Kraft faced insulation ceiling already drywalled

[pnut]

I can't find unfaced 24". Is there any reason I should not use Kraft faced with paper facing the (existing) drywall?

New construction with 24" spacing in ceiling already drywalled. In Michigan and will be heated to 60-65f. Walls already done with vapor barrier. I want to use batts so that I can do an hour here, an hour there for install, for easier access under it, and so I don't need soffit baffles.

 

[nmk_61802]

I would think you would want the kraft faced anyway, assuming you did not put up a vapor barrier already behind the drywall.

 

[pnut]

There seems to be mixed opinions on this based on the high gloss paint I will apply and also the breathability of the attic.

The Kraft faced I would put down would be far from a barrier since the drywall is already up and I would have the trim or fold back the little ears since the 2x4s are not exposed.

 

[Mike_C]

I was able to find faced and unfaced rolls in my area, but Menards was the only place I could find it locally. The other local home improvement centers only had faced.

 

[redneckcharlie]

Why not just use blow in and save yourself alot of time and some money.

 

[rsa]

Blown cellulose would be my choice. Lots of blown cellulose.

But to address your questions as asked: from Building Science Corporation Research Report 404: Roof Design

In addition to an air barrier at the ceiling line, a Class II va- por retarder should be installed in Climate Zone 6 and Climate Zone 7. A Class III vapor retarder is acceptable in Climate Zone 5.

Class I vapor retarders (i.e. vapor barriers) can be installed in vented roof assemblies in Climate Zone 6 and Climate Zone 7 but should be avoided in Climate Zone 5 as top side condensation may occur in the summer months during air conditioning periods.

No interior roof assembly-side vapor control is required or recommended in climate zones other than cold or very cold.

Also from BSC,

Three classes of vapor control are defined depending on the vapor permeance of the vapor control layer.

• Class I . <0.1 perms e.g. polyethylene sheet, sheet metal, or aluminum facing.
• Class II. 0.1 - 1.0 perms e.g., kraft faced fibreglass batts, and some vapor control paints.
• Class III. 1.0 - 10 perms e.g. latex or enamel paints.

What climate zone is Michigan in? Depends on where you are. This map will tell you: Michigan Climate Zones by County.

You don't want air moving though the fiberglass so don't skimp or skip on air sealing the ceiling and rethink omitting the soffit baffles.

Stewart

 

[pnut]

Why not just use blow in and save yourself alot of time and some money.

Read original post again.

 

[pnut]

Blown cellulose would be my choice. Lots of blown cellulose.

But to address your questions as asked: from Building Science Corporation Research Report 404: Roof DesignAlso from BSC,What climate zone is Michigan in? Depends on where you are. This map will tell you: Michigan Climate Zones by County.

You don't want air moving though the fiberglass so don't skimp or skip on air sealing the ceiling and rethink omitting the soffit baffles.

Stewart

Rethinking the baffles. Just wondering why other than shifting of batts as mentioned above.

Blown is better but batts are what I want or various reasons.

 

[TRC51]

I have found faced and unfaced in Home Depot... but... not in the same HD. One in one... and one in the other. I would put faced in there just for the separator between the insulation and drywall... but I am not expert.

 

[rsa]

Rethinking the baffles. Just wondering why other than shifting of batts as mentioned above.

Air moving through and around fiberglass insulation can reduce its R-value greatly. From GBA

...air moving through insulated cavities can cut the efficiency of the insulation by as much as 50%.

The baffles reduce air moving through, over and under the fiberglass. Here's a picture from a Journal of Lightweight Construction article, Air-Sealing Attics In Existing Homes:

Figure 4. Wind-washing — air moving under and through the ceiling insulation at the eaves — degrades insulation performance, as is evident from the dark areas in the ceiling next to the exterior wall (above).

BTW, fiberglass batts aren't as bad as loose fill fiberglass (reduced convective loops, per Oak Ridge Laboratory tests).

 

[pnut]

Thank you for that explanation, that makes complete sense. I will rethink it. Look sometime later this winter I will post up my complete garage redo with what I end up doing.

(garage project underway = flooring, lighting, insulation, drywall, electrical, compressor, cabinets, counters, trim, etc.... on a new construction house)

 

[Falcon67]

I sheeted my ceiling, then put in kraft faced batt (joists 24" OC) for the same reason as you - I could go buy two bundles this week, put them in at night or early morning. Little at a time, soon we're all done. Cost difference wasn't enough to outweigh the scheduling convenience.

rsa's post just gave me an idea about WTF is going on at the ceiling/wall interface in our front bedroom. That edge is hotter in summer than other rooms. It faces south to prevailing winds and we have blown in insulation in the attic. There are two vents in the eve on either side of the window and no baffles in the attic. Hmmm.