Building it backwards
This rambling old farmhouse in rural Maine has an attached 3-bay garage that connects to the kitchen. The garage has a two-bedroom, seasonal or guest apartment overhead, so it is a large structure, with 2X4 studs.
As we age we have wanted to find a way to have all of our living needs on the first floor level of this house and have decided the best way to add a master bedroom/bathroom/sitting room suite is to utilize the garage. This will require building a garage onto the side of the existing one, which is an easy and logical way to preserve vehicle storage space without building an entire new structure.
The issue we have is finishing the garage structure for living. Here are the issues:
1. The garage is 2X4 framed with the exterior finished by tongue and groove 1″ profiled boards directly applied to the studs. The first problem will be how to seal the exterior wall cavity for insulation and air/draft sealing.
2. The floor of the garage will need to be raised 8″ in order to mate properly with the existing finished floor height of the adjoining kitchen. The garage floor is concrete, presumed to be merely a poured floor over gravel. The floor/framing assembly will need to be insulated in some manner from thermal bridging and against heat loss. It has been suggested that a first layer of rigid foam be applied prior to framing? comments?
I am thinking now about using mineral wool in the stud cavities, a smart vapor barrier inside of this along with a layer of Insofast. Finally, after sheetrock, a high-perm rated interior paint to finish the wall system. Comments?
The ceiling above will arguably be mineral wool also, although I am wondering if 8″ of fibreglass bats might serve as well given that the second floor apartment will remain in place. Comments?
I have also considered building an additional wall system inside of the 2X4, using 2X3’s which would enable a complete thermal break from the exterior studs. This is quite a lot more work and expense although since we are very much in the theoretical stage of this project, exploring all the options at this point is time well spent. There is only one window in the garage that I do not wish to move, for what that is worth.
Any observations or comments are much appreciated.
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