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Insulating a Basement

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Posted by: from Salisbury
6/17/2012 at 10:53:44 PM

I am about to frame and insulate my basement but I am unsure on how to proceed regarding vapor barrier.

Spray foam is not something I am going to do and I am aware that the vapor barrier goes on between the sheetrock, studs and fibreglass batts.

Is it necessary to put vapor barrier directly on the concrete wall or no. I am hearing both, one saying - no, its a mold paradise, and the other saying - yes, to prevent moisture from being in contact with the batts.

I need to make this happen soon, please help.

REPLIES (23)
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Kevin from Urban Improvements in Orono
Date/Time6/18/2012 at 12:16:52 AM

Your insulation should not make contact with the concrete wall in the first place as there should be an airspace behind the wall.

Your vapor barrier should be applied after your insulation install only.

Also make sure that there are no drainage issues to cause moisture to enter your basement.

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Date/Time6/18/2012 at 12:24:27 AM

Hi,

Normally you frame your walls with a foam sill gasket under the bottom plate, then you run your poly on the inside of your insulated walls and use acoustic sealant on all joints in the polyurethane barrier . This is the code. Also make sure you have 1" air space between your foundation wall and your framed wall.

Regards,

Andrew

Sabre construction 2011 Inc.

Richmond, B.C.

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Mark from Arbutus Sundecks in Richmond
Date/Time6/18/2012 at 12:45:32 AM

A simple rule of thumb with vapor barrier INSTALL ON WARM SIDE ONLY.

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Date/Time6/18/2012 at 1:15:03 AM

Vapor barrier must always be installed on the warm side of the wall. Frame you wall 1/2" off of the concrete so that the framing and insulation are not coming into contact with the concrete. That being said make sure you aren't creating a dead air space behind the wall that isn't vented to the outside, because that will definitely cause a mold issue.

Glenn Hamilton

GH Construction Services

1 250 661 4155

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SVS General Contracting in Conklin
Date/Time6/18/2012 at 1:22:43 AM

As contractor I do foundation repairs continually see vapor barrier on the wong side of the studs. think of the saying vapor barrier allways goes on the warm side of the wall that means keep the space between the batts and the foundation clear of any vaapor barrier.

I have been dealing with foundations for 5 yrs and in that time I have seen many homes with this problem.

780-381-3773

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Ramandeep from Fat Boy Renovation in Regina
Date/Time6/18/2012 at 2:19:18 AM

We I make simple for you and I do this for living.

The answer is yes you shud put poly on cement walls.

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Date/Time6/18/2012 at 2:27:05 AM

Hi Rick,

Spray foam maybe something you don't want to do but it is what you should do 2lb polyurethane Eco Waltite is the best application you can get at R20 which is new building code.

You see Rick you want to stop air from coming into your house that is what turns to vapour so when you do that you prevent heat loss and cold from coming in, now when you frame make sure you spray foam first so you don't have thermal bridging in other words frame in front of the spray foam.If you don't use spray foam then make sue you put Tyvek against the concrete first, frame, insulate R20, then vapour barrier and drywall.

Thanks

Brian

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Paul from Paul's Contracting in Barrie
Date/Time6/18/2012 at 6:25:27 AM

Hi Rick,

We work with building permits, and have inspections along the way. Though opinions vary, I like to ensure a due point barrier is installed directly on the concrete wall that is either tar paper, or Tyvex. This allows for the concrete to breath without moisture droplets gathering in the insulation. Even with a 1" gap between the foundation wall and then stud / insulation. Do both, install Tyvex (writing side toward the concrete foundation wall) and build walls 1" from foundation wall. Use a sill gasket when you use steel or wood studs. Insulate the wall (check the code for your application), then 6 mm poly vapour installed (warm side) prior to drywall. Ensure all your seams and joints are either tuck taped (red roll) and / or acoustical sealant to ensure no air gaps. Check that the electrician also installed vapour shells around each of your electrical devise boxes and tape them to your vapour barrier to ensure a good seal.

Note: if you put the Tyvex on with the writing side facing inside the room, it may mould. Make sure the writing side faces the other way. Also, if you have the builds insulation wrap on the walls already, take it off. Don't build over it.

Hope this helps steer you in the right direction. Don't be afraid to speak with your local building department on these things. They're a great resource!

Paul Counter

Owner

Paul's Contracting

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Date/Time6/18/2012 at 6:49:28 AM

The most common way to insulate you basement walls is To install your insulation into the studs first, then you vapour berriour, then the drywall. It has been done this way for over 40 years.

However, Some changes have taken place within the last five years. As more people have starting to use s/m insulation on their homes.

