Cfrgtkky

I have an attic with blown in fiberglass insulation, probably original and 27 years old. The attic appears to have had some moisture issues in the past (bathroom vents being vented out of the soffit vents, which have been corrected) and the insulation is a little clumpy and a little dirty, but not terrible.

I want to add more insulation, but I'm not sure whether or not to use more blown in fiberglass or cellulose on top of it. I've read cellulose is the superior product. But I've read and saw videos of cellulose just being blown in on top of the fiberglass. I've read conflicting articles that says it's fine to do that and others say the cellulose will compact the fiberglass which isn't good for the existing fiberglass.

What should I do? Thanks!

Here is a pic of my current attic insulation:

Add the cellulose right on top, I have seen folks remove the old but this is crazy both materials are insulation and combined the provide a higher R value. I would caution if all the moisture issues are not taken care of cellulose will pick up moisture and hold it longer than fiberglass.

I would add more fiberglass insulation to the top of what you already have as it will not compress as much as cellulose does. But if you have clumpy fiberglass insulation in your attic now, you may want to check it with a moisture meter before adding anything on top of it. Also, cellulose is a dusty product, whereas fiberglass blows in pretty clean. I've been insulating for over 30 years and we have never added cellulose over fiberglass. Insulation works better when you add the same type to existing material. Just piling material up in an attic doesn't always make for a better insulated space.

I'm a insulation installer and any time you compress insulation you lose R-value our company I work for wouldn't blow over the fiberglass we would remove it, if it was the other way around you might be fine. But I personally would just add more fiberglass blow and not have to deal with removal, also fiberglass doesn't settle. You should have at least a R-45 in your attic the normal use to be a R-38 but new energy standard is a R-45. That should be around 22-24 inch hight depending on manufacturer. You should remove any fiberglass that has had gotten wet just to be safe.

I have also heard not to add cellulose over blown fiberglass because cellulose is heavier and will compress the fiberglass. When fiberglass is compressed it loses R-value (is a poorer insulator). Makes sense to me.

I think the best option would be to blow more fiberglass on top as it will not compress the existing stuff too much. I know Home Depot will sell blown in fiberglass and the machine so it should be about the same as doing cellulose yourself.

If you are set on blowing cellulose, you could probably put it right on top but just know it will compromise the effectiveness of the existing insulation. If you blow enough cellulose as if you had no existing insulation it will give you the R-value you need.

I agree that trying to remove the existing blown in will be hard and not worth it. Just leave what is there regardless of what you add on top.