Newbie questions:

I have a home in SE PA built in 2004. I believe my attic has r30 sprayed in fiberglass (it looks like about 5 inches in height). I don't/won't be usning attic for storage.

I am getting a geothermal system and was told that adding more insulation to my attic is 'low hanging fruit' for energy savings.

1) How much more insulation (r value) would i need (if any) before diminishing returns?

2) Batt, or blown?

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I also am considering laying radiant foil over the insulation on the floor.

3) Anyone have experiences/suggestions on this? Was told it will reflect heat away from 2nd floor ceiling in summer, and reduce heat loss in winter.

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 I'm looking for inexpensive ways to stop heat or cool loss. Any ideas would be much appreciated.

5 inches of fiberglass won't give you an r-30. You can estimate fiberglass R value as roughly 3 per inch. Without knowing details on the rest of your house, just an off the cuff estimate would be R-40 to R-60 depending on wall insulation, so you want between 12 to 18 inches of fiberglass. You could better estimate the point of diminishing returns knowing window U value, wall insulation, and crawlspace/basement/slab insulation. I don't think a radiant barrier would have a return in PA. It will reduce your cooling bills in the summer some, but I can't imagine that is too big of a deal up there.

thanks aadrvarus - do you have any idea of cost per sq foot on 12 inches?

i cant spray foam over sprayed in fiberglass, right?

If you want more in depth answers, I would get the free "HEED 3.0" simulation software and try different things and see the effect on yearly costs.

Blackflag
I would think that before you spent the money for a geothermal system, it would be cost effective to hire an energy rater and do a blower door test and discuss directly with him what the most cost effective things you can do in the house.

Air sealing is often the biggest thing you can do to stop heat loss in a retrofit. Fiberglass does a poor job of preventing air leaks. A day or 2 crawling around in the attic with expanding foam, might be the first step.
 The other thing to consider is that blown insulation is relatively inexpensive. If you blow in cellulose insulation, on top of the fiberglass, there is often little penalty in increasing the depth of insulation significantly. One thing to keep in mind is that you are adding a fair amount of weight. Another thing is to insure that any soffit vents are not closed off with insulation (if you have a vented attic.)

Also, before you blow in additional insulation, check and seal/insulate any ducts that are in the attic, either forced air ducts or vents for the dryer, showers range hood etc. Make doubly sure all vents don’t end in the attic.
 
I don’t have all that much faith in nor experience with radiant barriers so I can’t answer that.

Cheers,
Eric

Foil RB over the top of fiber would be a BAD idea in your climate zone unless it were a perforated air & vapor permeable type. Any vapor retarder on top would be a condensation point all winter long, but vapor permeable air barriers would improve the performance of fiberglass (due to lower convection losses that would otherwise occur when it's really REALLY cold out.) Applied on the attic floor rather than the rafters it will lose a significant fraction of it's radiant barrier quality as dust accumulates, and combines with moisture to corrode the aluminum. On rafters it'll stay clean for decades, and degrade only slowly.

At 5" of depth you're talking at most R20 with even the best-available blown fiberglass. Blowing 5-6" of cellulose on top of that would fix several shortcomings: Cellulose blocks convection better, and doesn't lose R-value at extreme temps the way fiberglass does. Cellulose is opaque to radiated heat, and won't heat up internally at the top layers under a hot roof deck the way fiberglass does- it retains it's R value in both extreme hot & cold. At 6" of depth you're only adding about a 1lb/square foot, but if the ceiling/floor can handle higher loading doubling that wouldn't be out of the question, especially if it allows you to downside the geo system (less well drilling, smaller ground heat exchanger, smaller compressor, etc.)

But radiant barrier isn't cost effective (and may even be slightly cost negative on an annualized basis) in your location at ~R20 insulation levels, since the value of the attic heat in the shoulder seasons reducing the heating load on the building is more valuable than the increased cooling load during the summer. Once you're at R38 (which is about where you would be with a 6" overblow of cellulose) the net-present value of radiant barrier relative to cooling bill saving with even a standard-efficiency air conditioner is less than $0.06 per square foot of attic area, according to Oak Ridge Nat'l Lab tables, and with a higher efficiency geo system it's probably worth less than $0.04/square foot, well UNDER what you would actually pay for it even as a DIY project.

