Insulation confusion - What to do in my attic?
Last Post 21 Jan 2018 07:22 PM by Dilettante. 15 Replies.
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dgoldstein78User is Offline
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14 Aug 2013 04:39 PM
I've scoured forums, read tech documents from building scientists, contractors, university professors and DIY sounding boards and I'm really confused about how to handle some insulation projects for my home. The house is located in NJ about a 1/4-mile inland from a major river and 2 miles inland from the bay and ocean. Fortunately, my property didn't flood during Super Storm Sandy, but the flood water did come within 2 blocks. I am in Flood Zone X. The home is a mash-up of full-time living 1950's beach bungalow and a 2-story addition that was completed recently, but done over the course of 10 years by the previous owner. I'll likely post separate topics on the areas in question so as not to mix things up. So, first off, the single-story bungalow side of the house has old hardwood planking for the roof deck topped with modern asphalt shingles (I'm not sure if there is underlayment or water/ice applied - doubtful). The roof is ventilated through soffit vents, gable vents and a ridge vent. I don't currently know the ventilation ratio. The underside of the roof deck is not insulated. The "floor" of the ceiling is a mess of R19 and R25 fiberglass batts. Some missing in spots, some installed with the paper face up towards the roof, all in all, a mess. The attic is accessed through a wood hatch in the ceiling in a hallway. It isn't sealed or insulated. There is no modern air sealing. So, my quandary has been what to do with this mess to make it better for not more money than I may potentially save in reduced utility bills. I currently average about $150-$200/month for electric & $15/month in gas during the summer, and about opposite that in the winter. I use window AC units and have a Munchkin condensing boiler for hot water baseboard heat - this is installed in a spare insulated utility room attached to the house. Anyway... I don't know if I should: 1. trash the bad, dirty fiberglass batts and just replace with new 2. trash the garbage batts, and then blow in enough cellulose to bring me up to an estimate R49-ish 3. trash all of the fiberglass insulation and get closed cell spray foam applied to the attic side of the ceiling 4. trash all of fiberglass insulation and get closed cell spray foam applied to the roof deck 5. do the same as #4, but make the attic unvented 6. Or, some other combination of the above or something I don't know about yet... FYI - this attic doesn't have to serve any storage purpose or need to be accessed after this is done unless we're doing some electrical work - that's a whole other thread ;) Any practical, financially prudent advice would be massively appreciated!
jonrUser is Offline
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14 Aug 2013 04:56 PM

Very easy to do is just blow cellulose over the existing insulation. Build a XPS foam box with soft foam seals to sit over the hatch. Use the money you save over more complicated plans to add a couple of mini-splits.
Dana1User is Offline
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14 Aug 2013 05:37 PM
Before adding any insulation to the attic floor, air-seal the attic floor/upper-floor ceilng plane, and all electrical/plumbing/flue penetrations. If you can get that nice & tight, a cellulose overblow on the existing crappy batts, filling in all the gaps to a combined depth of ~14-15" is pretty cheap, and puts you in the R50 range.

But if you don't have at least 16" between the top of the exterior studwall plates and the roof deck you'll have a thin wedge of insulation along the eaves. Depending on how much you ACTUALLY have there dictates different approaches to that loss-of-performance factor.

Insulatiing at the roof deck does a better job of air sealing, but the most expensive way to go. That said, putting 3-4" of rigid polyiso on the EXTERIOR of the roof deck and filling between the rafters with open cell foam is a much cheaper and FAR GREENER way to go than R20+ of closed cell polyurethane, and would be a more resilient assembly than closed cell foam on the interior. With few exceptions closed cell foam is blown with HFC245fa, with a global warming potential (GWP) in excess of 1000x CO2, whereas polyiso is blown with pentane (~ 7x CO2), and open cell foam is blown with water (very low GWP).

XPS is even worse, blown primarily with HFC134a at ~1400x CO2 GWP. (EPS is the same polymer, but blown with pentane.)

