Adding attic insulation

rakuz66 · 07-22-2011, 11:00 AM

I'd like to add some insulation to my attic. I just had the house sided and re-roofed, so I now have a vented soffit and ridge vent. I know I will need to put in some rafter shutes, baffles or whatever you want to call them in between the rafters. I presently have about 7 inches of blown in insulation on my attic floor which is under the reccomended amount for S.Eastern Pa. So my question is this , Can I use unfaced batts on top of the blown in insulation running them perpendicular to the joists, or do I need to use more of the blown in insulation? Thanks.

operagost · 07-22-2011, 01:54 PM

You can use the batts. That's a great way of mitigating the thermal bridging caused by the joists. While you're up there, you might want to check the existing insulation for dirty spots, which would indicate air intrusion. Seal up any gaps.

AGWhitehouse · 07-22-2011, 02:12 PM

While your crawling around adding the chutes and batts, add a tyvek air barrier on top of everything as well. Air movement within fiberglass batts greatly reduces the effectiveness. So if you put an R-30 batt up there without an air barrier, then you only really be getting an R-20, or so gain, as the top layer of batts will be compromised do to attic air movements. So, for the $150 or so that a tyvek roll costs, you'll reclaim that lost R-10 or so.

operagost · 07-22-2011, 02:18 PM

Does the Tyvek block moisture? That would be bad.

**Gary in WA** · 07-22-2011, 06:02 PM

If blow-in fiberglass, yes that will reduce the R-value, by compressing the existing. If blow-in cellulose, just use more, it will also stop any convective loops in your blow-in f.g.: The "biggest loser" in fiberglass insulation....

Tyvek (58 perms) won't block moisture, (I've repeatedly sited that) compared to Typar (16 perms), which will. Moisture movement optimum is 18-32 perms....

Gary

07-22-2011, 11:00 AM	#1
rakuz66 Newbie Join Date: Mar 2008 Posts: 21	Adding attic insulation I'd like to add some insulation to my attic. I just had the house sided and re-roofed, so I now have a vented soffit and ridge vent. I know I will need to put in some rafter shutes, baffles or whatever you want to call them in between the rafters. I presently have about 7 inches of blown in insulation on my attic floor which is under the reccomended amount for S.Eastern Pa. So my question is this , Can I use unfaced batts on top of the blown in insulation running them perpendicular to the joists, or do I need to use more of the blown in insulation? Thanks.

07-22-2011, 01:54 PM	#2
operagost Member Join Date: Jan 2010 Location: Pennsylvania Posts: 548	Adding attic insulation You can use the batts. That's a great way of mitigating the thermal bridging caused by the joists. While you're up there, you might want to check the existing insulation for dirty spots, which would indicate air intrusion. Seal up any gaps.

07-22-2011, 02:12 PM	#3
AGWhitehouse Architectural Designer Join Date: Jul 2011 Location: Connecticut Posts: 1,370	Adding attic insulation While your crawling around adding the chutes and batts, add a tyvek air barrier on top of everything as well. Air movement within fiberglass batts greatly reduces the effectiveness. So if you put an R-30 batt up there without an air barrier, then you only really be getting an R-20, or so gain, as the top layer of batts will be compromised do to attic air movements. So, for the $150 or so that a tyvek roll costs, you'll reclaim that lost R-10 or so. __________________ Life's too short...so enjoy it! To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

07-22-2011, 02:18 PM	#4
operagost Member Join Date: Jan 2010 Location: Pennsylvania Posts: 548	Adding attic insulation Does the Tyvek block moisture? That would be bad.

07-22-2011, 06:02 PM	#5
Gary in WA Moderator Join Date: Mar 2009 Posts: 8,843	Adding attic insulation If blow-in fiberglass, yes that will reduce the R-value, by compressing the existing. If blow-in cellulose, just use more, it will also stop any convective loops in your blow-in f.g.: The "biggest loser" in fiberglass insulation.... Tyvek (58 perms) won't block moisture, (I've repeatedly sited that) compared to Typar (16 perms), which will. Moisture movement optimum is 18-32 perms.... Gary __________________ Clothes taking longer to dry? Clean the dryer screen in HOT water if using fabric softener sheets. They leave a residue that impedes air-flow, costing you money. Clean the ducting in the last six months? 17,000 dryer fires annually!

Adding attic insulation