insulate between CMU and brick veneer?
I’m building an addition on my house that is essentially two story – CMU (cinder block) walled first floor that is an exposed extension of the existing house basement which will be a garage and regular wood framed second floor living space (see attached pictures for a better idea of the layout). I am hoping to get some advice regarding the best sheet insulation product to apply to the CMU wall underneath the brick veneer, and the recommended way of bonding the insulation to the CMUs. I figure that I will seal the block walls anyway (both outside and inside) to minimize water / humidity migration, but I didn’t know if an asphault-based sealer on the outside could be used as a “glue” for attaching the sheet insulation, or if I should just use a portland cement based sealer and just use the brick ties to pierce the insulation and hold it in place.
Any advice will be very welcome!
BYW, I am located in middle TN, so the insulation will be more important to minimize heat infiltration in the summer than heat loss in the winter.
Thanks!
-Chuck
Replies
Bump up - I was hoping to get a little feedback on this, or is it too dumb a question for anyone to bother with?
I must first provide the disclaimer that I know nothing about actually building said question. Being that I am a student, I'd love to hear what all the builders out there actually think. I surely don't want to make the mistake of taking something I learned in school and applying it in the future and find out it is the wrong advice when something I specify goes wrong! At the very least, I hope that some of my comments are helpful.
What I was taught in architecture school this summer about brick veneer and CMU wall construction is to put the insulation on the exterior which allows you to put a minimal furr strip/drywall application on the interior. It would make no sense to have a rain screen backed by a CMU structure backed by an entire framing system for the interior wall finish. That would result in one thick wall! However, if it is a stud backup, as opposed to CMU, you should put the insulation between the studs just as you would in a normal stud wall. Will the brick veneer only extend to the top of the CMU? Or will the entire facade be constructed with brick veneer? Depending on your answer and your intended alignment of the studs and CMU (which appear to already be constructed) the answer to your question might lie in whether you have the allowable room for insulation to the outside of the CMU.
A question worth asking is if you have any walls that extend from the first floor all the way up through the second floor. If you do, you would most likely want the drywall to be continuous....so plan your insulation placement so that you don't have to do extra furring in order to get your drywall to line up with the change of construction methods.
Another point I'd like to address is in regards to you wanting to use some sort of vapor retarder on both sides of the CMU. My instructor was very firm when explaining that it is very important for us to allow any water that might come into contact with the CMU a path back out again. Sealing both sides would cause issues with allowing water a path out. In a utopian world, one might argue that the brick veneer is a rain screen and thus preventing water from contacting the CMU. In that utopian world, you can also be guaranteed that the rain screen would never fail. But with real world rules in mind, you have to make your plans considering the possibility that water could reach the CMU.
Jen,
Thanks for the reply. I will try to cover all the excellent points you make.
The CMU walls of the basement will not be furred out or drywalled on the inside - I was just planning on painting the walls with a drylock-type masonry paint, so there will be no insulation on the interior surface of the walls.
The brick veneer will cover all of the exposed walls (both CMU and wood framed). The brick ties in the mortar joints extend far enough to use sheet insulation as long as it is 1" thick or less. I guess I could carry the sheet insulation up onto the wood framed walls too, or I could just leave a wider air space between the sheathing and the back side of the brick. I am planning on insulating the stud bays of the framed upper floor, of course.
Regardless of whether or not I put sheet insulation on the exterior of the CMU walls, I plan on covering it with either a cement-based or asphault-based coating to mitigate water entry through the blocks should any water get through the brick veneer. There will be weep holes in the brick veneer, of course, to prevent any water from staying trapped between the wall and veneer.
Those are all good points that you make - thanks for taking the time to respond!
this may be a silly question, putting the 1" or less thick insulation between the brick veneer and the CMU still allow you atleast a 1" clear air space between the veneer and the insulation?
I also have limited experience in exterior residential construction but what follows is what i learned in arch school and in the feild.
1. Do NOT seal both sides of the CMU (Concrete Masonry Unit) wall. As stated by Jen this will only temporarily trap water in the wall. a) Eventually the hydronic pressure will push the interior sealant off causing it to fail. b) If the exterior sealant fails you want to know ASAP so you can fix it ASAP before ity does any other damage and c) The interior sealant will be gassing off for a while and you don't want these fumes inside the house.
2. The sheet/ rigid insulation is applied to the CMUs with a powder accuated gun using long nails with washers. You don't need that many per sheet (8).
