Replies

1. 
   acrobaticnurse_Eli | Dec 11, 2023 05:38pm | #1

   Given that the mineral wool batts are likely 48 inches long I'd break each one in half and turn them 90 degrees to fit the 24 inch space. I've been doing something similar for my climate 3a attic, using 2 layers of r15 mineral wool in 2 by 6 rafters (not trusses) that are spaced 16 inches on center. To fit the 2nd layer I settled on HVAC strapping that I staple on each rafter to hold it in place. A single layer of r30 mineral wool would have been less effort but was less available and doing 2 layers lets me overlap the edges better. Temperatures have improved from being ambient temp in the winter and in the 140s the rest of the year to being within 10 degrees of interior temps and humidity has stabilized vs having wild swings from 18 to 80% throughout any given day.

   I've been removing the last bit of attic floor insulation as I finish up the attic ceiling. As I do so the attic temp further improves and I haven't noticed any real energy penalty so far. Bringing the ductwork into the thermal envelope should help, though it also increases the amount of space being conditioned.

   
1. 
   JoshE372 | Dec 12, 2023 08:00am | #3

   Thanks for the idea to cut perpendicular to the length. I will give that a try today.
   I assume you installed the batts in contact with the roof sheathing, leaving no ventilation path between them. It also looks like you have left an opening in the insulation along the ridge vent. Did you install a vapor permeable membrane at the ridge vent and close up any soffit vents?
   It also appears you have left the mineral wool exposed to the attic from the underside. I was under the impression that an air barrier would need to be placed beneath the insulation in order to prevent the transport of moisture laden air through the insulation where it could contact the cold roof sheathing (in winter). Have you noticed any condensate or moisture damage in the space?
   And lastly, did you provide HVAC supply air to the attic space or install a dehumidifier?

1. 
   acrobaticnurse_Eli | Dec 12, 2023 02:48pm | #5

   Thank you. It's a work in progress. Had I known just how much work in the beginning I would have been more open to paying someone to vacuum out all the old insulation and add closed cell spray foam. Instead I bought 50+ bags of rockwool and have since installed most of it. I have been monitoring humidity levels and checking sheathing over the past year and humidity has been better than before. No moisture issues noted. For whatever reason when a ridge vent was installed by prior owners soffit vents weren't added so I won't need to close them off.

   I plan on using Siga Majvest for a vapor diffusion port when I redo the roof in the next several months since I appear to be able to get it in an 18 inch width for a reasonable price and it's 68 perms. If the roof were newer I would just replace the ridge but instead will likely do all of it once the weather is warming back up. I planned on doing it in October and then temps dropped 30 degrees. 

   I will likely use either an intello or siga air barrier on the interior once everything is complete. I plan on adding a conditioned air supply to the attic but wanted to get more of the old insulation out first so I wouldn't get anything into the ductwork.. I may see if there is a very basic filter I could put over the supply vent that wouldn't negate the purpose of having the supply until I could remove it when the air is clearer. I've used construction filters on vents when renovating inside but only for hours instead of months. In the crawl space when I encapsulated it I added a freestanding Santa Fe dehumidifier, and I have an in-wall santa fe MD33 in the main part of the house. I track humidity and temperature in the crawlspace, both attics, the kitchen, and main bedroom to help guide improvements.

2. 
   acrobaticnurse_Eli | Dec 11, 2023 06:06pm | #2

   My house has two attics, one over the main 2nd floor which I'm working on now, and one over a lower single story portion that is vented with a ridge and soffits. For the single story portion I added baffles that go from the top to the bottom of the attic ceiling and furred out the rafters like a bonfiglioli wall to hold the 2nd layer of r15, cutting EPS foam and attaching it to strips of plywood. It worked and could be worthwhile if planning on adding a drywall ceiling, but otherwise the HVAC strapping is much easier, and you could then go over it with a smart membrane and maybe add wood strapping after that to help hold everything in place.

3. 
   walta100 | Dec 12, 2023 11:41am | #4

   acrobaticnurse_Eli

   Photo is of a very risky idea that I call the free lunch. Installing new insulation at the roof line and leaving the old insulation on the attic floor combined with the failure to add any HVAC registers to the attic all but guarantees that from time to time parts of the attic will get colder than the dew point of the air in the attic. When that happens stuff will get wet how wet and for how long is unknowable. Will it grow moldy and rot? Only time will tell if you win the free lunch sometime in the right climate you can get away with it.

   Note fluffy insulation like rockwool and fiberglass must have air and barrier and vabor retarder to keep the warm moist air from flowing thru and coming in contact with the cold roof sheeting and condensing with the resulting mold and rot

   Walta

1. 
   acrobaticnurse_Eli | Dec 12, 2023 03:01pm | #6

   Thank you. I'd call it a photo of a work in progress as I mentioned in the first post that I was still removing insulation from the attic floor. I didn't mean for it to be an example of finished work, more of a way of attaching rockwool to the attic ceiling. There are no soffit vents and I'll be adding a vapor permeable membrane to the ridge vent soon. Once I get more of the insulation mess settled it won't be too hard to add an hvac supply. I plan on adding either siga or intello to the interior once I'm finished adding insulation.