Improve efficiency and comfort of this room?
Please see the 2 attached pictures of a room that I would like to improve the efficiency of. The room is between the garage and the main house. I don’t like coming in from the January cold only to be greeted by a cold room. I dislike paying the oil man even more that.
The house was built in 1986 and I am in zone 5 (seacoast NH). Right now, the 2 half walls are gone, the wood frame half of the floor is stripped down to the joists and has 3.5 inches of cut n’ cobble polyiso between the joists. I tried to create an air barrier below the polyiso using plywood, caulk, and tape between each joist. I also spray foamed around the semi-loose fit polyiso at each layer. This part of the floor is located over the ground and has only about 6 inches of clearance. There is a poly vapor barrier in place to limit vapor migration into the construction above. The original floor framing used ground contact rated pressure treated lumber that appears to still be in great shape.
The tile half of the floor sits about 5.25 inches above the wooden step down floor. The tile sits directly on an uninsulated slab. The main house has a full basement. I think half of this room shares the garage slab.
The wooden construction half was added later. At the end of this project, besides improved efficiency, I would like to have one level floor. Not too particular about the kind of finished flooring (whatever will work), more particular about not wanting a cold slab floor or the step down.
The walls are 2×4 with R13 batts. I already brought the cathedral ceiling up to code minimum. The room is currently on its own zone (oil heat). You can see 2 of the base boards in the picture. There is also a sort of kick space register out of view that is heated off the same zone. Now that you have the lay of the land, here are my main questions:
1) The uninsulated slab floor seems to be the biggest hurdle. The window for insuating underneath the slab has long since closed. Perhaps I could insulate around the perimeter by digging, but there are obstacles such as the existing paved driveway and a deck that sits too close to the ground to work underneath it. Putting insulation and sub-flooring on top is probably doable, but I have 2 doors to contend with then. The single door leading to the garage, which is in one of the pics, and a double french door leading to the front deck, which is not pictured. It seems both doors would have to raised to accomplish much as there is at most 2 inches to work with and probably less. There is also the possibility of radiant heating the floor, but I don’t know anything about the options, cost, or effectiveness for my situation. Do you agree that it will be hard to make the room comfortable as long as this uninsulated slab takes up half the floor? What would be a reasonable approach to the problem?
2) The wood framed half of the floor has at least 5.25 inches of vertical space remaining in which to add additional insulation (to get to the level of the slab). It could be more depending on where the height of slab floor ends up (question #1). What would be a reasonable approach to building up this floor while also adding additional R-value? Build another floor frame on top and perpendicular to the original? Or, forget the joists and just lay down more foam board with a sub-floor on top of the foam and timber screws through to the original joists? Something else? Also, would any of this require pressure treated lumber? Worried about the earthen crawl space underneath as well as any new wood construction that would contact (or come close to) the slab. The old plywood sub-floor is gone now, but my recollection is that it might have been pressure treated.
3) What is a reasonable way to increase the R in the 2×4 walls? I’d really like to do this from the inside even though I have read enough on this site to know that applying foam sheets on the outside is ‘better’. I was thinking of perhaps a Mooney wall approach in order to get a thicker wall, but I will not pay a contract outfit to dense pack the cellulose, so i would probably use Roxul for center cavity R, I would first seal all the bays with acoustic sealant, tape, or caulk, then add a sheet of some sort of rigid foam over the whole thing before the drywall to serve as a thermal break. However, I would certainly like to hear of a better plan, even one that calls for exterior rigid foam, assuming that you can convince me that this is a retrofit that is just as easy to accomplish for a DIYer. I would have to remove the cedar lap siding (can this be done without ruining all of it? — doubtful), and my windows and doors would no longer be in the correct spot according to the new wall thickness, right? Wouldn’t they have to be physically moved ‘outwards’ to sit flush with the new wall that might now be located 3 or 4 more inches to the exterior ?
4) What is a reasonable way to create one level floor given that the floor is built with half slab and half wood frame construction? Preferably one that doesn’t call for the cement truck.
Thank you for you input and thank you for this site. It is great.
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