Author Topic: rockwool versus fiberglass  (Read 2000 times)

affordablehousing

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rockwool versus fiberglass
« on: July 08, 2019, 04:48:48 PM »
Forum, I took down the ceiling in a lower room to clean up old wiring and add new lights. It also gives me the chance to insulate the ceiling underneath our bedroom. They are 2x8 joists. Should I spring for rockwool or go with fiberglass? I've never used rockwool before but am excited by the sound attenuation possibilities if this lower room gets used more as a guest bedroom (likely possibility). And what thickness would you put in, 3.5" or 5.5"? This is ~250sf so the cost difference is likely ~$200 I would think.

electriceagle

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Re: rockwool versus fiberglass
« Reply #1 on: July 08, 2019, 07:40:37 PM »
Rockwool.

The difference in material cost is dwarfed by the extra labor cost/hassle if you are not satisfied with the noise attenuation properties of the fiberglass.

SunnyDays

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Re: rockwool versus fiberglass
« Reply #2 on: July 09, 2019, 09:23:19 AM »
Yeah, get the Roxul Safe and Sound  - works well and fewer itchies.

affordablehousing

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Re: rockwool versus fiberglass
« Reply #3 on: July 09, 2019, 10:29:51 AM »
Thanks all for the advice.

Syonyk

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Re: rockwool versus fiberglass
« Reply #4 on: July 09, 2019, 12:27:11 PM »
Dunno, do you enjoy working with fiberglass?  I'm sure someone, somewhere, does...

Otherwise, rock wool is nicer to work with and does a better job on sound.  The 3.5" stuff won't support between the studs overhead, the 5.5" stuff should, though you may still have to anchor it in place a bit.

BNgarden

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Re: rockwool versus fiberglass
« Reply #5 on: July 09, 2019, 01:03:19 PM »
If using rockwool (which I would also recommend and have used in two applications for sound-proofing to good effect), make sure you don't pack it in.  Just friction fit, leaving a little air space against floor above (?), and you can use multiple layers if the depth of joists allows it.

Dogastrophe

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Re: rockwool versus fiberglass
« Reply #6 on: July 09, 2019, 01:16:48 PM »
Rockwool, but I am biased as my company is a distributor of the line.  Just a note on Safe n Sound - it does not have an official R rating as it is designed for sound proofing of interior partitions.  If you go with it, keep this in mind if you have leftovers and want to use for exterior walls.

ysette9

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Re: rockwool versus fiberglass
« Reply #7 on: December 29, 2021, 08:53:56 PM »
Rockwool, but I am biased as my company is a distributor of the line.  Just a note on Safe n Sound - it does not have an official R rating as it is designed for sound proofing of interior partitions.  If you go with it, keep this in mind if you have leftovers and want to use for exterior walls.

I realize I am necroposting here but I hope you don't mind if I raise the topic from the dead. We are talking with interest now about insulating the house after some unseasonably cold weather is pointing out just how cold and drafty this old house is. Someone mentioned rock wool and now I have these visions of wrapping all the exterior walls before replacing the siding. I'd also love to put it under the new floors before they go in on the main level to provide sound dampening from the basement.

Do you have any smart thoughts about rock wool on existing buildings and how to integrate that on the exterior? In particular, how do you deal with the extra thickness of the walls when it comes to windows and doors and the like?

samanil

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Re: rockwool versus fiberglass
« Reply #8 on: December 29, 2021, 09:37:16 PM »
I think you need to make jamb extensions for the doors and jambs for the windows. A building science guy I work with is of the opinion that exterior insulation is very superior to the way it's typically done in the US, because studs are thermal bridges that work against the insulation in between them. My company has been using Gutex for exterior insulation, which is a wood product. I watched a building science youtube video (Balinda Car) on Gutex and she spoke very highly of it. I don't know about rockwool for exterior insulation, but I'd guess it'd work well.

Dogastrophe

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Re: rockwool versus fiberglass
« Reply #9 on: December 30, 2021, 04:58:43 AM »
Rockwool, but I am biased as my company is a distributor of the line.  Just a note on Safe n Sound - it does not have an official R rating as it is designed for sound proofing of interior partitions.  If you go with it, keep this in mind if you have leftovers and want to use for exterior walls.

... I have these visions of wrapping all the exterior walls before replacing the siding. I'd also love to put it under the new floors before they go in on the main level to provide sound dampening from the basement.

Do you have any smart thoughts about rock wool on existing buildings and how to integrate that on the exterior? In particular, how do you deal with the extra thickness of the walls when it comes to windows and doors and the like?

I'm not a building science guy and cannot comment on using Rockwool in this application. They do make an exterior sheathing board but not sure if you can install it over existing sheathing (I've since moved on from the building supply industry and have lost contact with my old Rockwool rep). I'm sure that you can find something that will work.

I will point out that Rockwool (depending on where you're from, people still call it the original name, Roxul) comes in different varieties.  Safe n Sound is an acoustical / sound deadening product meant to be used on interior applications (between floors and rooms) - it has no stated insulation properties.

