# Insulation: Mineral Wool or Fiberglass?



## kilgrosh (Apr 29, 2014)

Hey Everyone,
I am under contract to purchase an old farmhouse on 10.3 acres in Chester County, PA (outside Philadelphia). The original farmhouse was built in 1848, with an addition in the late 1890s/early 1900s, and a final addition in the 1980s. The pre-1980s walls are stone a 12"+ thick. 

I pulled up one of the floor boards and its vacant, no insulation!. Nothing on the underside of the roof either. So I definitely need to put in some insulation! 

Would you put in mineral wool batts (i.e. roxul comfortbatt) or fiberglass batts (the pin stuff)?


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## Maura (Jun 6, 2004)

I would either put in real wool, or if I couldn&#8217;t afford that, I would use spray in cellulose (newspaper). We put in cellulose when we built this house. It was fast and easy.


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## melli (May 7, 2016)

I use nothing but Roxul. It is better on so many levels. Rodents don't like it, it is virtually impermeable to water (I tested it by pouring water on a batt...it just puddled on it for hours). I even took a blow torch to it...nothing happened (fire resistant). Definitely less toxic to handle than fiberglass, retains its shape better, and slightly better R value per inch over fiberglass. And when you cut it (long serrated knife), it holds it shape better. It is spun basalt rock, like cotton candy. It is more expensive than fiberglass, but it will never slump/sag like fiberglass. Lastly, your lungs will appreciate it as it is less toxic and it doesn't promote mold. Well, if you've ever seen lava fields, nothing likes to grow on them. 
Geesh, I sound like a booster for the stuff, but having played with fiber glass for years, there is no comparison. 
I really think fiberglass days are numbered.

BTW- congrats on the farmhouse purchase! 12" stone walls! Must post pics of that...jealous. On the west coast, stone buildings are a rarity (other than fake stone paneling). Seismic issues here...


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## kilgrosh (Apr 29, 2014)

Thanks melli. I am thinking of going roxul and just buying in bulk to save money. 

_Where should I start the thread on the farm purchase? I want to tell every one about my experience!_

Maura, regular wool is too expensive for the amount of space. Blown-in stuff would be a little more expensive than batts because its a huge attic, and not to mention it goes everywhere! Thanks though!


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## unioncreek (Jun 18, 2002)

I would blow i cellulose in the attic, far cheaper than anything else and seals air movement better. It will settle some, but I always add a lot extra to compensate for that. It also fills in all the little areas that bats can fill.

Bob


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## goodatit (May 1, 2013)

melli said:


> I use nothing but Roxul. It is better on so many levels. Rodents don't like it, it is virtually impermeable to water (I tested it by pouring water on a batt...it just puddled on it for hours). I even took a blow torch to it...nothing happened (fire resistant). Definitely less toxic to handle than fiberglass, retains its shape better, and slightly better R value per inch over fiberglass. And when you cut it (long serrated knife), it holds it shape better. It is spun basalt rock, like cotton candy. It is more expensive than fiberglass, but it will never slump/sag like fiberglass. Lastly, your lungs will appreciate it as it is less toxic and it doesn't promote mold. Well, if you've ever seen lava fields, nothing likes to grow on them.
> Geesh, I sound like a booster for the stuff, but having played with fiber glass for years, there is no comparison.
> I really think fiberglass days are numbered.
> 
> BTW- congrats on the farmhouse purchase! 12" stone walls! Must post pics of that...jealous. On the west coast, stone buildings are a rarity (other than fake stone paneling). Seismic issues here...


where did you buy it? what is the cost? thanks in advance.


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## melli (May 7, 2016)

goodatit said:


> where did you buy it? what is the cost? thanks in advance.


http://www.roxul.com/products/residential/overview

It appears it is a Canadian operation, but they opened a factory in Miss. Roxul is owned by Rockwool, HQ in Denmark. 
I've been using it for the past 7yrs or so, and it really outperforms fiberglass. Forgot about sound dampening....

