Simply piling up insulation in the attic isn't of much use if you don't air seal thoroughly, especially in an old house where no thought was given to this in the first place.

Air seal throughout, then insulate.

Instead of worrying about only the attic, spread your efforts throughout. A tremendous amount of cold air will be coming into your basement around the rim joists.

Here is a link that might be useful: Air Sealing & Insulating--US DEERE

Mari,

Yes, the air sealing thing will really help and it is what I would do after adding whatever insulation you can lay between the joists in the attic (before adding a second layer).

It will also help with the cold floors problem, though not elinminate it entirely. In theory, if you totally prevented cold outside air from entering your basment, then the floors would be no colder than 55F (year-round temp of soil below frost line). But, of course, your foundation is exposed above ground and the upper part of the underground portion is in contact with frozen ground. Some people have insulated the portion of the foundation above ground, but many others feel this exposes it to danger of cracking. I'm not sure about this so I haven't undertaken any it, yet. You can improve things under the first floor with air sealing around the perimeter and sills, especially where utilities run up your wall cavities.

The thing about sealing cracks and manaical weatherstripping, inside and out, is that keeping infiltration to a minumum will make it feel much better without the drafts.

Molly~

Sorry for not being clearer, I thought that it kinda went without saying that insulating the rim joist area would automatically be part of insulating under the floor. Ditto for closing whatever air leaks are in the attic before the insulation batts were laid in place. I spent some quality *cough* time down cellar last fall with several cans of that spray foam stuff filling in every hole and crack I could find. But, the floors were still cold enough over the winter that being in the kitchen for more than a brief period was pretty unpleasant on the feet.

We actually have little noticeable draftiness, and I'm such a wuss about it that I'd notice 'em. :-) (Fibromyalgia and drafts do not get along. Cold = pain.) The doors, including the cellar door, are weatherstripped and the windows don't need it - they're new, PO's doing, and although they're ugly as sin you can sit right in front of them comfortably - and PO insulated the exterior walls when he resided the house. We don't quite get why he scanted the attic insulation so much.

So, my original questions remain. In order to insulate below the floor (in addition to the rim joist area), do we just sort of stuff the batting in (without packing it) around whatever utilities happen to be in place, and does it defeat the purpose of double-layering the attic insulation to leave part of the area with only a single layer of insufficient R-value?

how much of the total area would have less insulation? just roughly,jonmari, don't go crawling around measuring!

The areas with less insulation will have less thermal resistance.

if it is over half of the area that will have minimal insulation then is generally is not worth the hassle.
IMO.

I know you foam sealed but did you caulk? most caulking can be done from inside the home. Sealing floor moldings to walls & floor with a clear caulk will reduce air infiltration. Same with ceiling moldings, caulk at top to ceiling and bottom of molding to wall.

Areas around stove vents, recessed lights and bath fans can allow dust, insulation particles and attic temps to enter the home. If you can stop the bulk of the air flow then it will be easier to conditon. and reduce the 'dust'
that enters from the attic.

With adding insulation..fill joist bays to top of 2x.
add an additional layer of unfaced batts (or blown insulation) over the insulation that is in place.
I've added batts across the joists to reduce thermal transfer, but it makes it difficult if not impossible to work safely once this is done because you can't see the joists to safely step.
If you want to have storage areas..fill joist bay with insulation tonail 2x's into joists and fill with insulation then lay your 2'x4' sections of plywood and screw in place. Mark with a perm. marker any wires or pipes and where they are under the plywood. (learned that the hard way!)
always use an unfaced batt over any existing insulation as two vapor barriers can cause condensation between them.

sorry I can't help with the crawlspace/cellar issues
we don't have those here & I'm afraid I would give you wrong advice.

best of luck.

I would insulate under the floor joists in the crawlspace and keep all the piping and wiring on the warm side of the joists. One thing you don't want is freezing pipes.

Hi energy_rater_la, long time no see. :-)

Interior trim is all thoroughly sealed to the walls and floor by about 19 layers of paint *wry chuckle* but when the trim gets stripped we'll be sure to caulk those seams well. (Even if we repaint instead of refinish we'll have to strip it anyway because PO painted right over chipping and peeling paint so it all looks like some horrible skin disease.) Sealing things in the upstairs ceiling would be done when we insulate the attic so we mess around with that d@mn cellulose only once! We're just going to shovel it into big bags, one of our friends says he can use it. I did catch a posting (I searched the forum thoroughly before posting) about those gasket jobbies for exterior-wall electrical outlets and ordered some.

