OK, My Apologies again.

Here is my message, retyped:

Hi All,

I would like some advice with respect to my attic. I live in a house that was built in 1948. The current square footage is about 1750. The house is in the mountains of Colorado, and measured HDD are of the order of 9000. The attic has cellulose blown between the floor joists, and someone has laid fiberglass batt insulation on top. The attic roof rafters are 2x6's. The walls are poorly insulated - I will fix that, but that is another story. There are numerous penatrations into the attic, and I am slowly trying to locate them and seal them. Heat loss through the attic is obviously significant, and there is considerable ice damming. The house is on the north slope of a mountain, and gets little sun. Snow has been on the roof since September.

I'm considering the following:

1. Move all the fiberglass batts out of the way (I hate working with fiberglass), rake away the cellulose, and embark upon a careful caulking and sealing of all penetrations into the attic. Then replace cellulose (maybe add more) and replace batts. This is the labor intensive, low cost option. It leaves a cold attic roof. It probably won't guarantee an airtight attic floor.

2. Pay a contractor to foam a six inch layer of closed cell foam, covering rafters with foam as well. This gives me an airtight attic, and reduces thermal bridging It's the least work for me; I only have to remove cellulose from between floor joists near eaves. It is also expensive - my one estimate is near $9000!

3. Pay a contractor to foam a 1" layer of foam under attic roof and rafters. Rely upon cellulose and batts on ceiling floor to bring R value up to something useful. (I'm worried about this; it seems that the distance from floor to ceiling would allow large convection currents, negating utility of floor insulation.)

4. Pay a contractor to suck up the cellulose and spray an inch of foam over the ceiling. Replace cellulose (and maybe batts, although I think I will have to remove them from the attic to allow spraying.) My one bid for cost to suck up cellulose is about $1250. My roof rake is 6:12, so I estimate the foam would cost about $8050. No savings here.

5. Do as in 3 above, but not rely upon cellulose. Fir out rafters and put up thick fiberglass batts.

6. Or, what would you suggest?

Thanks for the help, and again, apologies for the bad posts.

Regards,

PMH

$9000 is a lot to get a payback on. I'd at least consider just adding another 6" of cellulose. Or using Tyvek instead of foam under the insulation. Or use an IR camera to find where leakage is occurring.

Just don't block your soffit vents with insulation or you'll get ice dams

I don't follow your math in #4. Spray foam is roughly $1/BF here, so 1" on 1750 = $1750(flat ceiling area; the SF is less if you have a two story house). Total of 1250 + 1750 + cost to reinstall cellulose. Doing the job piecemeal (#1) may not be as difficult as you imagine since the penatrations are likely to be in fairly obvious areas - over partitions, exterior walls, recessed lights, bath fans etc.

Posted By Robbie245 on 14 Feb 2010 08:28 AM
Just don't block your soffit vents with insulation or you'll get ice dams

Maybe, maybe not- it all depends on how much heat continues to leak into the attic space.  Soffit venting only mitigates ice damming by keeping the roof deck cooler, slowing (but not eliminating) snow melt from the bottom layer of snow.  The same result can be achieved with a better air sealing & insulation job.  In some instances soffit venting contributes to ice damming by only spot-cooling the roof deck right at the soffit (a symptom of insufficient soffit vent area.

With 6" of 2lb foam under the roof deck and sealed soffits the ice dam hazard drops to near zero in most of the lower 48. 

With perfect air-sealing of the ceiling/attic floor with foam plus R40 of cellulose on top (with at least 4" of thermal break over the joists/trusses) the roof deck temps maintains relatively even and low temperatures. This carries somewhat more ice-dam hazard than insulating the roof deck if not done well, but it's not hard to do when it's still wide-open, bare of insulation. (Easier in new construction than in retrofit.)  It can become a PITA if you have 40 recessed lights and 3 flues to contend with though.

Half pound (open cell) foam under the roof deck sealing the soffits and air-sealing the attic floor (with or without additional fiber) is usually cost effective. Closed cell foam under roof decks makes leaks difficult to detect and locate, and puts a highly vapor-retardent layer on the exterior, which can lead to higher attic relative humidity when combined with fiber insulation on the attic floor, or a moisture trap if vapor retarders are also used. Half-pound foam allows the structure to continue to dry toward the exterior (a more reliable stackup in heating dominated climates.)  But closed cell foam does add significant structure to the roof deck where half-pound stuff does not, and can can make it more hurricane resistant in areas prone to that.