About the only places where radiant barrier is a clearly cost effective are hot sunny climates (the gulf coast, parts of southern CA, the desert SW, etc) with more than 2500 annual cooling-degree-day climates, and even there once you're at R38 or more it's somewhat squishy. (Many homes in these climate zones were built with R19 or less.) Very few places in PA see more than 1000 CDD, most are well under that, and in your heating dominated climate R30 is cost effective even with a highest-efficiency heating system.

In general, when upgrading the efficiency of a building envelope it's more cost effective to start with air-sealing, then insulation, then high-efficiency mechanical systems. Radiant barrier would be well down the list- you are likely get a higher internal rate of return from drainwater heat recovery on the main shower or solar hot water than RB in your neighborhood (and even those may be less than cost effective on a net-present-value basis.) The more money you put into the building envelope to shrink the heating & cooling loads, the smaller you can make the mechanical systems, and with the upfront cost of geo you can spend a LOT on insulation & air sealing. Knocking a ton or three off the peak load can make a difference. When all capital costs are equal, spending it on the envelope is a better investment, since that lowers the operating costs as well. But it takes a fine-tipped pencil to determine exactly where the crossover is.

thanks Dana1,

So if i air seal (in attick?), and do 6" cellulose - that would be the most bang for my buck?

any harm in laying permiable radiant foil over cellulose? ( i already own the foil...)

Posted By buck3647 on 14 Apr 2010 11:58 AM
No you cannot spray over the already blown in insulation that is on the roof truss, if the roof truss are bare spray the open or closed cell foam in between the rafters not only will seal the roof and glue it all together you will elimiate air leaks and reduce your energy consumption by 30%. 
Many people do not understand the R factor and the variables used to obtain insulation values, one aspect is air leaks, eliminate air leaks and your R value almost doubles.
Perhaps you should visit sprayfoam.com to learn about this revolutionary product, soon blown in and rolls of insulation will become obsolete.
My 2 Cents

If this is a vented attic then spraying the underside of the roof would be a huge waste of money. It would provide little benefit as the venting would bypass the spray foam insulation.

I disagree and suggest you go to either sprayfoam.com or contact a local sprayfoam applicator in your area
My 2 cents

When re-insulating I prefer to not to mix products, use cellulose over cellulose, fiberglass over fiberglass, etc. that way you assured of no adverse reactions

Posted By blackflag on 14 Apr 2010 11:45 AM
thanks Dana1,

So if i air seal (in attick?), and do 6" cellulose - that would be the most bang for my buck?

any harm in laying permiable radiant foil over cellulose? ( i already own the foil...)

In $ per unit R terms fiberglass & cellulose are usually cost-competitive with one another (and far cheaper than foam), but R as measured in an ASTM C 518 test under which it's labeled is only 1/2-2/3 of the story (the rest being radiated and convected heat transfer issues.) In a horizontal cold-side-up application (such as an attic in heating dominated climate), cellulose has a performance edge at the same R rating. But it's density becomes a limiting factor when going for very high R on a low-load capacity surface (such as half-inch sheet rock on 24" o.c. framing).  Adding 6" will get you up to something like current code-minimum for your area, but adding a foot is probably cost-effective when looking at what it does to the size & cost of a geo system.

As long as it's the perforated foil, there's no harm in laying RB on top of the fiberglass or cellulose, but it'll be more effective if stapled to the rafters/trusses with a 1"+ air-gap to the roof deck: On the rafters it not only stays cleaner, it's not in contact with the insulation, so the high reflectivity on the exterior side bounces the first 95% of the radiated heat away, and with the interior side being only in contact with air, not the insulating layer, it's low emissivity cuts down on the remainder as well.  In conducted heat transfer terms, having only air on both sides adds a true ~ R3-R5 average due to the dual insulating air-boundary layers.  If you only have enough for the floor, not for 100% coverage on the roof deck, applying it to the south and west facing pitches & gables is where it'll do the most good.  The north & east pitches don't get nearly as hot as the south or west sides, but if there's enough to do a little more, the eastern side is usually a better bet than the north.

Air sealing at the attic/conditioned space boundary is a must, but doing the whole house is cost effective- don't stop there- it's less than half the problem. 

