7" Mineral Insulation, for walls but now attic?

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  #1  
Old 09-07-15, 05:59 AM
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Unhappy 7" Mineral Insulation, for walls but now attic?

Hey all... I'd like your two cents, or three cents with inflation here...

I think I made an oopsie but yesterday had a Eureka! moment. I ordered what is called 'R-30 Mineral Wool Insulation 15"W x 7"D x 48"H' from Menards for my house walls a month ago (special order item). I originally planned on furing out my walls the extra 1.5" to be able to use this wonderful, thick, expensive R-30 insulation. My thoughts were since I was achieving R30 instead of R23 that it would be worth the blood, sweat, and tears ...aka sweat equity of my home. I am striving for low energy costs being an all electric home in Zone 5 climate. I have slowly been getting closer to working on the interior, and have had my family say it sounds like a lot of work and now I am just letting that sink in. I know I can do it...but it's going to be time consuming and my doors I order have to have extra thick thresholds which means they take longer to have shipped and also cost $80 more each.

I was hoping to hear some opinions. If I don't use this stuff in the walls, I would absolutely have to use it in my attic. It would cost a ton of money to return because it's a special order item. I calculated and I wouldn't quite have enough to cover my attic floor. The main problem I would see is it's 15" instead of 22.5 or 23" wide so I would be taking a...knife?...to cut it down the middle and install 1.5 pieces per truss bay. *24" oc vs 16" oc walls

I would then blow in cellulose over this R-30 to achieve better attic insulation.

I would also most likely try to order the 5.5" mineral wool, which is made for 2x6 framing. But I would lose R-7 whole house wall performance because it's R-23 and not R-30 with the furred out wall. Worth the hassle?
 
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  #2  
Old 09-07-15, 06:48 AM
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Hi CTS,
These are just estimates, but they will put your concerns into perspective. As you suspect, adding more and more saves less and less, called diminishing returns.

Assume a 1,500 ft² home with 1,200 ft² of wall area in a climate with 5,000 heating degree days.

Then calculate the annual heat loss with r-30 and then r-23. The difference will amount to about $50 a year.

There are many small variables and this is just an approximation, but it illustrates those diminishing returns. If you like to play with numbers the equation is:
Q = U x A x HDD x 24
Q is your total heat loss in BTUs
U is 1/R
A is the area in question
HDD is your local number and the 24 is part of the conversion from from days to year.

The less expensive concern would be air sealing, framing, penetrations, and electrical boxes.

As for the 7" mineral wool, I have use Roxul and it is easy to cut. You could build a box 5.5" deep where you could drop in a batt and then use a hand saw sliding across the top of the box to shave those batts down to 5.5"+ a touch to be tight. Those scraps could then be use in the attic below the blown in insulation. I use a bread knife for small detail work but when I run into a stud bay other than 14.5" I use a saw to cut the needed length and install them across the bay.

Bud
 
  #3  
Old 09-07-15, 01:18 PM
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Hey Bud, sounds like I will be doing some finagling. I figured it would be less work to just cut them down the middle and use them in the attic versus shaving off 1.5". I will have to wait and see what the material is like. I can't picture it being very easy to shave off 1.5" without having tear out of material...meaning that there would be variances in amount of material per stud cavity. If it cuts better than I think, I can see building a 48" long x 15" wide x 5.5" box would work, assuming I have a long knife that I can glide along the box to shave that excess off.

Otherwise, if it doesn't shave off nicely - it looks to be cost prohibitive to use it in the attic (as in, cost per R value?)

To me it looks like Cellulose would be 6 times cheaper 1.57 versus .28 for the cost of 1 square foot of R-30 insulation.
 
  #4  
Old 09-07-15, 01:50 PM
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Don't put all you eggs in the basket based on an erroneous calculating method.

Keep in mind you must use the actual U values of the wall/ceiling/roof assembly. Using the R value of the insulation materials in a wall will not test out in hot box test in a lab as you calculate. Because of the heat loss on the studs/joists. Closer spaced studs/joists will not test out in as well as thought in an assembly because of the higher heat loss. The same applies for wood stud verses steel studs. - It is called a thermal "short circuit". Somehow, the "Pink Panther" slipped this it the standards years ago and somehow held on through the years, the false concept of U and R values of bulk insulation in building assemblies has continued. I have never seen any information from advertising where the bulk insulation. As an example, a wall with R20 insulation in the cavities may actually test out as low as R9.5 when tested in a guarded hot box because of the "thermal short circuit" effect - I found this in ASHRAE document.

Dick
 
  #5  
Old 09-07-15, 01:50 PM
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Is the brand of mineral wool you ordered "Roxul"? If so, it cuts very easily and for a 15" wide box I would use a hand saw.

