I've been following this thread since the beggining and there is some great information. Thanks for helping me work towards our decision. I talked to a family friend that is a homebuilder yesterday and he said that since Calgary has temp. fluxuations of about 60 degrees C that the 2lb CC foam isn't a good choice. He said when it gets cold it contracts away from the trusses and leaves air gaps. He suggested maybe 1/2lb is a better choice as it can "stretch" a little more. Any input on this?? Thanks, Sean

I haven't heard of 2lb foam contracting & separating being an issue (not saying it isn't but...), still half-pound foam is clearly more flexible.

2lb foam is a lot more rigid, but it's also a tremendous GLUE, adding a lot of structure to a roof or wall. It should stick extremely well to most surfaces if properly applied. It's used quite often in arctic climates for his high vapor retardency and high R-value/inch. I'm not quite sure how the temperature swings & interior/exterior delta-Ts in Calgary are worse for 2lb foam than conditions in Yukon or AK (?). I'm not sure a blanket statement really applies- I'd want more detail about when/how the problem really occurs.

Thanks for the reply.

 

I've been researching quite a bit and I want to go with the 2lb unvented cathedral ceilings. I'm not convinced by opinions but I had wondered if I had overlooked something. I think I will continue as planned with the 2lb.

 

Thanks again,

Sean

This post has been haunting me for awhile.  Particularly this part "if the blowing equipment temps & chemistry is set up for getting the .7 lb density......"   My question is, can the air/foam balance be manipulated upon applicaton?  How do I know if I'm really getting the R value stated or just a bunch of air bubbles?   Can the technician inject more air and less foam to "stretch" the material to cut his costs?

I'm getting wildly divergent price bids and I'm wondering why the difference.

The manufacturers specify the conditions under which the "standard" material is to be installed. The blowing agent isn't air- they can't "fluff" to the same extent that unscrupulous open-blow cellulose installers can, and the penalty for diverging too much from the standard recipe is a sagging mess of an install- it'll plain LOOK bad, amongst other things. The chemistry and installation temps pretty much determine how much (and how fast) the dough rises. The foam comes in 2 parts, with both chemicals pumped & temperature-controlled separately to the spray gun. If the flow & temps of either are off by a whole lot it makes a mess.

There's a number of reasons why quotes will diverge significantly. Some installers don't want to be bothered with smaller projects if they have a number of larger multi-day commercial work already lined up. Others may be running short on work and need to keep making payments on their equipment. Building boom/bust cycles and local market conditions mean a lot to smaller operators.

There is ALWAYS a bunch of drips/drabs overblow, etc. I suppose if you want to know the absolute density, collect a few blobs, weigh them first, then measure their volume. If your half-pound foam ended up less than 0.4lbs/ft^3 in multple samples I'd say it's not up to snuff. If the material (Demilec) was supposed to be 0.7lbs/ft^3 to meet the and the samples measure only 0.5lbs/ft^3, then you have to derate it to generic half-pound foam status (and demand a pro-rata refund.) But that level of error is probably rare. While foam installers may be prone to exaggerating the virtues of the material, I haven't heard of any cases where they had their thumb on the scale while installing it. The more common issues have to do with crummy installation, not lower density (intentional or otherwise). Less-experienced installers have been known to do a thoroughly messy and inadequate job. DO take a look at their work before signing the deal, and be critical of details of how it looks in hard-to access corners, and any actual gaps/voids that might be apparent. It should look fairly uniform in depth, with no obvious voids/thin-spots where it didn't meet the contracted-for thickeness (but thicker spots are OK). Generally if it looks good, it IS good (or at least as good as the manufacturers' specs), and conversely. I'm not sure it's possible to go very far outside the manufacturers parameters and still get a decent LOOKING results, but there must be some range.

thanks that puts my mind at ease. I really appreciate your reply

Alright, just when I thought I had it figured out, I spent an extra hour going through this forum. Here's my dilemma and maybe someone smarter than I can help me glean the proper advice.

