Finishing Basement - want to validate plan


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Old 11-17-13, 09:03 AM
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Finishing Basement - want to validate plan

I have 138 linear feet of exterior poured concrete walls in my basement. The house is 3 years old and has zero moisture/water issues. The above grade portion has 1.5" Dow Thermax installed by the builder directly to the concrete.

I live in climate zone 5 (northern ohio). In looking at my options, I think I have an idea of what I want to do, but the more I read, the more confused I get.

Heres my thinking:

2" Foamular 250 (XPS) adhered to the concrete from the bottom of the existing insulation to the ground. Standard 2x4 stick framing with the pressure treated bottom plate attached to the concrete. 1/2" drywall.

The XPS is R-10, so I'm not sure if I need to do batts in the walls in addition to the foam boards. If I do, should I use faced or unfaced?

For the ceiling, I'm planning on uninsulated drop ceiling tiles.
 
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Old 11-17-13, 10:54 AM
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I have 138 linear feet of exterior poured concrete walls in my basement. The house is 3 years old and has zero moisture/water issues. The above grade portion has 1.5" Dow Thermax installed by the builder directly to the concrete.
Kudos to the builder. Hopefully the rim joist area was also insulated and sealed.

Providing it was installed properly ( well sealed ) provides a continious thermal break and a far better method over the typical interupped method of insulating between studs.


I live in climate zone 5 (northern ohio). In looking at my options, I think I have an idea of what I want to do, but the more I read, the more confused I get.

Heres my thinking:

2" Foamular 250 (XPS) adhered to the concrete from the bottom of the existing insulation to the ground. Standard 2x4 stick framing with the pressure treated bottom plate attached to the concrete. 1/2" drywall.
Your idea is a method we have used around these parts for a number of years and is very effective.

Just ensure that all your seams are well sealed. I like to use low expansion foam in a can ( window & door ) and seal all exterior seams --- along the bottom and corners --- use housewrap tape to all the butt seams.

One thing though --- if the builder applied only 1.5 inch to the above grade portion --- which is colder than the below grade portion of the foundation -- this must be within your local code and passed inspection.

If that were the case then using 2 inch XPS is costing more money than needed.




The XPS is R-10, so I'm not sure if I need to do batts in the walls in addition to the foam boards. If I do, should I use faced or unfaced?
Your local building codes will dictate the minimum required R value but I would suspect you would more than meet that with rigid foam.

Where I live our winter conditions are more severe and I would meet the required minimum with the 2 inch rigid foam continiously applied as a thermal break.

Remember the key word is minimum which doesn't gaurantee the level of comfort you may want. Therefore, we sometimes add batt insulation in the stud bays for increased performance and comfort.

If you were to add batt insulation ensure it's *unfaced* otherwise you risk trapping moisture between the two layers of insulation --- which is not a good thing.

The 2 inch extruded foam will provide the required vapour retarding and you don't want another vapour retarder ( like faced batts ) over top.
 
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Old 11-17-13, 01:53 PM
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Thanks for the detailed response. The R-Value on the thermax is 9.8, so I was thinking that the 2" r-value of 10 was comparable. I see what you are saying though about that being colder above grade, so we wouldn't need as much.

In that case I'll probably go 1.5" on the XPS as well.


Thanks for your help!
 

Last edited by jdolluc; 11-17-13 at 02:08 PM.
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Old 11-17-13, 01:55 PM
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Good post by canuk, he covered most of it. The Thermax is R-9.8 with the minimal R-value of the concrete wall, made code. http://www.dow.com/webapps/lit/litor...5.pdf&pdf=true

May be able to use regular plate rather than pt if you install it on 1" thick XPS for a thermal/air/capillary break, though in your newer house you have the required perimeter insulation under slab, check locally. Be sure not to cover the above-grade portion of concrete on the inside- the only means of drying the wetness- with a vapor barrier/retarder.

