Wall insulation without windows
TreeNate
| Posted in Energy, Heating & Insulation on
Working on a new build cabin and waiting for windows that won’t be installed for another 6 weeks due to delays. I know lots of builders are experiencing these delays and just wondering if you all see potential downsides with installing rolled batt insulation in the walls prior to installing windows and having it stay that way for 4 weeks or so. Currently the windows are taped over with plastic but the doors are open so there’s plenty of ventilation and the rain will not be an issue. Seems like it shouldn’t be a problem if things stay dry and well ventilated but looking for some thoughts from others in case I’m missing something.
Replies
I would think it ok to install batts.
might think twice if these bats include a vapor barrier, about leaving some not stapled, so that you can check for moisture or critters setting up housekeeping if you will leave open for some/most of the time. Keep in mind that 6 weeks does not always mean 6 weeks.
Thanks a lot for the advice on that! No kidding on the timeline haha. Looks like we're still on track for our date of delivery.
I wouldn't install any insulation until you get it closed in. What is going on the outside walls? Do you know that putting the insulation on the outside is more effective than any insulation put in the stud bays? Every stud creates a bridge to the outside conditions. If you used the best fireproof insulation the most you could expect is an R-13 to maybe an R-15 using Rockwool which is more dense than fiberglass. Rockwool is more resistant to critters; insects will die burrowing into it and it is very abrasive to mammal critters. Rockwool is also fireproof and water repellent. It will not absorb water even when submerged.
So you put 4 inches of polyiso aluminum faced rigid board on the outside with no bridging effects and you will get an R-value of 26. If you fill the stud spaces with Rockwool you would get an average R-value of 12. Combined that gives you an R-value of 38. Next you should insulate the roof in the same manner or use 6 inches of polyiso and a screwed on overhang framing attached through part of the insulation roof layers. You can use 2X4 or less for the overhang because it supports very little weight even with an asphalt shingle roof. If the overhang is built onto the insulated roof, the roof and sidewalls can be sealed off together. The exterior wall and roof sheathing can meet and then be sealed together creating an airtight barrier to the outside. Then the exterior insulation layers can be joined and sealed together. Use peel-and-stick flashing material to join and seal the layers. Building Science now recommends a weep or drainage or anti-capillary layer between the plywood with the Tyvek or equivalent house wrap and the exterior insulation board. That weep layer should be carried to the outside. There is the potential in some climates for the moisture on the inside of the structure to get out to the insulation board and possibly condense or form droplets that need a way out.
Furring strips are screwed through the insulation board to the interior structure and then the final exterior layer is attached to the furring strips. This creates a drainage space or rain screen for wind driven water that gets past the finish material even if it is metal siding, lap siding, stucco, brick, or Hardie siding. All leak to some degree. That space allows water to drain and air movement to dry the space.