Spray foam insulation with radiant barrier????

gthigpenMarch 5, 2007

Ok, this is probably a really really stupid question but I need clarification.

Can you use a spray foam insulation (such as Icynene) with a radiant barrier?

In what I've read regarding spray foam, you apply it directly underneath the roof rafters to create an "envelope" in your attic. There are no roof vents or soffit vents.

With radiant barrier, you leave an air gap (if insulating the rafters) and there are soffit vents and roof vents.

So this tells me if we applied spray foam to the underside of our radiant barrier coated roof decking, we've just wasted the extra cost of the radiant barrier decking? Plus our brand new roof complete with ridge vent is now a waste.

I really like the idea of using spray foam. I'm wondering if we would gain any efficiencies by just applying it to our exterior walls and using regular blown cellulose on the attic floor? And then upgrading to more insulated ductwork?

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Sealed attics would not have a radiant barrier inside -- you are correct.

You talked about placing the furnaces in 2 attics in your other post, so the attic cannot be sealed. The furnaces need an air source.

You could do foam on the attic floor -- that's what we did. You could also apply a radiant barrier to the inside attic roof, but I would put the extra time and money into spray foam first.

    Bookmark   March 6, 2007 at 11:03AM
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dallasbill - so the foam on the attic floor would help with air leakage to/from the attic, but would not help with keeping the ducts in a conditioned space. It's a 2 story house, so the attic is above the 2nd story....there are no recessed lights in the 2nd story, which I've read are the primary offenders of air leakage. Still worth the $$$ to put foam in the attic floor?
What about foam in the walls and also spraying/covering the duct with foam? Worth the $$?

We do have radiant barrier already installed.

    Bookmark   March 6, 2007 at 11:45AM
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Generally there's no harm in two types of insulation, presumably the radiant barrier is to prevent the ingress of heat from the sun hitting the roofing?

Most conventional wisdom dictates the ceiling inside is insulated, and as much effort as possible is made to ensure the roof space receives no heat, and is well-ventilated. In summer, this minimises ingress of heat from the roof space to the house, and in winter, minimises ice damming from snow on the roof melting - in this case, the less heat in the roof space the better. I suppose radiant barrier works both ways in this instance.

    Bookmark   March 6, 2007 at 2:31PM
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Some of our duct work is coverevd with foam and some is not. Get R8 if you are getting flex duct -- that's about 99% of jobs in Texas now... flex duct.

Foam in your walls will do very well and stop all air infiltration, unlike fibreglass batts. Is your remodel doing the outside too? If so, you could do insulating foam board outside before you re-side and do batts inside the studs to accomplish a similar sealing of the envelope.

If you aready have the radiant barrier, you are a step ahead in reducing attic temps.

    Bookmark   March 6, 2007 at 3:54PM
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I am in the same boat trying to figure out what to use. We too used the radiant barrier Solarboard for roof decking as well as sheathing on the exterior walls. The house will be bricked. The house is 3470 livable sq. ft. and I got a bid in today from a foam company of 14,000.00 to spray the exterior walls, pony walls, and underside of roof decking. He promises us we can cut the tonnage of A/C required by using the foam. This makes up for some of the cost. He uses a company called Energy Wise to do calculated load reqirements to properly size your A/C. Their website below tells of their speil and their guarantee. If I don't use the foam, I am thinking of using a blown fiberglass insulation called Optima. Do a google search and read about it. It is supposed to have a better R value than cellulose and not pack and settle in the wall cavity. The wet spray in cellulose is the cheapest but I can't find any info as how much it may settle in say 10 years. The cost of the cellulose is 4100 vs. 6050.00 for the Optima. Decisions, decisions.


Here is a link that might be useful: Energy Wise Structures

    Bookmark   March 6, 2007 at 9:36PM
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First off, if you have Solarboard then you do NOT spray the underside of the roof decking. That will render the radiant barrier null and useless. Radiant barrier must face an air space of at least 3/4 inch in order to work.

Spray your attic floor with the foam -- and it will be less area and thus, less cost, than the roof's underside. You may want to get a quote from a Sealection500 installer here in town.

We used EnergyWise, on the recommendation of our ICF supplier and our ICF installer. Richard Rue is excellent and you will not be disappointed if you follow all the recommendations. And you can't beat that 2 yr guarantee!

