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brettmarl
Vapour Barrier Confusion

[Excuse the British spelling :)]

I'm back for more advice from the TOH gurus :)

We have an old 1914 home in Seattle. About once a year, during very heavy rain, our basement would take on up to 1-2" of water in one low-spot. The concrete walls never got wet, and so it appeared to be a water-table issue. There are small traces of effervescence but I have never seen moisture on the walls.

We had a basement waterproofing company come and install interior French drains. As part of their installation method, they insert a dimpled plastic barrier against the walls as shown in this photo:

The idea is that if moisture comes in from the outside, it hits the plastic and drains down into the French drains. Normally, they rivet the same material all the way up the wall to above the dirt-line. We didn't do that bit – and it's way more expensive to have them come back and do it.

I'm looking at using spray-foam insulation as it has the advantage of obtaining R21 in a 2x4 cavity (vs. 2x6 for fiberglass). I'm getting conflicting messages from insulation companies.

1. Aqueous Basement Systems suggest that I install 6mm plastic sheeting on the concrete and tuck it into the plastic dimples – so that if moisture enters from the outside, it has a place to run. They can spray open or closed cell foam onto the plastic in-between studs. Makes sense to me.

I know that most vapor barriers (or "retarders") are installed on the "warm side in winter". So I assume I would ALSO install an additional barrier on the dry wall side. Something like this "smart barrier" looks interesting. Which changes its permeability with humidity.

2. Burnham Insulation strongly advise AGAINST a vapor barrier on the concrete side – saying that it could cause moisture to be come trapped in the insulation and have no way to breathe. Interestingly, they also only recommend closed-cell foam for the Pacific Northwest – claiming that the open-cell shrinks over time and so doesn't not fully fill the cavities.

3. To confuse things further, this excellent article, cited by previous posts: suggests there should be no dry-wall side barrier: "The best insulations to use are foam based and should allow the foundation wall assembly to dry inwards". However, I'm not sure if Seattle qualifies as a "cold climate".

So what do I do? Install a drywall-side barrier? Also install a concrete-side one to channel foundation leaks into the drains?

Pointers much appreciated - I know that this issue has been discussed a TON of times - but I'm having a hard problem deciding which advice is region-specific as there is such a diverse geographical group on the forums.

Confused and bemused,
:confused: Brett

canuk
Re: Vapour Barrier Confusion

Brett .... excuse my poor spelling.:)

The efflorescence is from water being forced through the cement under pressure ( hydrostatic pressure) from the soil outside.... and forces the salts to leach causing the white powdery stains.

If these stains are located along the bottom of the wall where it meets the floor can mean the exterior perimeter drains ( weeping tiles or weepers ) are not functioning as they should. They could be blocked or broken which allows water to accumulate in the soil and eventually make it's way through the concrete ..... concrete is somewhat porous.

It may also be that this water is building up along this area and coming up through the concrete floor .... water will take the path of least resistance.

The method that was done for your situation was to install a weeping system along the foundation footing along the inside in hopes to drain the water that may be coming from the outside under the footings . In many cases this method is done because it's more affordable than digging the exterior of the foundation and rectifying the issues from outside.

Also insuring the ground outside slopes away from the house as well the down spouts from the gutters extend at least 3 - 5 feet away from the house will greatly help.

Now having said all that ....

By the sounds of things there stands a chance of moisture penetration from outside.

Personally I wouldn't suggest applying plastic to the walls and adding a second vapor barrier as this would indeed trap moisture.

The dimpled product would be the best choice if there was moisture penetrating the outside walls it would have a path to flow down to the floor drain. The gaps produced by the dimples allow for this and the air gaps would allow the concrete to eventually breath allowing the moisture outward as well.

I would have to agree with you in that Seattle wouldn't be considered a cold climate.

So having said that .... here's another recommendation.

If space is a consideration .... Instead of using 2x4 studs for the wall framing use 2x3.
Erect the wall framing about an inch away from the concrete and have the 2 lb closed cell foam sprayed so that it also goes behind the studs and into the cavities.
This will provide a continuous thermo break and is far better than the interrupted method of just filling the stud cavities .... increasing the insulation performance.

Another method would be to apply rigid sheets of foam insulation to the concrete walls first. Sealing the butt joints with a house wrap tape and filling any gaps with a canned spray foam.
Then build the wall framing in front.
This will provide a sealed continuous thermo break and the insulation you need.

With the closed cell spray or rigid foams there will be no need for any vapor barrier toward the inside and you certainly wouldn't need to go to the expense of using the "Smart barrier ".

However .... you might consider checking the humidity level and moisture issues in the basement first. If it's too high things like standard drywall will have mold issues.

