Yes, do insulate. At least R-13. Put the vapor barrier side up against the floor.

worthy - We have stone walls that weep when it rains. That is a whole can of worms we will tackle in the spring! Until then, I doubt it is wise to insulate the walls, right?

bus_driver - thanks for the confirmation. And yes, I know of too many people who have the paper facing down...I know that is incorrect.

I did not look at the linked website. No doubt at all that insulating the basement walls is helpful. But if the basement is not to be conditioned to the same temperature level as the floors above, the floor insulation will help. My basement walls are at least R-5 every where and are R-24 at most places-- and my floor immediately above it has R-13 between the joists. The basement has no heating or cooling provisions. Winter lows within the basement are about 53 deg and Summer highs are about 78 deg. Temperature changes in the basement are very slow. Not bad at all. But the floor insulation helps keep the upstairs isolated from the basement temperatures.

We have stone walls that weep when it rains. That is a whole can of worms we will tackle in the spring! Until then, I doubt it is wise to insulate the walls, right?

Handle the leaks first. But you can tackle the rim joist, sills and all above grade areas, where most thermal change occurs.

bus driver confirms the importance of insulating the walls. Once that's done, the basement is essentially part of the conditioned space. The summer/winter differentials are then so minimal there is no problem with vapour drive and no need for a vapor barrier. See Martin Holladay's comments here, for instance.

My basement today is 57 degrees. The floor above it is heated to 70 degrees. I do not consider the basement to be part of the conditioned space. It is an undeniable fact that the heat moves from the warmer to the colder area and the rate of movement is greater when the temperature differential is greater. So my heat loss to the basement would be greater and faster if the basement was 49 degrees rather than 57. But the insulation immediately under the floor does slow the heat loss from the area above to the lower temperature basement below.

When I put insulation in paper side up, how do I secure the insulation to the joists?

A house my daughter is buying has the insulation paper side down in the basement ceiling. Is it working at all?

Yes it is working, my research has determined the issue is about trapping moisture, not the effectiveness of the insulation.

I do not consider the basement to be part of the conditioned space.

Once you insulate and seal the basement from the exterior it is conditioned. That's the point of the insulation and sealing. Most basements would then be warmed in the winter, directly or indirectly, by the heating system in the basement.

A house my daughter is buying has the insulation paper side down in the basement ceiling. Is it working at all?

Probably not doing much at all because of the difficulty of effectively sealing off the basement from the first floor, whether the paper is up or down. That's an important point made in the brief US Department of Energy link above.

I guess that our perception of conditioned space is different. It is indisputable that my basement most of the time has a different temperature from the living space above and for that reason the insulation between the basement and the living space has real value in slowing the loss (Winter) or entry (Summer) of heat from the basement. I do not grasp how the presence or absence of insulation affects the definition of conditioned space. I lived for some years in an uninsulated house heated with wood. No insulation but I considered the living space to be conditioned in the Winter.

I just wanted to comment that I have the same dilemma and also agree with a point made in this thread.

We will be finishing our basement where rim joists are sealed and walls are insulated, BUT the new basement living space is not used daily (in winter it will remain cooler than first and second floors).

SO - it is a conditioned space, however as one poster mentioned, it will NOT be as conditioned as the first or second floor, or used daily as the first or second floor are, and so can easily be a 10+ degree difference.

Thus - does one remove the existing fiberglass batt in basement ceiling for creating a proper building thermal envelope/shell, or leave it in?

I posted a reply in the other thread, but if you are going to finish the space you really should make it usable for most of the time. If you expect it to be such a different temperature than normal, you will not enjoy using it and finishing it will be a waste. I suppose if you were to just use the area as simply storage it is not as big of a deal. Think of the future though.

To note other comments above, i would not use vapor barrier between basement and main floor. Vapor barrier is meant for floor insulation with a vented crawlspace below. VB creates the building envelope. So if you use vapor barrier between floors you make a envelope between floors. However nothing wrong with insulation between floors, noise control is important between floors and something commonly complained about. Certain insulation perform better than others.

Another note about VB, it always goes on the warm side of the building envelope. Cold climates VB is on the inside. Warm humid climates, VB is on the outside.

Can you elaborate why it may not be good to use a VB (rigid foam) between floors? Especially given basement will be infrequently used as have its own heating?

by infrequent, mostly weekends. We will not have anyone living downstairs daily.

I notice you are talking about your rim joist/sill plate area. This is a good place for rigid foam. This is insulating from the outside cold and contributes to the building envelope. Dont forget the area between the sill plate and the basement wall. This is a common leaky spot and should be sealed as well as the rim joist.

No my rim joists will be spray foam and my basement walls and ceiling will be rigid foam

Dont really need rigid foam in the ceiling, wont do much and is just more expense.

I have a master bedroom above a garage that gets freezing (in NH). There is no insulation in the attic, so I plan to add insulation up there. Should I also add insulation in the floor of the master (above the garage)? Thank you!

Absolutely!

And the type that works best is closed cell spray polyurethane foam (ccspf) start at 46 seconds.

As a builder, I've tried the typical fg batts and 6 mil poly and layers of foam board. Even piped in hot air supplies as per HVAC design. All to Code. All to no practical avail. But precautions must be taken.

Similar climate to southern NH here in TO.

Thank you worthy!!

My cellar ceiling is well-insulated, paper side up, leaving exposed fiberglass. House comfort is fine. How can I cover the fiberglass to contain the fibers from going airborne while retaining the benefits of the insulation?

You could put drywall up or put rigid foam under it? The only downside is that it will be very annoying to access any electical or plumbing that may be up there.

There's a tremendous amount of plumbing and electrical. I just want to contain it to prevent it from being disturbed and not cause any vapor locks. Any issue if I just staple screening to the rafters? I could cut that infinitely more easily than putting up drywall. My cellar is dry and I run a dehumidifier constantly for any moisture in the air along with an air purifier. I want to put a pool table down there and don't want the kids exposed to airborne fiberglass as well as to prevent them from poking the cue sticks into the pretty "cotton candy" as they call it.

If you add more than an inch of foam board between the joists it wil act as a vapor barrier so be careful with that. And as a previous poster stated you only want a vapor barrier in the basement ceiling if there is ventilation such as in a crawlspace

I've begun putting up fiberglass screening stapled to the joists. The electrical and plumbing is so complicated anything solid would be impossible to put up other than a hanging ceiling which would end up probably 6' off the floor. I figure the screening should prevent a vapor barrier while keeping the fiberglass from being disturbed and releasing particulates into the air. I keep a dehumidifier going in the cellar all the time that keeps it at 45-50% humidity so there should be little opportunity for the insulation to get damp. I also keep an air purifier going down there and am in the process of sealing the walls and floor with Drylock Masonry Waterproofing. Overkill? Perhaps? I never have water other than occasionally at the bottom of the sump pit.