    Bookmark   March 7, 2007 at 11:23AM
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One other consideration, is if you have gas or fuel based heat and the furnace is in the attic, you need makeup air. Electric heat does not need makeup air. Adding makeup air to a sealed attic will reduce the effectiveness of the attic.

I am looking at using spray in foam on my existing attic floor. I found a DIY product (tiger foam) that is about $1.15 per sqft for materials for a 1-2 inch foam application (2 passes). This has a higher rating than the blown in insulation that was originally used. The foam will seal the attic cracks into the living space and increase effectiveness even greater than blown in insulation. When I discussed insulating the underside of the roof, I was cautioned against it. The installer claimed the foam would cause wood to rot, if not done right.

    Bookmark   March 7, 2007 at 6:14PM
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Well let me tell you what I discovered today. I was at the site today about 5:00 p.m. and was looking at the Solarboard siding. It was getting direct sun from the West at that time and I was feeling along the exterior walls on the inside to see how hot they were. They did not feel that hot today as it was only 74 degrees today. I felt along and kept feeling these warm spots in the exterior siding. I thought WTH as I couldn't imangine why one spot in the middle of the board would feel that much warmer. It would vary from 84 to 95 degrees. I looked at the spot and went on the outside and noticed in the spot that felt warm was the company logo, name, ect. Just the blue printing on the outside foil caused the inside temp to vary by 6-9 degrees on a 74 degree day. I went home as I only live a few miles away and got my laser thermometer and found these readings. There was also a little decal sticker thingy on each sheet about 2x3 with the barcode. That too read 7-9 degrees hotter on a 74 degree day. I have heard that you need the 3/4 inch minimum airgap and this confirms my belief if a thin little silk screen and decal can make this difference. I have just about decided not to use the Sealection 500 because it would negate the benefit to the roof decking and if I put in on the attic floor, the ductwork would still be in unconditioned space. I am looking toward the Optima blown fiberglass. It is supposed to have better R-value than blown cellulose and not settle.


    Bookmark   March 7, 2007 at 8:05PM
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You realize, of course, that your conduction-experiment proves nothing in real life, because the Solarboard will be covered with your roofing material of choice, and will not be exposed to direct sunlight energy at all.

You still have not explained how you plan to keep your ductwork out of "unconditioned space," regardless of what kind of insulation you put on the attic floor. Unconditioned space is unconditioned space. Insulation on top of or around the ductwork up there does not change that fact. It simply negates -- to a greater or lesser degree -- heat transfer thru the duct walls.

    Bookmark   March 8, 2007 at 3:27PM
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I studied my insulation options on my new house for many months and here were my conclusions:

1. Sealection 500 foam for the entire envelope on my entire house would have been about $12,000.

2. I am not sold on the "envelope" concept. I don't see how it can be efficient air conditioning the huge attic that I have with a 12 pitch roof. I read numerous real world studies and found the actual cooling load in a house with the envelope is actually more than a house with good ceiling insulation and ducts that are not leaky.

My HVAC contractor assured me that his R8 flexduct won't leak and all seams are sealed up with mastic. Some of the duct is actually between floors and in other conditioned space anyway, but maybe only 20% of it.

I went with sealection 500 in the walls and cathedral ceilings. Everywhere they put OSB on top of the joists for HVAC access etc has foam on the bottom side of it. All walls with attic exposure have foam in the wall cavity plus the backside foamed in the attic to stop thermal bridging on the studs.

We put 1/2" R3 rigid foam on the outside of the wall sheathing (osb) to reduce thermal bridging of the wall studs.

The foam contractor sealed all openings leading to the attic, and he also foamed around the windows and doors. They spent many hours calking the bottom plate and every seam between studs, like where there are double studs.

The foam went in, it was a massive mess and lots of work. They spray it and it expands thicker than the wall and they use some kind of rubber grinders to bring it back flush with the wall studs. They carried at least 20 huge trash bags of wasted material with them, saying that it is recycled somehow.

There were some voids, the stuff is very hard to control, so they come back with a different foam and fill in these voids where they didn't get the foam where they wanted it.

The foam contractor also subbed out the rest of the insulation job, with no markup. This involved putting in baffles between each rafter and foaming around the base. This is to keep the loose fill insulation from getting back into the eaves and spoiling the ventilation.

The front side of the cathedral was 2 by 12s, which are 11.25" thick. They put 6" of foam in that and declared it sufficient, but I had them put 5.5" batts on the bottomside of that. Why not get all you can get in there while you're at it.