They also produce an entire insulation line in different thicknesses and R-values, framing types (metal or wood), application, etc. I like the product because it is easier to work with than fibreglass insulation - it cuts very easy and you don't itch for a week after handling it!

How old is your house and was it built with insulation? There are companies that will blow insulation into the exterior wall cavities but this is typically done with old houses that either didn't have insulation or the old insulation has crumpled to the bottom of the wall.

DeepEllumStache

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Re: rockwool versus fiberglass
« Reply #10 on: December 30, 2021, 08:18:19 AM »
I will point out that Rockwool (depending on where you're from, people still call it the original name, Roxul) comes in different varieties.  Safe n Sound is an acoustical / sound deadening product meant to be used on interior applications (between floors and rooms) - it has no stated insulation properties.

They also produce an entire insulation line in different thicknesses and R-values, framing types (metal or wood), application, etc. I like the product because it is easier to work with than fibreglass insulation - it cuts very easy and you don't itch for a week after handling it!

Our 1950s built house had zero exterior insulation and after the crazy winter we had last year we decided to start a project to insulate our walls. We're pulling down the sheet rock and inserting the Rockwool between the studs. Can confirm that the insulation line is easy to work with.

ysette9

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Re: rockwool versus fiberglass
« Reply #11 on: December 30, 2021, 08:34:17 AM »
Rockwool, but I am biased as my company is a distributor of the line.  Just a note on Safe n Sound - it does not have an official R rating as it is designed for sound proofing of interior partitions.  If you go with it, keep this in mind if you have leftovers and want to use for exterior walls.

... I have these visions of wrapping all the exterior walls before replacing the siding. I'd also love to put it under the new floors before they go in on the main level to provide sound dampening from the basement.

Do you have any smart thoughts about rock wool on existing buildings and how to integrate that on the exterior? In particular, how do you deal with the extra thickness of the walls when it comes to windows and doors and the like?

I'm not a building science guy and cannot comment on using Rockwool in this application. They do make an exterior sheathing board but not sure if you can install it over existing sheathing (I've since moved on from the building supply industry and have lost contact with my old Rockwool rep). I'm sure that you can find something that will work.

I will point out that Rockwool (depending on where you're from, people still call it the original name, Roxul) comes in different varieties.  Safe n Sound is an acoustical / sound deadening product meant to be used on interior applications (between floors and rooms) - it has no stated insulation properties.

They also produce an entire insulation line in different thicknesses and R-values, framing types (metal or wood), application, etc. I like the product because it is easier to work with than fibreglass insulation - it cuts very easy and you don't itch for a week after handling it!

How old is your house and was it built with insulation? There are companies that will blow insulation into the exterior wall cavities but this is typically done with old houses that either didn't have insulation or the old insulation has crumpled to the bottom of the wall.
House was built in 1924. It has been modified and jerked around with a good amount so it is hard to tell how it was originally built. There is some evidence of fiberglass in some walls from a few projects we have done but I dont have a clear picture of what is where.

In our previous house (built 1947) we had cellulose blown into the cavities. It did help but Im hoping for better.

Thinking of this I suspect that we should look into replacing the windows at the same time. We have lots of big windows and I am not convinced they are great. What is a good way to assess their quality?

Paper Chaser

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Re: rockwool versus fiberglass
« Reply #12 on: December 30, 2021, 08:55:03 AM »
What's the exterior siding material on the home currently?

Instead of dealing with completely residing the entire home and possibly getting new windows and/or doors, have you considered foam insulation injection? It's great at air sealing and eliminating drafts but wouldn't require a ton of expensive exterior work like exterior insulation does.

https://www.youtube.com/watch?v=_dOm0a4unEw

ysette9

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rockwool versus fiberglass
« Reply #13 on: December 30, 2021, 11:09:59 AM »
To my best guess the exterior is wood siding (ground level) and shake (upper level) in various statues of disrepair with plywood underneath.

If you can drill and fill with foam then Id be very interested in that. So far alll of the companies Ive gotten quotes from only offered cellulose and fiberglass blow-in.
« Last Edit: December 30, 2021, 11:11:41 AM by ysette9 »

Sibley

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Re: rockwool versus fiberglass
« Reply #14 on: December 30, 2021, 06:30:42 PM »
Keep in mind that the old houses were built without vapor barriers, and they were built to require air movement to prevent moisture issues. Exterior wall insulation can seriously mess with those systems and can in turn have unintended consequences. I haven't done all the detailed research, but you're going to want to be careful here.

ysette9

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Re: rockwool versus fiberglass
« Reply #15 on: December 31, 2021, 05:18:00 PM »
Keep in mind that the old houses were built without vapor barriers, and they were built to require air movement to prevent moisture issues. Exterior wall insulation can seriously mess with those systems and can in turn have unintended consequences. I haven't done all the detailed research, but you're going to want to be careful here.
From the little I have researched so far rock wool is permeable and so doesnt create those moisture issues as other materials might.

nereo

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Re: rockwool versus fiberglass
« Reply #16 on: December 31, 2021, 06:49:39 PM »
We used rock wool comfortboard80 to add exterior (continuous) insulation on the exterior walls of our 120 year old home. I spent a lot of time going over the details and perms but ultimately the work itself was easy and the final result more than doubled the Rvalue of the entire wall assembly.

