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Insulating my attic... Do I need to use baffles?


mickberna's Avatar
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11-03-13, 12:00 PM   #1  
Insulating my attic... Do I need to use baffles?

Hello,

I am planning on putting blow-in insulation over the existing (and thin) batts in my attic. I know that normally I should use baffles to keep insulation from covering soffit vents, but I can't find any vents except for the single attic fan. I posted this video on Youtube that explains it pretty well:

Baffles or not? - YouTube

So do I need baffles? Do I even have any ventilation? What's the best way of doing this before winter shows up?

Thanks very much!

 
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Bud9051's Avatar
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11-03-13, 01:49 PM   #2  
One of the primary reasons for ventilation is to exhaust any moisture that leaks into the attic with the warm air. So the first step is not adding more insulation, but sealing at least the large leaks. Once you have reduced the moisture flow into the attic, then the required amount of ventilation goes down.

Having basically no ventilation right now makes it difficult to decide if more is better or even needed. Your climate will help us decide how much.

Bud

 
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11-03-13, 04:29 PM   #3  
I live on Long Island, NY, if that gives you an idea about the climate. Hot, semi-humid summers and moderately cold winters with not much snowfall.

I am sure that plenty of warm air is entering the attic space along the one interior side. The rafters and plywood are discolored at the bottom all along that side. There is even a large gap where the central AC ducting was passed through to the lower level (it's an old split-level home).

The only other spots that would likely need to be sealed would be around the AC intake with some expanding foam, and the access hatch (probably with a piece of rigid foam and weatherstripping... it's just a hole in a closet ceiling).

But let's assume I am able to seal up those areas... wouldn't adding insulation still be advisable? I mean, the existing insulation doesn't look like it would provide much R value, and the blow-in stuff is cheap and easy to get in all the nooks and crannies.

If it helps, the attic space I'm talking about is only 600 sq. feet, and it's only a crawl space, so we're not talking about a huge area. But the rooms under this area are definitely less comfortable than the rest of the house during hot/cold weather, and I just want to do something to improve it.

 
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11-03-13, 06:20 PM   #4  
Addressing the big leaks with some sheet metal and/or fire rated caulk/foam is more productive for improving comfort than adding insulation. Plus, once the extra insulation is in, no one is going to be moving it to get to those leaks. Combine the two steps and you will notice the difference. I have had a LOT of people say they added more insulation, but it really didn't make any difference. You want to avoid that .

As for the benefits of adding insulation to the attic, it is only one part of your heat loss. The reason most people do that first is it looks easy. But it is still a small part.

As for those baffles, if you have or plan to have some sort of soffit or edge venting, there needs to be an air path above the new insulation. As you increase the attic insulation, the attic will get colder and increase the moisture problem you already have.

Bud

 
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11-03-13, 08:06 PM   #5  
So if I have this right, my plan of action should be:

1. Air sealing in the attic (most important)
2. Install soffit vents (3 16x8 or 6 16x4 vents, along with the existing power ventilator, if I calculated right)
3. Install baffles between rafters where soffit vents are located
4. Blow-in insulation, stopping an inch below top of baffles

OR... instead of steps 3 and 4...

Should I cut down on the dust and mess and baffles, and just lay down additional batts? Unfaced, I would guess, if it were to go on top. At least then I could do the project at my own pace, without a rental truck and another person running the hopper.

 
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11-04-13, 05:47 AM   #6  
Although the rectangular vents meet the required vent area, it is normally preferred to have a vent for each rafter bay. But as long as those vents open to a soffit cavity that feeds all bays, it should be fine.

You are correct about using batts in that it does allow you to work at your pace. Blown in cellulose does have a greater density than fiberglass batts, but Roxul could be an option. If using batts, try to fill each bay to the top and then add another layer at 90 degrees to cover the floor joists. Neatness counts ans each gap reduces the total possible r-value.

Hang markers fron the rafters pointing to any electrical boxes buried under the insulation. If there are any ac or heating ducts up there they should all be sealed and insulated as well.

As for the power vent, they only work when running and then often depressurize the attic too much. The air sealing and added vent area will help a lot.

Bud

 
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11-04-13, 06:41 AM   #7  
I have no clue whether the soffits feed all bays. I guess I would need to poke around before I start cutting holes in the eaves, but this is good to know.

Luckily the AC unit was installed relatively recently, and was the ducts seem properly insulated, although they could use some extra taping around the seams. Heating is all baseboard in the house, so I won't have that to worry about. My main issue is the side along the interior wall... sealing up that area that will be a ton of claustrophobic fun.

I really appreciate your help, these are some great points and I'll definitely work on sealing up the leaks before I work on the rest.

Thanks!

 
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11-04-13, 07:15 AM   #8  
Drag some pieces of plywood up there to lay on. I am claustrophobic and now to old to even think about crawling into those tight spots. Batts can be pushed into place using a "T" on a piece of strapping with nails pointing forward.

Here is a link with pictures, I love pictures .
http://www.buildingscience.com/docum...n-roof-venting

It is doubtful the ac guys sealed the metal ducts before covering them with the insulation so tape the insulation good and hopefully it will control the leakage. It will take another decade to get all contractors on board for energy efficiency.

Bud

 
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