It only takes a few btus of heat flow  to start to turn a 32F snow covering into water. And only a few btu less (removed over the soffits) to turn it back to ice (in the form of dams or icicles).

Ventilation + x inches of insulation will pass far less heat than x inches of insulation alone.

Posted By jonr on 15 Feb 2010 02:29 PM
It only takes a few btus of heat flow  to start to turn a 32F snow covering into water. And only a few btu less (removed over the soffits) to turn it back to ice (in the form of dams or icicles).

Ventilation + x inches of insulation will pass far less heat than x inches of insulation alone.

I'm inferring you mean heat passing through the roof deck, not the insulation (which would be largely unaffected.)

Ventilation rates from soffits isn't well controlled, and the averages will be all over the place.  It can't be counted on for ice dam control.  Even when ridge venting is added the ventilation rates are driven by delta-T between attic & exterior, which will be lower with high-R on the attic floor. When there's a bit of melt-out high on the roof (sealed or ventilated attic) the interior attic temp is driven by direct solar heating of the roof deck, not heat loss from the interior. In shallower snowpack conditions it typically results in sheet-icing, not ice damming, but the deeper the snow, the higher the liklihood of it eventually forming an ice dam.  This type of ice dam is greatly reduced when the roof deck itself (not just the attic floor) is insulated, and it takes a LOT of ventilation to control it anywhere near as well.

In general, if the roof deck isn't insulated, you're safer to run with well-ventilated attic, but it's not an absolute gimme than a sealed attic with an uninsulated roof deck without will form ice dams or that a well-ventilated attic never will- it just depends. 

But a sealed attic with an insulated roof deck is pretty foolproof, fixing a world of ills in terms of heat & air leaks at the attic floor level, and reducing the solar-heated attic melt ice dam potential by a HUGE fraction.  And if you insulate the roof deck DO block the soffits, since otherwise that ventilation is nothing but a thermal bypass of the insulation for no good reason, offering very little (if any) additional ice-dam protection.

More...

and

yet more...

Posted By philipmhowe on 12 Feb 2010 10:11 PM
I'm considering the following:

1. Move all the fiberglass batts out of the way (I hate working with fiberglass), rake away the cellulose, and embark upon a careful caulking and sealing of all penetrations into the attic. Then replace cellulose (maybe add more) and replace batts. This is the labor intensive, low cost option. It leaves a cold attic roof. It probably won't guarantee an airtight attic floor.

6. Or, what would you suggest?

There was a post some time ago where someone was putting polystyrene/beadboad/eps and then using one of the DIY spray foam to seal it.  I think that they were doing this in a wall, but it would probably work under the roof sheathing.  Beadboard is relatively low cost and you use the high cost foam only to seal it into place.  I don't know whether you'd have a problem with it not being absolutely sealed to the sheathing, I can't think why you would, but others may be able to.

You could also use the DIY kit to seal under the cellulose.  Clear out a space, spray on a thin layer of foam, put the insulation back.  Labor intensive, a little more costly than trying to caulk, but should seal pretty well.

Don't know where you are in Colorado, but a couple of places in Denver offer good prices on rigid PU foam.  Tough to transport because it's bulky but you could use that instead of bead board and it should do a good job on the walls if you're planning on residing.

As a DIY, cobble & cut EPS w/spray foam sealants would come in somewhat cheaper, but if you count your labor for anything you do better by letting the pros spray in half-pound foam. The EPS itself is maybe half the installed cost of half-pound foam per unit R-value, then by the time you add the costs of sealants and labor it's a losing proposition. EPS has about 10% more R per unit thickness than half-pound foam though. (5" of EPS is R20, but it takes 5.5" of half-pound foam to get there.)

When re-roofing, 1-2" of EPS or XPS above the roof deck does wonders for ice-dam prevention (sealed attic or ventilated) in all but the snowiest climes. By putting the insulation at the roof deck melt-out from thin spots transfers far less solar heat into the attic, so the attic stays cooler, and doesn't continue the melt by transferring the heat under the un-melted portion via solar warmed attic air. (The air isn't as warm, and there's now insulation between the attic air and the remaining snow.) The melt is then pretty much limited to the interface where the remaining snow meets the exposed solar-heated section of roof.