Flue & plumbing stack chases can/should be air sealed at the bottom as well as the top. Foundation sills & band joists are also a big draft source- bigger than all the doors & window leaks combined in "typical" homes.  (This is an appropriate place to spend the bucks on spray foam insulation too.) Atmospheric-drafted fossil-fired hot water heaters suck air 24/365 whether heating water or not (power drafted or sealed combustion units, not so much.)  Dryer, kitchen, & bathroom vents with lousy backdraft prevention, etc are also big offenders,as are fireplace flues with old-school steel flap dampers at the firebox (top sealing dampers generally seal tighter.)  Then there's electrical & plumbing penetrations to the outdoors (or between floors) etc.. it can go on for quite awhile.  The biggest offenders aren't always obvious, but both pressurizing (blowing outdoor air in), and depressurizing (blowing indoor air out) are useful in chasing them down.

It pays to have a pro run a blower door to find & fix all of the leaks, large & small, but it's not rocket science, and as a DIY project you can do a lot with a big window fan and running around with a smoke pencil (or smoky incense sticks, if you can stand the stink) a can o' spray foam and some labels to mark the leaks that aren't treatable with foam.  If you fix all of the easy & obvious stuff, a pro with a calibrated blower door can tell you whether & when it's cost effective to chase the rest.

On multi-story houses there are often hidden air leaks at the band joist between floors that become thermal bypasses- wind tunnels between the joists. These too can be mitigated but it's not often an easy DIY fix.  On older construction balloon framing there can be multiple thermal bypasses from the basement to the attic in un-insulated un-fireblocked stud bays. These can be retro filled with foam (which blocks the draft completely) or cellulose (which blocks it 95-99%.)  If your walls have old-school low density batting, that too can be an air bypass between floors that can be rectified by packing cellulose or slow-rise foam into the cavity.

It all adds up- what's cost effective or appropriate will vary a lot.  But if you have only ~5" of blown fiberglass in the attic, I'm guessing that there is considerably more cost-effective work to be done than a mere R-boost in the attic- attics are just the most dead-obvious & easy assessment to make- not necessarily the most cost effective, even when obviously cost-effective.  Getting the natural ventilation rate down to something  well under 2 air exchanges/hour can be a bigger deal from an energy use point of view.  Under 1 ACH would be awesome, as a retrofit.  Only in the unlikely event that you get it under 0.35ACH do you need to consider mechanical ventilation, but that would usually take fairly extensive work to achieve.

Posted By cmkavala on 14 Apr 2010 02:20 PM
When re-insulating I prefer to not to mix products, use cellulose over cellulose, fiberglass over fiberglass, etc. that way you assured of no adverse reactions

Have you EVER seen adverse reactions between FG & cellulose? (I haven't, but I'm not in the biz.)  Can you point to anything available on the web where it has been an issue?   It's a fairly common practice in my neck of the woods to blow one over the other (in any combination.)

The weight of a heavy cellulose overblow over 5" of fiberglass might cause enough compression to get a 10-20% reduction in the R of the fiberglass layer, but that's about it.   At 6" I'd doubt it's anywhere near that much.  Chemically they're both fairly inert- if fiberglass reacted with cellulose you'd have issues with putting fiberglass in contact with wood.  Glass fiber is impervious to the fire retardents used in cellulose too.

wow thanks for the reply. so much to chew on. im only looking for the low hanging fruit right now as im investing 20K+ in geo.

I do have solar pv panels on the south/west portions of roof - covering about 80% of the roof area there. Is it fair to assume that they will take a lot of the heat that would have made it into the attic?

the reason im stuck on the foil on the floor is beause heat loss in winter is more of an issue where i live. i saw a video: http://www.youtube.com/watch?v=L-FNAP1UFZU that got me stuck on the floor install.

i do have an ERV that sucks in clean air and pushes out stale air - not sure what that does to heat loss?

I also have a dehumidifier in master bath because of moisture - it is vented outside - it sucks the moisture out (basically fan in a box that kicks on by humidity). The master bathroom is the worst room in the enitire house for healting/cooling. It is far from heating/cooling system, it is over the garage, has a high vaulted ceiling and has unfinsihed crawl space on one side. It is easier 1deg.+ colder then rest of house in winter (nad hotter in summer) - cermaic tile floors are super cold. - Any ideas to help here?

Thanks again for all the good advice. I didn't know what I didn't know...

