I have insulated a hot-roof barn project with 12-14″ of Icynene SPF against the roof deck. I would like to completely fill the remaining truss space with cellulose (which would vary from 0″ deep at the heel of the truss to about 16″ deep at the peak), then finish the interior with drywall. After reading through various FH messages, I am concerned with settling of blown-in cellulose. However, since the SPF is already in place as an air barrier, perhaps this is not worth worrying about. Furthermore, with the trusses on 2 foot centers, should I be concerned with the weight of the cellulose on the drywall (would i need furring strips horizontally)? Any suggestions appreciated.
Shawn
Replies
FYI, SPF is code for Spruce/Pine/Fir, at least around here. Icynene is PIR (closed-cell spray foams are PUR). Enough with the acronymns though.
Furring strips are a good idea (we call it strapping in New England, and do it on every house).
Where are you located? Sounds like you have an adequate amount of insulation, so if you decide to blow in cellulose I wouldn't worry about a little settling. You could dense-pack it and then you wouldn't have to worry about settling, but if you just loose spray it you'll get a little settling but still some benefit.
Cellulose, especially loose-sprayed, is not an air barrier or vapor barrier so you don't need to worry about that either.
Sorry about the acronyms...but now I am trying to guess what PIR and PUR stand for?
This project is in northern MN- land of 10,000 lakes AND 10,000 heating degree days :) We are building a LEED home and trying to get it as tight and efficient as possible.
What type of mesh/fabric do you use to hold back the cellulose in this case?
thanks,
shawn
Shawn
This is far from my area of expertise but down here in Iowa, land of the 9000 heating days :) I've seen what you're proposing a lot.
Sprayed in spf followed by blown in dense pack, usually the stuff I see blown in is more white so I'm assuming something different then cellulose.
The mesh thing someone else will have to answer.
One other thing, why didn't you just have them fill the cavity with spf?
I'm going to do something similar in my upstairs/attic and the reason that I cant go full spf is because of cost, I have to budget the money on my own place some.
Doug
Edited 4/6/2008 10:23 am ET by DougU
Good Morning Doug
If it's white it's probably FG.
Rich
If it's white it's probably FG.
Lot I know, I figured because it wasnt pink that it must be something else!
Is fiberglass better then cellulose? I dont think I can blow fiberglass though so cellulose is probably what I will use.
Doug
Doug
I think the consensus at BT is that cellulose is superior to FG.
Especially at stopping air infirtration.
Rich
BIBS (blow in blank insulation system)I uses a chopped fiberglass, much different than the bat.It is blow with an adhesive.It is also blown behind a mesh like desnse pack cels. Don't know if that is also called BIBS or not..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
BIBS (blow in blank insulation system)
Hows this compare to cellulose? Better, worse?
Where can I read more about it ( BIBS ) ?
Doug
I don't have any specific resources, but a google on it gives a number of hits.IIRC both Piffin and Blogett (sp?) use it often..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
More about Bibbs
http://www.arcat.com/arcatcos/cos30/arc30635.htmlDont forget you tax breaks
http://www.energystar.gov/index.cfm?c=products.pr_tax_credits#s6http://www.dsireusa.org/library/includes/map2.cfm?CurrentPageID=1&State=MA&RE=1&EE=1
thanks
10 inches of icynene and you guys are worried about air sealing ?
i'm pretty confident that part's done.
insulmesh and then blow in cellulose. with all that foam, i can't imagine you'll even notice the difference.
who gets to drywall that ceiling ?
edit: maybe Mike Smith will chime in on insulmesh over 24" centers
carpenter in transition
Edited 4/10/2008 7:01 pm ET by timkline
hot dog.
View Image
carpenter in transition
Edited 4/10/2008 6:58 pm ET by timkline
I'm not worried about air sealing with my bldg- like you said, that part is done. However, I am concerned about conductive heat loss and that's why the cellulose is going in. Considering our rising energy costs and concerns with global warming, I don't think I'm going overboard by any means. Plus, I'd rather see the cellulose put to use in my ceiling instead of filling up a landfill.
The air sealing discussion relates to the foam vs. cellulose debate, which is still going on in my head. Cellulose is considerably (exponentially!) cheaper than sprayfoam, with the same R-Value as open cell. But, can it be air-sealed as well as the foam???
