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Seal then flash and Rockwool or just seal and Rockwool.

efficient_disciple | Posted in Energy Efficiency and Durability on
I live in valley stream, NY marine 4… My plan so far is to have r10xps on the exterior of the home and to airseal the cavity and install Rockwool. This way the house can dry to the interior if any water were to somehow either get into the cavity or to get onto the exterior sheathing. Another option I was thinking of was to flash the inside of the cavity with 1″ of closed cell and then install Rockwool batt in front of that. This way approximately 1/3 of the total insulation is still on the outside of the house.

I already have the r10 XPS on the outside, would it be overkill to install 1″ of Closed cell on the inside? No matter what I do, I do not want to use open cell since it’s more like a sponge and would take for ever to release the moisture it absorbs.
Also I used, from my understanding it wouldn’t make sense to do all spray foam in a 2×4 wall with no exterior insulation because the cavity would have r21ish but the studs would only be r4 max. But r10 on the exterior plus r15 Rockwool in the cavity equates to r25 in the cavity and r13 at every stud. Much better overall r value, plus the Rockwool is fireproof when compared to closed cell, also Rockwool is vapor permeable but moisture resistant as it is made from either rock or steel. For my roof since it was a new shingled roof by previous contractor, I will be using 4″ of closed cell plus r23 rockwool in the attic, I will be sealing off the soffits with the same r10xps as blocking and then the spray foam will be applied 4″ on roof deck. Total r51 roughly between cavity, 2×10 SL rafters with no exterior insulation on the roof unfortunately. Next time I do the roof over I’ll install exterior foam there as well. I will have a return and supply in the conditioned attic as well to control humidity at the ridge. Does this sound like a well thought out plan? 

I will have an erv and minisplits in the home. Any suggestions or modifications you recommend? My vapor barrier is installed on the outside of the sheathing.
From outside to inside:
Vinyl siding>taped r10 XPS>tyvek house wrap>1/2″ plywood> (two options)

Option a: caulk air seal, 1″ flash and batt (cc and compressed Rockwool r15)
Option b: caulk air seal and then Rockwool 
I read the Rockwool can be compressed slightly and the r value actually increases a little, please correct me if I’m wrong. Also would 3.5″ Rockwool be able to be compressed by 1in? Or should I forgo the closed cell in the cavity. 

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  1. kiwiscott | | #1

    Great questions - looking forward to the answers as you have the same problem set as me (1920s house, northern NJ, needs insulation) in a very similar zone.

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