RE-INSULATing an attic - remove or not remove old?

[DogwoodTales]

Alongside my previous thread about ridge venting there is the issue of re-insulating the attic. 
The existing insulation is old and matted, thus little R value - as is indicated by the fact that when it's 90+ outside here in SE Indiana my ceiling is also 90+ degrees (by an infrared thermometer, assuming the emissivity is within proper range) whilst the floor is 70 degrees.
According to the home inspection last year he doesn't think the insulation contains asbestos, but we didn't have it tested either.

Question-
I'm finding two schools of thought, so to speak, on the subject of removing the old insulation before adding more  - one is to remove it and the other is to leave it.
I find both to be fairly compelling in their pros and cons. I'm leaning towards just leaving it only because it's less work, but what would you do/recommend?


On that note, I also read that since the existing insulation has a paper face that additional insulation (on top of the old) should be unfaced. Does that sound right?
Lastly, I'm wondering that if I leave the old insulation should I run the new rolls of insulation between the joists or cross over the joists?
At the moment I'm not considering doing blown in insulation. One reason is because the new vented soffit won't be don't done for quite a while (due to contractor availability) and I need to get this attic re-insulated asap (as soon as it cools down a bit) and I'm thinking it will be exponentially easier to slide baffles up into the eaves from the outside of the house when the old soffit is taken out rather than me trying to crawl under a 4/12 pitch to get the baffle back in there from inside the attic. So with rolled fiberglass I can keep the insulation from blocking up the eaves whereas with blown-in insulation I won't be able to keep it out.

[jteneyck]

I had the same situation when I decided to add more insulation to our attic, except the old insulation was in good shape so I didn't have to think about removing it.  However, had it not been in great condition, I still would have left it in place.  I see no reason to remove it, any R value it adds is good.  

I used unfaced fiberglass roll insulation and ran it cross wise to the floor joists.  I stopped it even with the outer walls, not out to the soffits.  My roof pitch is about the same as yours, and it's a hip roof. It was a true pain to get the insulation in place near the outer walls. I did it in the late Fall. No way I'd want to do that job until it got pretty cool.

John

[EatenByLimestone]

Ok, so you have fiberglass batt insulation. Why not encapsulate it by adding cellulose on top. You’ll get air sealing also if you do that.

[EatenByLimestone]

https://youtu.be/xdSBRPnFvlM?si=8nQOiLAR2Z5GjSEj

[fredhargis]

I wouldn't remove the old, but if you choose to use rolls for the new stuff I'd make sure it's unfaced. Seems to me that if you put a barrier between the new and the old moisture could potentially get trapped in the old insulation. I'm pretty sure that would be a huge problem over time.

[ajkoontz]

My house had blown in that had settled plus disturbed (by me) running various new circuits and what-not. No way was I going to pull/ suck all that old insulation out. I ran new fiberglass rolls, cross ways. In the end, it was totally worth it. I didn't measure energy savings, but the house is certainly more comfortable. I also added a foam 'box' with foam lid around the access hole. So-

- I would not remove the old given your circumstances
 definitely cross joist if you already have insulation between the joists
- definitely worth doing the project
- do something over your access stairs (or whatever you have) or you're leaving a big chimney for all your conditioned air to escape

[taxman]

My house had blown in that had settled plus disturbed (by me) running various new circuits and what-not. No way was I going to pull/ suck all that old insulation out. I ran new fiberglass rolls, cross ways. In the end, it was totally worth it. I didn't measure energy savings, but the house is certainly more comfortable. I also added a foam 'box' with foam lid around the access hole. So-

- I would not remove the old given your circumstances
 definitely cross joist if you already have insulation between the joists
- definitely worth doing the project
- do something over your access stairs (or whatever you have) or you're leaving a big chimney for all your conditioned air to escape

Hi AJ, 

How solid is your "Foam Box?"   I use my attic regularly and wondering how much abuse that will take. If you have a pic would be great. 

Thanks,

[brianwelch]

If I were to add a foam box, I would use the extruded foam (not beadboard), or polyiso laminated to a box made of lauan or masonite to provide some protection...

[ajkoontz]

Hi AJ, 

How solid is your "Foam Box?"   I use my attic regularly and wondering how much abuse that will take. If you have a pic would be great. 

Thanks,

I don't have a picture, but something like this. Mine is not even this nice. Instead of foam walls, I used additional 2x framing around my opening. That makes getting into and out of the attic a little harder because it's almost a foot tall. But like your comment said, the walls are going to take a lot of abuse from getting in and out. The 2x framing is attached to the joists and they're not going anywhere. I can get 2" extruded foam scraps at work so I saved 2 pieces and doubled them up for a 4" lid/ cover. I copied this idea from a magazine or somewhere. Before, I had nothing over the stairs. I did this all at once so I can't say for sure how much a difference the cover makes, but seemed worth it to me to do this little extra to prevent basically just 1/4" plywood between my ceiling and roof.

[DogwoodTales]

Ok, so you have fiberglass batt insulation.    Why not encapsulate it by adding cellulose on top.  You’ll get air sealing also if you do that.

I could, but like I said it will be impossible to insulate to the eave without getting that into the soffits (revisit what I said about that above).


As to the attic access - that's in the garage anyway, so not as important as if it was over living space.
But I do have an attic fan that I need to build an insulation box around as part of this re-insulation project. There's examples on YT of people building one with a hinged lid that just holds in place with gravity and lifts by air movement when the fan is used. I'll probably build something like that. In a couple of those YT videos the DIYer measures before and after with an infrared thermometer and it shows that just 2" foam board results in a remarkable reduction in heat transfer.