As an energy auditor one of my functions is to evaluate all improvements for their payback over time. Even my deep energy retrofit would never repay its cost if I were to hire it out. Being a retired contractor I find it next to impossible to hire things out.

But sometimes folks just want the satisfaction of knowing their house is wrapped in an extra thick blanket, that's me especially after oil touched $6 a gallon a few years back.

If you haven't received it as yet you might ask. They may grumble but might cancel. Worth asking.

You will love the mineral wool in the walls and cellulose in the ceiling.

While those walls are open, go crazy with air sealing, it will make a big difference.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
  #6  
Old 09-07-15, 08:04 PM
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Dick,
What you are talking about is what I call thermal bridging. I realize with 16" O.C. walls I receive a hit to my whole wall performance because of that.

I am trying to take extra care in terms of air sealing. Using silicone between house wrap flaps and window/door bucks to prevent that common air channel caused when folding house wrap in and tacking it to the window sills. I also am sealing between the top plates, and between subfloor and bottom plate. I have read about using silicone between each and every exterior stud, but that seems like a lot of work. I am considering sealing the OSB Joints from the interior, I can see plenty of light shining through the joints even with house wrap on (it's opaque).

Bud,
The brand is Thermafiber - I assume it's similar in material content and makeup - I hope. I have decided it would be absolutely foolish to use it in the attic because I can receive better R value for the fraction of cost with cellulose because thickness is not as important compared to a limited stud cavity. Here's to hoping 1.5" shaves off fairly easily -- Would cost $540 to cancel the product because it was special ordered and already in store now.
 
  #7  
Old 09-07-15, 08:28 PM
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When you open a bundle they will need to fluff up, but whatever is cut off it is what is left that needs a good fit. I had several bays on a remodel that were other than 14.5" so had to cut to length and fit them in. Came out nice and didn't take that long.

The idea behind sealing the full length of every stud is to catch those osb seams where then cross each stud or vertical osb seams that end on a stud. When sealing the lesser important seams I use the large tubes of construction adhesive. Three times the volume for less money and I have had to go back and remove old construction adhesive and it is tough stuff.

Be sure to seal all electrical and if exposed, any plumbing penetrations.

Bud
 
  #8  
Old 09-07-15, 08:36 PM
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Bud, I will look into making some jig to cut. Any other tips besides the ones you provided?

I gathered this evening while testing various silicones (different prices and mixes) that while I sealed along the OSB Joint I could not obviously seal behind the stud and therefor it's not continuous. So as a result, what I am doing without sealing along the studs is either not doing the job right, or perhaps it's better than nothing. Will have to look into cheaper alternative like you said if I end up sealing each side of each stud.

Forgot to mention I bought two rolls of certainteed's MemBrain Smart Vapor Retarder & Air Barrier Film. Planning on installing it and stapling it at the stud centers.
 
  #9  
Old 09-08-15, 04:10 AM
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I don't think it has been mentioned but it would be interesting to know what the background moisture levels (relative humidity) are for the structure.

Every time someone wants to add or enhance insulation, one has to think about the fact that the sheathing temperatures will be colder than previously scenarios allowed. A house with high humidity becomes more problematic with enhanced insulation as the sheathing and siding become more likely to get cold enough to condense water vapor. Air sealing the exterior, while a good practice and one that I endorse, also serves to increase the humidity within the structure if there are no mechanical means provided to reduce it.

Sheathing materials have varying abilities to deal with vapor and condensation. OSB happens to be one of the least able to absorb moisture and cycle it without suffering from the effects of condensation.

The "MemBrain" vapor diffusion retarder is probably a good move for you since it will allow two way transfer of vapor. It won't though, prevent condensation from forming under the worst of circumstances.

Not trying to dissuade you from your goal, just bringing up some points of consideration. Most people would never have an opportunity to look inside their walls in the heating season to see what can happen under certain situations but I assure you, condensation does occur in wall cavities and osb is the sheathing material it favors most.
 
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Old 09-08-15, 05:39 AM
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Calvert, this is zone 5B with all four seasons. I don't know how humid our winters are. I assumed air sealing would be okay and that using MemBrain product the wall would dry to the inside if needed, otherwise permeate through the osb sheathing instead of the osb joints (that I am trying to seal).
 
  #11  
Old 09-08-15, 10:38 AM
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I am referring to indoor RH. Tightening a structure usually results in a higher indoor generated relative humidity. If you are starting with a damp environment, i.e., wet crawl space or basement, no moisture barrier on exterior of foundation, inadequate provision or use of bath and cooking fans, ...these are all contributors to indoor humidity. That works through wall and can condense appreciably on sheathing.

The Two way vapor retarder helps but it doesn't prevent the occurrence of conditions favorable to water vapor freezing on the sheathing.