With plank roof decking you can usually get away with open cell foam or dense-packing cellulose against the roof deck in your zone-4 climate, but that can be risky with OSB decking. A pretty-good compromise on cost/benefit/damage would be to air seal the roof deck on the underside with a ~1" flash-foam of closed cell polyurethane, which in addition to air-sealing, is a non-wicking condensing surface and ~1-perm vapor retarder, which protects the roof deck from interior moisture drives, while still allowing it to dry toward the interior. You can then take it all the way up to R50 with wet-sprayed cellulose or 1.8lbs density Spider or Optima if you like. In those stackups do NOT install an interior vapor barrier, but "smart" vapor retarders like Intello Plus or Certainteed MemBrain can be used, though they're not absolutely necessary in your climate. For more info on the flash-foam + fiber approach, see:

http://www.buildingscience.com/documents/reports/rr-1001-moisture-safe-unvented-wood-roof-systems

Skim the whole thing, but in particular look at tables 3 & 4. The climate most similar to yours in those simulations is Boston, which is somewhat WORSE off than NJ, so if the 1" ccSPF + Spider works there (and it does- if you read down the correct column in table 3), it'll surely work in your location.

Assuming the bungalow has 6" rafters, a full rafter fill of flash-foam + 4.5-5" of fiber gives you a center-cavity R of about R25, and if at the time of re-roofing you added 3" of polyiso you'd be above the code-min R38 by quite a bit, but it would substantially outperform R38 between joists/rafters, since the ~R6 thermal bridging at the rafters now has an R18 thermal break over it.

Roofing iso runs about 10 cents/R-foot f.o.b. the distributor's yard, but in my neighborhood reclaimed goods can usually be had for about 2.5-3 cents/R-foot through businesses that get it from demolition or commercial building re-roofing channels. When using reclaimed goods it isn't a whole lot more expensive than cellulose. If you have a lot of square footage and can take a truckload Insulationdepot.com delivers (for a price), but a handful of other vendors local to me in MA advertise primarily on craigslist. Try searching the local craiglslist materials section for "rigid insulation" or "polyiso", or similar terms- I'd be surprised if there weren't similar smaller-time vendors of reclaimed roofing foam in NJ. Seems like the northern NJ craiglist comes up with a few, but mostly from NY & CT:

http://newjersey.craigslist.org/search/maa?query=rigid+insulation&zoomToPosting=&srchType=A&minAsk=&maxAsk=


Eric AndersonUser is Offline
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15 Aug 2013 07:46 PM
Take pictures and post them. Makes giving advice easier.
First off you have to air seal between the attic and the living space. Don’t add insulation unless the airsealing is done first. You can look at the existing fiberglass and look for black streaks indicating air flowing through. The glass acts as a filter. Look for really big leaks, like chimney chases, the access hatch, and holes where the plumbing goes through. Look hard at can lights Be very careful with non IC can lights, use http://www.tenmat-us.com/thermal-product-ff130e.html covers or similar. If you have a chimney chase you can stuff the opening with rockwool insulation and then use aluminum coils stock and high temp calk to seal it. where the fiberglass has the craft paper on the wrong side, just peal it off and leave the glass. While you are at it, make sure that all the vents for the bathrooms, dryers and range hoods are vented to the outside, not into the attic. Preferably they should be short runs and straight in rigid , insulated ducts not flex duct. ( You don’t want to airseal an attic that already has moisture problems). While you are at it take a sheet of paper and hold it up to your bathroom fan at the vents to make sure you have flow. (It would be better to measure it at the outflow. Use the plastic garbage method of finding cfm for that.
http://www.cmhc-schl.gc.ca/en/co/maho/yohoyohe/inaiqu/inaiqu_003.cfm
Once you know that the venting is ok, next up is to add baffles to prevent wind washing of the insulation near the soffits. Using reclaimed sheet insulation to make the baffles is cost effective and helps with the R value near the soffits where there may not be enough room for full insulation
Lastly blow in cellulose on top of the fiberglass insulation. It will push down the existing fiberglass, but so what. It is not a bad idea to use 3-4 long 12” deep I joists and nail them down the center of the attic floor about 2 ft apart. If you space 2x6’s every couple of feet perpendicular to the I joists, across the top and nailed to the I joists, you have a platform to use if you ever need further work in the attic (do this before you blow in the cellulose) 12” or so of cellulose should do you nicely.

Sweat equity plus cellulose is your best bang for the buck.
Cheers,
Eric
Think Energy CT, LLC Comprehensive Home Performance Energy Auditing
dgoldstein78User is Offline
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21 Aug 2013 12:30 PM
See attached photos. The original 1950 roof was left intact and an addition roof was tacked onto it without removing the old shingles or decking. Other than a small cut out in the original roof's decking, they are nearly separate air-spaces. I have intended to widen the opening so I can get through to the other side. You can also see rolled up insulation the previous owner "graciously" left me. I intend to remove all of the plywood boards on the attic floor, and also figure out how to re-organize the wiring (it's all coming from a sub-panel in the 2nd-floor section of the house.

