Posted By Rosalinda on 25 May 2010 06:33 PM
Thanks Dana, that is exactly what I needed to know. I can't open that PDF, tried to get it from their site yesterday to no avail. Could someone get it and email it to me as a message rather than a link to [email protected] ?

I talked to a few contractors today and also got suggestions for 1.2# medium density OC for the full rafter depth and also using 3 inches of 2# CC and fill the rest with .5 OC. I must admit the blow in fiverglass or cellulose gives me the heebie jeebies (though I am reading about the spider system now)  given the sealed roof, though I know it shouldn't. Should have ball park prices in a few days.

If I live long enough to need to replace the roof, we will hopefully have lots of new amazing technologies available. It is bad enough to have to rip down a brand new ceiling, pull out all the new guts and rebuild it, I just can't manage having to rebuild the brand new roof. Unfortunately I just can't live with the wrong ceiling they gave me no matter how hard I tried to convince myself to do so. At least the company who sold me the home is making the ceiling right, so I will take the opportunity to do the insulation right, even if it costs much more than I was planning on spending. Hopefully it will save me a grand or so on the heating system, so I consider that a rebate.

-Rosalinda

I'd be concerned that medium density open cell to full rafter depth mighte need an interior vapor retarder in your location.  It'll have the necessary R, but may be too vapor permeable. Do they have a permeability spec on the 1.2lb goods?  The 3" cc and 6.25" oc approach is pretty much the same as 2" of oc. and 7.25" of Spider from a moisture & total R point of view.  Cost wise it might be a wash.  You may be required to put up gypsum/other as a thermal barrier if you go all-SPF though, whereas if you went with Spider the IT would be the thermal barrier for the SPF.

Wet-sprayed fiberglass or cellulose is bound with adhesive- I'm not quite sure what the heebie-jeebies would be about.  They don't outgas, the particulates are glued in place, and restrained by netting in a blow-in-bag under rafters.  SPF has short-term outgassing issues- are you worried about that too?  Spider (and several other fiberglass products) don't have formaldehyde issues the way old-skool stuff does.  (If you're worried about cellulose maybe you should stop reading printed paper material without a respirator, eh? )

It's certainly not worth ripping up a brand new roof to put down exterior insulation- the utility savings of being at R60 vs. R40 on the roof won't be anywhere near the cost of a roof replacement over the lifetime of the shingles, but when the time comes...

Thanks again Dana,
The contractor who is checking on the medium density for me said the permeability at 9.25 inches meets code, but the ceiling will be sheetrocked and painted regardless. It will be my finished ceiling surface - until I decide to cover it with something (luan mahogany being my favorite)

I guess my worry about the fiberglass is about moisture, though it shouldn't be an issue. The other issue with the spider is finding someone who will install both the spray in foam and the spider, rather than trying to get 2 contractors out to do the job. I couldn't get any ballpark figures on the cost of the spider system online, anyone have a rough idea? I have 798.6 ft2 of roof deck to cover (that is the gross area).

I should have ball park prices for the various options by the end of the week - I hope.

Today my insurance company spent the day trying to drive me crazy, and I think they succeeded. Amazing how the most simple things aren't!

-Rosalinda

Spray foam insulation is a superb product. As far as comparing thickness of foam to fiberglass, that is a simple comparison on a product-by-product basis. You need independent test results that confirm what the R-value is per inch of thickness of a given product. R-value is a measurement of thermal efficiency; it is a measurement the resistance to heat flow. The higher the R-value number the greater resistance the insulation has to the movement of heat.


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roofing contractors

I ended up going with 7 inches of 2# soy based Demilec on the interior of the roof deck and 3 inches of same in band joist. Cost $5.20 per ft2 at 7 inch depth. Since I put up all the plastic in preparation for the spray, I got the band joist and a few bits and pieces (such as the one pipe in the whole house that ended up in an outside wall - the drain pipe from the kitchen sink) thrown in.

