Insulation Considerations - Batts or Blown in??

[fastsvo]

I have a 1969 built home in Southern California that has existing blown in insulation (fiberglass?) from what seems like back when the home was built.

As you can see in the pictures, it's well below the joist levels and is dirty (will be vacuumed completely). I currently do not use it for storage because of it's semi low pitch (4.5ft standing height inside at the ridge).

So going forward, I am stuck deciding between R38 batts or blown in cellulose or maybe a combo of batts+cellulose blown over the top?? The plans is to air seal everything possible including where the roof meets the eaves (no soffits vents) which is really tight and difficult to reach. I have plently of canned lights (mix of old and new) everywhere and some are NON-IC rated, but I think with the LED conversions it's ok now to have the insulation contact these cans. Though, that one white can in the photo most likely will be replaced because its really leaky (I can see inside). Another option is to invest in those organic "hats" to cover all the cans.

The attic is well vented with fans. Another consideration, would be to add radiant barrier against the roof rafters. I have a couple of knee walls facing the exterior (with gable vents) - would adding batts here be a good idea?

One guy I spoke to wants to use unfaced batts, but for the small difference in cost, wouldn't it be better to have them faced? I think over the years it will look/stay cleaner, but I don't think the vapor barrier is needed in an attic like mine? He also mentioned that they can pull a sheet of clear plastic over the fiberglass to keep it cleaner in the attic. Won't that trap moisture?

Anyways, how would you do it?

Thanks!

 

[Snoonyb]

Who ever did that, "just throw the romex where ever" needs to be shot. Attic wiring need to follow rules, in place, which prevent the possibility for damage.

Clear the Insul. from around the cans, because you don't know what lamps future occupants may install.

The vent 90, needs to terminate through the roof, in a roof jack.

I'd, and I've done this several times, lay R-13 unfaced in the joist bays to fill, then lay R-30, unfaced, on top, perpendicular to the joists.

 

[fastsvo]

I'd, and I've done this several times, lay R-13 unfaced in the joist bays to fill, then lay R-30, unfaced, on top, perpendicular to the joists.

I am assuming this is to cover the top of the joists where insulation batts would normally miss it? (I see this as one advantage to spray cellulose).

The 90* vent is an old A/C vent that is no longer used (closed up with drywall from the inside) but it should be plugged at least.

 

[Snoonyb]

The R-13 is to fill the joist bay, and the perpendicular R-30 covers.

 

[fastsvo]

This video is pretty informative:

 

[MattinCA]

Did you ever finish your insulation project? I am looking at doing my 1950s So Cal home.

 

[voyager]

See my post in the above thread for more info.

I had to chuckle a lot seeing the pics here.
Either It was a lousy job of blowing it in or it has been very badly disturbed by people moving around there.
Probably a combination of both.
The blow-in should be even and smooth across the attic floor area, but not compacted, and properly installed.
The R value is determined by the depth of the insulation.

 

[jjredmond71]

I am assuming this is to cover the top of the joists where insulation batts would normally miss it? (I see this as one advantage to spray cellulose).

The 90* vent is an old A/C vent that is no longer used (closed up with drywall from the inside) but it should be plugged at least.

Batts are no longer used to insulate attics. Blown-in fiberglass/wool or cellulose is ideal in that batts create a concept known as thermal bridging, which lessens the overall effective R-Value the attic as a whole.

https://www.finehomebuilding.com/project-guides/insulation/thermal-bridging
For instance, say you have 20 voids and 19 floor joists (your average stick-built wall or floor is 27% lumber). Depending upon your Energy Zone, you have the R-Value of the batts you install, but in order to calculate the overall R-Value of the attic floor, you must account for the approximately 3.5 R-Value of the joist. When you average all of the joists, and batts across the floor the EFFECTIVE R-Value is much less than intended.

It is also important that in order to reach an effective R-Value of what is intended in your Energy Zone, all penetrations between the attic and living area must be air sealed as noted in the original post.

So in terms of the attic, blown fiberglass or cellulose to the intended R-Value coupled with with appropriate air sealing is the trick.

For kneewalls, your best wall set-up is an air sealed 6-sided wall (drywall, studs/lumber around perimeter, and a solid substrate on the outer side of cavity (drywall, plywood, rigid foam board, etc.). If there is an excess heat build up in the attic, we often use a product called R-MAX which is a rigid foam board that possesses a radiant barrier scrim on one side; this scrim will reflect the heat from the attic away from the wall cavity and not allow it to permeate into the adjacent living area.

You asked about radiant barrier. Overall it is a great product that works extremely well, but only in the right application. If you have an excessive heat build up in the attic, AND the floor joists are properly insulated to the level required by code, then a radiant barrier might be worth the money. If you are not properly insulated radiant barrier does nothing in that it has no apparent R-Value. In the right application though, it can work magic in that will help enhance a properly insulated thermal plane.
NOTE: DO NOT buy anything but radiant barrier rolls for the roof rafters; the bubble rolls are junk and end up being good money after bad.