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eastside 09-05-2011 10:36 AM

insulating attic
 
I have a small attic over the kitchen 14x16 (access with a drop down ladder) currently there is no insulation up there. What I would like to do is put the insulation in the rafters and not on the floor of the attic. Is this okay?

The reason is the attic floor in built like a crate, ceiling joist running the length and then cross pieces every 24 inches. This would entail me cutting small pieces of insulation, fitting them in. The ceiling joists are full 2x6. If I wanted more insulation than 6 inches I will lose the utlity of the floor space in the attic to store things.

open to any ideas. thanks.

1910NE 09-05-2011 07:22 PM

If you insulate the rafters instead of the floor, you will be paying to heat the attic. You will also end up dealing with all of the issues surrounding a hot (insulated) roof system. Have you looked at blown in insulation?

gregzoll 09-05-2011 07:42 PM

Get some blown in, and break it down into some 32 gallon garbage bags. Wear long sleeves and a face mask, and face shield. Once you get the bags up in the attic space, you can use a plastic leaf rake upside down (fingers facing upwards, not into the insulation) to help spread the cellulose. It will actually fluff out as you tossing it across the space in front of you. Use a fan on low speed to help blow some air up there while you work in there also. It is probably the cheapest way, instead of renting machinery from Home Depot or Lowes. Otherwise as you have seen, it will be a PITA to use batt insulation.

househugger 09-08-2011 01:18 AM

There's no choice but to go blown in foam. To go batt insulation of R40 you'll need 12" rafter depth to allow for the required ventilation above the thickness of the batt. Blown in foam doesn't require the ventilation space. It's what we're using in our 2x4 rafters in the attic.

heybales 09-08-2011 02:41 AM

While slightly annoying, you could probably slide a longer length in the joist bay right under the cross pieces. Just don't get too thick. And pull it through.
And then the second layer of batts perpendicular to the first between those cross pieces.

shazapple 09-08-2011 08:51 AM

Quote:

Originally Posted by househugger (Post 723497)
There's no choice but to go blown in foam. To go batt insulation of R40 you'll need 12" rafter depth to allow for the required ventilation above the thickness of the batt. Blown in foam doesn't require the ventilation space. It's what we're using in our 2x4 rafters in the attic.

Why does batt insulation need ventilation but not spray foam? Ventilation is for the roof, not for the insulation.

I would go with the cellulose plan outlined by gregzoll.

gregzoll 09-08-2011 10:52 AM

Batt in order for it to work, you have to have air flow. The reason for the roof vents or sofitt vents, is so that any air movement that has happened due to batt breathes, and heat movement passes through the roofing material, that air has to be removed from the space. Spray foam is like a foam cup and does not need to breathe, plus it insulates and reflects heat off of the room. That means, heat can not pass through. It insulates and does not cause condensation. You place batt in the joist bays against the living space, where as you place spray foam against the roofing material.

househugger 09-08-2011 11:10 AM

Thanks for explaining that so well.

What has happened on many houses, including the house we just bought, is that the batt insulation gets jammed into where the air flow should be and heat is then transfered up through to the roof. That portion of roof is then warmer than the ventilated portions and the snow there melts creating an ice dam. Water from that dam then leaks into the house. Like in our house it has caused major damage to the ceiling and exterior wall.

One side of our house had the batt jammed in and the other side didn't. The only portion with damage is where it was jammed in.

Windows on Wash 09-09-2011 09:30 AM

If you are going to treat it as conditioned space, it will need some supply and return side air.

If it is just dry storage, we usually frame up a floor on top of a floor to allow us to get the proper blown in depth up there (i.e. 2x8s overtop existing floor).

shazapple 09-09-2011 11:00 AM

Quote:

Originally Posted by gregzoll (Post 723671)
Batt in order for it to work, you have to have air flow. The reason for the roof vents or sofitt vents, is so that any air movement that has happened due to batt breathes, and heat movement passes through the roofing material, that air has to be removed from the space. Spray foam is like a foam cup and does not need to breathe, plus it insulates and reflects heat off of the room. That means, heat can not pass through. It insulates and does not cause condensation. You place batt in the joist bays against the living space, where as you place spray foam against the roofing material.

The whole point of insulation is to stop air flow (convection), which is the main cause of heat loss. Fiberglass doesn't need air flow to work, it just isn't as good at stopping air flow as spray foam.

Shingles break down due to heat, which is why ventilation is used to remove the heat from shingles. Proper insulation will stop heat coming from the inside, but you still have to deal with heat from the outside (the sun).

gregzoll 09-09-2011 12:03 PM

shazapple, I already explained that in my posting. And Batt insulation uses air pockets to help insulate. Part of the process of keeping air flow in the space. Yes batt does not need to have air to do its job, but it helps, so that it will do its job. Majority of the complaints that people have thinking that they have improper insulation in a attic space, is improperly installed, and improperly ventilated spaces.


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