# Question on insulating this space



## Windows on Wash (Aug 30, 2011)

I would be more concerned with just getting some conditioned air circulation in there to see if you could get the air moving. 

Any way to have a vent in that wall. That stagnate air will create an issue if it can't vent and the roof/attic isn't functioning as vented right now.


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## giansean (Mar 4, 2015)

It's always possible but at the same time I would also be worried about colder air migrating in to that space through a vent. I'm not so much concerned that no air will get into that space (it is not airtight by any means ) as I am keeping it out of the finished room. 

My original goal was to just leave it open and insulate any room that adjoined it
However the fiberglass crew pretty much ended up sealing it all off. They said that unless I wanted to insulate the rim joists as well it was the best I could do. I just really worry that this wall in the pic (the uninsulated studs on the flat and kneewall )will be really cold come winter


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## Windows on Wash (Aug 30, 2011)

If the roof isn't vented, you can just clad those roof rafters with rigid foam prior to drywalling.


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## BarryP (Jun 14, 2015)

You did it perfectly. Just drywall the dead space. It won't get any colder than a closet.


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## giansean (Mar 4, 2015)

Thanks Barry.. hoping that's the case  Worst case I guess I could wait until winter and bust my way back in if it ends up too cold (there are ways in that don't require breaking down walls... not pretty but they work)

@ Windows... the fiberglass crew did put baffles in before they did the rafters, and I was planning to do a ridge vent at some point in the future. I know that this won't vent this particular space itself. What would the rigid get me that the fiberglass wouldn't except maybe for better air sealing?


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## Windows on Wash (Aug 30, 2011)

Better air sealing is all and a bit more R-Value in the framing to eliminate some cold spots.


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## SeniorSitizen (Sep 10, 2012)

Who ever insulated that which is there needs to be informed how to install that type of insulation. The flaps were manufactured at the roll edges for a vapor barrier and they are to be stapled to the stud edges and not the stud face which also compresses the insulation.


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## giansean (Mar 4, 2015)

Yeah for some reason everyone inset staples here (Southern CT). Supposedly there was an issue where a crew face stapled and was sued. Makes no sense to me either... I always face staple myself. Passed inspection with flying colors though.


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## giansean (Mar 4, 2015)

Windows on Wash said:


> Better air sealing is all and a bit more R-Value in the framing to eliminate some cold spots.


Thanks Windows. I have some lying around so if I get time I can bang them in. 

As far as the little triangle area where the dormer wall starts (to the right of the mass of foam), I just shoved some more FG in there (non kraft faced) since I'm sure there will be some colder air coming through those eves. Still open though so let me know if you think it should remain exposed.


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## BarryP (Jun 14, 2015)

giansean said:


> Yeah for some reason everyone inset staples here (Southern CT). Supposedly there was an issue where a crew face stapled and was sued. Makes no sense to me either... I always face staple myself. Passed inspection with flying colors though.


The reason is that dry wallers like to GLUE and screw the drywall. Face-stapling doesn't allow them to glue.

Even so, the kraft paper over the face of the studs is hardly an issue. Many contractors are using staple-free batts which do not have a flange that goes over the stud.

Any measurable compression is not happening when you staple on the inside.


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## ront02769 (Nov 28, 2008)

SeniorSitizen said:


> Who ever insulated that which is there needs to be informed how to install that type of insulation. The flaps were manufactured at the roll edges for a vapor barrier and they are to be stapled to the stud edges and not the stud face which also compresses the insulation.


No worries the way it was stapled...unless it bumps against a local code. Insulation manufacturers give instructions to staple either on face of inside of stud. While I personally prefer stapling to the face because it seems easier, inside is fine also. 

Ron


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## Gary in WA (Mar 11, 2009)

The flaps are not there for a vapor barrier but to support the insulation in vertical installation. They can be stapled either way as the wood studs are not very vapor/air permeable. Inset stapling does, however, give a reduction in R-value- depending on the gaps/density, pp. 45-47; http://www.buildingscienceconsultin...010-03-10_When_R-Value_Doesn t_Measure_Up.pdf

Gary


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## BarryP (Jun 14, 2015)

Here is the picture that you cited.









