You can go either way. The air supply should be with a device designed for the task and interlocked with the furnace so if there is no air supply, the furnace will not start. I would do both if it is possible. Give the furnace its own space sealed off from the living space. Install an interlocked air supply. http://www.hoyme.com/

There is so much differing information out there in regards to insulation, attic spaces, and knee walls- I am just looking for the best solution for my specific case. I'll try to be as clear as possible. This is a long post so I apologize in advance!! We have a "4th bedroom" located over the living and dining room areas in a split level. This room has 2 air vents- one that blows in conditioned air (heat/cold) and one that returns in, so there is air circulation in the room. BUT it is always colder/hotter seasonally in this room that the rest of the house. FYI this room is on the second floor; furnace is directly below the living room in basement on this side of house.. It also, however, has a knee wall door, and a closet that has two additional openings- a door to the main attic, and another knee wall door to the side portions of this room. These all have to be addressed separately since they must be insulated better- they are just plywood slabs- the two in the closet just latching into place with hook and eyelets. The one inside the room is also plywood, but with a doorknob. Here is a diagram of the current insulation situation- I'll add actual photos later to further illustrate. The roofline for this portion of the house has a ridge vent running along the length of it and there is a louvered vent at the upper portion. The kneewalls have no insulation. The roofline does- it is older, so I"m not sure of its value and was probably installed when the house was built- 1959. Some of it is falling down. There are no soffit vents in the eaves. no baffles either- insulation is placed between the roof timbers and stapled- there is nothing behind it, just the timber The living/dining room areas have the ceiling insulated with newer r30 i believe until the start of the knee walls from what i can see, kraft side towards living room ceiling. A couple of can lights (IC rated). Is this creating an envelope problem? These side walls (attic space) even with the insulation in the rafters are pretty cold in winter and pretty hot in summer, so perhaps this was done to keep the lower space better conditioned? But now i'm not sure how this affects this 4th room. It's kind of a wonky situation. Part of this kneewall space has plywood flooring- only about 1/3 does not, hence I can see the insulation type and can lights where I can see them. What is the best solution here to improve the conditioning of this space (separate from the knee wall door issues, those I will tackle as well)?? Remove the insulation from the rafters and insulate knee walls? Re-insulate the rafters with better insulation? Just thinking how I would ever get the insulation in the rafters correctly in that small triangular area. Fix/replace pieces that have fallen down (a few pieces show water damage from a previous, old roof leak issue (before we bought the house))? Where i can fix/replace portions, but can't get to the pieces in the sloped area (about 5ft length) - can i tape the seam of the new insulation to the old??? I should also mention that these triangular storage spaces for lack of a better word, do have openings directly into the main attic area ( main attic access is from the closet in this room, does not have rafters insulated, just floor, no soffit vents again, just a vent at each gable- one has a fan that works in the summer to expel heat). I am assuming, I should cut off this access (it doesn't serve any purpose)- there are framing 2x4s there, and insulate the triangle storage side as well + drywalll?? I'll add pictures once I'm home to better explain. I just don't know how to address this, since generally i see the two options of insulating around the kneewall room and not the rafters, or just the rafters and not the kneewall room - which is similar to what is here- but the floor insulation is throwing me off. I want to make this room more comfortable, but i don't want to cause additional issues in terms of moisture. For now, here is the diagram of the main room, plus a diagram showing the main attic problem area. Here are some actual photos- as you can see in the first one- this is one of the walls that opens up into the attic space- this actually backs up into half the bathroom wall- this should probably be insulated too right? the duct you see is our range hood fan. In the upper left hand corner you can see that empty space is open into the attic. this entire area should probably be closed off from the attic and insulated as well right? In these next pics you can see the rest of the space- insulation on floor under the plywood, insulation in rafters- although these are stapled in, instead of on the face of the rafters, and the very back exterior wall is also insulated. This insulation continues up to the top of the room. Obviously some is in quite bad shape, but we're not opening up the ceiling of the room, so insulating with new becomes tricky- can i install new insulation and tape the seams to the old where I can't reach into that angled area to pull out? Not sure how to approach? And then drywall over it for an air barrier?? There are no soffit vents as i mentioned, but I'm thinking if I do pull out the insulation I can reach (to where the angled ceiling starts, and maybe stuff some baffles up there?) Not sure what to do.

A lot will depend on your ultimate goals for the space. If you want legal habitable space, you need to run all of the required infrastructure first. Like wiring. Or plumbing. Insulation is no where near the first step. By the time you are done with running the necessaries, you should know what a vented vs invented attic assembly is. And the pros and cons of each. You are way jumping the gun. Or just hire a contractor to do all of the necessary steps to convert the storage space to habitable space. Like shoring up the joists. And framing it out properly for the type of assembly that you choose. You don’t just throw some fiberglass at it and hope for the best. You can rot out your house if done improperly.

Central Texas - sometimes humid, sometimes dry but always hot in Summers and occasional blast of sustained freezing in Winter I'm really not sure I like the idea of foam in the roof over the un-conditioned garage space. At least not if it effectively 'seals' the attic space over the un-conditioned garage space. Perhaps ensure the foam doesn't close off soffits or ridge vents...? We will have a tankless gas hot water heater off the garage in a closet. We're going with foam insulation in the roof over the living space (with a partition between it and the garage). I think the venting for the hot water heater could easily protrude thru the garage roof and I'd be able to 'see' it. E.g. leaks. I worry about protrusions in roofs with foam insulation because you might not see leaks - at least not for a long time after damage builds up... The roof will be standing seam metal roof. Can they put a cap or whatever it's called for metal roof over the garage portion that allows venting but doesn't look much different from rest of house roof that would not have ridge vent? Blown in loose insulation isn't my favorite either. I just don't like the stuff whenever I get up in current attic... And I do plan on putting 4 or so sheets of plywood up over the garage attic with a pull down ladder for storage of 'stuff' like seasonal decorations, boxes, etc. Some sheets of decking would only allow the blown in up to the rafters and compress it a little. Not ideal. WINTER/COLD: I'm not opposed to insulating the garage as I think it can help take the edge off in the winter months. The water heater and water softener will be in a closet and I think should be OK. But there will be a wash basin against back wall by entry door that could be exposed to freezing. I moved the hose bib from the garage wall - no hose bibs on un-insulated exterior walls. SUMMER/HOT: For this use case - I'm having a hard time seeing much value to insulating an un-conditioned attached garage. To me it seems to mostly 'time shift' hitting 115 or so in the garage - that is it peaks at a high temp a little later in the day and retains that heat a little longer into the evening is all... I do like the concept of a vent in a garage exterior wall that would allow outside air in, and a vent in the garage ceiling to allow hot air to escape up into the attic and out the ridge vents... And soffit vents just at the garage exterior walls, not the living space walls. Still undecided and ambivalent about how to approach insulating the un-conditioned garage - or even whether to do it at all. :)