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  1. #1
    Join Date
    Jun 2004
    Location
    St Louis, Mo for the past 25 years
    Posts
    7,624

    Default garage conversion to room

    I have looked at a garage that will be converted to living space. It will have a mini split for HVAC and is attached to the house. It is a 2 1/2 car garage now and will become one big room. We will be adding some windows and walls when we take out the garage door. They will be having blown insulation put in the ceiling as well as upgrading the rest of the house.

    My question has to do with the floor and insulation for that area. There are drawings that show I joists to span the space and they sit about 10 inches above the concrete floor. The plans show paper faced fiberglass insulation with the paper flanges stapled to the flanges on the I Joists. The insulation is set up against the plywood subfloor. There is no mention of anything else but the staples holding the insulation in place, no support under the insulation. Personally I do not like it. It makes me wonder how long before the insulation either pulls away from the paper face of the paper flanges tear and the insulation is laying on the floor.

    I am looking for other solutions or thoughts on how long the staples and insulation will stay in place.

    My first thought was to add 4 inches or maybe even 6 inches of foam board insulation right on the floor, seal it well to contain any moisture and then build the floors.

    Thoughts?

  2. #2
    Join Date
    Jul 2010
    Location
    Northeast Nohio
    Posts
    336

    Default Re: garage conversion to room

    Hi, Mark.

    First question: who/what prepared the drawings?

  3. #3
    Join Date
    Apr 2008
    Location
    SF Bay Area (East Bay)
    Posts
    2,506

    Default Re: garage conversion to room

    As far as keeping the insulation up, http://www.strongtie.com/products/co...isccat#gallery

    But I'd want to be sure about the possibility for condensation before worrying about that (and it sounds like you are too, since you're talking about air sealing rigid foam at the slab.)

    Any call in the drawings to ventilate that space between the slab and the insulated floor?
    “It is difficult to get a man to understand something, when his salary depends on his not understanding it.” - Upton Sinclair

  4. #4
    Join Date
    Sep 2012
    Location
    Greenville, SC
    Posts
    111

    Default Re: garage conversion to room

    I'd seal 6 or 8 mil poly to the floor and up the walls behind the new floor system. Your idea about the rigid insulation is a good one, but an expensive one compared to what's been specified. If you air sealed to perimeter walls and floor you could staple chicken wire to the bottom of the I joists and fill the joist cavities with insulation. I don't think you need paper faced insulation because the poly should seal out any air/moisture and the glue in the subfloor provides a vapor barrier.

  5. #5
    Join Date
    Jun 2004
    Location
    St Louis, Mo for the past 25 years
    Posts
    7,624

    Default Re: garage conversion to room

    architect provided drawings, approved by city plan review guys.

    no call to ventilate it that I can see. Ar you thinking of it needing some sort of vent like a crawl space might have?

    I have thought of those wires to help keep the insulation in place and that might work. But I was wondering how many would fall out just from us bumping the I joists until we got the plywood installed. Room is a little over 22 wide so the joists could have a lot of movement until it gets some plywood installed.

  6. #6
    Join Date
    Jul 2010
    Location
    Northeast Nohio
    Posts
    336

    Default Re: garage conversion to room

    Hi, Mark.

    If the architect gave specifications, it's not up to you to second guess. Obviously architects, in most instances (at least around here) don't know squat ... engineers seem quite competent, on the other hand.

    However, follow the specs ... field changes are only to make something work about which some blithering idiot architect knew nothing.

    Onus is on the holder of the stamp.

  7. #7
    Join Date
    Jun 2004
    Location
    St Louis, Mo for the past 25 years
    Posts
    7,624

    Default Re: garage conversion to room

    I will have to look at the plans again sometime.

    I do not always work with a architect for some of the repairs we do but am using one now. The set I am currently working on for a rebuild of a 2nd floor dormer has an interesting line. In some areas the architect has called out "add a 2x6 sister joist min". So I asked about it since most places he was calling for 2x8's I wanted to know why he spec out a 2x6. He said because that one or two floor joists do not have the load of other places and you could save a few dollars by getting a 2x6.

    To my way of thinking the few dollars saved was not worth it because I would probably end up putting the 2x6 in the wrong location. So I got all 2x8 and installed them.

    So I am thinking if I can do a better way to build it why shouldn't I? I would run it by the architect first but the fiberglass stapled to the joists just does not seem like a good idea to me.

  8. #8
    Join Date
    Jun 2004
    Location
    St Louis, Mo for the past 25 years
    Posts
    7,624

    Default Re: garage conversion to room

    thanks for the replies. I have decided to pass on this job. The homeowner's have some real interesting thoughts on the process and I have decided to pass. Among them are things like, we are going to build the room get it inspected and then we can tear out walls and add a bathroom and other stuff and no one will know the difference.

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