I estimate that if we covered over an 8x8 area (2 sheets of cut-up plywood) a little less than 20% of the floor would have just a single layer of R-30 instead of the double layer. I also figured that if we needed to work up there we (or whoever) could flip back the top layer of insulation and lay plywood pieces down on top of the joists to step/kneel on, then put the insulation back afterward. We've already learned our lesson about trying to walk on the joists, DH has already slipped and put his foot through the plaster ceiling in the upstairs hallway!

I'm not quite sure I understand "fill joist bay with insulation tonail 2x's into joists and fill with insulation then lay your 2'x4' sections of plywood and screw in place". Can you rephrase for my poor addled brain, please? :-)

We have both a cellar under the main house and a crawlspace over a small (~12x12) ca.1960s (?) addition; we'll have to find a skinny person who isn't claustrophobic to get through the tiny access hole from the cellar into the crawlspace to examine everything more closely and fill two holes that I know are in the sill plate (recent electrical work). The crawlspace's subfloor has fiberglass batts, PO did it when he replumbed/rewired; I see some foam when I peer in but I don't know how extensive it is. Neither DH nor I could get in there with a shoehorn and a 5-gallon bucket of vaseline (and I'm wicked claustrophobic anyway). :-) The cellar's subfloor under the main house is the uninsulated part.

Thankfully even in subzero temperatures last winter we did not have any problems with pipes freezing, knowing how much damage that can cause that was one of the things we were twitchy about.

and howdy yourself stranger..good to 'see' you again!

I knew this would be difficult to understand....

I'm not quite sure I understand "fill joist bay with insulation tonail 2x's into joists and fill with insulation then lay your 2'x4' sections of plywood and screw in place". Can you rephrase for my poor addled brain, please? :-)

I'll try to describe it a bit better here

your ceiling joists will allow for x amount of insulation.
ideally they would be taller allowing for full depth of desired insulation.
if you put a 2x on top of joist you can nail it into the existing joist (toenail..nails at an angle catching part of the new 2x and nailing into existing 2x)
this added depth would allow full insulation value.

however when you run the new 2x's in the same direction as the existing ones and toenail them together it is not as strong as running the 2x's across the existing joists.

the added 2x when installed in the same direction as existing joist will be wobbly. the strength will be
in installing the new 2x in opposite direction..across the
existing 2x. Oh and I generally use screws instead of nails.
once this area is built up..then you would install your
plywood.

hopefully this will be a better description??
if not email me & I'll draw & attach a picture of what I am talking about.

Ah, I have your train of thought now. As I said in my initial post, building up the joists with another layer of 2x8s isn't really a manageable option, even though that would definitely be the most logical thing to do. Beyond the real trickiness of getting the lumber up there, 1 1/2 story houses are not known for headroom in the attic - even right in the middle, which is where we'd put the storage platform, losing another 8" (yes, I know a 2x8 is really 7 1/4", I'm counting 3/4" plywood too) in headspace would be a distinct PITA.

when you say story and a half house...
let me ask you this...
when you are in your attic are the walls for the second story acessable?
are the walls well insulated?
can you see between floors?

there may be options that will serve you well
besides just adding insulation.

The "parts of the roof that make the slanty ceilings upstairs" ;-) (which is where the bedrooms are) appear to have the same cellulose blown down into them. It is VERY hard to get into those corners to look! The slanted ceilings are cool but not freezing cold to the touch in the winter, and the snow on that part of the roof melts much more slowly as compared to the topmost area of the roof where it melts so fast it's not funny. Multi-foot-long icicles are extremely picturesque but they are a marker for ice dams, which are very much bad, and we need to squeeze as long a life out of this roof as we can while we save up for a new one! The completely vertical parts of the walls upstairs, the kneewalls, are not accessible from the attic area. There's new blown-in cellulose in the exterior walls of the main house (PO had it done when he stripped and re-sided the house), and the addition has fiberglass batts.

Here, to give you an idea of the proportions, I'll post a picture. Please note that the windows and siding are not my fault. :-) The bedroom ceiling is maybe a foot at the most above the tops of the upper window sashes (not the trim), so about half the roof is over attic and half is "slanty bedroom ceilings". (It's actually quite a small house, under 1300sf total.)

Mari: first, let me start out by saying I'm probably full of it, or have missed something in your posts that renders my entire idea moot. I'm sure if I am full of it someone will come along and tell me why shortly. : )

But if it were my house, what I'd do in the basement and crawl is as follows:

1) Buy a professional-type foam insulation gun that uses the big canisters. Fill every penetration,seam and crack you can find in the floors, walls and foundation.

