Old Rock Wool Insulation

Hello,

I’ve had two insulation contractors out to provide estimates for a project at my house. Unfortunately, they provided vastly different opinions. Hence, I am hoping someone here can shed some light.

I am considering having cellulose blown into my finished attic to help mitigate snow from melting near the ridge of my roof. My house was built in 1941, and the third floor contains a bedroom, bathroom, and an storage space (the storage space spans the entire front of the house). The insulating material currently in use is rock wool, and I’m assuming it’s original to the house. The storage area has the rock wool held into place with pegboard nailed to the 2x6 rafters.

The first contractor says that all of the rock wool needs to be removed and replaced with cellulose. He would be charging a nice chunk of cash for the removal. The second contractor recommended that I leave the rock wool, not because it’s the most effective, but because he thinks it’s unsafe to disturb the wool and potentially cause fibers to become airborne. He thinks the risk of the fibers outweighs the benefit of replacing the insulation. The first contractor doesn’t seem nearly as concerned as the second. He did say that his employees would be properly covered with protection. The second contractor did provide some recommendations of stuff he could do, including blowing cellulose into the crown to better pack it with insulation.

Do you have an opinion?

Thank you in advance.

 

I fall into the "leave the old insulation in place" camp. I feel the added expense and dirt generated removing the old insulation probably won't be offset by the slight gain in efficiency. Plus, it would be very easy to simply apply whatever insulation thickness needed to get to the desired R value. You probably don't care that your desired R value took 17" of insulation versus 16".

 

The only difference between new and old installations is, well, nothing, insulation is insulation.

The beauty of cellulose is that it has some bulk to it and provides a little better air sealing than blown in fiberglass.

But that being said, air sealing is still a very important step in the process, along with making sure your ventilation is correct.

Blowing in big piles of insulation without the other fixes in place may create bigger issues down the road!

 

That’s a good point about ventilation. I don’t really have any ventilation. There are no gable vents, no ridge vents, and no soffit vents. I was considering having a contractor at least look into adding gable vents. The roof is slate, so I don’t think a ridge vent is an option. Additionally, I don’t think soffit vents are possible because there is very little overhang from the eaves.

I am having a roofer come over to replace the gutters, downspouts, and fascia. Is there anything I can ask him to do while he’s performing that work?

Thank you.

 

Impossible to say not seeing what you have but at least you now know so take the time to investigate!

 

I recommend that you find a (state) certified energy auditor and have them do a complete evaluation. It costs ... NOTHING. They will tell you what you need for ventilation, insulation, home sealing. They should do a pressure check to determine the before and after air infiltration value. The cost is partly covered by a tax rebate. I did it and am very happy with the results, because they got me the proper amount of insulation and installed a good vent system and also tightened up leaky sources like the attic entry hatch.
Also, I just want to mention that rock wool is fine except some old materials of a similar type that included fiberglass shards. I would remove that stuff because it is NASTY if you ever need to root around in it.