The changes are as follows:

First you apply your vapour berriour bonded to the concrete wall, then you fasten a s/m styrofoam insulation to the concrete wall , you studs, then your batt insulation, and drywall. We have used this system, and found that it is the best way to go. The vapour berriour will stop any moisture coming through the concrete wall, The s/m will stop the transfer of the cold concrete walls, then the batt insulation will keep The basement warm. Increases the R value dermaticly, saves a lot of money. Have not found any problem with hold. Just seen the savings On bills, and noise .

Paulo

Winnipeg drywall and stucco

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Date/Time6/18/2012 at 6:56:53 AM

As indicated already, install tar paper on the concrete wall first.

If you don't like foam, you could have the walls sprayed with cellulose fibre, versus fibreglass, better R-value, no mold or rotting, no insects or vermin, 85% recycled material, still need your 6 mil vapour barrier just under the drywall.

Brent

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in
Date/Time6/18/2012 at 7:51:21 AM

Good Morning,

Follow the Building Code which states, Building Paper on the backside of your interior walls, then your insulation between studs and make sure your floor cavities are stuffed. Then your 6mil poly. Then you can apply your blue drywall horizontal on studs. This is the only correct way that the Building Department will accept. Unless you foam and that is very expensive.

Jim

Degruyter Home Improvements (since 1984)

Ottawa On.

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Date/Time6/18/2012 at 8:05:51 AM

Vapor barrier against concrete is an absolute NO. Leave a 1" air gap between the concrete and the framing. R12 in the frost walls and R20 in the rim joists. Acoustic sealant at all the perimeter of all the poly.

Big tip....use pressure treated lumber on your bottom plates rather than a poly wrap on spruce, if you ever have a flood or sewer back up it's much easier to clean.

Dan Walker

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Date/Time6/18/2012 at 8:35:53 AM

Definitely do not put the vapour barrier on the concrete wall. It is a huge mistake if you do....mould trap.

The rule of thumb is that the vapour barrier is to always go on the warm side of the walls or ceiling just behind the drywall. Look in your attic if you can and depending on the age of your home there should be a vapour barrier underneath the attic insulation.

Regards,

John Maugeri

Woodland Construction

416-225-2896

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Rick in Salisbury
Date/Time6/18/2012 at 12:55:21 PM

Thanks for all your feedback. It seems that their is still 2 opinions but mostly for no vapor barrier on the concrete wall.

The walls are painted with what looks like a type of sealant and I had planned on using a 1" gap when framing with 2x6 to accomodate R20 batts, ploy the frame and eventually drywall it.

I should also note that I have already used a 3/8" foam - foil both sides - on my rim joists to stop extra airflow into the basement.

I also have a call into the local building authority to make sure I don't trip myself up in another area.

Again, thanks to all for your input.

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Date/Time6/18/2012 at 2:31:47 PM

Hi,

You should use black tar paper between your studs and the fondation then put your insolation and your 5ml plastic who will act as a vapour barior. This is the best way to keep moisture away from your stud and insolation specialy if you are planning to use wood studs.

But nothing beats spraying the foam directly on the fondation after your finished with your framing.

Thanks

D.

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Jeff from Newson Interiors in Dunrobin
Date/Time6/18/2012 at 9:14:10 PM

Rick,

Just to clarify, while dealing with basement walls there are 2 separate sources of moisture you are dealing with. The first being the condensation of moist air on a cold surface. This moist air originates inside your home.( Shower, cooking, laundry, human respiration etc.) The 6mil poly vapour barrier is used to keep this moisture out of the insulation.

The second is from outside. Ifyou have noticable moisture on your concrete, this is likely a sign of other foundation problems. if the dampness only seems to be there in the cold months, I would expect insulation and a warm side vapour barrier will block the moist air from contacting the cold concrete.

At the risk of sounding like Mike Holmes, spray foam is the best solution for this application as it provides a thermal as well an air/moisture barrier. If you are using batts keep your framing and insulation 1" from the concrete wall and Isolate the bottom plate from the concrete. I recommend roxul for this as it resists moisture better than fibreglass and will stay put (not sag into the 1" void).

Before you write off spray foam, price the insulation and vapour barrier needed and compare those prices.

Let the concrete breathe unless using foam. Hope this helps.

Jeff

Newson Interiors

Ottawa, ON

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Date/Time6/18/2012 at 10:19:05 PM

The poly always goes on the warm side what you can use and what we have done is either tar paper attached to the concrete wall or put rigid insulation foam in taped and sealed.

When you install the vapor barrier make sure to tape every seam and apply sealant where necessary.

Ryan

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Date/Time6/18/2012 at 10:22:46 PM

Hi,

The right way and only way to do it: R12 foundation wrap, insulate all joist spaces, Tuck tape all voids, then stud, insulate stud spaces, drywall.

