Question about Insulation

russstar · 08-20-2009, 08:06 AM

My wife & I just purchased a small loft home.

The building is a cinder block construction, no real attic to speak of just a crawlspace. The roof has a ridge vent. there was no access to the crawlspace, in the process of renovating we cut a hole in the ceiling.

What we found was that there is a vapor barrier over top of the ceiling joist leaving an open space between each joist.

Insulation was then placed over the vapor barrier on top of the joist.

This seams very strange to me!?

Can anyone give me any insight?

OK...it's an attic space very small

It does not have kraft paper it has a black material laying over the Joists that has clearly printed on it Vapor barrier.
someone when through alot of trouble to install it because there are 1x4 slats supporting it.
The Joist themselves are 2x6 studs 24in on center.
with fiberglass insulation on top of the "vapor barrier" I found this out by poking a hole in it.
I can't see on top so I don't know how thick it is.

The space from the top of the 2x6 to the bottom where the drywall sealing is, is void/open. & there seems to be a sort of steady draft flowing through. the draft is very warm now but it's summer time, my concern is when winter comes all the insulation on top of that barrier will be pointless.

the ceiling in the rooms is only 7.5 ft.

Scuba_Dave · 08-20-2009, 08:28 AM

I'm not sure why they did it that way
The normal way is to simply lay insulation with paper (vapor retarder) down towards the conditioned space
How far apart are the joists? Size - 2x4, 2x6 etc ?
How much insulation is up there now - thickness/R value ?
Where are you located?

Michael Thomas · 08-20-2009, 09:09 AM

First a little terminology: A "crawlspace" is an area in enclosed by foundation walls and under the habitable portion of the structure, think of it as a "basement" that's not tall enough to stand up in, and is reached via an access hatch of some sort rather than a set of stairs.

The space below the highest habitable level of a residential structure and below a sloped roof, and accessible via a stairway or access hatch is called "attic". If it's underneath a "flat roof" or the height is insufficient to allow a person to traverse it (say, less than about 24 inches) it's not an attic, it's "something else" - I describe it as the "inaccessible portion of the roof structure and decking ", but as far as I know there's no generally agreed on technical term for this portion of the typical residence.

In either attic or inaccessible under roof area if there is insulation, there should be a vapor retarder of some sort between the "conditioned" (heated and/or cooled portion of the structure) and the "unconditioned" (not heated and/or cooled) attic or under roof area, and the VR should be toward the conditioned space (under the insulation):

- http://content.managemyhome.com/Imag...ion/1369_R.GIF

This VR can take a number of forms, in newer construction a plastic sheet is often placed across the joists and then is insulation placed or blown it on top of it. In this case if the VR is not pushed down into the joist cavities there may be a gap between the underside of the VR and the ceiling below - IMO that's sloppy installation, bit it's not "wrong" in the sense that it compromises insulation efficiency as long as the VR can support the insulation above. In both older and newer construction you will also find VRs which fit between the joists, either in the form of material attached directly to the insulation or some sort of material between the joists with insulation that installed above it. Here's an example from an inspection of an older property earlier this week, a treated paper VR has been laid between the joists and cellulose insulation installed above:

So if you are looking at the layers from below and finding drywall, then a VR, and then insulation, this is a standard building practice.

___________________________________________
I’m paid to be suspicious…

MJW · 08-20-2009, 09:30 AM

I don't consider kraft faced insulation as a vapor barrier, but I guess in some places it is recognized. Poly overlapped, taped, and sealed is a good vapor barrier.

Nice post Michael Thomas.

I don't see much wrong with the way it was done, but it the ceiling joists are getting much more moisture than they would if it was done correctly.

Still probably much better than it was originally though.

Michael Thomas · 08-20-2009, 12:05 PM

Quote:

Originally Posted by MJW

I don't consider kraft faced insulation as a vapor barrier

According to most building science authorities most everything used in residential construction to control vapor diffusion is a vapor diffusion retarder rather than a vapor barrier. Polyethylene sheet (0.03 perm) however a much more effective retarder than asphalt-coated kraft paper (0.40 perm).

