Replies

1. 
   idahobuild | Apr 13, 2022 10:19pm | #1

   Hey Nick,
   I'm not an Expert. However, my understanding is that the dense pack cellulose won't act as any type of air barrier that would cause "the walls to be more air tight". For airtightness a lot of attention to detail is required at the air-barrier envelope. I think that your cellulose will still quite readily dry through the materials that you've listed---much as the wall materials in there have over the last 80 years. But the cellulose will hold more water in the wall than previous so it will need more time between 'water events' to dry out.

   my 2¢.

1. 
   narnal | Apr 16, 2022 01:39pm | #5

   Thanks for the response IdahoBuild. I was thinking the dense pack would act as a low grade air barrier. I did some research after your comment and here's what I found...

   The dense pack improves air tightness by about an order of magnitude, but it is still about an order of magnitude from "air tight". Perhaps in my case, this is a good thing since it will make the wall assembly a little more forgiving.

   https://www.buildingscience.com/documents/insights/bsi-043-dont-be-dense#:~:text=Dense%20pack%20cellulose%20and%20dense,they%20sometimes%20come%20pretty%20close.

   Here is a relevant excerpt about dangers of this retrofit:
   "Two caveats: First, if the wall is leaking rainwater, you have to fix the leak before you insulate. Anyone not get this? I mean, it is pretty obvious that if your basement is leaking you need to fix the basement leak before you insulate your basement? Right? And, if your roof is leaking, you need to fix the roof leak before you insulate your attic. Right? Walls are no different. Fix the leak first. Don’t be dense.

   Second, the energy flow across the assembly is reduced when you dense pack. We talked about this in BSI-028: Energy Flow Across Enclosures). The cladding and sheathing will stay colder and wetter longer. Paint problems are not uncommon as a result of dense packing walls in older buildings. Recall, old paint is not as vapor open and flexible as modern, newer paints. And, don’t forget about the lead. Remember to “get the lead out.” Even so, I still think dense packing of walls is a good idea, but it is not risk-free."

2. 
   user-2310254 | Apr 14, 2022 09:18am | #2

   Nick,

   Not an expert either. But if it were my house, I would focus on adding insulation to the attic/roofline and air sealing the rest of the structure. This seems to be where owners earn the best return in terms of energy savings and comfort.

1. 
   narnal | Apr 16, 2022 01:25pm | #4

   Thanks Steve. I already have blown in cellulose in the attic. Part of the reason to add wall insulation is to satisfy a Manual J for a room addition and also to reduce noise from the road.

1. 
   user-2310254 | Apr 16, 2022 02:22pm | #7

   If the interior plaster and the exterior cement siding are both in good condition, I would go with blown-in cellulose. I'd also consider using Aerobarrier to seal up remaining air leaks. To mitigate noised further, I would put in noise suppressing windows or interior storms.

3. 
   trustblding | Apr 14, 2022 01:24pm | #3

   https://www.buildingscience.com/

1. 
   narnal | Apr 16, 2022 01:43pm | #6

   Thanks David. I found a good article that I referenced in my reply to IdahoBuild