Actually, winter exterior RH can be quite high since the air temperature does not allow for large volumes of vapor to accumulate. It is the "absolute humidity" that is, due to the cold conditions, kept at a low number.
 
  #12  
Old 09-08-15, 07:14 PM
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Hmm, well there is a basement that in the future will have rigid foam on the interior. So are you suggesting I shouldn't bother sealing the walls on the main floor at all, or just not completely (like leave the osb joints alone?)
 
  #13  
Old 09-08-15, 07:52 PM
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Where it is true, changing one thing affects others, air sealing is not something you skip, especially when the opportunity presents itself. Although extremely tight home will require some form of ventilation, it is rare that a retrofit will have an issue and the remedy, if it were required, would be fairly easy, like a timer in an exhaust fan. But I doubt you are going to reach that point.

The reason air sealing is so important is because air leaks easily bypass insulation. That not only increases energy use, but risks moisture issues.

There is a group in Maine (I believe) that has written some articles on building a "good enough" home and I absolutely agree. At every level we need to judge where best to apply our money and efforts. If you had to tear the walls apart to seal each side of each stud it obviously would be ridiculous. But when the walls are open, then it becomes tempting. Personally I would invest the minimal cost and effort even though the savings will be small. Heat loss in a house is based upon the accumulation of many small areas of heat loss.

If you happen to get it tight enough that your windows begin to form condensation on the very cold nights, then you will know you have done a good job and need to introduce a little fresh air.

As for what type of caulking to use, no one is going to see it. That is why I use the construction adhesive, least expensive and will last forever. Silicone is nice, but at a price.

Bud
 
  #14  
Old 09-09-15, 03:39 AM
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I think Bud has put it into good perspective. I've met people who will agonize over one tiny hole. Generally, any typical house can be improved upon but the worst of situations is usually not discovered until a stretch of extreme weather is encountered that will bring about a series of issues not previously thought to be a problem.

I just brought up the issue because in my insulating contractor career I have seen many problems develop as a result of not understanding that one thing affects another. I certainly don't discourage energy upgrades but do encourage a thoughtful approach and the "sensibility" Bud is talking about.
 
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Old 09-09-15, 05:49 AM
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That is true. And yes, I don't want to be the person who skips it when I can easily do it...but I also don't want to be the energy nut who knew just enough to be dangerous and rots his house sheathing or grows mold in there for 5+ years because it can't dry out.

Do you think I would need to have an air handler that brings in fresh air? I wanted to avoid having that tight of home. I believe it would be beneficial but in my life style I prefer to know my home does that naturally but just enough to breathe and ventilate on it own without the extra cost of a venting system + electricity to run it. (I'm already fretting about having a radon power fan, hoping I have low enough levels to have passive)

I don't know if I were to seal between every stud and then around the plates if, and also use that smart membrain product if that would be 'good enough' or if it would be too air tight that I'd have to consult with a specialist to spec out an air handler that I can't really afford. :P I also don't want to have the thought that 'Ehhh, my walls may be collecting moisture right now and I have no way to see it' for the life of my home. Is there a happy medium I can obtain, as a DIYer, to help lower my energy burden?
 
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Old 09-09-15, 06:16 AM
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There are some climates that are worse than others and I suspect NE is not one of them. Washington and Oregon coastal areas are noted for being damp where Denver CO is dry almost all of the time, along with many others.

The test for how tight a home is, is called a blower door test and that is part of my energy auditing. From before and after data, I usually advise existing home owners that it is nearly impossible to make an existing home too tight. The steps for an extremely tight home begin during construction. As you have noticed, those seams on the osb disappear behind every stud, well there are going to be butt ends of top and bottom plates, ceiling joists, drywall to bottom plate, and a host of other areas you will never get to. Even an electrical outlet in the middle of the house communicates with attic, basement and outside. How many nails were installed and removed in all of that osb?

As for fresh air, all home exchange air. The typical threshold is around a complete air change every 4 hours, most are in the 2 to 3 hour range. Sounds like a lot, but it illustrates just how leaky our homes really are.

If you have been doing a lot of reading on this subject you will have come across the shift between using vapor barriers and switching to vapor diffusion retarders. The shift is recognizing the need to dry somewhere. In fact, in your climate I believe they no longer advise using a (plastic) VB. Far north and deep south only. And definitely only one if at all.

Beyond the outside climate home have varying inside moisture issues and that is where we would start if you suspected (or tested) your home was too tight. Bathroom exhaust fans, a good range hood, and no inside moisture activities like wet firewood, drying laundry, or 1 hour hot showers (I raised 2 daughters).

Our guiding phrase is, "seal it tight and ventilate it right". By controlling the ventilation we limit the moisture passing through our walls.

Sorry for going long.
Bud
 
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