Putting more insulation over existing roll insulation (2 layers approximately 8″ total). For only $2 more I can put down R30 vice R13. Would it be of more advantage to put the R30 since I’m up there putting it in anyway or am I just wasting my money? The current insulation is the 21 year old stuff.
Adding more insulation is always better then less.
But adding insulation alone is not always the answer to solving your energy woes.
Fiberglass insulation works by trapping heat and preventing or slowing its movement through the fibers. Anytime air is blown into the insulation the heat is drawn out lowering the ability of the insulation to do its job. This is why we see people adding more and more to overcome this dilemma So what to do?
Next time your in your attic do a little investigation of the current conditions.
Does your home feel drafty? When picking up insulation in various areas within the attic, does the insulation appear to be black? Check around the wall areas that are below. Look around the access door, lift up insulation where the fiberglass is covering ceiling fixtures. Do you see this black staining in the glass fibers? All this black stuff is dust that has been trapped in the insulation fibers. Meaning you have air loss or movement from within the home. Check around the chimney and plumbing pipes. All sources of air movement. Remember your house acts as a big chimney, as air is heated it rises. When that happens air is pulled into the bottom areas of the house as it does. We often see complete air exchanges of five to seven times per hour in a 25 year old home. This means your not only trying to keep the house warm, your reheating it completely those five or seven times as well. No wonder it cost so much to keep warm or cool in summer.
Adding insulation will slow down this movement a bit, but not really stop it. What you need to do is before you add anything to the attic, you need to air seal it. Using a few cans of spray foam, some plastic gloves, mask and eye protection get up into the attic and pull the insulation away from all of the wall areas, pipe areas, plumbing areas, and areas where wires are being brought up into the attic and seal them tight. Foam works the best, but even low cost caulk that is on sale will do it, Your not trying to insulate, that is the fiberglass job. Your stopping the air that is blowing through the pink stuff so it does not cool down on you.
Once your done with that, you need to focus around the edges of the attic. Using foam baffles, Ones that I am sure Tom as talked about several times on his shows. Place one in every space between the roof rafters. This will allow you to push the insulation up tight to the roof area along the eaves which will stop any air that is entering into the attic from blowing into the fiberglass. It will bypass and move up and above as it should. On the gable ends of the attic those spaces where the walls continue up to the roof line, Those spaces must be sealed tight. This is a great space for the foam. It does not have to fill them, but it needs to seal all the way around so no air can move up from the walls.
Now there is one more area in which you need to go. The complete other end of the home, basement/crawl space. You need to find every wire opening, pipe opening and any other hole you can that allows air to flow up into the wall cavities of the house. Foam them closed. There is fire rated foam sold in cans that can be used. Then along all the mud sill areas, if there is any fiberglass insulation there, pull it out. Bet your going to find all sorts of black stains. All dust from air moving through it. Using foam boards 2" are ideal, cut them to fit as tight as you can between the flooring joists. Then use spray foam to fill any gaps that remain.
Just by doing this on the average home, you will see close to a 15% improvement on your energy bills not to mention more comfort. Then go up into the attic and install your pink stuff, You want to get at last a R-30 or better. If you do not use the attic at all, consider using blown in insulation. Much easier to do and you get to pay with some cool tools while doing it.
Hope this helps.