I need to get up there and take some measurements.

You can also see the likely-mold-making master bathroom vent fan exhaust zip-tied to the West facing gable vent - classy =\ I'll be fixing this similarly to the rigid bath exhaust fan vent that I did for our guest bathroom.

Looking West through cutout in original attic section at 2nd-addition attic:

Looking slightly South-West at 2nd-addition attic:

Looking North from original attic side at inside wall of 2nd-floor addition.

Looking towards Southern gable vent in original attic side:
Dana1User is Offline
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21 Aug 2013 02:01 PM
Are those 2x8 joists on the attic floor, with 2x8 rafters? If yes, with the code-required 1.5" clearance between the roof deck and insulation you're not going to get more than ~R30-R35 at the edges, and would require cutting & stacking a rigid polyiso in the wedged-down section. but that would at least come closer to meeting current code. If the joists & rafters are 2x6 you won't get there without exterior insulation.

To hit R49-ish with cellulose you'd need at least 14-16" of initial depth, PLUS the clearance to the roof deck all the way out over the top plates of the exterior walls. With 3-4" of exterior iso above the roof deck and open cell spray foam between the rafters extending all the way down to the top plates, plus insulating & air sealing the gables you'd be in pretty good shape, but that is a lot more expensive, to say the least.
dgoldstein78User is Offline
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21 Aug 2013 08:26 PM
Attic floor joists measure 1 9/16" x 5 3/8" (2" x 6") in original bungalow section.

Roof rafters measure : 1.5 x 5.375 (2 x 6) in original bungalow section.

There are 1" x 2" strips under the attic floor joists.

Rafter bay width: 22.5", 24" Center-to-Center

I'm not sure if the cost of pulling the shingles off to put down polyiso is worth the time, and cost when there is nothing otherwise wrong with the roof. There must be an alternate, but better than nothing solution.
dgoldstein78User is Offline
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22 Aug 2013 01:15 PM
After further code investigation I found that NJ's Rehabilitation Building Code allows for pre-1959 (this structure was apparently built in 1959 as per the deed), to have insulation applied in such a way to fill the cavity voids. Since there is no financially feasible way to reach the modern code R38 value, filling the cavities with insulation material is acceptable.

Removing otherwise good condition shingles is not financially feasible or likely cost effective until when or if the roof requires replacement.

Reference: http://www.nj.gov/dca/divisions/codes/codreg/pdf_regs/njac_5_23_6.pdf
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22 Aug 2013 06:21 PM
Posted By dgoldstein78 on 22 Aug 2013 01:15 PM
After further code investigation I found that NJ's Rehabilitation Building Code allows for pre-1959 (this structure was apparently built in 1959 as per the deed), to have insulation applied in such a way to fill the cavity voids. Since there is no financially feasible way to reach the modern code R38 value, filling the cavities with insulation material is acceptable.

Removing otherwise good condition shingles is not financially feasible or likely cost effective until when or if the roof requires replacement.

Reference: http://www.nj.gov/dca/divisions/codes/codreg/pdf_regs/njac_5_23_6.pdf
 Just because it's legal doesn't mean it's always good idea. 

In many cases it would be an actively BAD idea, adding to the expense when you have to re-roof with punky sections of roof decking.

If you're going to fill it up to where it's contacting the roof deck it's STRONGLY recommended to spray a flash 1" of closed cell foam onto the underside of the roof deck in those areas of contact. (That's about a buck a square foot for bigger jobs, but DIY-doable for about $1.25/ft with the 600 board-foot foam kits like TigerFoam /Fomofoam, et al.) Without the flash-foam the risk of moisture accumulation developing into a mold or rot problem for the roof deck near the eaves at some point before you re-roof is pretty real, particularly on any mostly-shaded or north facing pitches.

Cellulose is still the preferred material, since it will share the moisture load with the roof deck, and without losing effectiveness.

Only when it's time to re-roof is it reasonable point of opportunity for adding insulation above the roof deck. Similarly, there's little point in adding exterior foam to the walls if the siding is in good shape, and the only reasonable chance to add insulation to a basement slab is before it's poured.  In the mean time we just do what we can, in such a way as to not create other problems with the building.
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23 Aug 2013 06:51 PM
> filling the cavities with insulation material is acceptable.

I suspect that if you blow in cellulose and then wait awhile, you will have small gap; enough for drying purposes. If not, press it down and you definitely will.
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23 Aug 2013 07:24 PM
Posted By jonr on 23 Aug 2013 06:51 PM
> filling the cavities with insulation material is acceptable.

