Not sure if this is the right forum... its the only heading that mentions insulation and concretem 

I’m getting ready to finish my basement, located in West Michigan. Half the exterior walls are daylight ~4’ of cement and half are full height ~8’ of cement. For the exterior walls I’m considering the following construction….

1) 1” rigid closed cell foam insulation board against the cement
2) Full depth 3.5” stud wall installed tight against rigid insulation board to secure the insulation board
3) R-15 high density craft faced fiberglass batts in full depth 3.5” stud wall
5) Latex paint

Does this sound like a good method for my area/climate ?
Other questions...
Does the insulation board have to be glued against the cement or is pressure from stud wall enough?
Would thicker foam insulation board be better, how could I weigh the cost/benefit of thicker insulation ?
Is it critical to seal the gaps between the rigid insulation boards? If so, is spray foam in the can sufficient?
Should the fiberglass batt be faced or unfaced?

Thanks in advance for your advice/tips! :)

Not sure what is in between the fiberglass bat and the latex paint in your description, but let's just say you want wood siding, if you want stucco or such the answer I would give would be similar. I think Quad Lock makes a product that would be very good for this. It is basically ICF panels (EPS) with a provision to attach them to a wall surface directly and embedded furring strips to go from there to siding. Of course with stucco you could just use foam and stucco over it. What you are describing sounds difficult to do the way you have described. What does the stud wall sit on? It sounds like you are planning to hang it off of the concrete wall by attaching it through a layer of foam. If you do go that way, may I suggest that you simply use furring strips even if they are 2x4s on edge attached straight to the concrete, not through any foam and use foam, sprayed or pieced in and sealed to the strips, to the full depth of your strips. But I do believe, better yet, look at the Quad Lock retrofit product. By the time you include labor and materials it may well the best r value for the buck if labor is part of what you will be shelling out for.

Best of luck,

DBollermann

I think you are asking about the inside walls in your basement! I too would like to read some answers. My problem is I would like to use the ICF wall system or some type of it but I do not think I can use it for heating and cooling mass in my area (Ottawa Canada)!
I'm just looking for a quiet, superinsulated wall system from the footings to the rafters, a bungalow and walkout basement!

Regards, John

Add "4) drywall" and yes, use a vapor barrier of some type. I would use tape to seal the insulation board gaps.

This may be worth a look. It is a completely different system than you are describing, but addresses the same concerns. Installs very quickly. http://www.insofast.com/isf_video.html

Posted By jokin on 12 Apr 2010 02:24 PM
Not sure if this is the right forum... its the only heading that mentions insulation and concretem 

I’m getting ready to finish my basement, located in West Michigan. Half the exterior walls are daylight ~4’ of cement and half are full height ~8’ of cement. For the exterior walls I’m considering the following construction….

1) 1” rigid closed cell foam insulation board against the cement
2) Full depth 3.5” stud wall installed tight against rigid insulation board to secure the insulation board
3) R-15 high density craft faced fiberglass batts in full depth 3.5” stud wall
5) Latex paint

Does this sound like a good method for my area/climate ?
Other questions...
Does the insulation board have to be glued against the cement or is pressure from stud wall enough?
Would thicker foam insulation board be better, how could I weigh the cost/benefit of thicker insulation ?
Is it critical to seal the gaps between the rigid insulation boards? If so, is spray foam in the can sufficient?
Should the fiberglass batt be faced or unfaced?

Thanks in advance for your advice/tips! :)

Thicker foam, and UNfaced batts are more like it. 

Kraft facers are still a vapor retarder, and the foundation has to be able to dry toward the interior or the foundation will saturate, raising the moisture level at the foundation sill for higher rot potential, and create spalling & efflorescence issues on the exterior above-grade portion of concrete. At the same time, the wood in the studwall has to stay warm enough to not get condensation & mold from condensation of interior air vapor levels during the winter.

The solution is to boost the foam to at least 1/3 of the total R-value (half is better) but not more than 2" with XPS (pink, blue) since thicker than that becomes too impermeable for sufficient foundation drying (with unfaced EPS or fiber-faced ISO you can go with more since they're more vapor-permeable).

The foam board need not be glued, but it needs to be air-tight (1-part foam, mastic, caulk or FSK-tape the seams), which is easier to do if it's glued to the wall, and before the studwall goes up.

Interior paints & finishes need to be at least semi-permeable, (most latex is good), which precludes the use of vinyl or foil type wallpapers etc.

It sounds like you're looking for a ~ R20 clear wall R-value.  This can be had using highly permeable 3" fiber-faced iso insulation (sold as roofing insulation in commercial space), held in place with furring through-screwed into the foundation, onto which you can mount the wallboard, for a wall thickness slightly less than what you were contemplating, no studs.   (Last time I checked, it was running ~$55 for a 4x8' sheet, f.o.b. the distributor's warehouse.)  Or,  2" XPS (R10) and a 2x3 R8-batt studwall (or 2x4 R13-R15 studwall) also works.  But at only R5 of foam and R15 batts the risk of mold or rot on the cold edge of the stud is high in your neighborhood.

You may find this discussion of the issue useful (with pretty pics & mayhaps clearer explanations than mine).