Rancher 1200 sq ft footprint just outside of DC (very close to the Potomac and a feeder creek, so lots of morning dew and frost - extremely high humidity). The existing insulation in the attic is a mix of rock wool, loose fiberglass and cellulose, random tar paper, and random depths (from R-9 to R-18 approx). First thing I did in the house was add soffit vents and a powered attic fan (which I now have read the powered attic fan is not a good idea as it reduces pressure in the attic pulling conditioned air out of the house). Then I was planning to blow in more cellulose and be done with it. However, a neighbor recommended a radiant barrier like he had done 2 years ago (and swears it not only controls temperatures in both their upper level and basement, but also cut down on dust in the house). Then another brand new house in the neighborhood (billed as "net zero energy") put in spray foam and I got an estimate for that too.

I know we are climate zone 4 but we have higher than average humidity, and the inside of our house is frequently humid (the a/c is oversized but is 20+ years old so will be replaced with a two-stage and will do a proper Manual J), plus we had a water infiltration issue through improperly-installed windows (high mold levels and the framing under the windows was completely rotted away), so we are a little nervous about excessive humidity levels.

Cellulose sounds like the safe bet, and it is the cheapest. Sounds like I should unplug the attic fan too if I did that.

Radiant barrier on top of the existing insulation might help with air infiltration (we have fairly new IC air-tight recessed fixtures but there are plenty of obvious gaps) but worried about condensation collecting on the underside in the wintertime.

Removing the existing random insulation and tar paper and spray foam the underside of the roof deck (cathedral) conceptually sounds great, plus gain storage space, but there are no mechanicals or ducts in the attic (all ducts are between the main level and the basement) and the thought of having to add an HRV/ERV on top of the cost to do all this work seems to be getting a little ridiculous. Plus, if we had to mechanically dehumidify the attic in the wintertime, that is yet another excessive electric cost. And it seems like the spray foam should be painted with a water vapor barrier because of our high levels of humidity down here.

Am I driving myself crazy with the options, or is there an obvious choice that I just can't see?

Thanks in advance for any advice.

Best,

Steven

Actually, if you're bumping up your R-value much (with cellulose or other) the absolute value of the radiant barrier drops precipitously. See my comments on this thread:

http://www.greenbuildingtalk.com/Forums/tabid/53/forumid/14/postid/59267/view/topic/tpage/2/Default.aspx

(Assuming you can get RB prices down to $.010-$0.15, at R9- R18 it's better than break-even in a 25 year present-value financial analysis for Washington D.C., but not if it's over R22 or so. See: http://www.ornl.gov/sci/roofs+walls/radiant/rb_tables.html#table4 )

It sounds as if your neighbor had a HUGE air infiltration problem that was much reduced by the air-barrier aspects of his radiant barrier. If you think you're in the same situation (could very-well be), a housewrap-type air-barrier (Tyvek, et al) would usually be cheaper, and easier to seal/install, since it comes in 9'-10' wide rolls rather than 4' wide rolls. But if prices are comparable, you will still get some small benefit out of RB.

Dehumidifying a sealed attic in winter is not a huge load- a tiny fraction of a summertime air conditioning load, and certainly not "excessive electricity cost" given the extremely low duty cycle. But if you're staying with a vented attic and air-sealing the attic floor, the point is moot.

A reminder to everyone. Keep your internet security programs active and up to date. There was a message posted to this thread by cocosan which was forwarded to my email before being deleted from this board. It contained embedded links to porn sites which were quite obvious when I opened the message with Eudora, the email program I use. I don't know what would have happened, if anything, if I was using Outlook. I'm sure, based on the content of the message, the message was legitimate. Undoubtedly cocosan's computer has been hijacked by some trojan.

Here's ccosan's message with the porn links removed.

