[westmanj]

Hi All,

So after reading many of the posts on this forum, I've decided to finish my basement. I've found a number posts that deal with parts of my question, but not the entire thing.

I've currently got a layer of r-12 roll installed 4 inches from the ground by the builder. I plan on removing this garbage as soon as possible.

I've decided to go with a Rigid board against the naked cement walls - most likely the Corning CodeBord 1.5in C200 product. This will give me an r7.5 value (r5 per inch).

After insulating all of the outside walls, I plan on framing with 2x4's and then brining the r-value up by installing batt insulation (r-13 or higher). My understanding is that I require r-20 in finished living spaces in my area.

My question is about vapour barriers. My understanding is that the codebord against the walls acts as a vapour barrier, but on the Owens Corning site, they have a number of basement drawings where they install an additional vapour barrier on the 2x4s, so the order is as follows:
Concrete-->CodeBord-->Framing with batts-->Vapour barrier.

My understanding was that the vapour barrier traps moisture, so is adding the 2nd vapour barrier a bad idea? Will it trap moisture between the two barriers (codebord & plastic) and create a mold breeding ground in the wood? Vapour barrier is normally installed this way without the CodeBord, so does it really make a difference?

Should I forego the internal vapour barrier altogether? If so, why does Owens Corning recommend doing so in their product sheets?

Any help is greatly appreciated.

Joe

 

[Bud9051]

@joe "If so, why does Owens Corning recommend doing so in their product sheets?"
My only guess is the recommendations change with the wind and that was the last best when that was written. Here is what I believe should be done, and this may not meet your local code requirements, they are often farther behind than Corning.

Your "Corning CodeBord 1.5in" is not actually a vapor barrier. It is more accurately referred to as a vapor diffusion retarder, which means a small amount of moisture will/can be moving through it. Since moisture will always move from wet to dry until the moisture levels are equal, if a real vapor barrier is installed as stated, on the inside of those studs, the inside of that vapor barrier will slowly increase its moisture level until it is as wet as the soil outside. In most climate zones, that's not good.

My preference is to use the rigid as you stated, but no other vapor barrier such that the small amount of moisture passing through the rigid is allowed to dry to the inside. It would be a very small amount and thus easily handled inside.

The only other caution is to watch your ratio of rigid r-value to batt insulation. The batt insulation is air permeable and you do not want moist air reaching the inside surface of the rigid if it is cold enough to cause condensation. There are guidelines for that ratio.

Bud

 

[westmanj]

Thanks Bud! Great info - One further point of clarification:

"The only other caution is to watch your ratio of rigid r-value to batt insulation. The batt insulation is air permeable and you do not want moist air reaching the inside surface of the rigid if it is cold enough to cause condensation. There are guidelines for that ratio."

Where can I find these guidelines? Are these the ones on the codebord side, or are they local guidelines that I can find from my municipality?

 

[Bud9051]

Here's an article on the subject related to exterior walls. I don't recall seeing a recommendation for basement walls, but there may be something in this link.

Basements are, of course, different in that everything below grade is not exposed to the same extremes as normal outside walls. Where basements can get in trouble is with air circulation from floor level up to the above grade area where it is much colder. Making your wall assembly closed on all 6 sides and keeping it tight against the rigid should minimize any problems along with some reasonable ratio. Just a guess, but 1.5" with r-13 batts would probably not be a problem. Of course I like Roxul so that would be r-15.

Bud
http://www.greenbuildingadvisor.com...lating-minimum-thickness-rigid-foam-sheathing

 

[westmanj]

Thanks Bud.
Now for the money saving question.
Are both of the following products the same?
FOAMULAR® CodeBord® Extruded Polystyrene Rigid Insulation http://insulation.owenscorning.ca/architects/products/codebord.aspx
AND
FOAMULAR® C-200 Extruded Polystyrene Rigid Insulation http://insulation.owenscorning.ca/architects/products/c-200.aspx

When I look at the technical sheets, I get lost, and the codebord references c-200, so I'm not sure if the two are one and the same. If so - isn't it better to use the 4 foot sheets of codebord vs the c-200 sheets so that I am saving money on square footage, tape, adhesive, etc?

Looking for more insight!