MJW · 08-20-2009, 12:11 PM

I don't think we could get away with using kraft faced using the IRC code, unless you sealed on every joist or stud.

Scuba_Dave · 08-20-2009, 01:03 PM

I've always stapled the kraft across the face of the 2x - overlapping
Once the sheetrock is in place it effectively seals the paper to the stud & seals each bay
I've yet to see anything else used on any new house around here

russstar · 08-20-2009, 01:31 PM

This is an older house, a small carriage house I think built around 1900.

MJW · 08-20-2009, 05:25 PM

Dave, that flap on the kraft faced is supposed to be stapled on the 5 1/2" part of the 2x6. Not sure if that is what you are saying or not.

When I said sealed, I meant using an acoustical sealant. Have to use this to meet code on the poly and around penetrations like outlet boxes with the rubber flange. That's why I'm almost positive that kraft faced simply stapled would not be considered a sealed wall. Look at the sheathing behind the insulation in the winter. If there is any moisture in the room it will turn to frost on the sheathing when it's not sealed. Eventually it turns to mold if it doesn't dry out.

To the original poster.....where is the draft coming from? Is the ceiling built up into the attic space?

It's hard to tell what someone may have done to a home of that age. There may have been many renovations by different homeowners or contractors. Codes have changed so much, it's hard to tell what people were thinking sometimes. Same is true for manufacturers. The vapor barrier you saw may have been suitable for the time, but maybe it isn't up to par with what poly is now. In your ceiling you have less to worry about as far as moisture and mold ruining anything because the roof is vented. Walls are to be a sealed system. Ceilings aren't as bad because they can breathe.

Is there any ductwork running up there? Any PVC? There may be something ran up there that is supposed to stay warm......like I said it's hard to tell in that age of home.

Scuba_Dave · 08-20-2009, 05:47 PM

Nope - I staple across the shorter dimension
I know its not what the Mfg states, but I'm not reducing the RValue

Quote:

As you can see, the insulation can get crushed at the edges, and the R-value will be reduced slightly there

From Owens Corning site:

Quote:

Available Vapor Retarder Facings Kraft

MJW · 08-20-2009, 06:58 PM

Yep, that picture is correct. Back when kraft faced was acceptable (not sure if it is anymore without poly), I saw an entire house that had to be redone because they stapled it to the edge of the 2x6's. The inspector wouldn't pass it that way.

Vapor retarder isn't a vapor barrier which is required for the sealed wall that the IRC explains.

OC and Menards sells alot of stuff that isn't code compliant.

**Gary in WA** · 08-20-2009, 07:29 PM

Doesn't matter which, side or face:
Should I staple the facing to the front of the stud or to the inside?
Either is acceptable. Most drywall installers prefer to have the kraft paper stapled to the inside. Inset stapling allows them to glue the drywall and gives a smoother surface to attach to. The flanges are not part of the vapor retarder so faced stapling does not give you a better seal.
From: http://saveenergy.owenscorningblog.c...questions.html

And the reason why: http://www.certainteed.com/additiona...n_Products.pdf

My personal idea is that stapling inside creates a convective air channel that reduces the effectiveness of the insulation.

Be safe, G

Scuba_Dave · 08-20-2009, 07:31 PM

This from Certainteed seems to indicate not required as of March 21st, 07
But they seem to be basing it on IRC 2003, statement issued May 5th, 05

??

http://www.certainteed.com/additiona...n_Products.pdf

Ha....GBAR faster on the Kb

MJW · 08-21-2009, 11:10 AM

Maybe we just go more by the rules up here, haha. Not sure. I've seen where the entire house had to be re installed stapling the kraft paper to the side of the 2x6. believe it or not..........This was back in the late 90's before the newer energy codes.

IRC2006 has passed, I believe we are on IRC2009 now, with amendments. We can't even pour a basement slab without poly anymore.