I currently have blown-in insulation, that reaches the top of the attic floor. I was told by several insulation companies that I need a R value of at least 49, meaning, I need to add a good 12-18" more of blown-in material.

I want to perform the work myself. The first thing I did was lay down some 2'x4' pieces of plywood across the attic floor so I have a surface to walk on when I blow in extra material.

The other thing I noticed, was I only have soffit vents spaced approximately 36-48" apart around the house. I can see light appearing in the attic where they are.

I also have a fan on the roof that I can turn on with a light switch, however, no matter how long I leave it running, I feel no difference in air temperature.

I have a few questions regarding the project I'm about to take on.

1) Should I install soffit venting along the entire edge of the lower roof line? Or is what I have enough?

2) Should I see vents on the roof on the upper part of my roof exactly where the vents are on the lower section? If I don't, should vents be added?

3) Do baffles need to be installed between each rafter if the vents are spaced every 36-48" apart? Or just install where the vents are? Do they need to go all the way up the roof or just a single 48" length is sufficient?

4) Anything else I should be aware of?

5) Is ventilation not even necessary anymore? I've been reading a lot of material that ventilation doesn't even help and what was previously done was wrong.

1 Answer 1


Your research is pointing you in the right direction: the need for attic ventilation is overblown (pardon the pun). The attic fan is useless; don't use it, because it will cost you more money than it will ever save you. The air inlets are the soffit vents. What are the outlets? Gable vents? a ridge vent? Turtle vents? Whatever they are, they're probably fine. If the only outlet is the fan, just turn it off or remove it and let the air naturally escape from the hole.

You do indeed need to put baffles in the rafter bays to keep the insulation out of the soffit vents. Other than that, you're pretty much good.

Finally, let me mention that one of the best things you can do BEFORE adding all this new insulation is to air-seal your attic floor. Anything that makes a hole in the drywall needs to be sealed up. This includes electrical boxes, holes for wires, can lights, etc. For much more information on this subject, see http://www.greenbuildingadvisor.com/blogs/dept/musings/air-sealing-attic

  • Yeah, I'm going to leave the attic fan powered off from now on. So from what I'm told it looks like I have adequate ventilation already. I have the side vents - one on each side of the house (gabel I'm assuming). I don't think I have a ridge vent. I bought a few cans to cover all the holes on the top plates. I'm also going to remove all the outlet covers on the walls and fill up between the sheetrock and the plastic boxes. Jun 7, 2015 at 18:27
  • As far as the baffles go, do I just place them where the soffit vents are? Or do I place them between each rafter? And if I just place the baffles at the vent, I'm assuming I can blow-in all the way to the edge on the non-baffle rafters? Jun 7, 2015 at 18:28
  • Only where the soffit vents are. And yes to your second question too. Since you're doing this yourself, I recommend piling it as deep as you can. 20" (R-60) should be barely more expensive than 15" (R-45). Blown cellulose is preferable to blown fiberglass, but fiberglass is fine.
    – iLikeDirt
    Jun 7, 2015 at 18:35
  • Awesome! I really appreciate your help. I'm using cellulose over the existing blown-in cellulose - GreenFiber brand from HD or Lowes. Free machine rental too. I'll probably go up to R60 since its only 6.25 per bag. And I'm saving money on labor already. Jun 7, 2015 at 18:46
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    I'll use adhesive along the plastic and the drywall and see how that goes. That way if the next owners want to use it, they can simply unwrap it. I don't want to go through the hassle of framing it, then drywall, then texture/painting it. Would cost a lot less with plastic and sealing it if the results are basically the same. Jun 9, 2015 at 1:59

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