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Ziggy75 03-21-2013 10:29 AM

basement renovation 2x4 vs 2x3 and using XPS
4 Attachment(s)
Hello, I am new to the forum but I have been doing a lot of research on google and it brings me to this forum so I thought I would register and ask some questions regarding me project. I am in the process of doing a basement finish. My rough area is 13'-4" x 39' -5" and is concrete block. One side of the 39'-5" room is actually a concrete bearing wall. It separates both sides of the house. I am only finishing one side (13-4x39-5). I also live in Michigan.

My plans or thoughts as of this moment would be to use a 1" Owens XPS from Home Depot. I would then frame a 2x4 wall against and use batt insulation. At this point, I do not know if I should use faced or unfaced batt insulation or if it really matters. To maximize my room size, I thought about using 2x3 instead of 2x4. Not sure if this is a good idea or not. Other route could or would be using a 2" XPS with 2x3 framing and NO batt insulation in wall. My concrete load bearing wall will need framing as well. Should I still use XPS on this wall or can I get away with just framing a 2x4 over it with the batt?

I want to do this the right way the first time but I am also on a budget so I would prefer not to go overkilll if unnecessary. Thanks in advance for any suggestions.

Ziggy75 03-21-2013 11:02 AM

I was wondering if..

2-1/2" x 2' x 8' R12.5 FOAMULAR 250 Rigid Foam Insulation

Using this with the furring strip and mounting drywall to would provide enough R value being in Michigan.

SquishyBall 03-21-2013 11:07 AM

I'm doing a similar thing and have a similar basement size. I actually tore out the 2x4 framing because I'm using 2x3's sideways which are only 1-1/2 thick. This gains 2" all the way aound. It's not a lot... but when you have a small space every inch counts. We put in the 1" XPS foam on the walls first, so we A) are now insulated w a barrier B) still have more space (1" around) than we started with.

Should you put XPS on the other wall?
Yes. The point of the XPS on the wall is to eliminate the existence of a cold surface. If that wall is cold to the touch, then when it's warm and pleasantly humid in your basement water will condense on that cold wall behind your framing. Instead with the XPS, mine, after install is simply room temperature everywhere I touch it. No cold surface = no condensation. The XPS should to be glued TO the wall with foamboard adhesive, not just in there. The previous owners who did our first remodel just shoved cut sticks of XPS in the stud cavities. (groan)

I would not use batt insulation anywhere in the basement. Where I took mine out they were all varying degrees of yuck. If you want more insulation do two layers of XPS offsetting the seams. Ours is pleasant with 1". Where you need insulation most is for cooling in the summer... and our basement stays cool on its own.

Ziggy75 03-21-2013 11:15 AM

You make some good points. I understand that the XPS should be glued. I have yet to find out exactly which glue I should use. The inner concrete bearing wall is cold to the touch but my thoughts were that it is cold because its cold in the basement. On the other side of the bearing wall is the furnace. I would say that the wall is not cold to the touch behind that furnace. But either way, being safe than sorry is good with me. Instead of purchasing two layers of 1" XPS, I would probably go with 2". There is a Menards (not sure if you have any) that has the 2" on sale this month.
2" x 4' x 8' R10 FOAMULAR 150 Rigid Foam Insulation $24.95 each.

I would use this IF I knew I could get away with not using the batt insulation. You mentioned not using it at all. My concern is the R10 value that it would leave me. Is this sufficient?

SquishyBall 03-21-2013 11:36 AM

This is a great resource...

"My concern is the R10 value that it would leave me. Is this sufficient?"

Definitely. Buildingscience recommends up to 2" of XPS. Additional insulation between the studs is optional, tho if you do it it should be unfaced so as to not block air flow.

"I have yet to find out exactly which glue I should use."

Menards has it. It's in the caulk section by the paint. It's just called foamboard adhesive.

Ziggy75 03-21-2013 11:53 AM

Again, thanks for your help.

I did see at the end of that link in one of the diagrams that it makes reference to 'unfaced cavity insulation, cellulose, or low-density spray-applied foam'.

It sounds like its an option. I'm still on the fence between the 2x4 vs 2x4 plan.

brockmiera 03-21-2013 12:13 PM

PL 300 Foamboard Adhesive. I believe Loc-Tite makes it.

<*(((>< 03-21-2013 12:20 PM

In my opinion you don't have to go overboard insulating basement walls as you are only insulating against 50-55* (ground temperature) exterior. If it were me I would do the 2" foam glued to the wall seams taped, double or triple up the 2" foam on the rim joist with edges sealed with expanding foam and 2x3 (or full 2x4 if you don't care about the loss of an extra 1") studs on top of the 2" foam on the walls, and call it a day.