Batt is not required for your Zone, read footnote "c"; 2009 IECC Climate Zone Map - Ohio

The fb outside should have some type of covering on it- parging, stucco, etc.- you didn't mention.... if not, use some mastic/mesh tape on the joints as some tapes will fail under movement as they age; http://www.buildingscience.com/docum...a-foam-shrinks
Be certain to fire-stop the top of wood frame wall and every 10' as per code; Chapter 6 - Wall Construction

Are the rims foam board on exterior?

Gary
 
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Old 11-17-13, 02:19 PM
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Not sure if this is what you were asking, but the thermax is installed on the interior wall, so it is not covered.

Thanks for the code links. That helps.
 
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Old 11-17-13, 02:43 PM
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jdolluc --- you're welcome

Just to clarify -- are you intending on using a different rigid foam on the below portion than what exists on the upper portion ?

As long as they are both *extruded* and have the approximate same R value then it makes sense to use the same thickness for ease of butting them and able to properly seal the joints.

Otherwise, if *expanded* polystyrene is being used you would have to use HD ( High Density ) and it would be thicker. In which case I would use the foam in the can to seal those seams where the upper and lower join.


I believe what Gary was asking ( I was was wondering also ) the rigid foam the builder installed shouldn't have been left exposed. As with any foam insulation there needs to be a fire barrier covering applied --- which can be simply drywall.
Not that it will matter if you are finsihing the walls anyway.


Another thing we do here --- the bottom plates are standard non-PT lumber. However, we use foam sill gasket to provide a thermal , air and moisture barrier.
 
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Old 11-17-13, 04:59 PM
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from dow website: THERMAX™ White Finish Insulation has a glass-fiber reinforced polyisocyanurate foam core faced with 1.25 mil embossed white thermoset-coated aluminum on one side and 1 mil smooth aluminum on the other.

the foamular is extruded polystyrene.
 
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Old 11-17-13, 05:44 PM
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Thanks for the information we have different brand names for similar products up here.
Then there will a difference in R value and you may have to go back to your original idea of using the 2 inch to maintain the same value for the entire wall.

I originally thought you were going to use the same product on the lower portion , just thicker --- sorry about that.
 
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Old 11-18-13, 06:50 PM
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I'm just starting to plan finishing my basement, I've been intrigued by InSoFast panels (InSoFast | Engineered Simplicity), which acts as both the insulation and has built in "studs". When I initially priced out comparing XPS with InSoFast it seemed very comparable...maybe even cheaper once you add the cost for wood and hardware.

Would love to know if you've considered this or if anyone else has opinions of this product (I'm probably a year out from my project, so I have time to plan).
Thanks
 
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Old 11-18-13, 07:51 PM
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It's an interesting concept but what I've seen of the product there's a couple of things I find are short comings.

1 - the grooves in the back can cause convective loops ( think stack effect ) along with a reduction in the actual thickness of the material contacting the foundation --- together these I believe can reduce the insulation performance.

2 - the way the electrical is installed. Cutting out the foam to install a box is silly.
You compromise the monolthic thermal and vapour retarding barrier you want to achieve.
Also when the finished wall is in place , good luck trying to add or change any wiring down the road.

I'm all for new and innovative materials and methods but this one falls a bit short for me. In the meantime the method discussed above has better advantages in my opinion and experience.

Just my 2 cents worth.
 
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Old 11-18-13, 09:11 PM
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Good points - and I don't mean to hijack the thread. I need to look over the site a little closer, but I believe at least some of the insulation values on their page are results from actual installations. Need to read more. I didn't see a direct comparison to the method outlined above, which is definitely a possibility.

The electrical does seem silly, but effective if you oversize the hole and then spray foam around it. I guess that ensures the envelope is as intact as possible, and acts as a strain-relief for the cable itself. I can't figure out, though, how the outlet stays in place while the spray foam cures...unless you glue it to the backwall, I guess.

Good points to think about though...thanks!
 