Average January temps in say, Grand Rapids MI are ~20F (with much colder lows, of course).  The dew point of 68F,  30% relative humidity (the min recommended humidity for health & comfort) air is  in the high 30s, the dew point of 70F, 60% relative humidity (max humidity recommended for health & comfort) air is ~ 55F.  The point in the R-stackup where the the average temp is the dewpoint of the interior air or lower needs to be in  the foam for mold to be well-controlled.   If the average temps are 70F inside and 20F outside, halfway through the R  at grade level & above is 45F, and 1/3 of the way in from the exterior is 37F.  So you're good with 1/3 of the R as foam if you keep the interior at 68F/30% RH, but if you go higher in overall humidity you're pushing your luck. If half the R is foam you have a bit more margin, with far more winter-time drying hours than condensing hours.  The greater the ratio of above-condensing to below condensing temps anywhere within the studwall, the lower the risk of mold from wintertime condensation.

And to reiterate, if you put an interior side vapor retarder up to guard against winter-condensation, you trap ground moisture in both the studwall to create a year-round mold hazard, and the foundation. If you put the vapor retarder against the foundation, you risk sill rot & spalling concrete.  Any vapor retarder with a permeance of 1.0perm or less increases the risk of problems (despite the generic Canadian codes that call for for 6mil poly at ~ 0.05perms.)  In perma-frost zones they may be worthwhile in some situations, elsewhere they generate more problems than they solve.  But air-tight permeable or semi-permeable foam is good on concrete foundation interiors almost everywhere.

That's one opinion on vapor barriers/retarders (generic terms that include a wide range of perm ratings), and there are many others (including building codes and simulations) that say otherwise (some say PE at perm=.03 and some say as little barrier as possible (even paint counts - there is no such thing as no vapor barriers)).

Moisture at the outside concrete surface is not driven by drying to the interior and is driven by what is happening outside. You can run the WUFI software with local data for a comprehensive simulation of that.

Some less controversial things - avoiding any material effected by moisture is a plus and dehumidification of humid basement air reduces moisture problems.

Posted By Dana1 on 13 Apr 2010 03:48 PM

........    It sounds like you're looking for a ~ R20 clear wall R-value.  This can be had using highly permeable 3" fiber-faced iso insulation (sold as roofing insulation in commercial space), held in place with furring through-screwed into the foundation, onto which you can mount the wallboard, for a wall thickness slightly less than what you were contemplating, no studs.   (Last time I checked, it was running ~$55 for a 4x8' sheet, f.o.b. the distributor's warehouse.)  Or,  2" XPS (R10) and a 2x3 R8-batt studwall (or 2x4 R13-R15 studwall) also works.  But at only R5 of foam and R15 batts the risk of mold or rot on the cold edge of the stud is high in your neighborhood.

Just reviving this old topic... as I need to finally execute the plan, order/gather supplies, and finish the basement.   My dad purchased some "recycled" sheets of rigid foam from a commercial building demolition.  Would that be the same as the insulation referred to above "fiber-faced iso insulation"?    The insulation he has is light yellow or off white in color with a thin black (itchy) coating/facing on front and back. 

If it is not the same,  how would I know if this insulation would be permiable enough to allow drawing for an application on a cement wall above and below grade in a basement in Grand Rapids, Michigan?? 

It's probably iso with an asphalt/other loaded felt facer on one side, probably fiberglass-reinforced paper or something else on the other. Depending on what's IN the black facer, it could be permeable enough, or maybe not. If you can read the manufacturer's name or product name (often printed on the non-black side) there may be a spec available indicating its perm rating. It might be Certanteed Flintboard, but it could be any number of other products designed to go under torch-down roofing.

The permeability requirements don't change with climate zone, but the ratio of foam to fiber does, if you're coupling it with a batt-insulated studwall to raise the total R. Assume the R value of iso to be ~ R6 per inch of depth when calculating the depth at which you'll run into condensation issues. As long a the dew-point temp of the interior air occurs in the foam for any given winter month and not the studwall, you're golden.

Above grade the permeabilty of the foam matters somewhat less than below grade, as long as the concrete is sealed on the exterior with a good sealer to limit uptake of rain/dew.

I checked out the insulation again.  It has the same black facing on both sides.

It has.... "QCA03242 1.5" R-10" printed on one side of each sheet.  No luck on a google search.  This insulation is from an existing building so it could be 15-25 years old. 


I'm pretty confident it is "polyiso..."  and not xps.   So I don't know the permiability of the facing thus I'm still not sure if I should use it against the concrete wall below grade ??   Not sure where to go from here.   Any ideas on how to determine the facing/layer permiability??     I'd love to be able to use this very cheap insulation source, but don't want to end up with water trapped in the wall.

Thanks in advance for any help or advice.

It has to be iso if it's R10 @ 1.5" thickness- the question is whose, and what's in the facer...

Use InSoFast. We just got done with 1900sf in a basement, including the underside of precast concrete planks.