I micro managed the project, pi$$ing off the isulation contractor at times but I have been planning this for a long time and it was by golly going to be done right.

For example, they wanted to baffle every other rafter and I insisted on every rafter. Then when I inspected their work I found that they had separated the perforations on the baffles and put only half in between the rafters. Clearly, the baffles are 22" unseparated, designed for the gap between rafters on 2-foot centers. You are supposed to pull them apart only for 16" on center or other smaller gaps. He said "we can rip them out if you want". I said "I do", and they did, and now its done right.

I also found about a 6" round void back in my fireplace chase after they had left. I called and they came back and filled it in, even though it was hard to get to. All in all, they did a great job, although I must say it does not produce a perfect monolith like I thought, but rather requires some work to get it right. And, it makes a HUGE mess. The crew took about 4 days on my house, and thats just the foam. The loose fill has not been done yet.

My entire job with the extra batts and stuff I had them add, plus interior wall batts for sound insulation was $8500. There are only 2200 square feet of living area, but lots of porches, cathedral, big walls up in the attic, plus I sealed off a section of the attic for cool storage. The part thats done was $7200. The remaining $1300 is for the loose fill that will be done later, after the electrical is all checked out and such.

We used the radiant barrier decking and foamed the underside of it on the cathedral because it was easier for the decking crew not to have to worry about which kind of osb to use on which parts of the roof. Its only about $3 per sheet more and it was maybe 12 or 14 sheets we foamed.

I have read about a method whereby you staple the baffles all the way up to the ridge vent and then spray the foam to the underside of the baffles. That way, you get the foam, the radiant barrier, and the ventilation too. We didn't feel this was necessary.

The foam is now covered up with drywall except the attic part of it. I like it and think it is going to be great. The insulation contractor would liked to have done the entire envelope and I explained to him I wasn't sold on that. In the bidding stage he seemed insulted that I would doubt his claims and it sounded like he didn't really want the job if I was not sold on the product. The fact is that I AM sold on the product, just not the whole envelope concept, or at least not enough sold on it to spend another $3500.

Sorry, this was kinda long, and I don't have any real world results yet as we are just in the taping and bedding stage, but will report later.

    Bookmark   March 10, 2007 at 12:32AM
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Sounds like you did a stellar job!

two things pop out:
"2. I am not sold on the "envelope" concept. I don't see how it can be efficient air conditioning the huge attic that I have with a 12 pitch roof. "

You are not A/C'ing or heating a the attic. You are simply sealing it agaist outside air. There are no ducts feeding into the attic with a sealed attic.

"We used the radiant barrier decking and foamed the underside of it on the cathedral because it was easier for the decking crew not to have to worry about which kind of osb to use on which parts of the roof."

If I read this correctly, then you have just rendered useless the entire radiant barrier on the cathedral roof. An RB needs at least 3/4 of an inch of open space facing into the house behind it, and you have foamed it shut.

    Bookmark   March 10, 2007 at 12:02PM
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I don't know why you're not sold on the envelope concept, Texas_al. It's one of the benefits of icynene or sealection type foams. In selecting my HVAC contractor, knowledge of Icynene and how to condition air in a sealed envelope was essential in choosing who I would hire. My HVAC took training courses regarding Icynene and knew exactly how to do the calcs for homes with it. As it turns out, I'll be using smaller, more efficient, heat pumps than I would if I went the traditional route of radiant barrier and insulating the attic floor. Plus I saved the cost of the radiant barrier, though I'll still be spending more overall for the insulation. What I'll end up with, though, is a more energy efficient and comfortable home in the hot, humid weather in SW Florida.

All of the above, though, is not the reason I went with Icynene. It's just a bonus. Living in hurricane country I wanted to eliminate one of the biggest failure points on a home - the soffits. Soffits often fail in a hurricane allowing wind and rain to get in the attic space and exert pressure on the roof and ceiling, often to the point of failure. Our unvented attic won't have any way for the wind to get inside the attic. There won't be any ridge vents and the soffits will be solid and stuccoed.

Good luck with your project. You'll have a well insulated home. You've just lost out on having it even better insulated and wasted money on radiant barrier, though you knew that already.


    Bookmark   March 10, 2007 at 12:26PM
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I believe the cooling load in my home will be less with R50 insulation in the ceilings that it would have been with an attic 7 degrees hotter and no insulation in the ceilings. The Florida roofing material tests bear this out. I have not seen ONE real world test that shows a lower heat load in the living space when using the full envelope concept, unless the ducts are in bad condition.

