Insulation, Radiant and Vapor Barriers - Adding more insulation to attic

We just had a new home built this past year. It is energy star qualified, but they only put R-38 in the ceiling on the second floor. I am now finishing off my bonus room over my garage and while running the electrical, decided it might not be a bad time to throw R-11 up there to get the recommended R-49. Two questions: 1) is it worth adding the insulation at all. 2) the joists arent completely filled with R-38. Is it better to just lay R-11 over the top of R-38 or should I still go perpendicular with it.


TY163

Its usually never a bad idea to add more insulation. When you say the joist arn't completly filled, do you mean that there are gaps where the insulation doesn't touch the joist or they just missed some areas when insulating? If you add more insulation, you will want to add the new insulation perpendicular to the old. Meaning if the old insulation is going left to right, have the new insulation on top of it going from front to back. However, if you are going to add new insulation, why not just add a blanket of cellulose over the fiberglass? It will hold heat in better and will fill up any holes that the fiberglass missed. You can install it yourself too.

Well, I took a closer inspection of the joists today. See, we have a hip roof, and the garage roof obviously designed to match. The issue is that in the bonus room there is a joist that runs the middle of the room east/west. Off of this joist, the others run north/south which are filled with R-38 batts well above the ends of the joists. The problem is that there are other joists that run at a 45 degree angle off the east/west joist, up to the roof. Laying batts perpendicular would be ok until I get closer to the mid joist. I would be cutting little squares and just laying it between the joists at that point. Sounds like your idea about blown in may be the best way.

I also took a peek at the rest of the attic becuase I wanted to do that as well. With the hip roof, it just looks like a maze of nooks and crannies and trusses with very few places to actually walk. They did install baffle vents but I can see daylight in some of the places where the vents and insulation meet. Is that normal. The strange thing is that I don't think there are soffit vents on the eaves. I'll have to take a closer look. Anyway you look at it, it seems blown in may give the best chance of doing the work. What is the difference between cellulose and blown in fiberglass?


TY163

What we do when we install the air vents is either put fiberglass tight near the roof line so that the cellulose won't fill over into the soffit vents or we place cardboard cutouts made for whatever size joist we are in. Either way it makes it fairly tight so when we blow in the cellulose it won't get blown into the soffit vents and block them.

Fiberglass blow-in has a R-value of about 2.2. Cellulose is between 3.6 and 3.8. Visit this link: http://www.bragdoninsulation.com/cons_report4.pdf It has great information about the differences.

I would just blow in some cellulose. It is messy, but you'll find that it is cheaper and almost just as/ if not as efficient as Fiberglass. The bags were around 7-8 bucks when I did my walls. I bought 35 bags which do 80sq. ft. of 2x4 studded walls. I used cellulose in my attic and walls, but my house was built in 1940's w/ no insullation!!! Where do you live that you need R49 value?!? WOW!!! I had a guy come to give me a quote on doing the walls b/c I didn't wanna tackle the job and he looked at my attic that I already did and it has 2x12 joists and they were packed full. He said I need another foot of cellulose on top of my attic floor to have the appropriate R value for central PA. WELL GOOD LUCK!

I'm not sure what you mean by "almost just as/ if not as efficient as Fiberglass" but cellulose beats fiberglass hands down. Its a superior product.

So I guess when I go to do the rest of the attic, I need to make sure that the fiberglass batts are up tight with the baffles, then blow in the insulation. Sounds good, and I like the idea of the cellulose.


TY163