For 2x6 bundle 16" OC it covers about 40 sqft - it was about $30 USD. 
Seems the problem down south is finding it...up here it is supplanting fiberglass. When I go to the lumber yard, they have a better selection of Roxul than Fibreglass. 

I'd say right now, it is about 20-25% more expensive than fiberglass...if you can get a contractor rate, that % narrows. 
I can almost guarantee you won't be disappointed. Although the batts are heavy...
http://www.roxul.com/stone+wool/overview/origin+-c12-+properties


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## melli (May 7, 2016)

kilgrosh said:


> Thanks melli. I am thinking of going roxul and just buying in bulk to save money.
> 
> _Where should I start the thread on the farm purchase? I want to tell every one about my experience!_
> 
> Maura, regular wool is too expensive for the amount of space. Blown-in stuff would be a little more expensive than batts because its a huge attic, and not to mention it goes everywhere! Thanks though!


Start a thread here! Similar to what FtoF or I did...
I like pics!


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## haypoint (Oct 4, 2006)

Underside of the floor and underside of the roof has no insulation, right? Where are you planning to put insulation? 

I don't think anyone insulates the underside of the roof or under the floor. Above the upstairs ceiling needs lots of insulation. Insulation under the floor needs a vapor barrier against the heated side. Insulation under the roof needs to be ventilated.


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## kilgrosh (Apr 29, 2014)

haypoint said:


> Underside of the floor and underside of the roof has no insulation, right? Where are you planning to put insulation?
> 
> I don't think anyone insulates the underside of the roof or under the floor. Above the upstairs ceiling needs lots of insulation. Insulation under the floor needs a vapor barrier against the heated side. Insulation under the roof needs to be ventilated.



There is no insulation under the roof. When I pull up the boards on the attic floor (so it would the ceiling of the 2nd floor) there is no insulation either. Do I need a vapor barrier with mineral wool in the attic floor?


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## topside1 (Sep 23, 2005)

Does the second story have a ceiling or is it just the underside of the roof you are looking at? I would not insulate the first story floor joists in your crawlspace, mold will become a serious issue if you do. The heat loss downward is minimal and molds will accumulate as most homes have inadequate cross ventilation to keep the air moving. Also by insulating you will accelerate floor joist deterioration. Topside


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## melli (May 7, 2016)

Code around here dictates vapor barrier on exterior walls and ceilings/rafters. 

No vapor barrier in floor joists as heat/moisture rises (if floor was on ground (ex. slab), then vapor barrier required - 2x6mil (underneath concrete)). Some areas require Radon mitigation. My old house (built new about 10yrs ago) had no floor vapor barrier but 2x12 pink between joists and sheathing was tacked on underneath joists (crawl space well ventilated). It actually became a topic of discussion with us (38) new home owners, but we found out it wasn't required on a raised floor system. 

If one puts insulation in rafters, there must be an air path above insulation to vent outside. If you put insulation on/between ceiling joists, air ventilation shouldn't be an issue provided you have attic/roof vents. 
Would be hard to retrofit your attic with vapor barrier, as it usually is put on underside of ceiling joists, then drywall/etc. 

Really comes down to moisture - dew point. A warm house has higher dew point, as warm air holds more moisture. That air will hit colder air in attic at night. Vapor barrier is there to keep hot/cold air from mixing. Building science experts say you want the dew point line (temp at which dew forms) on exterior side of vapor barrier. Supposedly, to keep moisture out of house. Daytime heating in attic creates airflow and drys out attic if it acquired any condensation overnight.

