Replies

1. Expert Member
   BILL WICHERS | Jul 29, 2023 07:05pm | #1

   If your plan is to try to reclaim old fiberglass batts that are currently installed, I’d advise against that. Old batts tend to come apart while being removed, which makes it very difficult to install them well somewhere else. It’s also common for old batts to have nasty things like mouse poop and dead insect carcasses scattered around, both inside and on the surface of the batts.

   If the old fiberglass batts are in good shape, clean, and not full of nasty stuff, then they’re fine to reuse as the fiberglass material itself doesn’t really degrade over time. The paper tends to get crumbly though. You don’t have to worry about the Kraft paper trapping moisture, since the Kraft paper is a sort of old-school smart vapor retarder that will actually help to reduce moisture levels in the cavity. Just install the paper facing towards the “warm in winter” side of the space.

   The only issue I see with your proposed assembly is that you’d only have around 19% of the total R value in the form of closed cell spray foam. Even in CZ, I’m pretty sure you need more than that (but I don’t have my table handy at the moment). In CZ5, it’s recommended to have 40% or more of the total R value in the spray foam layer in an assembly like this (I prefer 50% or more to be safe). CZ4 is ok with a lower percentage, but I think it’s still around 25-30%.

   Bill

2. 
   DaveyBuild | Jul 29, 2023 07:28pm | #2

   Thank you so much bill. The total I need is R-49 in my climate. See chart attached. Says R-15 min CC. Hopefully the insulation is in good condition to reuse. Would this assembly be ok with Sheetrock over as well? And is there a cheaper alternative to hold it up and keep fiberglass out of the air?

3. Expert Member
   BILL WICHERS | Jul 29, 2023 07:58pm | #3

   As long as you follow the tables for the R value ratios for your climate zone, you should be ok. I would recommend going a little heavier on the spray foam than the minimum in the tables for two reasons though: one is that it’s safer, and two is that it gives you some insurance against thin spots during the application. It’s very difficult to get a perfectly even layer of spray foam, and you need to make sure ALL of the spray foam is AT LEAST the minimum required thickness. You can’t just be concerned with the average thickness here, because the thin spots could potentially dip below the dew point and give you condensation problems.

   Drywall is probably the cheapest air barrier material you could use here if you want to seal in the fiberglass to avoid dust issues. You don’t need to fully finish the drywall, although you do want to tape and mud the joints. I recommend priming it too, which will let you finish it in the future if you want. I primed drywall tends to yellow a lot over time.

   BTW, I recommend you use a full respirator with dust cartridges and a rubber seal against your face while working with the old fiberglass. This gives you much better protection than a paper dust mask, and the rubber seal tends to not leak. There will be lots of dust when you pull out the old batts, and you do NOT want to breathe that dust.

   Bill

1. 
   DaveyBuild | Jul 29, 2023 08:32pm | #4

   Thanks for the tips!

4. 
   walta100 | Jul 29, 2023 11:39pm | #5

   Why are you moving the insulation to the roof line?
   You are very unlikely to ever recover the cost of such a retrofit.

   Walta

1. 
   DaveyBuild | Jul 30, 2023 07:15am | #6

   The hvac equipment is all in the attic, the ceiling below (attic floor) is not air tight due to recessed lighting/hvac penetrations etc and would be very hard to make it air tight now, the roof has a complicated roof line and is hard to properly vent etc. I’m doing it to prevent issues more than save money in energy costs

5. 
   walta100 | Jul 30, 2023 12:34pm | #7

   OK you are boxed into this choice as a result of poor choices you listed.

   Are you prepared to declare your attic conditioned space, buy and operate the equipment necessary to keep the space at more or less the same temp and humidity as the rest of your home understanding that from an energy perspective the improved is likely to be marginal?

   What is your plan for holding the old insulation in direct contact with the new spray foam?

   Walta

1. 
   DaveyBuild | Jul 30, 2023 08:50pm | #10

   The poor choices were not mine. Yes we will condition it and have a dehumidifier installed. I’m aware that I will likely not see energy savings.

   Will probably Sheetrock over further reducing my chances of recovering the money.

1. 
   walta100 | Jul 30, 2023 11:46pm | #11

   Every morning you wake up and make the choice not to call a real estate agent and sell the house that is you chousing to buy this house and all its poor choices again for one more day.

   Every day you make a choice to keep this house and one day you will make the other choice the only question is when.

   I never much cared for the dehumidifiers much. In my opinion they lower the relative humidity more by heating the air than the small amounts of moisture they remove.

   Do you actually have enough rafter depth to get R38 of fiberglass seems unlikely.

   Walta

1. 
   DaveyBuild | Jul 31, 2023 08:58am | #12

   Come visit my area and you will find every single house has hvac equipment in the attic and every single attic is fully vented.

   I love my house and I’m not selling it because of the attic. I’m choosing to invest it in and have it how I want it. Thanks for all the input.

6. 
   klhoush | Jul 30, 2023 03:02pm | #8

   You should consider a perforated roll foil product with rip-stop. It can be stapled or battened up, is fire resistant and provides a radiant barrier. The Kraft paper presents a problem since it is flammable and must be installed in substantial contact with an approved wall covering.

   Kurt

1. 
   DaveyBuild | Jul 30, 2023 08:48pm | #9

   Thanks Kurt. Are the perforations enough to prevent it from being a vapor barrier? I know foil is usually vapor barrier.