[Greenbuilding] outsulating gut/rehab CMU house (was Re: embodied energy was Polyiso strength on roof )

[RT]

On Fri, 12 Dec 2014 10:36:41 -0500, AA-man wrote:

> A current project is the gut rehab of a modest '40's house, with walls  
> made of stuccoed concrete block.
>
> Current thinking is to fasten treated 2x's directly to the masonry, with  
> 1 1/2" thick Roxul Comfort Board installed between members.

> cover that with a continuous layer of more RCB, a good breathable WRB,  
> furring, and back vented siding.

As my Newfie fisherman friend might say :

    "Oither ye thinks beeg or ye goes home, By."

The aforemention scheme seems like a lot of futzing just to get 3 inches  
of insulation.

I'd be inclined to take those same 2x's and suspend them 8 to 12 inches  
away from the CMU wall (perhaps hanging the top end from the new roof  
trusses and attaching the bottoms to something like a torsion box beam   
...(ie a ledger anchored to the CMU wall with ply flanges attached) and/or  
metal brackets (similar to those used to hang pre-cast concrete stoops on  
foundations) and or tension cables back to some convenient spots higher up  
on the CMU wall ... and then fill the cavity with multiple layers of Roxul  
batts, joints staggered/overlapping between layers  -- R-40-plus with no  
foamed plast-ecchhh! (and attendant long fasteners so pricey that you feel  
that a pimp would be appropriate in the transaction).

Air-seal/WRB at the exterior surface of the block first, rainscreen  
cladding hung from the 2x's and lard tunderin jayzuz,  oi tinks yer dun.


-- 
=== * ===
Rob Tom ADT1
Kanata, Ontario, Canada
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