I'll be drywalling the arched ceiling myself, and am open to volunteers :) Free room and board to anyone who wants to see northern MN in the summer (that would be the one warm weekend in July...)
shawn
PS how do you size photos/attachments, as mine always come up too large??
I spoke with a tech rep from Greenfiber (makers of Cocoon brand Cellulose). He said there was no problem installing 12-15" of dense-packed cellulose with 2 foot truss spacing and 1/2" drywall. Since I need to go a little deeper with the cellulose (like 18") at the peak of my arched ceiling, he said just "add more screws" when installing the drywall.
For some reason, his overconfidence left me a little uneasy. I'd like to hear from anybody who has done it...
shawn
I have not done but would not hesitate to do it
Doug,
I left the truss space partially filled for cost reasons. The Icynene is very expensive! Originally, I had not planned to go any further with the insulation, as 12" of Icynene already provides R40 or so. But, in an effort to get the most energy efficiency possible, I now want to completely fill the truss space. So...cellulose seems like the best way to finish the job.
shawn
I left the truss space partially filled for cost reasons.
I figured as much, same reason that I'm doing it that way!
I have to pay about $1 per inch/per square ft, way more then you are.
Doug
I would recommend less foam and more cellulose- the installers like to spray two coats to be sure they get a good air seal, so 6" of spray foam (assuming you're using open cell foam) is plenty, and the rest can be cellulose. Next time, that's how i'll do it!
Around here I have to pay a buck a square foot per 1" thick.
I was going to have the spray foam done at the 1" and then dense pack the rest. My attic space is 1500 sq. so I'm already deap into it just to get that far. I wont get near the r-rating that I'd like but I cant have everything!
Doug
Doug,
Are you talking open-cell foam or closed-cell foam? In either case, I'd be hesitant to go that thin. The big benefit with the foam is its air-sealing qualities. With open-cell, they say you need at least 2-3" for this, and with closed cell, it is "possible" at 1" thickness. However, the reputable closed-cell installers that I've talked to won't spray this thin because you are likely to get leaks here and there; They like to layer it up with at least 2 passes to ensure proper air sealing, which requires more like 2 inches thickness.
I wouldn't use foam just for its R-value- its not cost effective! Open cell foam is about the same R-value as cellulose, and closed cell about the same (or less) as rigid foamboard. In both cases, the foam is a much more expensive choice....
If you do are very thorough job installating a vapor retarder layer, then blow in dense-pack cellulose, you could likely get the same performance (air seal + R-value) as a good foam job, but for a fraction of the price.
That's my two cents worth. Good luck!
shawn
Shawn
The 1" is closed cell and it would be for the air seal. I want the vapor retarder.
The guy actually puts out about 2" in all the applications that I've seen. We're currently in a house that he sprayed last summer, its still exposed because of changes the HO keeps making and I do see some areas that have shrunk away but I'd say that's less then 3%. I don't know how much that effects things.
If you do a very thorough job installating a vapor retarder layer, then blow in dense-pack cellulose, you could likely get the same performance (air seal + R-value) as a good foam job, but for a fraction of the price.
Your last paragraph pretty much sums up my goal.
My problem is that I don't have a large volume of area to insulate. This is in a 150 year old structure with real 3 X 6 trusses. I will strap, ala the Mooney wall system, to gain another 1 1/2" but that's all I have so its going to have to do.
If I was to use foam for the entire roof I'd have 1500 sq at 7.5" thick, at $1 per inch that would cost me $11,250! I don't know that I could ever save that much to warrant using all foam.
Doug
Edited 4/7/2008 6:57 am ET by DougU
So, why not just fill it completely with cellulose, then? When I priced it out last year, I figured cellulose at about $.05 per inch per square foot (installed myself). Compare that to a buck per inch per square foot for the foam, and it is a no-brainer. Is the minimal increase in R-value worth $1500?
Instead of the foam and Mooney Wall, what about a layer of XPS (or polyiso) sheathing on the inside of your ceiling, after the cellulose is blown in. This would boost your R-value, eliminate thermal bridging, and air seal...for about half the price of sprayed-in foam (if you do the work yourself)...
Just kicking around ideas, as I am working through the same issues myself.
shawn
Shawn
If I do the insulation the way you suggest, and that's certainly a viable option that I will look closer at, then I would need to run air baffles(or whatever they're called) to allow air to flow from the soffit to the ridge vents, right? I do like the idea of saving that $1500 for other things!
