Sunday, December 25, 2011

Mineral Wool Insulation - Batt installation (and difficulties)

More insulation information.

The insulation guys are at work. First they sealed the 2 x 6 stud bays with a minimally invasive foam, then they started installing the mineral wool insulation. As I mentioned in my insulation choices I talked about the difficulties of installing batts well. Insulation is graded I, II,  or III based on how well it covers the stud bays. Grade I is the best.

A class I installation  - see the picture below from Alison Bailes Energy Vanguard blog

grade I fiberglass batt insulation, no compression, gaps, or incomplete fill

He says that it is one of only TWO class I fiberglass installations he has ever seen as a home energy rater. 

The criteria for a class I installation include:

  1. Minimal gaps in insulation coverage
  2. Compression or incomplete fill (up to 30% of intended thickness missing)- up to 2% of total area
  3. Walls, rim or band joist between floors - enclosed on all 6 sides, in contact with interior or exterior sheathing
  4. Ceilings - in contact with interior sheathing 
  5. Floors - in contact with interior sheathing (subfloor)
  6. Floors over outdoor air or vented - enclosed on all 6 sides

This is from "Insulation Inspections for Home Energy Ratings - Assessing insulation gaps, compression, and incomplete fill provides a way to measure installation effectiveness" by Bruce Harley in Home Energy Jan/Feb 2005 pp 20-23. 

So here is an example in the shop. This photo shows the minimally expanding foam with some pretty well installed mineral wool around the top but not the bottom. 

The next photos show the installation of the batts. 

Neither of these installations is a class I installation for 2 reasons - too much compression and it does not completely fill the stud bay. You will not get the stated R-value because compressed insulation does not trap air as it should. It functions as a solid material that conducts heat. 

What to do about it? Now that's another question. If I was off tomorrow I would get a ladder, put on protective clothing and I'd fluff the stuff up. I'll talk to my contractor and we'll figure it out. 


  1. Hi Lucy. How did your insulation project go? I hope you and your contractor were able to find a way to address all the problems you’re encountering in your project. I think the next time you ask someone to work on your home, you should ask them first about their plan and if you are amenable with that. That way, you can save time and money.

  2. Well, that is a good question. One of the reasons we did the shop was so I would know about some of the difficulties of doing a building and working with subs. My contractor is a friend of mine who is one of the nicest guys in the world. And is able to learn and take directions. He truly has a very positive attitude and agreed that the insulation was not done correctly. He called up the insulation guy who came out and re-did some parts of the insulation and made it much better. Not perfect, but much better. I'll write a post today and go into a little more detail about some of my lessons on insulation.

    But remember this is just a shop that is only used maybe 20 hours per week. The highest temp it got this summer was 80F when the outdoor temp was over a hundred. John (my brother) only turns on the air conditioner when he is in the shop so it really works very well. The truth is that the shop is better insulated than any house anyone in my family has EVER lived in. That's just the reality in the South. The emphasis on energy performance is pretty pitiful in general.

    I kind of used the shop to educate my contractor and educate ME on how to work with the subs.