I suspect that if you blow in cellulose and then wait awhile, you will have small gap; enough for drying purposes. If not, press it down and you definitely will.
If you blow it at typical 1.5 density the cellulose will take on the majority of the moisture, and the moisture cycling will cause it to settle- maybe an inch, but maybe only a quarter inch which isn't much of a drying cavity for a low pitch roof.  The better solution would be to dense-pack those wedges to 3.5-4lbs density to guarantee it doesn't settle and always be protective, but that's more expensive & awkward to implement than a 1" shot of closed cell on the roof deck in those areas.

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18 Sep 2013 02:33 PM
I finished venting my master bath vent fan through the roof! Yay! No leaks, no more pressurized attic from the fan. In the process, I also applied fiberglass mesh tape and mastic to seal up the cracks, crevices and holes in the vent fan housing, housing to drywall, and also treated my recessed lights to the same - they use CFL bulbs, so low heat. So my attic air sealing is progressing - need to get back up there and finish doing the rest of the electrical boxes, smoke detector electrical boxes and all the wiring and radon pipe routing holes through the wall top plates.

I discussed the blown-in insulation option with my girl and she doesn't want to deal with the mess of cellulose when we have to work in the attic during renos, fixture updating, etc. She's pretty adamant about it.

I found some new-to-me information about another alternative to tackling the actual insulation for the attic. The roof has a very low pitch. I'll measure it soon, but short of filling up the cavity with blown-in, or jamming in compressed fiberglass bats, there is no physical way I'm going to get anywhere near code. I'm just going for the best bang for the buck and still have the attic accessible for future upgrades to fixtures and amenities.

I believe the floor joists on the West side of the attic (pic shows the corrugated bath vent fan flex tube - now gone), are 2 x 6 and have R19 fiberglass bats install. About half of the bats installed on the South West side were installed with the paper facing up (ugh..).

The roof deck is made up of planks, so it "breathes" quite well I think. There are two gable vents, soffit vents at the eaves and a ridge vent. I don't yet know the ventilation ratio.

So I've been hearing a lot about polyiso and how it's great to stick it on top of the roof deck prior to shingling. Well, my roof is years away from needing shingles (will need to be totally stripped at that point since it has 4 layers of shingles on it already). I've read in a couple of places of people cutting the polyiso boards to fit between the attic floor joists and then sealing the perimeter of the board to the joist.

If I were to do this and use either Homasote Ultra/R 2" thick (14.4 R-value) or 3" thick (21.6 R-value) or Dow Tuff-R (1" thick = 6.5 R-value), can even get reclaimed pieces for cheap, and layer these in each floor joist bay, then seal the edges with low-expansion foam, could this be this be the cheaper gateway to achieving an excellent insulation level without having to spend a lot of $$$ on closed cell spray foaming the whole attic floor?

My only concerns with this is how or if I need to mitigate thermal bridging of the joists themselves. Do I need to cover the exposed wood on the attic side with polyiso too, or maybe those can get shot with closed cell foam to keep them warmer than the rest of the attic space.

I realize cutting the rigid foam to fit will be a bit of a PITA, and that for irregularities I might need to fill in with expanding foam and/or fiberglass bats.

thoughts?
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18 Sep 2013 04:17 PM
First, I don't get how dealing with itchy fiberglass is somehow better than cellulose when working up there.

It doesn't matter which side the paper facers are on fiberglass batts, and it's in fact BETTER from a performance point of view to have them facing up.  During reasonable humidity conditions they're fairly vapor tight at about ~0.4 perms, but  when dampened from condensation they go to ~2 perms, so they don't actually trap much moisture.  With foil-faced batts it's a concern, but with paper faced, fuggedaboudit. The paper facer provides something of a top side air-barrier, which is important to have when low-density fiberglass is used.

Roof decks don't "breathe" to the exterior. With #30 felt & asphalt shingles on top it's about 0.1 perms between wood and the great dry outdoors, and even then sometimes the top-side of the 0.1 perm shingle & felt layer is saturated with liquid water.  A movement in the cracks between planks are nowhere near the volumes necessary for purging moisture. Code requires 1.5" of vent space on the underside, but on low-angle roofs 2-3" is better, for vented roof deck assemblies.

The performance of high-R/inch foam like polysio is largely wasted between joists, since the joists already account for a large fraction of the heat transfer.  In a 2x6 joist bay stacked with 5.5" of iso the center-cavity R might be a whopping R33, but at a framing fraction of 15% (it could be higher) you're looking at R21 whole-assembly.  With the same 5.5" filled cellulose or high-density fiberglass you're looking at ~R20 center cavity but a whole-assembly R of about R16.