3. The insulation applied to the OSB sheething is also long mnails with washers - plastic or metal. Hand nailed.
4. Are the tabs from the CMU walls long enough to reach the brick veneer wall if you use insulation? How thick is the insulation you plan on using?
Hope this helps.
F.
Hey Frankie,
Thanks for the reply!
It may not be obvious from the pictures I posted, but none of the walls of the addition will be below grade. I have a couple of piles of fill left around, but all of the walls will be exposed. I would like to paint the interior of the CMUs with a latex-based concrete paint (like Drylock) - both floors of this addition can be sealed off from the rest of the house since all of the doors and windows from the original end of the house are intact so I think I will be o.k. from an odor standpoint. Do you still think that any sealer coat on the outside of the CMUs is a bad idea in this scenario?
The veneer ties will be long enough as long as the insulation is no thicker than 1" (and still leave an air space between the brick and insulation). Do you have any recommendations as to the appropriate type of insulation? Blue board?
Thanks for taking the time to respond.
-Chuck
All I know is sealers go on the exterior surface to address where the water is coming from. I think parging/ applying a thin veneer of latex fortified concrete is way overkill. A roller applied material is good enough. I don't even think I would use it since it is already protected by insulation and a wall of brick. Even a driving rain would have a difficult time getting to the CMU wall. If the wall was below grade - well that's a dif disscussion. On the OSB wall sheathing I would still use Tyvek or similar.
How much air space have you planned for between the ins and the brick?
Weep holes are nec. Be sure to confirm the weep holes are clear after pointing.
Blueboard is NEVER used as insulation . That's sheetrock for plaster. What you want is either pink or blue rigid insulation. They both are available from the local lumber yard and the big boxes. Use whichever one has the highest R-value. I think it's the pink, but I may be wrong. If I am wrong, then it's the blue.
If using a powder accuated gun to attatch the insulation to the CMU wall be sure to use the right load. You will want the nail with the washer to make only a dimple in the insulation.
I thought the same thing as you did about the Blueboard, but immediately reassured myself that he meant the blue extruded polystyrene (we in Midland think it's all made by Dow and called Styrofoam). I have to re-read this thread from the begining to see if I can add anything useful. Probably not.
Okay, I've re-read and looked at the pictures: 1) Maybe I'm not seeing the photos clearly, but if you have an inch of rigid insulation and an inch of airspace, then your brick veneer, won't your windows and doors be inset pretty deeply--looks like they only stick out about two inches. 2) I guess Tennessee is warm, but is it worth the trouble for just 1" of insulation (maybe R-5?) (Maybe it is in Tennessee--will it be enough in summer to keep heat out?) 3) Revising my first number three where I said "if you glued the rigid insulation to the block, and taped the joints on the insulation, couldn't that act as a water/vapor barrier? (And I agree with whomever said don't put vapor barrier on both sides of blocks). Any wetness getting through the brick veneer would run down the rigid insulation and out the weep holes..." because you have to use the brick ties to hold the brick veneer on (duh)--so you can't use the insulation as a moisture barrier and definitely not as vapor barrier. The adhesive you use to attach the insulation to the blocks will have to be the vapor barrier. Vapor barriers are better on the outside in a warm climate anyway--but should still be on the warm side of the insulation. I suppose spray on foam is out of the question as being too expensive? That would solve a lot of problems.
Hope I made a little sense.
Hey Danno,
Thanks for the ideas. In the post above, I did mean the blue insulation board and not the blue backing board.
You are right, the windows will be inset pretty far with an effective 2" space to the brick. This may end up being the deciding factor to insulate or not. I didn't really plan on doing any exterior insulation, but just started thinking about it after things were pretty far along. The basement under the rest of the house stays a nice even cool temp in the summer because most of it is below grade, but I am a little concerned that this new section will get pretty warm since it is completely exposed. I don't think spray on foam is an option - both expense-wise and I would have to import someone from Nashville to do it (I'm in the boonies about 80 miles from there).
With all the good points brought up, I'm thinking that I would be better off to just go ahead and put the brick veneer on with no insulation in between, and then see how it works over the winter and next summer. If it turns out to need some "help", I can fur out and insulate on the interior.
I appreciate everyone taking the time to reply!
-Chuck
One thing about the brick and block is that it will take a little time to heat up and then it will release the heat. In spring and fall this may be welcome as it will tend to warm the inside of the house in the evening. Like you say, if it proves to get too hot, you can insulate the interior. Hope it all works out for you.