At 06/19/2009 3:48 AM a message was posted to a thread you were tracking.
RE: spray foam insulation for underside of roof by cocosan
Some local codes require air-vent chutes (like those commonly used with fiberglass) between the underside of the decking and low density foam in retrofits to give the decking some inward drying capacity. (Seems easier to just go with the 2lb foam and forget about it.) In my case (climate zone 5) I didn't do that, and with 6" of half-pound foam under the deck, higher than prescribed water vapor (not air) permeability. I COULD just go ahead and apply an interior vapor retarder or paint it with something with a vapor-permeability of 1.0 or less, but since I'll be re-roofing in only a few years, I'll add the prescribed R20+ to the outside of the roof decking just to be safe. (I was planning to do that anyway, to bring the total R-value of the assembly up to something more like code for new-construction in these parts.)

...which was clipped verbatim from the last paragraph of my post on page 1 of this thread back on 20 March:

http://www.greenbuildingtalk.com/Forums/tabid/53/view/topic/postid/55637/forumid/14/Default.aspx

(Cheap hack, ccosan-bot, or whatever...)

We recently had Icynene applied to our exsisting house on the roof rafters of the attic. We can notice the difference in the temperature of the attic now to when there was blown in and batt insulation (we removed the blown in cellulose and batt insulation per the installation companies requirements- we were allowed to keep the batt insulation over the cathedral ceiling). When will we notice a difference in how long our AC works (we live in Florida)? Will we begin to see a difference in our AC usage?

I would think you should notice it fairly quickly.  I guess the only real way to be sure of your savings would be compare this time last year but do compare the degree days also because they can vary from year to year.  Be sure to compare the Kilowatt hours consumed and not the money since rates can also vary.

I have not used Icynene so I would be very interested how much it reduced the usage.

Did you add much more insulation R value than you removed?

Icynene performance is pretty much the same as any other half-pound foam.  I used it beween the rafters behind my kneewalls in my attic space as both air-seal + insulation, since properly air sealing the floor & kneewalls would have been endless/impossible and the insulation levels in my 1923 bungalow leave something to be desired... (It's getting better as I go along.)

I live in a ~300CDD/7000HDD climate, so I can't say I noticed the difference in the AC bill (AC bill what AC bill? :-)  For me it's really "in the noise" of other electrical use.)  But the effect on the natural-gas therms/HDD on the heat bill was around 15%- far more than could possibly have been attributable to the R-value alone over so few square feet.  I did NOT remove the various blown & batt insulation (I'm not sure how/why foam installers get away with insisting that other insulation be removed in areas where it isn't interfering with the installation of their product.  I've yet to see any science or regulation behind that one- can anybody 'splain me that?)  It also dramatically reduced (as in "eliminated") the amount of winter ice damming on areas where it was installed, despite the fact that there was now no attic ventilation. 

My best-guess explanation for the performance gain is the reduced infiltration and blocked thermal bypassing between kneewall areas via floor joists.  Even though there was fiberglass batting friction-fit blocking the joist bays on one side, and full-depth blown rock wool on blocking the other end of the bays, that isn't anything like a real air-barrier. By closing off the soffits, wind induced air currents were no longer moving laterally in through one kneewall space and out through another, and air leakage from the floor below wasn't getting sucked out as quickly via stack-effect all winter.

When I gut the built out space in the attic I'll be foaming that section of roof deck too, and blocking the ridge vent.  Some amount of air is still getting sucked toward the ridge vent, causing minor condensation in the blown rock wool in the attic room cathedral ceilngs in winter. (I expect I'll have some structural repairs to contend with too, but maybe I'll get lucky.)  With only 6" rafters that's not sufficient insulation for my climate.  When I re-do the roof in a few years I'll be adding 3-5" of iso over the top of the existing roof deck.  I'm evaluating both Hunter & Atlas nailer-decked iso-board roofing systems, vented & unvented- not yet sure which way I'll go.  (Did I mention the insulation levels on this place leave something to be desired? :-) )

In a cooling dominated climate I suspect the performance is still pretty good, but not as good as if it had been in addition too, not instead of, the batt & blown insulation the foam contractor demanded they remove.  With insulation, more is usually better.  But air sealing the attic space blocking major infiltration paths is usually a good thing. (It's even better in places with AC/heating ducts in the attic.)

