what kind of snow loads do you see there?
I like metal siding, holds up well and im thinking that right now metal roof is cheaper than a shingle roof, but i could be wrong for you area.

aarOs

Well that explains why our house has so much dust in it all the time.
"Why 1/2 deck on the roof over 5/8?" Yes I was planning on 1/2 osb(cost) with trusses 2' on center, but then I'll be installing metal roofing over that I think with the solid osb backing under the metal roof it would be strong enough to walk on compared to fir stripes spaced 24" to 30" apart.

mebedave · Jan 25, 2010

OK everyone here could benefit reading the info contained in this web site brought to us by Stuart in MN post #13 http://www.buildingscience.com/docu...-310-vapor-control-layer-recommendations/#Map

Go to this web site (above) after you read this go to the bottom of that page and down load the pdf file BSD-106: Understanding Vapor Barriers this will help out a lot !!!!!! It's a very long read so make a pot of coffee

thanks Stuart

bazzateer · Jan 25, 2010

As I understand it you want any vapour barrier to allow moisture etc out of the building but not into it. That's my very basic understanding anyway.

RogerM · Jan 25, 2010

Will a subject I know a little about, am a insulation contractor. Most of what you have is fine except. Don't use kraft faced insulation and poly on the inside walls. One or the other. Poly will seal it up better. Most kraft jobs people inset the flanges in the studs and leave the stud face bare this way than can glue and nail the drywall on. But if done correctly by pulling the facing over the studs and face stapling you need to use screws to prevent nail pops same with poly. If it was mine I would use unfaced insulation and 6 mil poly on the walls. I would not use poly on the ceiling. Moisture has to get out some where and a gas heater is going to add moisture. Use a baffle or proper vent at the eaves to make a channel for air to flow from the eave up into the attic. Ridge vents or power vents to get it out, hot air rises. If you are using fiberglass insulation in the attic you want get any dusting. Yes old insulation made from new print or rockwool is dusty but not fiberglass.

I would also spend the money for 5/8" OSB for the roof and use ply clips between sheets in the middle of joist, helps prevent sags and allows for expansion.

One other thing seal the seal plate of the out side walls. Caulk or foam sheet seal plate sealer as you build the walls. Slabs are not flat.

Roger

mebedave · Jan 25, 2010

Roger that RogerM

thanks

does the big box stores sale blow in fiberglass insulation and the machine for us D.I.Y'ers I know they have that stuff made from newspapers,I'm not a big fan of that stuff.

TonyF · Jan 25, 2010

Roger, maybe you can answer why some of my poly vapor barrier in the basement have purposely done slits while some walls do not? The inspector looked at it and never said anything. I never had the chance to ask.

mpraddict · Jan 25, 2010

Just a couple thoughts from someone who's been designing buildings for about 20 years. Vapor barriers is really not a correct term. Both poly and kraft facing are forms of vapor retarders. They both slow down the movement of moisture through a wall but neither completely stops it (poly does a better job than kraft facing). This is a good thing. Some of the newer technology retarders actually adjust porosity to the climate conditions, Membrane by Certainteed is one example.
For under slab, I would not go with anything less than 15 mil, and use one specifically designed for that condition. Stegowrap and Viper Vaporcheck are two products I'd recommend. These are designed to stand up to the abuse they take during the construction process as well as being more durable long term. Standard visqueen can break down over time.

onewaydave · Jan 29, 2010

Hey Mebedave. I'm just 70 miles north of you and have 2 comments.

My shop is steel framed. I just ro;;ed 6" x 12' bats up one wall across the roof and down the other wall and screwed the tin on top of that. I'm shocked at how good the insulation is. a single 55 gal wood stove keeps it T-shirt warm and no summer AC needed.

My house circa 1975 was 2x4 with unfaced insulation between the studs with plastic on the inside between the studs and the rock. I remodeled recently and found no mold, rot or any evidence of moisture. Just my experience.

BTW, I sail Lake Perry and understand what you mean about the winds.

mebedave · Jan 30, 2010

Thanks ONEWAYDAVE
What R rating is that insulation you used on your shop? Don't spill anything flammables near that open flame stove of yours... I don't what you to break any windows out of my house

Yup I live on the west side of Lake Perry about 3 miles south of DJ's marina

how and why's of house wrap & vapor barrier

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