Posted By Dana1 on 14 Apr 2010 02:41 PM

Posted By cmkavala on 14 Apr 2010 02:20 PM
When re-insulating I prefer to not to mix products, use cellulose over cellulose, fiberglass over fiberglass, etc. that way you assured of no adverse reactions

Have you EVER seen adverse reactions between FG & cellulose? (I haven't, but I'm not in the biz.)  Can you point to anything available on the web where it has been an issue?   It's a fairly common practice in my neck of the woods to blow one over the other (in any combination.)

The weight of a heavy cellulose overblow over 5" of fiberglass might cause enough compression to get a 10-20% reduction in the R of the fiberglass layer, but that's about it.   At 6" I'd doubt it's anywhere near that much.  Chemically they're both fairly inert- if fiberglass reacted with cellulose you'd have issues with putting fiberglass in contact with wood.  Glass fiber is impervious to the fire retardents used in cellulose too.

Yes I consider crushing the fiberglass adverse

Posted By cmkavala on 14 Apr 2010 02:54 PM

Posted By Dana1 on 14 Apr 2010 02:41 PM

Posted By cmkavala on 14 Apr 2010 02:20 PM
When re-insulating I prefer to not to mix products, use cellulose over cellulose, fiberglass over fiberglass, etc. that way you assured of no adverse reactions

Have you EVER seen adverse reactions between FG & cellulose? (I haven't, but I'm not in the biz.)  Can you point to anything available on the web where it has been an issue?   It's a fairly common practice in my neck of the woods to blow one over the other (in any combination.)

The weight of a heavy cellulose overblow over 5" of fiberglass might cause enough compression to get a 10-20% reduction in the R of the fiberglass layer, but that's about it.   At 6" I'd doubt it's anywhere near that much.  Chemically they're both fairly inert- if fiberglass reacted with cellulose you'd have issues with putting fiberglass in contact with wood.  Glass fiber is impervious to the fire retardents used in cellulose too.

Yes I consider crushing the fiberglass adverse

Adding 12" (~R40+) to R20 of fiberglass, reduced that fiberglass from R20 to only R16 for a net- R56+ result instead of a potential theoretical max of R60+ it's not so adverse in my accounting.  Adding R40 of fiberglass to it would also "crush" it, just not as much since it's ~ half the density call at R58. The true performance of the result has far more to do with the quality of the installation, how evenly is it installed, etc, that whether the original R20 was reduced by only 10%  instead of 20%- it's still less than 5% of the total.

If the contract specifies the total settled depth of the entire insulation layer, it doesn't much matter if there was induced settling in the original by the weight of the overblow, independent of overblow type, but even a settled performance difference of R55-R60 will be somewhat academic- less than a 10% difference overall for this one heat loss/gain factor, and difficult or impossible to measure in the heating & cooling bills (other factors will dominate.) But getting it up to R50+ is still likely to be cost effective in a 25 year NPV, probably shorter if capital costs are factored in up front. 

At the temperature extremes the cellulose will still outperform the fiberglass, but it's the average that shows up on the heating bill.  If the ceiling is likely to sag under the weight, a better-quality fiberglass blowing wool would be a better choice.  From a comfort point of view, even if that fiberglass is only performing ~R50 at a near-record low -15F, it's still hard to tell the difference between that and R60.  The largest heat load on the structure will not be the attic at that point.

Posted By blackflag on 14 Apr 2010 02:50 PM
wow thanks for the reply. so much to chew on. im only looking for the low hanging fruit right now as im investing 20K+ in geo.

I do have solar pv panels on the south/west portions of roof - covering about 80% of the roof area there. Is it fair to assume that they will take a lot of the heat that would have made it into the attic?

the reason im stuck on the foil on the floor is beause heat loss in winter is more of an issue where i live. i saw a video: http://www.youtube.com/watch?v=L-FNAP1UFZU that got me stuck on the floor install.

i do have an ERV that sucks in clean air and pushes out stale air - not sure what that does to heat loss?

I also have a dehumidifier in master bath because of moisture - it is vented outside - it sucks the moisture out (basically fan in a box that kicks on by humidity). The master bathroom is the worst room in the enitire house for healting/cooling. It is far from heating/cooling system, it is over the garage, has a high vaulted ceiling and has unfinsihed crawl space on one side. It is easier 1deg.+ colder then rest of house in winter (nad hotter in summer) - cermaic tile floors are super cold. - Any ideas to help here?

Thanks again for all the good advice. I didn't know what I didn't know...