Here is a more full description elsewhere. This kind of gap would require extremely poor installation. One would have to really work at compressing that fiberglass batt to make a continuous gap.


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## SeniorSitizen (Sep 10, 2012)

Let them satisfy dry wallers on your building but it won't be done that way on mine. They have to live with it for a couple of days but the building suffers the remainder of its life.


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## Gary in WA (Mar 11, 2009)

Since you said you can feel air moving into that space, not insulating the abutting knee wall will give major R-value reductions. This is air permeable fiberglass, same as used in furnace filters for its non-restrictive (of air) qualities. It won't mold if there is air movement when it can dry out if ever wet. 
Where is the house located- State? Is a vapor barrier required? Will you be installing rigid foam board on the attic side of knee wall (may or may not require an ignition barrier, more on that later) or at very least- housewrap to protect FG from attic wind-washing?


If the insulation is not in FULL CONTACT with the drywall (air barrier), you will have a lacking design. Inset stapling alone is only a 2-3% reduction in R-value, but "


"These observations provide strong evidence of convective airflow due
 to inset stapling, 
resulting in moisture transport within the stud 
bay. Outward vapor diffusion through the painted 
drywall introduces interior moisture to the vert
ical channels formed between the facer and the 
drywall. These channels provi
de a clear airflow path; a conv
ective loop can form, bypassing the 
vapor retarder at the top of the wall and depos
iting condensation on the top portion of the stud 
bay sheathing, as seen in field results. Note th
at only a small gap is required at the top and 
bottom of the insulation to allow 
convective airflow: Brown et al
. (1993) reported that gaps less 
than 1 mm (1/32”) wide allow these loops to form
 between air spaces on both sides of insulation. 
It is unlikely that these results are due 
to one-dimensional vapor diffusion through the 
gaps at the edges of the batt facers, as show
n by the spatial moisture content patterns. 
Specifically, no moisture deposition 
was seen at the bottom of any 
of the inset-stapled stud bays. 
It is worth noting that two vapor retarder materials that were detailed as air barriers 
(polyethylene and PA-6 film) resulted in a
ssemblies with excellent performance (very low 
sheathing moisture contents). These vapor reta
rder materials were in
stalled overlapping the 
foam gaskets on the face of the st
ud, so they would have been ve
ry airtight. It is uncertain 
whether their performance is solely
 due to their vapor re
tarding characteristics, or also due to this 
detailing. 
Note that in this research, we did not see ev
idence of convective l
ooping within the cavity 
insulation in bays that did not have inset stapling.
 As noted in the literature (Powell et al. 1989), 
convective loops are more likely with these air gaps
, and less likely if an air barrier is placed in 
direct contact with the insulation. If significan
t convective looping were occurring within the 
insulation, there would have been greater depositio
n of moisture at the top portion of the latex 
paint cavity to due air movement. Instead, MC leve
ls were, if anything, slightly lower at the top 
of the wall (edges of cavity). On
e might conjecture that these su
rfaces were slightly warmer, due 
to thermal bridging of the framing. 
Furthermore, given (a) the mild climate (maximum observed 
Δ
T of 47° F/26.3° C), (b) 
careful installation of the insulation (cut to 
cavity size, not compressed), and (c) air barrier/ 
1-
318
2008 ACEEE Summer Study on Energy Efficiency in Buildings
compartmentalization efforts, convective loopi
ng within the insulation 
(as opposed to around the 
insulation, in the air channels) wo
uld be relatively unlikely. It 
appears that under this set of 
conditions, the density of this fiberglass batt 
is sufficient to prevent significant convection.' Read it better here; http://aceee.org/files/proceedings/2008/data/papers/1_8.pdf

Gary
PS. Barry, note the "1/32"?


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