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Converting garage to pool house (Houston)

Conker | Posted in General Questions on

Newbie here and I have been trying to read through all the posts and questions and starting to think I have some level of a handle on it to ask a question.


I’ve decided to turn my detached garage (20×20) into a pool house in Houston,TX (climate 2A). House was built in 1978 and a new roof put in 2018.  I would like to do a ventless cathedral ceiling to leave the garage feeling more open. There are no vents currently and soffit has no holes/openings.


I purchased a 18k Mr. cool (ductless) mini split to condition the space.


My question regards insulating the roof. Based on the cool hand Luke post, I believe I should spray the rafters with open cell spray foam and call it a day. I plan to shiplap over the foam for my ceiling.  My understanding is the excessive moisture concern near ceiling wouldn’t be as relevant in my cathedral instance and seemed to affect northern climates more.


I also am having an electrician add a ceiling fan box up top ( in case I want to drive some up the air up top – downwards).


Am I unintentionally creating a mold hot box in any way?  

(I clearly have a long way to go- ha!)

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  1. matthew25 | | #1

    Will this building be conditioned only seasonally? What kind of WRB is on the top of your roof sheathing?

    It’s true that interior humidity is more of a concern in Northern Climates but if this space goes unconditioned for long periods of time in the humid Houston weather you could have humidity migrate through your OC foam and condense in the winter time on the underside of your sheathing. I am thinking closed cell is the safer bet here. Maybe someone else can back me up. Exterior insulation would be the best but with a new roof already it’s probably not in the budget.

    1. Conker | | #2

      Plan to AC year round ( but may do more slightly extreme ends to save a couple $) as in 66 in winter and maybe 80 in summer.

      I admit I don’t know what kind of WRB it has- I’ll find out

  2. Expert Member
    ARMANDO COBO | | #3

    David Weekley Homes, in Houston, had a 100s of homes mess with rotted attics sprayed with ocSPF only. You need to install 2" R13.5 min. ccSPF to seal any moisture migration and then you could finish with 7" R25 ocSPF to have required R38 in CZ2.

    1. Conker | | #7

      Good to know! A couple articles mentioned combo’ing cc with oc like you mentioned. Any caveats I should be aware of- does the 2” of cc need to offgas/cure before adding the oc etc?

    2. Expert Member
      ARMANDO COBO | | #8

      All manufacturers have their own installation guidelines that you must follow.

  3. walta100 | | #4

    Have you read this article?

    In my opinion Cathedral Ceilings are 10 pounds of stuff forced into a 5-pound bag. There is never enough room to fit the required insulation given that every Cathedral Ceiling simply must have dozens of recessed lights.

    This is Texas I thought code required an attic filled with HVAC equipment! LOL.


    1. Expert Member
      ARMANDO COBO | | #5

      "dozens of recessed lights"??? Perfect for track or LED thin-puck lighting.

      1. walta100 | | #6

        ""dozens of recessed lights"??? Perfect for track or LED thin-puck lighting."

        I was half joking, in my opinion both are bad ideas when done together make the problems four time worse that for some unknow reason lot of people want both of them.

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