Boy does that stuff make a MESS!!!!

-Rosalinda

I am about to build....are you still content with your decision

dford,
Yes I am happy I went with the 7+ inches of 2#cc foam. The only thing I would do differently in this house if I could have, would have been to have some kind of foam board on the exterior of the framing to cut down on thermal bridging. If I ever need to replace the roofing shingles, I will probably do that for the roof at least.

-Rosalinda

Dana, first thanks for sharing your knowledge on time on this often misunderstood area of construction. You could probably save yourself some time by writing a guide for the different zones as it matters.

My question is on your stack: -shingles
-roof deck
-4" of ccSPF (~R25)
-5.25" of JM Spider blown-in-bag @ 2lb density (~R22) which also provides the ignition barrier for the foam.

In a cold-dominated climate would you recommend a vapor barrier below the blown-in cellulose (above the drywall?). I would think moisture could get there from the home and (eventually) cause rot\mold in the cellulose although I know cellulose is treated somewhat for that.

If there is a vapor barrier (plastic sheathing) then there will be a dead air space that contains the cellulose preventing moisture from entering. However I suppose if somehow there was a leak (air\water leak above or below) it could make matters worse however.

Before I read this thread, I was thinking of flipping them around (ccSPF below cellulose) but yes there is a fire issue then.

Sharter: This is a thread nearly 3 years of age, and I'm not going to re-read it to try to interpret the question. But...

"Cold" is relative (Ohio winters are "cold" to somebody living in Alabama, but practically tropical to someone living in the Alaskan interior), and the amount of closed cell foam required to avoid condensation accumulation in the fiber insulation layers when there are no interior vapor retarder (other than latex paint) will vary with the actual climate. But in NO CLIMATE ZONE does putting up a poly vapor retarder in an unvented roof deck work, since creates a moisture trap between the roofing materials and the poly- the assembly can't dry in either direction.

Flipping the stackup creates a fire issue, sure, but that's the LEAST of it! without venting between the roof deck and fiber you can't put 4" of ccSPF (~0.2 perms) on the interior side of the stackup since that creates a moisture trap between the shingles/felt and the foam. Putting the foam directly on the roof deck is something of a moisture trap for the deck itself, but roof leak damage would be limited to the leak point, whereas leakage into cellulose would take on HUGE amounts of moisture and spread it the full length of the rafter bay, likely rotting out both rafters & roof deck before being discovered.

There is a zone-by-zone prescriptive foam/fiber stackup for this sort of unvented roof, enshrined in the IRC:

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_8_sec006.htm

See table R806.5.

While there is plenty of science behind those prescriptions for R value exterior to the roof deck, there is very little (none, actually) behind applying the same prescriptions when the air-impermeable insulation is applided to the underside of the roof deck. WUFI simulations show that the roof deck is well protected with far less ccSPF than prescribed by code. See:

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

See tables 3 & 4, page 11 (p.12 in PDF pagination.) In most of the US under a shingle roof, using just 2" of ccSPF and doing the rest in Spider would be just fine (BETTER than just fine- it's an assembly where even roof leak moisture can dry at least a little bit toward the interior.) Even a flash-1" is good for much of the US.

Rosalinda: 7" of ccSPF is a very tight, very rugged roof, but the greenhouse gas footprint of the last 5" far exceeds that of the energy use it offsets over the next two centuries! This is due to the HFC245fa blowing agent used for the vast majority of the 2lb foam used in the US. There are newer, low greenhouse potential blowing agents hitting the market, but they are not currently in widespread use. (Some of the major players will be using it by the end of 2013.)

Interesting Dana - I wonder how NAHB and LEED can certify it as a product (Demilec HeatLok Soy 2# CC) given its negative greenhouse gas impact. Hard to know what criteria NAHB and LEED use to determine a "green" product.