Here is one done by the Florida Solar Energy outfit http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1220-00.pdf - see the bottom of page 16 of the pdf document that the cooler attic of the foam envelope home does not translate into a lower cooling load as compared to "other alternatives", such choosing a lighter colored roofing material.

The radiant barrier on the cathedral is not necessary. Therefore rendering it ineffective has no consequences.

I wish someone would find me a real world study that shows the envelope concept results in less heat load in the space that will be air conditioned. I sure couldn't find one. I find studies that show the attic is cooler, but this does not translate to a cooler living space when combined with the fact there is no insulation between the attic and the living space.

Further, if the envelope is not done absolutely perfectly, and some humid air gets in there, then it ends up being much worse. Honestly I wanted the envelope because of being able to have a "cool" attic, but it made no sense to accomplish this by having to cool it. If there is no insulation between the living space and the rooftop, then you are, in effect, air conditioning it. Even if there is only 7 degrees difference between the attic and the living space, there should be some insulation to keep the cool air down in the house.

I have no doubts that the enveloped house is a well insulated house, but the bottom line cooling bill should be the same or better using my approach, based on the real world tests that I have read.

    Bookmark   March 12, 2007 at 12:18AM
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Most of the studies I have read, are systems designed for cold climate houses. Several studies include hot climate conditions, but the final design is typically for cold climate. With this said, A contractor in N. Texas, built what he calls a net zero energy house. It is 3600 sqft. It reminds me of the CCC construction found on federal park buildings. This house used an insulated attic. The temperature in the Attic was the same as in the house when the door was open to the equipment room. The house used ICF block and large overhangs on the roof. The cooling was 1000 sqft per ton, and the house was comfortable all over. The house used chill water and solar heated water for heat and cooling. While the house was overpriced in my opinion, many of the features were outstanding. Using foam makes a difference.

I helped to finish a 2250 sqft house that was manufactured in St Louis and built in N. Texas. The walls had 4 inches of foam and the roof had 6 inches of foam. It was very tight. The problem with only one roof, is when it rains, the noise is anoying. It sounds like rain on a metal barn roof. Otherwise the heating and cooling has proven to be very effective for the last 20 years. The average bill is less than $75. The owner uses Propane heat.

From these two examples, I would believe that a total envelop is just one way to do the job. It is probably more efficient to eliminate the attic, but the attic acts as a sound asorber.

    Bookmark   March 12, 2007 at 3:08AM
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I"m researching this sealed attic concept for a renovation/addition in Virginia. It seems to me to make sense that if you seal your attic and your mechanical equipment is up there it will have less heat or cool loss - and the upstairs will be improved as it will be against a semi conditioned attic thus resulting in less heat or cool loss. I guess if you only insulated your ceiling - just the fact that your ac unit is running in a 130 degree attic or your furnace is running in a 30 degree attic - means you are losing cool/heat that you are paying for. A sealed attic (spray foam roof deck) would seem to be more efficient and result in lower energy usage.

the closed cell/open cell decision and the the thoroughness of the sealing of the envelope would seem to be critical.

Also - what are the real ramifications of roofing lifespan reductions due to hot sheathing. Will the sheathing really be that much hotter than when it isn't insulated under the roof sheathing? I suppose the heat cannot flow into the attic - but at some point doesn't the attic heat up to the point where there is no more heat flow and the roofing is as hot as it would be with a sprayed deck?

HOw might metal roofing effect this consideration? What about solar PV or Hot Water above a sealed attic (seems like the solar hot water could only benefit - i guess the pv panels could get too hot if not spaced enough to 'cool' off.

any thoughts?

    Bookmark   January 31, 2008 at 12:03AM
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You can't seal your attic and have the furnace up there. The furnace needs a combustion air supply. Ergo, it's not sealed.

    Bookmark   January 31, 2008 at 3:50PM
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I have a friend that is building a 3500 sqft house in N. Texas. He is doing a total envelope. One thing he is doing that I am hoping you can shed some light on. After he puts six inches of foam in the roof deck, he is having them put radiant barrier screens attached to the roof deck. He was told that this would stop anything that the foam lets through. I thought the foam was suppose to take care of this?