Anyone who told you different has no business giving advice in construction.

Good luck and make sure you check local code and permits.

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Date/Time6/20/2012 at 5:08:00 AM

Sprayfoam and R12 is the best way to do it as long as you use A 2 lbs foam, and hit the rim joist. However

I seen some people use a 1/2 pound foam To save money, and all the drywall had to be removed Because of moisture damage. Do it right, and don't cheap out.

It sounds like your on the right path. Check with the permit office, they have an engeineer There as well that can tell you the way he would like to see it done. If the concrete wall was painted with a concrete paint, it wouldnt be much different then Having a vapour berriour applied on the wall. If fact their are some paint coating being used right now. That will give you a build up of 5mil per coat.

Have fun

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Rick in Salisbury
Date/Time6/28/2012 at 8:29:32 PM

Thanks all.

Now. Walls are studded, batts are installed. Ready for poly.

The question I have now is....

The gap between the top of the stud wall and the rim joists. Do I wrap the poly over top of the top and whats the best way to do it?

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Ty;er in Winnipeg
Date/Time3/24/2013 at 12:30:05 PM

So, I've been doing a lot of research on this exact post, and have also run into differing opinions. If you place plastic against the concrete, leave it loose but only go above grade, build walls out 1", use batt insulation, and vapor barrier over that sealing all joints and edges with sealant you should be ok?

You have allowed the concrete to breathe, protected your batts from any moisture incursion from the basement walls, and sealed the warm side from moist air from your home. Or, have you created a closed space for moisture to be trapped in, and asking for trouble later on?

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Sid in Winnipeg
Date/Time5/30/2013 at 10:04:17 PM

I have researched the hell out of this. mbhydro says poly on concrete to just above grade then wrap around bottom plate of stud wall...fiberglass [or similiar] and wrap insulation on warm side. Supposedly will breathe. I still believe spray foam is best but its just too damn pricey. I also believe almost every home has mold in basement wall.

I am in a brand new home and was insulated as per code....stud wall, fiberglass, poly. Cut a couple of spots open this winter and had at least an 1/8 in of ice on concrete. While I realize new concrete is wet and I also have dimple membrane on exterior. I also know that concreete will always have moisture in it.

What I have concluded is to glue 2 in foam to concrete....ensure no gaps....then use reg fiberglass or roxul etc.... then NO POLY on warm side...the thermal break sfrom the styro should ensure no moisture migration and no poly on warm side will allow the wall to breathe. also....everyone talks about warm side poly...what about summer when warm side is reversed??? I will be doing this next year and will also apply 1 inch foam on floor....for comfort only. I

I hate to say this but mike holmes pushes this and while I think hes an idiot....I believe this is the best way (aside from spray foam).

Anyone got any input on this ??? [method....not holmes]

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Ram in Denman Island
Date/Time6/18/2013 at 8:53:11 AM

I've also researched the heck out of this, and have many years of experience in construction, carpentry and boat building. What I've concluded is that there's a very good reason why there are two opposing answers to this question, and anyone who tells you there's only one "right": way to do it doesn't really know what they're talking about.

The principle is simple. The purpose of a vapour barrier is to stop the transmission of vapour, in this case specifically to prevent moisture from being trapped in the insulation between the joists in the inner wall and creating mould and rot. The issue is that in a basement vapour could be produced on EITHER SIDE of the inner wall. Normally in a home the vapour is produced from heat and human sources inside the home, so the logic of "always install on the warm side" applies. But in a basement it's also very possible that moisture will penetrate through or be produced on the surface of the exterior walls, so the logic of sealing that off behind the inner framing applies. But experience has shown that attempting to seal the interior insulation on both sides is almost guaranteed to trap moisture in the insulation. That's because unless both sides have a perfect seal some moisture will eventually get in, and it will have no easy way to get out.

I've concluded that if the basement walls are quite dry on the surface year-round then it's ok to put a traditional vapour barrier on the warm side. If not, I believe you're better off using NO vapour barrier at all, and allowing the moisture to pass through the interior wall as much as possible in both directions. It only makes sense to put a vapour barrier between the interior and exterior walls if you can insure that there is an absolutely PERFECT seal throughout. As far as I can see the only way to achieve this would be with a really, really good spray foam application - or an extremely diligent application of rigid foam with taping, caulking, foaming, etc.

As far as an air space between the inner and outer walls, I would agree this is pretty essential. 1" seems to be a minimum, 2" preferred. And ideally this space should be vented at the top, although this seems difficult to achieve completely.

Lots of opinions on this, lots of misiformation. Think about it. Your mileage may vary.

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