There are to many dangers when it comes to foam, you'll never find another leak if there is one, and you'll never see mold mildew when it starts.
To just keep your attic cool you may want to consider a radiant barrier, that you can apply your self for 10 cents a sq ft, or have some one else apply this for 50 cents a sq ft.
Take a look at www.re-flectrc.com.

Hope this whas usefull.

Paul bogaars

Thank you to everyone who has posted on here, you provided some great knowledge for everyone. My question is regarding a retrofit situation I plan to tackle where I live in the Phoenix, AZ area. This is, of course, a predominantly cooling-oriented environment with over 3,800 cooling degree days per year and under 1,300 heating degree days per year. We rarely see any sustained humidity over 30% even in the winter, usually around 5 to 15%. The existing home is wood framed with a vented attic. The air handler and the old R-6 duct work are located in the attic and there is blown in cellulose on top of the ceiling. Needless to say, on a hot summer day the attic temperatures are very extreme and I can feel the heat through the ceiling sometimes.

So, from what I understand from reading everything in this post is that I could spray in EPS without a vapor barrier on the underside of the roof deck. The Oak Ridge model says I should have about a total of R-41 for the attic space. I’m assuming that the existing cellulose is about R-11, so I would need R-30 of EPS, or about 7.5 inches. If I seal the soffit vents and the two side vents to the attic, I shouldn’t have an issue with excessive moisture, right? Thanks for the help,

Brad

Hi,

I'm totally new to this list and wish I knew about it earlier.  We are in the middle of building an energy efficient home in Pennsylvania.  We used SIPs for the walls and some of the roof but it turned out to be easier to build and save some money to use a traditional roof over a portion of the house.  In that part, we applied spray-foam insulation to the underside of the roof and it won't be vented.  If anyone's interested, they can check out our project at http://carlislegreenbuild.blogspot.com.  We've designed in passive solar and will be using a geothermal system for heating and cooling and plan to put on PV panels.  We're hoping for net zero energy but not sure we'll actually make it.

Cheers,
David

Posted By jacksond on 05 May 2010 08:10 AM
Hi,

I'm totally new to this list and wish I knew about it earlier.  We are in the middle of building an energy efficient home in Pennsylvania.  We used SIPs for the walls and some of the roof but it turned out to be easier to build and save some money to use a traditional roof over a portion of the house.  In that part, we applied spray-foam insulation to the underside of the roof and it won't be vented.  If anyone's interested, they can check out our project at http://carlislegreenbuild.blogspot.com.  We've designed in passive solar and will be using a geothermal system for heating and cooling and plan to put on PV panels.  We're hoping for net zero energy but not sure we'll actually make it.

Cheers,
David

If you're concerned about your roof deck situation with the SPF below, read this.  Open cell vs. closed cell makes a difference here- without an interior side vapor retarder you'll have issues if it's open cell in your climate zone, but if closed cell, not so much. 

If yours is open cell (as it appears to be, from your blog pics), spraying vapor retardent latex paint onto the foam before putting up the code-required thermal barrier against ignition should be sufficient, and would still allow you to find roof leaks readily.  (There are now spray fiberglass solutions to the thermal barrier issue, as well as other spray-on stuff like Fireshell 10FE, etc. some of which may be paintable.)

If closed cell you're good from a vapor diffusion point of view, but roof leaks will be difficult to detect or locate.  A secondary ventilated roof deck above the structural roof deck would be a good (if not cheap) solution, since the structural roof deck could then dry toward the exterior, and roof leaks would drain into the ventilation gap.  Mounting the secondary deck on purlins would give it a slight R-value boost since the thermal short-circuits, but may slow the draining of bigger leaks.  Furring above every rafter/truss would also work, and would drain faster.  Secondary roof decks are the moral equivalent of rainscreen cavities on exterior walls, but improves the roof's drying capacity even more than rainscreens on walls. (But you probably already have the roofing up, eh?)
 

We had spray foam installed on our roof deck about 8 months ago. My husband is an electrician and he noticed the white wires in the attic were turning brown. Is this a concern for us and other people?