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Attic insulation

2yr old house. I have a big walk in attic with blown in insulation. More than half has decking (plywood) to walk around and storage. The insulation was in place before the decking. I want to increase the insulation. I can remove the decking and replace it fairly easy. Should I move (temp) the decking and add blow in, add rolled on top of the decking? I had problems with the building contractors so I am still doing minor (?) fixes. Proper insulation is current project. 

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Posted 2010-11-28T13:47:37+0000  by BigJ BigJ

2yr old house. Big walk in unfinished attic. 24 in knee wall from one end of the house to the other (70+ Ft) where the main roof meets the porch roof. Porch ceiling is vinyl with no insulation. Main attic is blow in insulation. I am going to use unface batts and maybe rigid foam or drywall (depending on cost). If I insulate the knee wall do I need to insulate a portion of the main roof. The end of the attic has no insulation on the outher walls. Is it worth it to insulate those walls as well.

Posted 2010-11-28T13:58:24+0000  by BigJ

Upstairs room has insulation batts on walls that are toward the attic. Batts extend about 4inches out from 2x4 studs. Room is often cold. If I would like to put up the ridged foam over the current insulation but am concerned about crushing the existing insulation.

Posted 2010-11-28T14:06:30+0000  by BigJ

Hey BigJ.

I have looked at your 3 questions and this is what I have come up with. The weak link we have here is the un-insulated porch, which is dragging down the R-factor of all of the rest of the insulation.


That knee wall is obviously studded, so I would recommend getting some faced R-19 batting, and a staple gun and putting it all the way down the wall. This alone will increase your R-value significantly throughout the house. It will not  even be necessary to put sheetrock over the insulation on the knee wall, for it will not increase your R-value much. Because this is such a large wall it will make a huge difference once finished and adding more insulation other places should not be necessary.


The only walls that need insulation are any that back up to living space. The walls at the end of the attic sound like they do not back up to living area, if this is correct then they will not need insulation. I would also make sure that the upstairs door going to the attic has the proper weather strip around it so no cold air is sneaking in.   


This room upstairs does not have a fireplace does it where maybe cold air is coming down the flue, or the window is not fogged up between the pains where the gas “ insulating factor” has leaked out, does it? These are reasonable possibilities for the room being cold as well.


Thank you for your questions and welcome to the community.

Posted 2010-11-28T16:22:13+0000  by Ingar_HD_ATL

I have a 60 year old cape cod house with a finish upstairs.  Can I blow insulation in the space between the SLANTED roof and the ceiling of the room?

Posted 2011-04-20T15:43:51+0000  by ssparks869

Hey ssparks869, and welcome to the Home Depot Community!


I will assume that your cape cod home is in a cold climate rather than down south.  Normally you would want both a vapor barrier on the ceiling side as well as a path for ventilation to occur along the underside of the roof from soffit to peak.  If you blow in insulation, neither of these will happen.


What you can do is take down the ceiling, install rafter vents and then staple faced insulation in before replacing the ceiling.  This provides ventilation to the roof which minimizes ice dams, and insulates the living space. Rigid insulation either tucked between the rafters or faced along them would also work as long as air can move up the roof.


I hope this helps,


Posted 2011-04-22T14:36:53+0000  by Chris_HD_CHI

no real benefit in removing that. also a lot of work. just go over it.

Posted 2011-07-06T18:17:34+0000  by steveat57

Just read the He'd guys response. I would go with his advice if you are able to. On the east coast moisture is a major problem. Out here in CA. most moisture is only in the winter months so we have more leeway.

Posted 2011-07-06T18:30:02+0000  by steveat57

Hey steveat57.  Welcome to the Home Depot Community!


Even here in Chicago it's both moisture and heat that cause problems.

Living spaces are conducive to higher than ambient humidity levels unless you live along an ocean coastline down south.


It's the heat on the roof that really gets us though.

We tend to use asphalt shingle roofing more than anything else, and you can tell when roof rafters have no airflow just by looking at the shingles.  They become cup-shaped like dipping chips instead of the flat pieces they originally were.

In extreme cases the plywood sheathing will warp as well.  This is not a good thing when the rains come!


Thanks again for your thoughts. 

If there is anything else you need, we are here to help.

Thanks for joining the community!



Posted 2011-07-08T12:54:21+0000  by Chris_HD_CHI
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