-Rosalinda

Posted By Rosalinda on 25 Jan 2013 10:55 PM
Interesting Dana - I wonder how NAHB and LEED can certify it as a product (Demilec HeatLok Soy 2# CC) given its negative greenhouse gas impact. Hard to know what criteria NAHB and LEED use to determine a "green" product.

-Rosalinda

They're all good, when used in proper proportion- it all comes down to "Greener than what?"

LEED is a bit bizarre in many respects, giving points for prescriptive aspects over actual measured performance, and have been much (rightly, IMHO) criticized by performance oriented builders. (IIRC for a long time they were even giving brownie-points for the thermal mass of concrete poured in un-insulated garages!)  I'm not sure where they stand today, but some builders roll their eyes and refuse to even start down the LEED accounting road for potential clients seeking LEED certification.  That said, they rightly give points for using reclaimed/recycled building materials over virgin-stock whenever possible.

NAHB isn't exactly known for being a driver of green building.

Closed cell foam and XPS can be "green enough" when used in proportion, in the right places, but no foam insulation is fundamentally very green.  The characteristics of spray foams that give them a greener tinge is their superior air-retardency as compared to fiber insulation, and the ability to adjust the water vapor permeabilty to a defined level, which allows the designer to build more resilient assemblies with wood framing & sheathing.  But the low vapor permeance of closed cell foam is a two edged sword, and can lower resiliance by creating moisture traps if the stackup doesn't offer sufficient drying capacity.  At high-R closed cell foam blown with HFCs is anti-green, but getting better with the newer blowing agents just now coming on the market. 

There are a few water-blown 2lb foams that don't have nearly the greenhouse gas down side (Icynene MD-R-200, or any-density of Aloha Energy foam), but even when some of the chemical components are from plant-based sources there is still a high fossil-hydrocarbon component to the material.

For high-R assemblies it's hard to make the case for closed cell foam, but in some instances open cell works.  It's still nowhere NEAR as low-impact R-for-R as cellulose, which is predominantly a biological-source recycled/reclaimed material, which makes it a "greener than..." option in high-R assemblies wherever it can be used in lieu of foam (any type of foam.) Reclaimed/reused rigid foam is about as green as it gets with foam, since it's simply extending the useful life of the material- the environmental hit has already been taken, and disposing of it rather than re-using it only makes it worse.

I can't speak to LEED standards, but as a NAHB member for almost 30 years I can speak about this organization. NAHB is a trade organization for builders and remodelors; one of the basic functions is to act as lobbyist and supporter for the building community. The NAHB Green effort is an attempt to enable NAHB members to compete on a competitive price level in the "green" market. If you're looking for information on how to build a superinsulated home with a respectable carbon footprint (which is the only construction I would consider "green")- the proper techniques, the correct materials, look first to Passive House - that in short is the overall goal of the nonprofit. Other organizations that can help are Building Science Corporation, which has a great website where they share lots of information and studies, and GreenBuildingAdvisor.com, whic is a collaboration of the publishers of Fine Homebuilding and BuildingGreen in Vermont.

I understand the NAHB Green program developed/promoted the ICC-700 National Green Building standard, but I confess that neither own nor have I read the book on that standard, and couldn't say how far they take it when looking at lifecycle aspects of materials rather than performance-only issues, etc., and how it's certification levels compare to LEED from a performance/other point of view.

Closed cell foam is great from a material performance point of view- it's those pesky other issues that are at odds with the point of view (still held by some) that it borders on being a panacea. Perfection is a lot to ask, and I won't- ccSPF is a great thing to have in the designers tool-kit, but it's important to keep the big picture in mind when specifying methods & materials.  I'll personally be happy when HFC245fa and HFC134a are in the "remember when..." category for this application, just like the ozone-eating HCFC blowing agents & refrigerants that preceded the Montreal Protocol era.  With the more benign blowing agents coming on the market the overall environmental footprint of ccSPF drops by orders of magnitude (but still should not be treated with panacea status.)

