Any problems with unfaced insulation on exterior walls?

[RNeumann]

How are you hitting code minimum R values with the polyiso or roxul? The thicknesses listed don’t hit the R value of a “conventional” 2x6 wall. Polyiso is something like R5.7 per inch and Roxul is like R5 per inch.

I’m not arguing the science behind the construction method. I’m wondering how you get it past a building department that uses federal standards or higher. I’m guessing it’s something like R19 in the walls and R40 in the lid.

Btw- I used 1” Roxul outside the OSB and building wrap except around the windows. In those areas I used 1” rigid so it would be easier to attach trim. The windows have 1 3/8” profile so the trim looks fine- no furring needed.
I then put 1” rigid below the trusses and attached the drywall with screws that are an inch longer. The recessed cans and other ceiling fixtures would adjust down to compensate for the extra 1”.
I filled the 2x6 walls and lid with cellulose - R50 in the lid and the walls were full....I think that’s R21 or R23.
This setup has worked very well for me. I’m all electric (heat pump, well lighting etc) and have been paying less than half of what my neighbors pay- $75/ mo vs $240 and $300 for two of my neighbors.

 

[LittleBill21]

New building

Use a 60 mil modified bitumen peel and stick membrane on exterior of basement walls and extending to roof line used as air and vapor control layer. All insulation applied to the exterior of the mod bit membrane. Below grade use 3" of expanded polystyrene. Above grade use 3" of polyisocyanurate board foam or 4" of Rockwool rockboard80. Apply furring strips to the exterior of the insulation and cover with drainage plane of your choice. Use vent screen and the bottom and top of the wall to provide a vented rain screen. Install siding over the drainage plane. You may use more insulation but it will not be absolutely necessary in my opinion.

Use pans below all windows with wicking strips to allow sealing of windows completely into mod bit membrane while allowing water to escape the pan to the exterior when the windows someday fail and begin to leak. Use head flashings above all windows with end dams to channel water to the exterior at top corners. Windows should be furred out to the outer plane of the insulation layer and should be argon filled and northern low-e.

On the roof install 5/8 roof decking and dry in with #30 felt. Install 6-8" of polyisocyanurate foam in 2 layers with seams staggered in both directions. Cover this with 1/2" or 5/8" decking secured with #10 screws and 3" washers designed for the purpose secured into the first layer of decking. There is not need to hit the rafters with these screws. Install shingles over an approved drainage plane. Use only sealed combustion furnaces and water heaters or all electric. Your attic will not ve vented and will be room temperature or 2 degrees above. Plan for using your attic as conditioned space but you will not need a ducted supply. Your HVAC will need to be downsized appropriately for the greatly reduced load.

Install timers on all exhaust fans and use them to remove moisture from cooking and bathing and in the laundry. Use an HRV for fresh air if needed depending on occupancy load and use patterns. Allow for supplementary dehumidification to be added if building use warrants a need for it. You will be able to run a bit higher humidity level in the winter than you are used to and you should let your window condensation be your guide. You will not need nor should you install a humidifier. This building will be airtight and will not run as dry in the winter as a leaky building does. There is no risk of condensation in your walls or attic with this system.

thanks for that, i will look into it, did you have any advice for the existing buildings? the new building is a couple years out

 

[RayfromTX]

Code minimums are for whole wall and the sheathing, air space and drywall are added. The polyiso is 6.2 LTTR and the Rockwool is R4 per inch. Code officials will usually accept a stamp and continuous insulation is worth more than cavity fill. Educating the inspector may be required. That has never been a problem when done respectfully. I have never understood how they accept 5" of opens cell spray foam in the rafter bays. The foam guys only recommend 5" because it makes their pricing more competitive and the fire testing is only done with 5". They may not even know why their supplier has the 5" guideline but that's the real reason. It's an ASTM test standard that causes them to recommend 5".

Sorry Little Bill. I can't dive into the existing buildings.

 

[pmsmechanic]

Keep up the interesting discussion. It's all very informative and a good reference for future builders.

 

[Lineman North Florida]

Yes I don't view this as thread hijacking I got the answer to my question and for the record my hunting camp now has R-38 faced batts in the attic and R-13 un- faced batts in the exterior wall cavity's, carry on with the discussion and thank's for the answers to my questions.