Posted By Dana1 on 13 Apr 2010 03:48 PM

Posted By jokin on 12 Apr 2010 02:24 PM
Not sure if this is the right forum... its the only heading that mentions insulation and concretem 

I’m getting ready to finish my basement, located in West Michigan. Half the exterior walls are daylight ~4’ of cement and half are full height ~8’ of cement. For the exterior walls I’m considering the following construction….

1) 1” rigid closed cell foam insulation board against the cement
2) Full depth 3.5” stud wall installed tight against rigid insulation board to secure the insulation board
3) R-15 high density craft faced fiberglass batts in full depth 3.5” stud wall
5) Latex paint

Does this sound like a good method for my area/climate ?
Other questions...
Does the insulation board have to be glued against the cement or is pressure from stud wall enough?
Would thicker foam insulation board be better, how could I weigh the cost/benefit of thicker insulation ?
Is it critical to seal the gaps between the rigid insulation boards? If so, is spray foam in the can sufficient?
Should the fiberglass batt be faced or unfaced?

Thanks in advance for your advice/tips! :)

Thicker foam, and UNfaced batts are more like it. 

Kraft facers are still a vapor retarder, and the foundation has to be able to dry toward the interior or the foundation will saturate, raising the moisture level at the foundation sill for higher rot potential, and create spalling & efflorescence issues on the exterior above-grade portion of concrete. At the same time, the wood in the studwall has to stay warm enough to not get condensation & mold from condensation of interior air vapor levels during the winter.

The solution is to boost the foam to at least 1/3 of the total R-value (half is better) but not more than 2" with XPS (pink, blue) since thicker than that becomes too impermeable for sufficient foundation drying (with unfaced EPS or fiber-faced ISO you can go with more since they're more vapor-permeable). ......

I'm wondering about the unfaced EPS, would that be the same as the basic white beadboard "styrofoam insulation".  I read elswhere that the white beadboard insulation is liable to break down if it ever gets wet, and should be avoided for basements or any below grade application that might get wet ??   Any thoughts. 

I'm basically down to R-10 behind the shallower stud wall and some unfaced fiberglass batt between the studs.   I ruled out the mystery polyiso board as I can't tell what's in the facers and can't determine the permiability.    So I'll use either 2" high density (2.5lb/ft^3) EPS (unfaced white beadboard -  R-10) from a local commercial supply company, or slightly less dense  2" XPS from HD or Lowes with R-10, against the cement.      

Between the studs, can I use standard thickness R-11 or R-13 unfaced batt and stuff it in a smaller cavity (1.625") between my slimmed down stud wall (I plan to rip standard studs in half) ? 

Or would I be better off buying the more expensive but thinner fiberglass batts to put between the furring strips/ more shallow studs.

Thanks!

EPS beadboard is closed-cell and does not break down when wet- it's used in boats, docks, floats, and surfboards everywhere! EPS is used under slabs, below grade on walls. Almost ICFs are 1.5-2lb EPS, to handle the stresses & compressions during pours, but you don't need the higher density for retrofitting on walls- the cheap 1lb stuff is fine, and has comparable R. (~R3.75/inch instead of ~ R4/inch for the higher densities.)

Rather than ripping studs, why not use 2x2s and R8 batting (or splitting R13 batting?) You'd end up with ~ R6 with batts compressed to 1.5" as opposed to ~R7 with batts compressed to 1.75".

Use InSoFast. (http://www.insofast.com) It's a terrific system.

We have used a lot of the Quad_Lock R-etro system - 2", 4" or 6" thickness, drip gap at the back and furring strips for direct finish fastening - gets rid of all questions of wooden studs rotting away quietly behind finishes and mold can't be supported on it - see http://www.quadlock.com/retrofit_insulation/ . This is a product we are using more and more.

Dana1  and others..

Belated thanks for the thorough responses to this thread.   I'm happy I followed the advice.  I figured out a way to totally enclose the daylight and full height cement walls in my basement finish project with foam insulation.  I struggled with a way to insulate the wall faces and daylight wall top edge with foam sheets while eliminating any short-circuit paths... all without using glue/adhesive. 

I ruled out the glue and adhesive because I thought the engineer in me would require almost same amount of time and materials for temporary bracing (to hold in place while the glue dries) as just building the actual stud wall pressured/tensioned against the foam to hold it in place.   

I went with 1.5" xps foam (I'll save the mystery recylced polyiso roof insulation discussed above for some future project above grade that can dry to inside and outside).  So 1.5 xps foam behind a 2x2 stud wall with standard R-11 fiberglass batts split in half (to limit compression) instaleld between the studs.  Drywall over it all of course.   The combined R-vaule should be roughly 13 -15 maybe and NO THERMAL BRIDGING !!   

Building the stud wall straight while applying even force to the foam against the cement was a challenge and required some LONG tap con fasteners, lots of shims, and some hard thinking but it turned out better than I expected.  To my wife's credit she supported my "crazy ideas" even though she had word from reliable family members/ home builders / contractors we know, saying that the extra steps and layers is really not necessary. 

During construction I dislodged a piece of the xps after it was in position for a full day and was amazed at how COLD the wall was behind it compared to the exposed cement wall adjacent to it, which had not been covered yet!   The insulation is certainly making a difference.
 
Thanks again...

-Jokin