After reading all 9 pages, I never knew that this type of sealed under rood deck was even performed.

I will be building a home in on coastal property northern Calif (41 degrees latitude) and still have some concerns about this approach with my future home.

Stats:
It's considered a temporal rain forest (Redwoods, ferns)
4400 HDD
rarely gets below freezing but it can (average lows in Dec/Jam/Feb are in the upper 30s)
High humidity year round: rains a lot in the winter and spring, marine layer fog off and on all year long, but especially in the summer.
----------------------------------

The home:
2 story standard rectangle; raised foundation crawl space
radiant hydronic floor heating
No AC needed (July/Aug highs average in the mid 70s and rarely get above 80)

-----------------------------------------------
My concerns is with humidity in the attic, since this approach means no attic venting. No forced air heating means nothing to dry the humidity in the air. Ditto with no AC (AC can be a dehumidifier).

The other concerns is not being able to know about any roof leaks (rain is 40-60 inches a year)

Also not sure if the extra load (of the conditioned attic) would be hard on a radiant hydronic floor heating system?

Love the idea of being able to do work in the attic for years to come w/o fear of compromising any blown cellulose.

I really fear the cost of spraying the under deck of the roof on a 1800 sf footprint.

Meekly requesting comments.

No forced air heating means nothing to dry the humidity in the air

How does forced air heating dry the humidity in the air?

The vast majority of houses are best served by a vented attic.

I too looked at spray foam for my attic. However, our climate here in Virginia seems to be on a weird cycle. For the last few years we have had colder weather in the winter and a shorter hot period in the summer that extends out into September. Cost was a factor and when adding the addition the estimate included a ridge vent. I installed a ridge vent in the attic of my existing house last summer and it helped a lot. I am concerned with increased shingle wear on the roof as well. I discovered a few things and worked this design in.

1) ridge vent works great but with a hot day the hot roof still heats the air quicker than it can be exhausted.
2)radiant barrier foil is great except for see number 1. With that installed the air between the barrier and roof deck gets a double dose, heats, and just moves around the barrier to heat the attic.

My solution.
Purchased some foil faced rigid foam and nailed it under the 2x4 trusses. I am in the process of making this go from the soffit to the ridge vent with an air barrier. I will then add additional insulation under it. This way air will get sucked in through the soffit vent, get heated, and rise out the ridge vent. The volume of air will be much smaller and should increase the natural flow rate. Already, I can reach into the gap between the first row and feel the heated air blowing out.

Since my existing house has 2x10 trusses I will cut some rigid foam, add 2x4 spacers, and place the foam in there. This will allow for the addition of r19ish insulation under it. I am hoping by allowing for air to move behind the foam that I will keep the roof temp lower and the ice damns down.

There will be a section of the roof in the addition that has no soffit vent and will not benifit from the ridge vent. I am planning on just putting the insulation on the underside of the deck. Since it is a small section facing north I dont think I will have a problem. However, it will serve as a comparison. If in 10 years I see a difference in the shingles in that area we will have our answer.

Either way I plan on adding a dehumidifier in the attic just to be safe.

Posted By JohnRLee on 04 May 2013 02:56 PM

My concerns is with humidity in the attic, since this approach means no attic venting. No forced air heating means nothing to dry the humidity in the air. Ditto with no AC (AC can be a dehumidifier).

No venting does not mean no air exchange. You will need to move some living space air through the attic to keep the air up there from getting too humid. With the tightness of an ICF shell, and the radiant heating being used, you probably should plan on installing a dehumidifier anyway, whether or not you insulate the roof deck. Also you will definitely want to have a heat recovery ventilator. If you have a good HVAC person to work with he can design the dehumidifier into the ventilator system. Sorry, but you are not going get away with zero air handling.

The other concerns is not being able to know about any roof leaks (rain is 40-60 inches a year)

This was discussed quite a bit here a few years ago. If you can't get the forum search to work good do a Google search using this "site:greeenbuildingtalk.com roof leak closed cell". That should find the discussions for you. Leave off the quotes.