That's a difference of more than R10 center cavity, but only R5 whole-assembly. To borrow from a Clinton era campaign motto, "It's the thermal bridging stupid!".   Covering just the joist edges with an inch of R6/inch foam and filling up to the top of those 6.5" with fiber insulation would deliver about R22  a whole-assembly R than a full cavity fill of R6/inch and no thermal break on the framing, since you've cut the heat transfer at the framing by half.  But if the reclaimed or scrap stuff is cheap and you have the time, go for it. Be aware that foil facers are extremely vapor-tight, which could create a moisture trap in the attic if you later go unvented with insulation at the roof deck if you do a full cut'n'cobble cavity fill.

If you cut 2" strips of 2" 2.5lb (Type IV)  XPS (R10 Foamular 250 or similar) and compressed unfaced R30 batts in them with a half-inch OSB floor as a topside air barrier it would perform as well or better than R30s in a 2x10 framing with no thermal break. Center cavity it would be about R28 at the compressed 7.5" thickness, but the framing would be about R16.5 instead of R11 in the 2x10 case. With either the whole-assembly R comes in around R25.  Type IV XPS has a higher compressive load than polyiso- enough so that it won't deform permanently on a joist-edge with the weigh of a person being distributed by the OSB deck/air-barrier.

If you're going to insulate on the underside of the roof deck you want it to have at least some vapor permeance or it will create a moisture trap.  Icynene just released it's water blown ProSeal Eco ~R5/inch foam that is about 1 perm @ 2.5", slightly denser but about twice as vapor tight as their MD-R-200 semi-open cell foam. Either would be good at 5" thickness. If you're going deeper than 5" with foam the MD-R-200 would be preferable.
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15 Jan 2018 08:39 PM
time for an update...

A year ago we had the roof redone thanks to the previous owner improperly installing the shingles.

We had the GAF Timberline HD shingles installed over their Deck Armor, Storm Gaurd and Cobra Snow Country ridge vent running the lengths of the ridges. All of our water control and leaking issues have since been resolved.

At the time, I had forgotten about pricing on polyiso for the roof exterior - =\

So, I'm back to reviewing insulation improvements and the first project I'm going to move on are the hatch/pull-down insulation. I'll create a coffin-like box, caulked and gasketed for the pull-downs and a stacked insulation gasketed hatch cover.

Next, I'll review the current options for effectively improving the rest of the attic floor. I had already air sealed, but the fiberglass insulation is a mess. Mostly poorly fit R19.

Due to the shallow rake of the roof, it's extremely difficult to get much insulation at the top-plates.
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20 Jan 2018 04:16 PM
Cutting and stacking rigid polyiso board on the top plates is one way to maximize R in that low-clearance location. There still has to be a 1" minimum ventilation gap between the stacked foam-board and roof deck though, whether there are soffit vents or not. Using reclaimed foam board for the cut'n'cobble is a lot cheaper than box-store pricing, and greener too. Search the local craigslist for rigid + insulation, there's usually somebody out there selling used roofing foam.
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21 Jan 2018 07:22 PM
If you're not going to go with cellulose (all you really need to clean it up is a shop vac) and are NOT going to be using the area for storage AT ALL.

1: pull out most of the plywood.
2: Insulate between the rafters with 6" batts/rolls of the appropriate width. This should get you R19. If you have ventilated soffits, make sure you don't stuff the batts all the way back into the bays and cut off the ventilation. If necessary, get some 2" foamboard and glue it in place as a stop point.
3: Lay plywood back down only in places you need to navigate to up there. Keep the plywood coverage to a bare minimum. I'll refer to this section as the "covered" area.
4: In the uncovered areas, lay down 9" (R30) batts/rolls across the rafter bays. If you require more insulation than R49, move to 12" R38 batts.
5: In the covered areas where you have to walk, lay down 2"-3" of EPS foam board.
6: If you DO want to create some surface space for storage, build 2x10 platforms and lay them across the rafter bays. Fill the space inside with 9" R30. Then top with plywood/OSB.
7: For the entrance itself, it depends on if it opens down into the living area or up into the attic. If down, box the entrance in on 3 sides and use a piece of foam board to close the box. If you have a hatch that opens up into the attic, simply attach a piece of the 9" R30 (cut to size) on top of the hatch door.
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