Concrete Block Exterior Walls for Bedrrom Remodel

Hello,
Last post I made at the Flooring section was, well, about flooring of a bedroom. But the remodeling goes beyond the floor, also including the walls. In this case, exterior walls mainly. The exterior walls are made of concrete blocks and furring strips and there has never been any insulation. I removed the the sheetrock (1/4), leaving only the concrete and wood furring strips. I am planing on install 1/4” pink panther rigid insulation. Some may say that ¼ is not thick enough, low R value, etc; but considering that there was no insulation at all before, it is a huge improvement.

I have few questions. Is the rigid insulation enough as a moisture barrier? I am planing on remove the wood furring strips, then lay down the rigid insulation panels, and subsequently use the wood furring strips as a support to hold the insulation in place screwing the wood furring strips with concrete screws; instead of cutting small sections of the rigid insulation and place then between the wood strips. Also I plan on filling the bottom edge with expandable foam in order to obtain a proper seal.

Below is a pic depicting the situation:



I was wondering if this would be a good course of action and approach to this situation. Thanks for any inputs.

We usually build a wall 1" away from the concrete but I think your plan would be better than what you have. I would go with as thick a foam as possible and sealing the joints would make it a vabour bearior.

Given that you're in MI I would think you'd want more than 3/4" ,which is the depth of the strapping. Depending on which rigid foam insulation you're going to use you'll get different R values.
I would sister on another piece of strapping at 16" on center, removing any of the others, and use 1.5 Polyisocyanurate.

Get some info here.

http://www.homeconstructionimprovement.com/foam-board-insulation-values/

Sorry to answer your question with a question but! Do you have access to the top of the block wall.We usually build them with a piece of rebar and a poured cell every 4' leaving the rest of the cells open.we fill the open cells with an insulating material called vermiculate.It comes in bags and can be poured down each cell.It' the same stuff they use in potting soil.

Is this wall above grade? I would certainly go with more than 1/4" of foam. I'd use PolyIso and shoot for at least 2 inches of it. That would give you an R16. Giving up 2" of floor space will be well worth it in energy savings since you're already down to bare concrete block.

If you can access the top of the block pouring vermiculate down the block would be a good start. While the walls are open you could drill into the cavity and do foam if you can't get at the top of the block. Another option to increase the R value of the wall would be to cover the exterior with rigid foam and then install a new siding over that. Of course if your house is brick or stone veneer on the exterior I wouldn't go that route, but if you had clapboards, vinyl or stucco it may be worth a shot. This is sight unseen of course.

tk, with no insulation existing, any moisture coming through the block is evaporated away as it forms, from the heated room. Problem with adding cavity insulation in a frame wall 1" away from CMU is convective air loops; 24/7 robbing your heat- never leave a gap between heated frame wall and cooled concrete wall (heat sink).

R-10 (continuous) insulation -rigid board; is required for your county- footnote "c"= Zone 5; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Michigan
Check with local AHJ for using less foam board than stated as R-10 (2"XPS) will give you safety up to 70%Relative Humidity in room, without any cavity insulation added. In fact, R-5 (1"XPS) gives to 65% RH at foam board inside face at 56*F for 3 coldest months of year temperature for your area; http://www.usclimatedata.com/climate/michigan/united-states/3192

But, you would only stop 84% of total heat loss through that wall with 1' foam board and no cavity insulation; compared to 91% (2") and no cavity insulation. The biggest difference is it would be a wetter wall as 2" XPS has twice the perm rating as 1"; it would slow the vapor coming through twice as well. Speaking of wet foam board, polyiso is 7 times wetter than XPS; AND R-value drops to 30%- Fig.7; http://commercial.owenscorning.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf And it is wet most of the year....

Gary

Sparky617 said:

Is this wall above grade? I would certainly go with more than 1/4" of foam. I'd use PolyIso and shoot for at least 2 inches of it. That would give you an R16. Giving up 2" of floor space will be well worth it in energy savings since you're already down to bare concrete block.

If you can access the top of the block pouring vermiculate down the block would be a good start. While the walls are open you could drill into the cavity and do foam if you can't get at the top of the block. Another option to increase the R value of the wall would be to cover the exterior with rigid foam and then install a new siding over that. Of course if your house is brick or stone veneer on the exterior I wouldn't go that route, but if you had clapboards, vinyl or stucco it may be worth a shot. This is sight unseen of course.

Click to expand...

Yeah, it is above grade or above ground. The exterior walls of the house are all made of very thick concrete. Only the interior walls (divisions) are wood frame. I could no have it otherwise (I prefer to live in a house made out of concrete and steel rebar in lieu of wood framing).


Sorry, it was my bad; it is 1/2" and not 1/4". Still 1/2 is rather thin for this application. As a matter of fact, there is no such a thing as 1/4" rigid insulation. Yeah, I am going go consider going with at least 3/4" . Accessing the top of the block would too problematic for me now. The house has stucco on the outside, it is relatively new and nice-neat stucco; but don't know whether or not the original installer used any type of exterior insulation on occasion of applying the stucco. Since I don't want to tear out the new stucco, maybe an exterior insulation will be a future project.

I went through that route (exterior rigid insulation + new wood siding) on the all season room addition to the house.

thnks!

GBR said:

tk, with no insulation existing, any moisture coming through the block is evaporated away as it forms, from the heated room. Problem with adding cavity insulation in a frame wall 1" away from CMU is convective air loops; 24/7 robbing your heat- never leave a gap between heated frame wall and cooled concrete wall (heat sink).

R-10 (continuous) insulation -rigid board; is required for your county- footnote "c"= Zone 5; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Michigan
Check with local AHJ for using less foam board than stated as R-10 (2"XPS) will give you safety up to 70%Relative Humidity in room, without any cavity insulation added. In fact, R-5 (1"XPS) gives to 65% RH at foam board inside face at 56*F for 3 coldest months of year temperature for your area; http://www.usclimatedata.com/climate/michigan/united-states/3192

But, you would only stop 84% of total heat loss through that wall with 1' foam board and no cavity insulation; compared to 91% (2") and no cavity insulation. The biggest difference is it would be a wetter wall as 2" XPS has twice the perm rating as 1"; it would slow the vapor coming through twice as well. Speaking of wet foam board, polyiso is 7 times wetter than XPS; AND R-value drops to 30%- Fig.7; http://commercial.owenscorning.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf And it is wet most of the year....

Gary

Click to expand...

Hello Gary, yeah, I get the idea the absence of any vapor barrier also means that the humidity and condensation does not get trapped, but that also would make easy for cold air and drafts to easily get and pass through; besides there would lots of heat lost due to convection on the wall surface.

I confess that you jargon is rather technical for me. I look into this convective air loop thing, and at first it seems that any air gap on between the interface wall-insulation can lead to a convective air loop, which will increase not only the thermal but also the moisture transfer within the wall. So, maybe foam glue should be use to create a tight vertical connection?

It seems that the pink rigid foam insulation also works as a moisture barrier, and then I will seal their joints with house wrap tape. At first I will rectify some small voids on the mortar with high strength concrete, then I I will replace the wire and install exterior grade wire box for the power outlet . Since it is a masonry exterior wall I will be using the same low profile studs = wood furring strips.

So, due to the moisture concerns should I go ahead and use xps (but something thicker). I also plan to fill all crevices and gaps with expanded foam.

Actually, I am not in MI. I happen to have a condo in MI and it still is my primary residency; but I have been spending more time in Columbus, OH, whereon I bought a distressed home (I will change the locale in profile to avoid confusion). But, the last few weeks it has been extremely cold over here (one of the reason I have been postponed the work to be performed in this bedroom)