Apparently, where I live, we plan to adopt the International Building Code (in essence, we already do). The new code has 'amped' up the insulation requirements, and has focused on 'thermal breaks.' One of the issues, for example, is traditionally one insulates between the studs, but the studs become a thermal break, as they do not have the same RSI (R value) value as the insulation. To mitigate this, it is recommended to put a layer of foam on outside (EPS, XPS, SIPs etc). This also why cellulose blown in attic is a favorite, as one can cover joists. One could use Roxul to accomplish to the same thing (fill cavities, then insulate on top of joists perpendicular to joists). This is why I went with ICFs. Kills a lot of birds with one stone...lol

The irony, is that now we have to have a suitable ventilation system because houses are getting air tight. They used to be sieves, and they would dry out easily, but they required a lot of energy to heat.


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## kilgrosh (Apr 29, 2014)

topside1 said:


> Does the second story have a ceiling or is it just the underside of the roof you are looking at? I would not insulate the first story floor joists in your crawlspace, mold will become a serious issue if you do. The heat loss downward is minimal and molds will accumulate as most homes have inadequate cross ventilation to keep the air moving. Also by insulating you will accelerate floor joist deterioration. Topside


The second floor does have a ceiling. The house has a third floor walk up attic and that does not have any insulation.



melli said:


> Code around here dictates vapor barrier on exterior walls and ceilings/rafters.
> No vapor barrier in floor as heat/moisture rises. My old house (built new about 10yrs ago) had no floor vapor barrier but 2x12 pink between joists (crawl space well ventilated).
> If one puts insulation in rafters, there must be an air path above insulation to vent outside. If you put insulation on/between ceiling joists, air ventilation shouldn't be an issue provided you have attic/roof vents.
> Would be hard to retrofit your attic with vapor barrier, as it usually is put on underside of ceiling joists, then drywall/etc.
> Really comes down to moisture - dew point. A warm house has higher dew point, as warm air holds more moisture. That air will hit colder air in attic at night. Vapor barrier is there to keep hot/cold air from mixing. Building science experts say you want the dew point line (temp at which dew forms) on exterior side of vapor barrier. Supposedly, to keep moisture out of house. Daytime heating in attic creates airflow and drys out attic if it acquired any condensation overnight.


So if I understand correctly, I would put a vapor barrier down in between the floor joists in the attic and then put insulation on top of that. I would not put insulation on the roof rafters. Right?


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## topside1 (Sep 23, 2005)

They by all means blow in cellulose insulation as deep as you can afford....Enjoy.


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## melli (May 7, 2016)

kilgrosh said:


> The second floor does have a ceiling. The house has a third floor walk up attic and that does not have any insulation.
> 
> 
> 
> So if I understand correctly, I would put a vapor barrier down in between the floor joists in the attic and then put insulation on top of that. I would not put insulation on the roof rafters. Right?


Yep, that is what I would do...no sense putting it between rafters, unless you planned to use the attic as a heated space. Putting it in between AND on ceiling joists is the easiest solution...imho
As for vapor barrier, that is a tough one...I would go to local building department and ask them. Every climatic zone has different issues. In the case of cellulose, it is not recommended to use a vapor barrier from what I've read. Just fill up attic. I've never used it, and we don't seem to use it up here in NW. No idea why...perhaps our cool marine climate plays havoc with the cellulose. IDK. Roxul is rock based, and nothing can mess with it. A lot of folks use spray foam up here, but that is pricey compared to cellulose or Roxul. 

Topside1 offered a solution. I would make sure you get the dense version of cellulose...apparently, there are different flavors....


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## GardenGekko (Jan 31, 2013)

Check out buildingscience.com Read every article you can find on it. Very good info on insulation. Here's one to get you started. 

https://buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting/view


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## kilgrosh (Apr 29, 2014)

Thanks GardenGekko! I will take a look and see where I can go from there.


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## melli (May 7, 2016)

GardenGekko said:


> Check out buildingscience.com Read every article you can find on it. Very good info on insulation. Here's one to get you started.
> 
> https://buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting/view


Yeah, I like this site...one of the few places where one can download thousands of articles without headaches...occasionally Fine Homebuilding has free articles, but you need to be a member to get all the articles ($). 
http://www.greenbuildingadvisor.com/blogs/dept/building-science is another great site. 
And North of the border, NRCAN does some great research and they publish it online. 