That's the part that's a bit confusing to me, I was trying to avoid the venting of my roof because I don't have any soffit vents, don't find those on 150 year old houses, Of course I can add them if needed.
Doug
I've questioned the whole ventilation issue ALOT in the past year, while trying to decide how to proceed with my house. After talking to alot of 'experts', as well as various postings here on FH, I don't see the need for it. Venting serves to evacuate 'dead' air from unconditioned spaces and/or to flush away hot air that is leaking from a poorly air-sealed ceiling. I gather that the practice of ventilation came about when we started insulating (albeit poorly) our houses in the 20th century. We are not in the 20th century anymore, but alot of substandard building practices still cause ventilation to be a good idea (I'm picturing recessed lights peppering the ceiling...).
However, if you remove the airspace (as in our cathedralized ceilings), insulate sufficiently, and properly air seal (with foam, or well-installed vapor retarders), then I see no reason to vent the roof deck. Essentially, you are building your roof like a wall, and we don't ventilate walls!
That said, I did use the foam on my project to ensure a good air seal. My budget for this entire LEED Gold certified house is less than $50k (self-built), so parting with the $700o to foam the entire structure was very painful. While the job was done very well, I don't think I would got this route again. There are too many examples of near zero energy houses built using foamboard, FG and cellulose- the key is in meticulous air sealing. I think the spray foam is more forgiving, but also more expensive. What's it worth?
Keep in mind I am a DIY'er building my first house- by no means am I an expert in building science. I have alot of research under my belt, but little experience. I'd love it if anyone else could comment on the topic....
Shawn
Oh, and why do you have a ridge vent if you don't currently have soffit vents...what are you venting??
I dont currently have a ridge vent, I was thinking that if I didnt have the spray foam then I would need to soffit and ridge vent. But I'm starting to see what your saying about the cathedral ceiling being just like a wall. Now I have to rethink my whole process!
Doug
shawn
This project is in northern MN- land of 10,000 lakes AND 10,000 heating degree days :)
And my brother in the Twin Cities would say
" The Land of 10,000 Regulations."
Search Mooney wall on this site. Mike Smith uses something like Insul Mesh from a insulation supply probalby on the net.
Rich
Take a guess at the acronyms and we will let you know if your close. ;-)http://www.regalind.com/techPDF/General%20Information/Insulating%20Cathedral%20Ceilings.pdfhttp://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htmhttp://www.insulationsupplies.com/Products.htm
So,, I like the way a Mooney Wall reduces thermal bridging, but I have a concern using horizontal strapping on this arched truss design. How do I install drywall and get it to follow a smooth curve? I'm not sure if the drywall should be laid horizontally or vertically.
shawn
Your trusses are a segmented arch, not a true curve. Do you want a true curved ceiling? If so you will need to do some additional framing to fair out those segments. Then two layers of 1/4" drywall wetted before it is installed should do the trick.BTW what did that foam job cost you?
Edited 4/6/2008 1:23 pm ET by reinvent
You are exactly right- it is not currently a true arch. So, my problem is how to make it into a true arch (and hopefully reduce thermal bridging in the process)! How to do that?
I was thinking of ripping 1/2 plywood into 2" wide strips, then screwing them vertically to the existing truss chords where they make contact. By laminating two layers, this would give me a solid nailing base for the drywall AND would take the shape of a true arch. Furthermore, could I also rip strip of XPS foam and sandwich them between the segmented truss and the plywood nailers, to act as the thermal break?
Or would the Mooney Wall concept work and give me a smooth arch for attaching drywall...
any thoughts appreciated,
shawn
PS The Icynene foam cost was about $3500 for a 10" deep spray. The roof area is about 900 sq.ft.; I think they were bidding the job at around 40 cents per inch per square foot....
The mooney will not give you a smooth arch.
The 1/2" ply might work. I would also try using strapping (it comes in longer lengths and you dont have to rip it) and see if you can get it to bend.
PIR is PolyIsocyanuRate
PUR is PolyURethane
Fabric is called Insulmesh, it's a loosely woven synthetic cloth. It holds back the cellulose (or fiberglass, I would think) without restricting vapor or air transmission.