Ziggy75 03-21-2013 01:21 PM

I did forget to mention that the wall on the right hand side of those pictures is exposed. Its a walkout basement. It is just one side of the basement that is 39"-5'. Would this change much of what you are saying regarding the 2" foam and calling it at day?

Gary in WA 03-22-2013 03:10 PM

The 2" XPS is better from a moisture standpoint than adding cavity batt insulation in front also. The first condensing surface- the inside face of the foamboard will be warmed by the room air. Batt insulation insulates/stops the room heat from warming, hence lowering the dew-point because the foam is now colder. The f.b. would require more R-value to make-up for the lost heat due to the cavity insulation. Basement insulation is about 1/2 the R-value of above grade insulation values due to no wind, rain, or exposure because the ground/concrete wall buffers. This is why minimum code for your Michigan location is EITHER R-10 continuous, or R-13 (cavity)= see footnote "c" under Basement R-value;

You don't need both, either will work, but cavity f.g. will not stop condensation from infiltrating/exfiltrating moisture vapor as foamboard does. Moisture wicking through the wall (looks dry now, wait until you block the room air currents with drywall) is constantly evaporating or having high relative humidity in the basement can also be problems. Also, as already said, summertime outside air condensing on the basement slab/lower wall sections due to the time lag, pp.4;
The interior rigid f.b. stops summertime condensation on the concrete. Without f.b., the wall concrete (at various heights) is at different temps throughout the year due to following seasonal temps of the air/ground. The temps are caused by the Geo-thermal warming of the earth, the deeper below grade, the warmer the earth. And, the deeper below grade, the longer the time lag of the basement temperature. 6' down is about 1-1/2 month time lag, average, depending on the soil type, solar exposure, water content of soil, snow cover, etc. At 6' down the soil is about 10-11*F warmer than surface temps. So, using this map, MI is about 42-52*F PLUS 10*F = 52-62*F----- 6' below grade, on an average... not during the middle/end of winter.

With your basement window above grade (2') and the "frost line" at 25-30", you have 4-5' you really need to insulate.

Notice the heat losses and insulating R-value of your CMU (block);

Even with today's above grade/frost line temps of 27*F, why not insulate that 50-60% of basement wall, while the lower 3' is around last month's temperature plus 10*F; You could use 1/2 as much in the lower 1/3 but hard to drywall for the minimal dollars saved.


Gary in WA 03-22-2013 04:58 PM

In answer about the f.b. only or f.b. plus frame wall/batts. Using your average of 3 monthly temps of 24*F;

At 70*F room temp; R-5 + batt R-13, good up to 29%RH in room

R-10 + batt R-13, good up to 38% RH

R-10 alone with drywall, good to 92% RH

R-10 + 2x3 frame (comp. R-13 to R-10; = 44% RH

PS. That would be for the city in MI listed at the bottom of the link. For five months your basement concrete would be at 50*F or above, as said, though the other 7 you would lose heat rapidly and have wet walls from condensation by weeping from the exterior soil or indoor relative humidity.

Ziggy75 03-22-2013 08:47 PM

3 Attachment(s)
I really appreciate the information that you have provided. I went to Lowes today and got them to do a price match of a Menards sale. I purchased 21 2" XPS boards. I took everything they had. Got them for $24.95 a piece. My plan as of now is to use the 2" on perimeter of basement wall. I have the concrete load bearing wall that I am unsure what I am doing with. The wall is not cold to the touch as previously mentioned. I have the furnace on opposite side of wall too. Anyway, the 2" will go up and will frame 2x4 over it. My thoughts were to use R11 unfaced batt inside the cavity. Its on sale at Menards and I can get 650 sq ft worth for $125 and $105 after mail in rebate. This will cover everything. The longest outside wall of the basement is above ground since its a walk-out basement.

The pictures show the back of my house just shortly after I closed on purchase in May of 2008. It looks a little unmaintained.

bryanp22 05-14-2013 10:54 PM

What did you do on the stairs for insulation?

Rekonn 05-17-2013 01:49 PM

Nice, I have a walk out basement that I'd like to finish someday too. I'm also thinking rigid foam and 2x4 framing, but using Roxul for cavity insulation.

Out2pasteur 05-19-2013 08:04 AM

What is your plan for flooring/sub flooring?

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