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Old 11-19-13, 08:11 AM
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Sure , I argree using foam in a can to seal the box around the cutout will aid in maintaining it's vapour retarding properties. However, you are removing the foam to make the cutout to fit the box -- that takes away from the insulating value. With a metal box 2-1/2 deep fastented to the concrete wall --- there is zero insualtion for that box -- with 100 % cold transfer ( or should I say heat transfer ) through that metal box.

How air tight is that box itself ? Without an airtight sealed box you actually have a potentional condensation source.

Even with a shallow 1-1/2 plastic box you still need to remove all the insulation for the cutout.

The integrated wiring chase is 1-1/4 below the surface --- for a 2 inch thick panel that leaves a series of portions where the insulation is only 3/4 inches which is pretty useless in my mind.


With the alternate method discussed above -- there is no disrupption to the continious insulating and vapour retarding envelope.

I don't mean to knock the concept of the product, just there are some short comings that -- in my mind -- reduces performance compared to the other method.


Again -- just my 2 cents worth
 
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Old 11-22-13, 06:32 PM
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I agree with canuk. From another forum I posted this a week ago; "channels for the moisture"- appear to be 3/8"x3/8" cut every 3/4" apart on the back= 1-1/2" x 3/8' missing foam per foot. Double that for 2' wide= 3" x 0.375" = 1.125 sq.in. per 2' panel.

Every 2' is a wiring channel cut (missing foam/R-value again); 3/4" x 3/4" or 0.56 (1/2") x 1" deep ----- added to the back drains = total of 1-1/2" wide where the R-value is only R-4.45---- that is every 2' times a 30' wall = 1.5 x 15= 22.5" almost 2' of only R-4.4 rather than your R-9.8--- full 2" of thickness.

The channels also promote air movement dispersing any moisture vapor through the network of channels- wiring every 2' horizontally and every 16" vertically. Where foam board should be applied with a 1' square grid glue pattern- IMO, to limit air movement behind the foam board; MYTH: LEAVE AN AIR SPACE BEHIND THE INSULATION IN THE BASEMENT TO AVOID CONDENSATION.

"No holes in your blocks letting even more water in."------- the water will find a way in regardless of holes. Best to use an interior drainage (block walls) with solid foam board as bought at local stores without the huge mark-up for an inferior product;
Redirect Notice

http://www.dow.com/webapps/lit/litor...0.pdf&pdf=true

Few other comparisons;

Inso. -- R-4.45 per in vs. R-5 per inch (true R-value, no thermal reduction by 50% every 2' panel for drainage).

Inso.- 3.5 perms rating vs. 1.5 or 1.1 perms for others sited. Less water per hour coming through at a slower rate- 50% slower- easier for HVAC to handle.

Inso.- 3% water intake volume vs. 0.9 % to 1.3%

Inso.- 1.25# cu.ft. density vs. 1.3- 2#

A good building inspector will catch the rated R-=4.45 per inch and product is 2" thick = R-9.8 not R-10 as most locals require- or more- what then buy more Inso. and double wall? You count the rated R-value of "continuous" footnote "c" not the inside air film= 0.68 plus the 1/2"gypsum board = R-0.45 to get code minimums; and under new codes- min. for Zone 5, 6, 7, and 8 are now R-15- redesign......http://publicecodes.cyberregs.com/ic..._11_sec002.htm

So it is all chopped up with wiring/drainage raceways that you may not even need, robbing the R-value. Much cheaper to DIY and add some 2x2 furring in front of full R-value XPS foam board as thickness varies per location. Most older concrete walls require a wood frame wall in front just to straighten them anyway, let alone the DWV lines tight alongside. More of a lazymans DIY with lacking design/R-value, IMHO.

Gary
 
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Old 11-22-13, 07:05 PM
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Gary -- It was a pleasant surprise to see you included a link to an article from Jon Eakes. I've met him and he is truly amazing with his knowledge in the building sciences.
 
 

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