A simple test .... cut a 1 foot square piece of clear plastic and tape to the floor as well on spots of the basement walls.... making sure they are well sealed.

After a few days ... see if moisture has acumulated on the top or under the plastic .
If it's on top ... this will indicate there is high humidity in the basement... if on the underside will indicate moisture from the concrete is infiltrating.

Hope this helps.

Cheers.:)

brettmarl
Re: Vapour Barrier Confusion
canuk wrote:

Brett .... excuse my poor spelling.:)

ha! that’s ok… i'm officially a US citizen now – so i'm slowly learning to drop my 'u's and use more 'z's.

canuk wrote:

The efflorescence is from water being forced through the cement under pressure ( hydrostatic pressure) from the soil outside.... and forces the salts to leach causing the white powdery stains.

If these stains are located along the bottom of the wall where it meets the floor can mean the exterior perimeter drains ( weeping tiles or weepers ) are not functioning as they should. They could be blocked or broken which allows water to accumulate in the soil and eventually make it's way through the concrete ..... concrete is somewhat porous.

It may also be that this water is building up along this area and coming up through the concrete floor .... water will take the path of least resistance.

the drains are actually brand new – installed in December. the efflorescence you see in the photo is probably a left over flood-mark from previous years. i'm fairly confident the new drains will do a good job at keeping the water at bay – but we haven't actually put that to the test yet…

canuk wrote:

The method that was done for your situation was to install a weeping system along the foundation footing along the inside in hopes to drain the water that may be coming from the outside under the footings . In many cases this method is done because it's more affordable than digging the exterior of the foundation and rectifying the issues from outside.

yes – for sure. digging up the outside would have been very disruptive for us – tackling from the inside was easier.

canuk wrote:

Also insuring the ground outside slopes away from the house as well the down spouts from the gutters extend at least 3 - 5 feet away from the house will greatly help.

check. done that.

canuk wrote:

By the sounds of things there stands a chance of moisture penetration from outside.

Personally I wouldn't suggest applying plastic to the walls and adding a second vapor barrier as this would indeed trap moisture.

The dimpled product would be the best choice if there was moisture penetrating the outside walls it would have a path to flow down to the floor drain. The gaps produced by the dimples allow for this and the air gaps would allow the concrete to eventually breath allowing the moisture outward as well.

from experience of living in the house the last 10 years, I have never seen moisture come in via the walls – it's always been a water-table issue. it takes about 4-6 weeks of continuous rain (yes – it happens every few years in Seattle) to breach and get wet – when it does – it always comes up via the floor when the water-table gets too high.

canuk wrote:

If space is a consideration .... Instead of using 2x4 studs for the wall framing use 2x3.
Erect the wall framing about an inch away from the concrete and have the 2 lb closed cell foam sprayed so that it also goes behind the studs and into the cavities.
This will provide a continuous thermo break and is far better than the interrupted method of just filling the stud cavities .... increasing the insulation performance.

not too worried about the framing depth. I think I have my answer though – I'll frame up with 2x4 pulled out 1-2" from the wall (it will be easier to come out this far to avoid the studs hitting the seismic plates I added), and use closed-cell foam to create the continuous barrier. with this method, I'll avoid any additional vapour barriers on either side of the foam as you mention.

canuk wrote:

However .... you might consider checking the humidity level and moisture issues in the basement first. If it's too high things like standard drywall will have mold issues.

A simple test .... cut a 1 foot square piece of clear plastic and tape to the floor as well on spots of the basement walls.... making sure they are well sealed.

we did do a more official slab moisture test where we put small containers of some chemical (calcium chloride?) on the floor covered in plastic and weighed the result. we ended up pretty low on the scale - 3.37 (out of 10 I think). so i think we're good there. maybe i will install a humidity meter and see if I can tie that into the whole-house-fan we're adding to kick-in above 60%.

canuk wrote:

Hope this helps.

very helpful – thanks!

brettmarl
Re: Vapour Barrier Confusion

Follow-up for future readers:

We ended up using closed-cell spray foam, and framed the walls 2" away from the concrete to create a continuous vapor barrier. It cost about $2400 for a ~900sq ft basement. They came and sprayed it in about 2 hrs - but we had to stay out of the house for a half-day while it cured (high VOC :)).

We didn't use a vapor barrier on either side as it's closed-cell and impervious to water.

We had some great storms this year in seattle - so put out french drains and insulation to the test - everything stayed bone-dry.

Here's a photo:

Timothy Miller
Re: Vapour Barrier Confusion

Howdy, Why did you spray foam the basement walls in a non finished basement when your main floor is not insullated?
Adding R22 fiberglass to the basement ceiling would of kept your home warmer and lots less expensive....

PS the water comming up threw the floor. One can add visqeen, plastic, over the floor as a vapor barrier.

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