    Bookmark   March 2, 2008 at 11:00AM
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One option for having both the RB decking and foam coating ceiling was used by www.bannisterhousetexas.com. They draped a vapor barrier fabric between the roof rafters to create the air space between the RB decking. Then hit it with the foam. This provided the required air gap and a path for ventilation between the soffit vents and the ridge vent.

    Bookmark   April 24, 2008 at 6:28PM
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That RB and sealed attic thing about that Bannister house that does not make sense.

They say:
Again, we turn to Dupont for a relatively new product called attic wrap. This material is similar to the house wrap, only it is laid across the rafters and "clipped" down, or depressed down one inch. When our decking for the roof is installed, this gives us an air space for air to travel from the soffitt to the ridge vents; much like conventional roofs only the air is confined to the one-inch space.

First see this:

Then, they spray foam it, see this:
and this:

As you can see with the RB, the way it's hanging, there appears to be no way there is a continuous, contiguous 1 inch airspace (required by an RB) running from bottom to top. When the foam is sprayed on (and it goes on with quite a force as a liquid) it is going to run that RB right up against the sides of the rafters and the underside of the roof decking and rapidly expand against it, further reducing the sir space and flow between it and the decking.

IMHO,I think that's complete overkill and an exercise in spending money to gain what can't be measured, compared to a sealed attic without an RB.

    Bookmark   April 25, 2008 at 3:52PM
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Does any one have information on how pleased they were with the insulation scheme that they chose. I am in the planning stages and I am in the same boat trying to get the most for the money.

    Bookmark   November 24, 2008 at 2:38PM
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Hi! I'm the originator of this topic. I'll share what we ultimately decided on.

While I did further research on the total envelope concept, and I decided that it was an excellent method, it was way out of our budget once the quotes came in.
We did the "blown in batting" in our walls. They stapled up netting or mesh and blew in fiberglass. Benefit is you get the insulating properties of fiberglass, it's economical, and it's extremely tight so you eliminate the drafts and leaking you get with traditional fiberglass batting.
Once they were finished, our exterior walls were completely sealed. They came back and used spray foam insulation to seal any additional gaps around doors and windows.

Ceiling insulation was blown in after all electrical/lighting work was completed.
We used radiant barrier on our roof decking to help reduce the heat in the attic.
Our ducting was insulated. I can't remember what the R-value is right now, but I remember it being one of the best there was.

Living in our house now for 1.5 years, we are extremely pleased. It's not drafty at all, rooms are consistent in temperature thoughout the house (floor to ceiling), our electric bills have been extremely reasonable considering it's a 2 story 3500 sq. foot home. They've been creeping up this year but that's a function of higher kwh rates.

    Bookmark   December 10, 2008 at 12:04PM
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So what does your energy bill run you in the summer and do you have a swimming pool?

    Bookmark   December 10, 2008 at 12:35PM
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We live in North Texas and no we do not have a swimming pool.

Summer of 2007 our highest bill (July/Aug) was $240.

Summer of 2008 our highest bill (July/Aug) was $380.

Same kw usage ~2000, but much higher prices. This winter when we are using our gas furnace and no AC, our bills are around $230 when last year at this time they were around $100. Energy provider is charging me $0.195 per kwh. We are in the process of switching providers.

    Bookmark   December 10, 2008 at 2:13PM
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This has been an excellent thread and I have a related question. I am sealing my exterior walls with a combination of 1/2 inch closed-cell spray foam and then R-13 batts. The spray foam gives me the tight seal and an R-3 and the R-13 batts give me whatever they are after being compressed 1/2 inch. This is a second story addition and working up there all summer I noticed a very large radiant heat gain on the wall that faces West-South-West. In fact, that area of the house was hottest towards the end of the day when it was starting to cool down.

So I got thinking about how to install a radiant barrier in my wall cavity without doing additional furring strips and my question to the group is what about using the radiant foil that includes a bubble layer? Home depot has one that is 5/16" thick and there is a website setting radiant bubblefoil that appears to be thicker than that. Any thoughts on how a combination of radiant bubble stapled in the cavity with 1/2" closed cell spray foam on top of that and then R-13 batts on top of that? This wall is approximately 270 square feet of a total of 1900 square feet of exterior wall space.

I will also do the radiant barrier foil in my attic, but only the side that faces the southerly sky as I don't think there is much radiant gain on the northerly facing side, does that make sense?


    Bookmark   December 19, 2008 at 8:22PM
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