I have applied polyurethane spray on my home wall and roof.It's result amazing

The Quality of polyurethane foam is following

1 Superior insulation performance

2 Control moisture infiltration

3 Controls air infiltration

4 Ease of application

5 Non-fibrous

6 Structural properties

Posted By jass on 18 Feb 2010 04:24 AM
I have applied polyurethane spray on my home wall and roof.It's result amazing

The Quality of polyurethane foam is following

1 Superior insulation performance

2 Control moisture infiltration

3 Controls air infiltration

4 Ease of application

5 Non-fibrous

6 Structural properties

#1 begs the question: Superior to WHAT?  (low density fg batts? sure.  cellulose? 2lb stuff maybe, half-pound stuff, a dubious assertion at best.  XPS? probably not, unless you put a lot of conditional statements around it.)

#2 is a two-edged sword when using closed cell foam at thicknesses of greater than 2".  It's also an problem for detecting/correcting roof leaks. Use closed cell foam with care & forethought.  Open cell has more forgiveness-factor, and forms a perfect air barrier without being fully waterproof or vapor retardent. Vapor retarders need to be properly placed in the assembly, and can create problems when placed improperly.

#3- clearly correct!

#4 is an odd assertion- While DIY spray foam application can work, it's not foolproof, and for larger jobs it's cheaper to let the pros do it. But it's not particularly easier than other insulations.  It can be harder to FIX when initially screwed up though.

#5 Who cares?  It's performance, that counts not the gritty details like fiber/non-fiber, open/closed cell.

#6 only applies to high-density foam.  Whether it's worth the premium for most for just the extra structure is questionable, but it's real.

I'll give you 2 out of 6 without other qualifiers.

That said, it's still good stuff when properly applied.

I have applied Polyurethane Foam closed-cell insulation materials. It’s materials offer high R values, one can use a thinner foam board to have the required thermal resistance one desires. This can be extremely helpful if there are space limitations involved. This strength involved the ability of the foam to resist deformation and the ability to main its shape when forced or loaded down.It can handles a wide temperature range, which makes it effective as a roof insulation. When combined with laminated aluminum foil facing, it is also an effective moisture and vapor barrier.

 

Posted By jass on 26 Feb 2010 06:00 AM

I have applied Polyurethane Foam closed-cell insulation materials. It’s materials offer high R values, one can use a thinner foam board to have the required thermal resistance one desires. This can be extremely helpful if there are space limitations involved. This strength involved the ability of the foam to resist deformation and the ability to main its shape when forced or loaded down.It can handles a wide temperature range, which makes it effective as a roof insulation. When combined with laminated aluminum foil facing, it is also an effective moisture and vapor barrier.

 

You have to be careful where you place highly vapor retardent materials like foil facers within the assembly.  In heating dominated climates putting foil-faced foam board toward the exterior (cold side in winter) can result in condensation within the wall for weeks on end during the heating season unless it's R-value is high enough that it's interior facer doesn't stay below ~35-40F ( the dew point of interior air at 68F with a relative humidity of 30%) for periods of days or weeks.  With an air & vapor barrier on the exterior the trapped air in the ceiling or wall will have the average humidity of the interior air, and layers within the structure that are below the dew point of the interior air WILL condense that water vapor into liquid water.  If it doesn't cycle regularly to temps where it is once again vapor, moisture will continue to accumulate within the structure, leading to mold & rot issues.

Placing a second vapor retarder on the interior side doesn't fix it, but rather, makes things worse, since the assembly then can't dry toward either the exterior OR interior.

It's more idiot-proof to build the assemblies in heating dominated climates with the more highly vapor retardent materials on the interior (warm side in winter), since that it the larger source of moisture, and the average moisture content of the exterior air will be lower than the interior, thus the assembly can dry toward the exterior. Closed-cell foam become highly vapor retardent in thicknesses of 2" or greater (whereas it takes many times that with open cell foam to form a vapor retarder.)  Aluminum foil is highly vapor retardent even at 0.001" thickness.

The tighter the house is, unless controlled with ventilation or dehumidifiers, the higher the relative humidity will be.  A house doesn't have to be super-tight to hit 30% or more at 68F.  Keeping it below 30% relative humidity may be better for the structural materials of the house if built with exterior vapor retarders, but going much lower than that becomes both a health & comfort issue for humans.  It's better all the way around to just build with the vapor retarders on the "correct" side for your climate, and keep the indoor RH between 30-50%.