Its a bit much to explain everything here, but the highlights are:
  • Removed the existing cladding (in our case vinyl siding)
  • plugged many gaps in sheathing (1x12) with caulk and foam
  • Added a vapor-permeable wrap and taped seams
  • Extended window and door jambs (made window bucks with lumber)
  • Flashed bucks carefully with flex tape
  • Installed rockwool in 2x4 sections (2 single layer - would have doubled up if I had the materials)
  • Used vertical furring strips to create a 3/4 air gap*
  • Reinstalled vinyl siding -required minimal cutting

Ultimately rockwool won out because of its ability to dry (perm rating) and sound absorption (as important to us for this project as thermal insulation). But many choose to use XPS or ISO rigid foam (be aware those foam options will not allow moisture to pass through, which is a major consideration for older homes without any vapor control layers) Installing an air gap between the insulation and cladding is key for preventing moisture issues, as is properly taping the window and door jamb extensions.

Working with rockwool itself is a dream. Its easy to cut, easy to fit, is less irritating than fiberglass and has enough form to allow installation of furring strips by a single person with just a chalk line.

We will be doing something similar this spring with our new (to us) 1940s home, but here the windows need to be entirely replaced (allowing us to do it all together)

Tl;dr - if you are handy enough to be Anne to remove your cladding and replace it, then its not any more difficult to add exterior insulation when you do. And if you are going to replace your cladding you should absolutely add a couple inches of exterior insulation.

Papa bear

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rockwool versus fiberglass
« Reply #17 on: December 31, 2021, 08:16:01 PM »
I dont have a direct link for you, but this is where you need to do all your research:

https://www.buildingscience.com

I have worked with Rockwool, as well as other mineral wools.  I actually prefer working with fiberglass. The mineral wool really can be nasty and bothers me.  Have to go full mask, long sleeves, glasses, gloves, etc. 

I think the mineral wool is a better product, though.


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LostGirl

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Re: rockwool versus fiberglass
« Reply #18 on: January 07, 2022, 10:26:12 AM »
Rockwool, but I am biased as my company is a distributor of the line.  Just a note on Safe n Sound - it does not have an official R rating as it is designed for sound proofing of interior partitions.  If you go with it, keep this in mind if you have leftovers and want to use for exterior walls.

... I have these visions of wrapping all the exterior walls before replacing the siding. I'd also love to put it under the new floors before they go in on the main level to provide sound dampening from the basement.

Do you have any smart thoughts about rock wool on existing buildings and how to integrate that on the exterior? In particular, how do you deal with the extra thickness of the walls when it comes to windows and doors and the like?

I'm not a building science guy and cannot comment on using Rockwool in this application. They do make an exterior sheathing board but not sure if you can install it over existing sheathing (I've since moved on from the building supply industry and have lost contact with my old Rockwool rep). I'm sure that you can find something that will work.

I will point out that Rockwool (depending on where you're from, people still call it the original name, Roxul) comes in different varieties.  Safe n Sound is an acoustical / sound deadening product meant to be used on interior applications (between floors and rooms) - it has no stated insulation properties.

They also produce an entire insulation line in different thicknesses and R-values, framing types (metal or wood), application, etc. I like the product because it is easier to work with than fibreglass insulation - it cuts very easy and you don't itch for a week after handling it!

How old is your house and was it built with insulation? There are companies that will blow insulation into the exterior wall cavities but this is typically done with old houses that either didn't have insulation or the old insulation has crumpled to the bottom of the wall.
House was built in 1924. It has been modified and jerked around with a good amount so it is hard to tell how it was originally built. There is some evidence of fiberglass in some walls from a few projects we have done but I dont have a clear picture of what is where.

In our previous house (built 1947) we had cellulose blown into the cavities. It did help but Im hoping for better.

Thinking of this I suspect that we should look into replacing the windows at the same time. We have lots of big windows and I am not convinced they are great. What is a good way to assess their quality?

You could have a home energy audit with an infrared camera. It would show you the points of cold intrusion and where to plug vs replace. With windows, it could be the windows themselves but also the quality of the thermal detailing at the opening.  Someone mentioned thermal bridging at studs but your studs are wood which are not a good thermal bridge (commercial is light gauge metal and needs to be addressed).

In terms of rock wool vs other, the two benefits are sustainability and soundproofing. Otherwise it would just depend on the specific material selected and the properties desired. 

There is likely little to no insulation in your exterior walls so if you are residing, you should definitely add insulation.  Many people I know that started this route (in old SF homes) ended up replacing the windows and other exterior elements at the same time, once they discovered the condition of those items following demolition.

Good luck!