Adding insulation and soffit questions

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  #1  
Old 01-08-03, 10:48 AM
robertdana
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Adding insulation and soffit questions

Our house, which was built in ~86, doesn't have adequate attic insulation- there's a single layer of fiberglass batts (fairly thin ones). We're right on the border between the zones where R30 and R38 are recommended. I'm finally getting off my butt to do something about it, and have been researching it.

Early on, I was advised that the best, most cost-effective thing to do would be to blow cellulose on top of the existing batts, using a rental blower from Home Depot. My initial research seems to confirm this, especially since the hatch to our attic is very small (16"x13") and hauling a bunch of batting up there will be difficult. Any thoughts about this?

Anyway, I read in several places that it's important to put barriers of cardboard or something similar at the edge of the attic floor to keep the blown insulation from blocking airflow from the soffit vents. In our house, we have partial cathedral ceilings, so the soffits are about 5-6 ft below the bottom of the attic. What I discovered when I went up there is that the space above the cathedral ceilings is full of fiberglass batts, and no provision was left for airflow from the soffit vents to the attic.

My question: should I be concerned about this? Is there anything I can / should do about it? Or should I ignore it and just blow in the insulation?

Thanks in advance...

-R
 
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  #2  
Old 01-08-03, 09:38 PM
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Attic insulation

For attic insulation information and to calculate the R-value for your ZIP, go to www.doityourself.com/insulate. It is not recommended that your insulate the ceiling of unfinished attic spaces. If you wish to improve attic ventilation, ridge vent combined with soffit ventilation is preferred. You will find helpful info on this website at www.doityourself.com/insulate.
 
  #3  
Old 01-09-03, 03:05 AM
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Since the insulation is getting on to twenty years topping up the existing with cellulose is a good idea. Over time, compresion & dust it has lost a lot of insulating value. The recommended R values are usually code minimums and since you say your on the cusp of R30 & 38, I'd go R40. It is essential to maintain ventilation into the attic space. Remove the soffits and pull or push out all the batt insulation in the vaulted area. Install U shaped vents ( a piece of PVC or ABS pipe cut length ways works well) in every second rafter space from the eave to the attic. Block off the bottom of the rafter space keeping this channel open. Tnis keeps the cellulose from running out onto the soffit. Replace the vented soffit. Blow cellulose between the rafters and over the remaining area. Install a ridge vent.
 
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Old 01-09-03, 07:04 AM
robertdana
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Follow-up

Are there any issues in putting cellulose on top of existing fiberglass? I've seen some recommendations that you shouldn't mix materials like that, but no explanations for why.

Also, I've now gotten several conflicting answers on the soffit ventilation issue, so I'd like to ask a follow-up. Obviously, the house was built this way, and from what I can tell, there haven't been any issues with moisture, etc... I'm wondering whether there might be architectural reasons why the soffit ventilation is blocked. The attic has a ridge vent, it has two large eave vents, and it has a powered temperature-activated ventilator. Will I really get a substantial improvement in ventilation by clearing a path to the soffits?

-R
 
  #5  
Old 01-09-03, 04:18 PM
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Adding insulation

Manufacturers of cellulose insulation claim that it tops fiberglass in performance. R-Value, they claim, is only one consideration in considering types of insulation. They claim the research shows that cellulose-insulated buildings may use 20% to 40% less energy than buildings with fiberglass, even if the R-value of the insulation in the walls and ceilings is identical. They also claim that cellulose insulation is the only wood-based building material that is always treated for fire retardancy and that is one of the safest materials used in home construction becaise fire roars right through fiberglass. Another advantage of cellulose insulation is that it fills odd-shaped cavities, completely filling the voids, providing a tighter and quieter finished home construction.
Manufacturers claim that because of the density of cellulose insulation that it superior in suppressing air infiltration because it is tighter and requires less energy to keep the home warm/cool. Because of cellulose density, studies show that it is more effective for preventing sound transmission.

With cellulose insulation, installed according to the Department of Energy's R-value recommendations (You can go to www.doityourself.com/insulate on this website to determine the amount of insulation required for your ZIP). Manufacturers claim that homeowners can usually realize a 20 percent to 50 percent savings on their utility bills with cellulose insulation and that in homes that already have fiberglass insulation that cellulose can be installed over the fiberglass for increased savings.

If you have ridge vent ventilation, you need to clear the soffit vents so the attic has adequate ventilation. Warm, humid air that leaks from the downstairs of your home into an unfinished attic can cause moisture and condensation problems. A breezy attic is best during the winter months when moisture is an issue. Insulation is important for keeping the heat in the heated areas below where you want to keep the heat. The ventilation is important for allowing any warm, moist air to escape outdoors.
 
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