 

[Bud9051]

Their opening statements are a bit different with C-200 stating "insulate above grade exterior walls and the interior of foundation walls" where the codebord only says "insulate exterior walls with energy-saving FOAMULAR® CodeBord® Extruded Polystyrene Rigid Insulation." But I have no idea as to why that difference is stated. I do like the shiplap edges as rigid foam is known to shrink. An overlap would avoid a gap opening. Is C-200 related to a Canadian code reference?

Bud

 

[westmanj]

Thanks Bud, you were right they do look the same and one is for Canada. See the following reply from the customer service dept.

Codebord is Canada's version of U.S. Foamular EXCEPT for the following differences:
>
> * Canadian law will NOT allow U.S. Foamular to be purchased and driven across borders to be used in Canada. It is NOT CSA approved, and the government will Not allow.
>
> * Also, Foamluar and Codebord are essentially the same material, however the Products Offered have different compressive strenghts; eg. U.S. has F150 (15psi) and F250 (25psi) and Canada has C-200 (20psi) and C-300 (30psi), they use the metric system.

 

[Bud9051]

Not sure how smooth your basement walls are, but mine have a seam every 2 feet or so that annoyingly protrudes a half inch or so in places. I'm using a diamond disk grinder which works great, except for the DUST. I built a hood for my shop vac so I can grind inside the hood. I have to clean the filter often, but won't have to shovel the dust out of the basement. But, it does smooth the surface nicely and the first sheets have gone up very easily. I was disappointed in the "up and down" variations in the top of my foundation and will have to use insulation or foam under my top piece. Currently only covering the top 4' and top with foil faced 1" rigid, but by my calculations it will make a huge difference. If I finish the basement in the future I will add the code required additional insulation. Even shoe makers have to budget when buying shoes. I'm also plagued by being able to calculate my savings for each step so always try to maximize each improvement.

At your code required level you will enjoy the improvement. Just be sure to detail the wood above, the rim joist, as well.

Bud

 

[westmanj]

Hi Bud I considered it, but my rough seams aren't too rough from what I've exposed so far. Time will tell.

I've got a note into Owens Corning to see if they sell the Codebord product in 4x8 sheets vs the 2x8 sheets. I bet there would be a small cost savings there and certainly savings in tubes of adhesive.

Thanks again for all your help.

Back to a previous statement about your preference of roxul. Why do you prefer this product to the standard pink stuff?

 

[Bud9051]

Roxul specifically states for basement use, higher r-value, and very dense. When fiberglass is used in a basement it must be isolated from any moisture. It cuts easily with a long serrated blade and fits tight.

Another reason I wanted a smooth surface for my rigid is the foil face on that side (both sides). I didn't want the protruding concrete to punch holes through it. The rigid you are considering would not be affected.

Bud

 

[westmanj]

Ahh understood about the foil. Thanks again for your help.

I'll let you know how the progress goes. I need to special order the 48 inch product unfortunately. They only carry the 1 inch thickness flavor at Home Depot. If I went with it I'd need minimum r15 Batts.

 

[Bud9051]

The r-5 rigid covered with r-15 batt is cutting the ratio close, but this isn't an exterior wall, it still has a foundation between the basement wall and the outside. If we give that an r-2 then your ratio looks fine. BTW, Martin states the r-5 with r-13 yields a ration of 38/62. "For example, the table recommends R-5 foam for a 2x4 wall filled with R-13 fiberglass insulation in Climate Zone 5 (38% foam and 62% fiberglass)." His 38% is 5/13, rigid to batt. If we add r-2 to your r-5 the ratio using r-15 Roxul would be 7/15 or 47%. I would calculate it differently using the rigid divided by the total, but in any case it should be fine. Sorry for the numbers, I just can't leave them out.

The caveat is, this must meet the approval of your local codes. If they want the 1.5" then they must get it .

Bud

​

 

[sbryant324]

Foam / Roxul Combo

I didn't read through all posts for details but I too live in Ontario, Waterloo. I chose a hybrid combo of 2 types of foam on the wall, both rigid, lower portion being open cell for air escape, upper being closed creating a snorkel effect for air movement below to above grade. I chiseled the seams in the concrete to smooth them and sealed all gaps in the foam. Then studded and added R-14 Roxul over top for fire resistance and ease of work... net +- R22. Basement is warm cozy and dry 5 years in. Energy audit results were so high they baffled the guy who took the readings. "Never seen it done this way"... FYI Roxul cuts with a serrated knife and holds it's shape among other benefits. Comes from Milton.