Also not sure if the extra load (of the conditioned attic) would be hard on a radiant hydronic floor heating system?

When I was doing the heat load calcs on my house during the design phase the calculations showed that the heat loss through the roof plus gables was very little different from heat loss through an insulated ceiling. The air volume in the attic has very little heat capacity. One of the reasons you're using hydronic heat is that water carries much more heat per pound of mass than does air.

Love the idea of being able to do work in the attic for years to come w/o fear of compromising any blown cellulose.

Believe me, it is really nice not to contend with blown insulation on the ceiling.

I really fear the cost of spraying the under deck of the roof on a 1800 sf footprint.

Spray foam is not cheap but I think the comfort and convenience it affords makes it worth the price.

What are you using for heating energy source, gas or electric? On a Btu basis is the gas cost on par with 1/3 of the electric cost? If not, you may want to seriously consider a heat pump. Your climate would be great for that.

Question, with your mild climate and using ICF, what is your overriding reason for using hydronic? Along with that are you going to do a sealed and insulated crawl space? With ICF from the footing up you may as well.

How about doing what I did? I have a sealed crawl space and sealed attic. I use a Daikin heat pump with the air handler in the crawl space. I use the crawl space as the supply plenum and the attic as the return plenum. I have fairly even heating around the house with the living room getting warmer from solar insolation during the day. There are no drafts anywhere in the house. The temperature stays steady. And one of the best benefits is by using the crawl space as the supply plenum I have a quasi radiant heated floor. It's never cold during the heating season. My climate is about 6000 HDD with lowest temps around -10°F.

Posted By dmaceld on 05 May 2013 07:25 PM

No venting does not mean no air exchange. You will need to move some living space air through the attic to keep the air up there from getting too humid. With the tightness of an ICF shell, and the radiant heating being used, you probably should plan on installing a dehumidifier anyway, whether or not you insulate the roof deck. Also you will definitely want to have a heat recovery ventilator. If you have a good HVAC person to work with he can design the dehumidifier into the ventilator system. Sorry, but you are not going get away with zero air handling.

The other concerns is not being able to know about any roof leaks (rain is 40-60 inches a year) This was discussed quite a bit here a few years ago. If you can't get the forum search to work good do a Google search using this "site:greeenbuildingtalk.com roof leak closed cell". That should find the discussions for you. Leave off the quotes.

When I was doing the heat load calcs on my house during the design phase the calculations showed that the heat loss through the roof plus gables was very little different from heat loss through an insulated ceiling. The air volume in the attic has very little heat capacity. One of the reasons you're using hydronic heat is that water carries much more heat per pound of mass than does air.
Spray foam is not cheap but I think the comfort and convenience it affords makes it worth the price.

What are you using for heating energy source, gas or electric? On a Btu basis is the gas cost on par with 1/3 of the electric cost? If not, you may want to seriously consider a heat pump. Your climate would be great for that.

Question, with your mild climate and using ICF, what is your overriding reason for using hydronic? Along with that are you going to do a sealed and insulated crawl space? With ICF from the footing up you may as well.

How about doing what I did? I have a sealed crawl space and sealed attic. I use a Daikin heat pump with the air handler in the crawl space. I use the crawl space as the supply plenum and the attic as the return plenum. I have fairly even heating around the house with the living room getting warmer from solar insolation during the day. There are no drafts anywhere in the house. The temperature stays steady. And one of the best benefits is by using the crawl space as the supply plenum I have a quasi radiant heated floor. It's never cold during the heating season. My climate is about 6000 HDD with lowest temps around -10°F.

For starters this is not an ICF wall house...standard 6" studs, with Tyvek, windows yet to be determined.

ICFHyrbrid: I misstated.  Forced air heating systems (as opposed to radiant hydronic floor) tends to draw moisture out of everything, including your skin (evaporative effect), studs, furniture, etc...but then. I think you knew that and were just being your usual coy self.