Radiant barrier on the cold side of the insulation does squat for retaining heat except in infra-red translucent materials like low density fiberglass. It's higher benefit above low density fiber insulation is as an air-barrier to slow down convective losses.  If you blow IR-opaque stuff like cellulose over it, it's ONLY an air barrier.  But cellulose suffers far less convective losses than fg in the first place, (the other reason why it's my first-choice for an overblow in an open attic), and in testing at Oak Ridge Nat'l Labs even a 3" overblow of cellulose has been demonstrated to "fix" the extreme-temp R-value loss of low density fiberglass attributed to it's considerable convective losses.  Also the thicker you make the fiber layer, the lower the convective forces, since the degrees per inch of depth go down as depths increase- it's the relative buoyancy of adjacent air layers that drives flow.  A cellulose layer won't get ANY benefit from the radiant aspect of the foil, and only ridiculously tiny benefit from it's air-barrier aspect (cellulose is practically it's own air-barrier, from a convection loss within the insulation point of view.  It is NOT an air barrier from a whole house air infiltration point of view at open-blow density in attics, but can come close if "dense packed" in wall cavites.)

Radiant barriers need a large difference in temperature between two element NOT in contact to get decent performance.  Surfaces of similar emissivity and temperature will emit and receive radiated heat in both directions. On an attic floor with R50 of insulation between the attic and conditioned space, the temperature difference between the top layer of insulation and the roof deck isn't going to be much with or without the RB. Condensation on the underside of the RB will eventually ruin it's reflectivity due to corrosion, dust on the top will more slowly reduce the reflectivity on the top side.  It will still have benefit in summer if installed at the roof deck however.  The attic air when it's 90F out might only be 100F, but the roof deck might be 110F+.  In those conditions, the top layer of the insulation quickly warms to something between attic air temp and roof deck temp, whereas with RB in place it'll stay much closer to the air temp. The delta-T in winter is likely be much much smaller, but there may be some measurable difference on the coldest of nights if there's no insulating snow layer above the roof deck. (Can't hurt.)

The ERV retains both moisture and heat as it makes the air exchange- it's a more energy-efficient method of mechanical ventilation than exhaust-only  (like most kitchen & bath fans.)

Putting a vapor retarder on the floor of the crawlspace, and putting XPS or EPS insulation against the exterior walls of the crawlspace, sealing & insulating the sill & band joist will improve the overall thermal performance of the master bath.  If the crawlspace vented to the exterior, that need to be sealed, and a small amount of ventilation air supplied from conditioned space, converting it into a conditioned crawlspace.  The R value of the vaulted ceiling may be an issue, and it may have unintended thermal-bypasses built into it from soffit/ridge venting etc. There may be ways to upgrade it, but the prescription isn't generic- it' have to be sussed out on site by somebody who knows what they're doing.

Adding 12" (~R40+) to R20 of fiberglass, reduced that fiberglass from R20 to only R16 for a net- R56+ result instead of a potential theoretical max of R60+ it's not so adverse in my accounting.  Adding R40 of fiberglass to it would also "crush" it, just not as much since it's ~ half the density call at R58. The true performance of the result has far more to do with the quality of the installation, how evenly is it installed, etc, that whether the original R20 was reduced by only 10%  instead of 20%- it's still

I think your predicted percentages are skewed,  with the human element is involved, installations are less than perfect.
Cellulose is heavier when first installed because it has moisture introduced to it and a mist is applied to keep it in place, so the initial weight is heavier than the dry weight , it is also hygroscopic. It’s able to soak and hold liquid water. Undetected leaks can wet cellulose causing it to sag within framing cavities. Water leaks can compress the blanket of fiber and in extreme cases, can create a void space, degrading its thermal value. Another concern is that chemicals used to protect cellulose from fire make it potentially corrosive in wet environments. Tests conducted by the Oak Ridge National Laboratory show chemical treatments used to treat cellulose can cause metal fasteners, plumbing pipes and electrical wires to corrode if left in contact with wet, treated cellulose insulation for extended periods of time.

The fact that R-value of cellulose is slightly better than fiberglass is perhaps a minor issue. Fiberglass batts and cellulose used in walls earn similar conductive ratings between R-3 and R-4 per inch depending on density. And while the low-density fiberglass insulation used in attics rates lower – there is typically very little space restriction in attics. So you can simply pile fiberglass deeper to achieve the R-value you need.