WRT article note above: 2" gap between insulation and roof deck is mandatory now up here (used to be an inch - they stamped my plans with that salient detail). I agree with having attic slightly pressurized. Nothing worse than have roof vent too big and it sucks out heat or cold like a vacuum cleaner, especially in a windy area (makes attic a low pressure zone).

Kilgrosh - it looks like sealing ceiling joists is the way to go....how one does that in a retrofit will be interesting (cramming in vapor barrier like 6mil poly will be fun)...I'd almost be inclined to use thin XPS in cavities (will suffice as a vapor barrier - glue edges), then Roxul or Cellulose over top, covering tops of ceiling joists, so you have no thermal breaks. 
Or if you want the attic a heated space and have deep enough rafters, insulate the rafters...then vapor barrier can easily go underneath. 
If you get the chance, a pic of your attic would be nice. I love really old homes...some of them were really built well, with heavy timber. They used full dimensional lumber, unlike the stuff we get nowadays. 
I had the chance to visit an attic in Germany, with slate roof...that was a piece of art. Huge timber rafters! Not so common in NA. best.


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## Farmfresh (Jan 11, 2009)

ALWAYS use a vapor barrier. (barrier against heated side which is usually the interior for most of us.) I prefer a sheet of 6 mil plastic if possible instead of the paper backed stuff that comes with most insulation because it works better with less chance of holes. Our old house had blown in cellulose with no vapor barrier and we had constant wet forming along the edges of the rooms where the cool air in the attic condensed and dripped. The insulation inside of one wall was so damp that it was a slime that ended up rotting out the studs along that wall. 

Talk about a pain in the neck. Try retrofitting a vapor barrier where blown in cellulose was installed! I had to sweep each cavity empty, install the vapor barrier and then re-install the insulation!! (I lived... only barely) AFTER the barrier was installed what a difference! 

In a perfect world where you have lots of money professionally installed foam insulation is the best. It acts as vapor barrier as well as superior insulation. 

In our "normal" poor world, I also vote for the Roxul. I bought mine via Lowes and Home Depot also carries it, but you may have to order it online for store pick up or delivery. It is nice stuff to work with and much better performance wise than the fiberglass. You can cut it to fit with a steak knife and it is just generally easy stuff to use. It is slightly more expensive, but the amount saved with a properly insulated home is so significant it will pay for it's self darned quick.


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## kilgrosh (Apr 29, 2014)

Thanks guys for the info. I will get a better picture of the attic soon. Still waiting on settlement! (Insert multiple bad words aimed at the bank who moves slower than pine sap in January)

I have been researching the DIY spray foam kits as a vapor barrier and then roxul on top of that. Like, spray 1" to seal everything, then put 5" Roxul on top to get to the top of the joists, then 7" roxul or fiberglass batts crosswise to stop thermal breaks. 

The roof was replaced in the last 10 years or so, so I assume it's vented. My GC is also a professional roofer so he said he would check it to make sure. I'm learning a lot about how important it is to have a properly vented roof! #noicedamsforme


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## Farmfresh (Jan 11, 2009)

Glad that you are getting it checked by a professional. 

One thing I have learned from living in old houses is to assume nothing. This current house that I am living in for the last couple of years has newer vinyl siding and vented soffit covers. When we had to replace the gutters and the fascia last year we discovered that the vented vinyl covers were installed over SOLID plywood that was original. That got us looking and we discovered that the attic had no ventilation at all! We drilled some large holes in the right spots, so now at least it has some ventilation. We still need to add vent caps to the roof and possibly gable end venting as well.


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## kilgrosh (Apr 29, 2014)

Wow! Glad you find that bit out!


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