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Insulation advice for historic rennovation

jzmckee21 | Posted in GBA Pro Help on


I am looking for some advice, suggestions, and inspiration for insulating and re-roofing our home in San Antonio, Texas 

I have reviewed much of the great content on GBA on this subject and others.  It has helped significantly and is much appreciated.  Now that I am in the thick of an in important phase of our project I am in search of more specific advice for our home.

3200 SF split-level home, designed and built, in 1962.  Two rooms with Cathedral ceilings,  11 set’s of sliding glass doors, shingle roof (4/12-Trussed, that is in need of replacement), and original siding.  

Currently, we are installing a new HVAC system and replacing all of the insulation in the attic space.  We are moving away from our hold central units to a combination of ducted and non-ducted LG mini-splits.  For the sake of architectural integrity, we opted for the ducted (short runs) in the Master Suite and Formal Living area.  We will achieve removing most of our ducts that were in unvented/unconditioned space and significantly reduce the length of supply ducts on remaining.   We will also re-capture a lot of valuable space by removing the two handler closets. 

My question is most directly aimed to make the correct insulation choices, while not compromising the goals of the future.

We would like to explore the option of converting to an unvented / sealed attic when we re-roof.  

The home originally had cedar shake and while we aren’t going down that road in this climate, we have found a synthetic shake product that we are happy with.  The roof is currently shingle on plywood on top of battens.  At the time of re-roofing, we are planning to add enough rigid foam to the roof deck to address areas that have cathedral ceilings, as well as supplement our attic insulation.  This direction makes a lot of sense for many reasons.  For one, we have a fair amount of cathedral ceilings with original insulation within them.   Without adding to the top, I don’t believe we can reach our R-value goals.  We like the idea of the thermal envelope approach as a goal to work towards for the entire house. 

We have removed all of the old insulation from the attic space and are looking for some advice.   I was planning to do a combination of batts and blown in on the floor, plus batts on interior facing walls.   I have also considered a radiant barrier on the underside of the sheathing in this combination.    

***Would the radiant barrier need to be removed if we decide to install foam on top of the decking?

***I think that the combo of batts and blow-in is advantageous vs just blow-in.  Does anyone agree or disagree?  

***I need to have cat-walk, or narrow stretch of the floor decked underneath ducted mini’s for service.  ***Would do these sections via cut and cobble with rigit foam and loose fill be advantageous to achieving r-value where I can’t go higher with blow-in?  I was also considering a similar approach at the narrow most end, near the eaves.

***Any suggestions for type of blown-in or batts?

***What should I stay away from if the goal is to eventually to go unvented?  Not definitive but I would like the optionality.  

***What R-value in the attic do I need to have and what other considerations do I need to make to be at before sealing off the soffit vents into the attic space?   It seems like I should consider doing it now, while it is all exposed.  However, I want to know if it would be safe to do given it would not yet be completely sealed.  

Any information appreciated!

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