2. Stuff joist bays underneath w/ unfaced roll or batt fiberglass, leaving a inch or two space at the bottom.

3. Cut foil-faced foam-board insulation so it *just* fits between the joists. Install it, then use aluminum foil tape (like you'd use to seal furnace ducts - NOT duct tape) to stick it to the (cleaned) joist bottoms.

3a. Alternately, you could just nail whole sheets of the foam to the bottom of the joists (dunno if that's feasible in your case) using long plastic-capped roofing nails, then tape the seams.

4. Before you do all THAT, though, use the foil tape to seal all accessible joints in your ductwork.

Some variant of this might be suitable for the attic as well. There, though, I'd use pink or blue foam insulation and go around the edges with the spray-foam gun to seal, shaving off the excess after it cures.

Jason

Jason, you're always "full of it", although what you're full of varies greatly from day to day, and is often pretty good. ;-) Appreciate the suggestions.

No can do on the foamboard, there's too much stuff sticking down below (and attached to) the bottoms of the floor joists. Doing the best we can with working fiberglass batting around the obstructions sounds like it's the best plan for that area. Last fall I foamed the holes and cracks in the cellar that I could find, although when we do the floor insulation I'll go around again with a foam can and a lit incense stick and see if I can find any more.

Ductwork in cellar was taped and wrapped when PO put in new furnace and most of the ductwork (original ducting to two bedrooms remains as replacing it would have necessitated tearing out walls).

Re: "pink or blue foam insulation" for the attic - you mean the sheet kind, right? I found Dow blue foam that's 4" thick and R-20, so if I get you right you say to lay that over the high-density (R-30) fiberglass batts placed in the joist bays instead of another layer of fiberglass? What is the benefit over using the two layers of batts?

I admit I'm rather cowardly about spray foam in anything bigger than the aerosol cans they sell at the hardware store (like "Great Stuff"). I'm not physically up to that challenge and I can just envision the unholy mess DH would make with it. ;-)

Hi johnmari. I only wanted to chime in to say I would insulate the bejeezes out of the attic and forget about storage up there. Is whatever you have planned to store up there worth the lost energy savings over several years? As for the first floor floor being cold, we had the same problem in our last house. When we actually sealed the biggest air leaks in the basement, the floor felt much more comfortable. I was pleasantly surprised, and we didn't need to insulate under the floor after all.

HTH.

Hey again...sorry I took so long to get back to ye here...

Re: "pink or blue foam insulation" for the attic - you mean the sheet kind, right?

Right, that stuff.

I found Dow blue foam that's 4" thick and R-20, so if I get you right you say to lay that over the high-density (R-30) fiberglass batts placed in the joist bays instead of another layer of fiberglass? What is the benefit over using the two layers of batts?

Two things:
1. Air infiltration gets cut way down.

Thinking about this more, though, it might actually create problems, given that the foamboard is basically waterproof. You'd basically be creating a vapor barrier over that part of the attic. Mainly you have to make sure that with all this filling and sealing, you're still getting enough air exchange into your house. Worst case is that you'd have to install an energy-recovery ventilator (ERV) to make sure any natural gas applicances don't backdraft and suffocate you w/ carbon monoxide. The infiltration issue also is a concern w/ moisture loads in the winter. Again, proper ventilation and humidity regulation would address that. (If NH is anything like Nebraska, you're crunchy dry all winter anyway, so some extra humidity inside is actually a good thing.)

(Wow, that was long!)

2) From what I've read and been told, the insulative ability of fiberglass insulation drops with the air temperature. Cellulose and foam don't apparently have that problem. Plus, foam has a better R-value per inch (witness the R-5 per inch of the 4" foam - even high-density fiberglass has at most, what, R-3.5?)

In fact, if it were ME, and I had addressed the moisture issues, I'd go solely with foam. If you were really nuts, you could even buy a DIY spray-foam kit and foam the joist bays in. Tigerfoam and Fomo Foam are a couple products that I've heard good thing about. Googling for those should get some info.

Something else to think about - it might pay to look into some alternate source of heating fuel, be it natural gas, electric, what have you. What's a typical winter heating bill in that area if you're using oil?

Jason

I have a question. I have ice damns. Part of the problem I think is in this area i have an interior chimney for my furnace. My city codes is that there must be a two inch structural clearance around the mason chimney, which there is......however......there is also heat loss due to the clearance. I called the fire department to see if insulating (with something non-combustible??? was advisable....he said no and that there was nothing that would be considered non-combustible.....anybody have any comments or help please............the ice damns are more than a pain in the you know what.

what you want to do here is actually "air seal" the chimney chase not insulate it. here is a good link showing how to do it with metal sheeting. I did my brick chimney chase myself but with fsk board and fire rated foam/caulk.

Here is a link that might be useful: sealing a chimney chase