Back to original topic...

Hydronic system will be professionally designed, and will include a proper ventilation design too. I feel that hydonic radiant will be easier on the utility bills over the long haul.  Will it justify the ROI?  Hard to say.  I plan on installing most of the pex and warm board (or similar product) myself and hiring a local contractor to install the boiler and heat pump.

dmaceld: This will be an electric house (Solar PV array), PG&E fed; strongly leaning towards Daikin Altherma heat pump to heat my boiler.

The house will be over a 36-48" high crawl space but I was originally figuring it to be a vented crawl space.  I have a mechanical room designed into the middle of the first floor and is plenty big enough to accommodate a boiler and air handler etc.  I have also designed a 2' x 2' chase into the attic from the mechanical room.

My climate is about 4400 HDD

I have not read any of the other threads about roof leaking being evident on sprayed under roof decks, but there is plenty on this very thread, at least enough to cause a concern.

I say this from experience. Case in point:

I built a house in Kansas 7 years ago. Standard, typical house.

I had a drain vent going through the roof develop a leak. The issue was a pebble got lodged in between the vent pipe and the rubber grommet seal, allowing rain water through. I did not discover it until mold starting developing on the ceiling sheet rock. If this had been a blown expanded foam under roof deck, no telling when it might have been discovered. Shit happens.

Posted By JohnRLee on 05 May 2013 07:59 PM

For starters this is not an ICF wall house...standard 6" studs, with Tyvek, windows yet to be determined.

ICFHyrbrid: I misstated.  Forced air heating systems (as opposed to radiant hydronic floor) tends to draw moisture out of everything, including your skin (evaporative effect), studs, furniture, etc...but then. I think you knew that and were just being your usual coy self.

Back to original topic...

Hydronic system will be professionally designed, and will include a proper ventilation design too. I feel that hydonic radiant will be easier on the utility bills over the long haul.  Will it justify the ROI?  Hard to say.  I plan on installing most of the pex and warm board (or similar product) myself and hiring a local contractor to install the boiler and heat pump.

dmaceld: This will be an electric house (Solar PV array), PG&E fed; strongly leaning towards Daikin Altherma heat pump to heat my boiler.

The house will be over a 36-48" high crawl space but I was originally figuring it to be a vented crawl space.  I have a mechanical room designed into the middle of the first floor and is plenty big enough to accommodate a boiler and air handler etc.  I have also designed a 2' x 2' chase into the attic from the mechanical room.

My climate is about 4400 HDD

Even though you're not using ICF, you can make the house about as tight as an ICF house. Ventilation and humidity considerations are the same.

When I designed my house ease of operation of the windows, with arthritic hands, was a criteria, as well as air leakage and U factor. The U factor depends on the glass and glass/frame area ratio and is pretty much independent of window style. As for ease of operation and fenestration data, my research showed casement windows to be the best. I used Andersen 400 series. Maybe not the absolute best in the world, but a very good window for the money.

I'll take a guess at the dimensions of the house, say 40 x 45 = 1800. 40 + 40 + 45 + 45 = 170 ft. 170 x 4 ft = 680 sq ft. If you insulate the crawl space walls you only need to insulate 680 sq ft vs. 1800 if you insulate the floor, plus it'll be easier, I think, to install the insulation. I may be nuts but it sure seems to me like it's a no brainer to insulate the crawl space walls rather than the floor and condition the crawl space.

Based on my experience with the Daikin VRV system I'd say you won't wrong using the Altherma.

I originally was going to go hydronic but when I learned of the Daikin system I dropped that plan. Had I gone hydronic in the floor I would have used Warm Board. Seemed to me to be about the best option out there. Since I needed A/C I had changed plans and was going to go with hydronic in the ceiling so I could use it for cooling. But all things considered, especially cost, the Daikin was the best choice for me.