biggreen
New Member
Posts:6
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| 10 Feb 2010 06:26 PM |
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I'm renovating a 1885 2 story wook plank farmhouse and am having trouble deciding how to insulate the walls. I only have room for up to 2" of insulation. The walls are a solid 4" thick with 2 - 2"X12" planks sandwiched together. Inside of that there are 1 1/2" thick by 2 1/2" wide ferring strips (16" on center) on the walls that were used to attach the plaster and lath. I'm planning on adding 1/2" foam to the top of the ferring strips and then the drywall will match the existing door, window and trim height. That leaves approx. 2" of space for insulation. The 2 cost effective choices I'm considering are:
1. Using 3 1/2" fiberglass R-11 or R-13, compressed to 2". According to the charts I've looked at the R-11 should still yield about R-7.5 and the R-13 should yield about a R-8.5. It would be much easier to install and would fill all the high/low spots completely.
2. Use 2" foam where ever it will fit with a R-10 value. Some places will require using 1 1/2" with a R-7.5 value. Fitting tightly between the ferring strips and eliminating all air gaps will be difficult.
One good thing about the house is the solid 4" thick wood walls should add up to a R-6 insulation value.
Any advice would be greatly appreciated. Thank you |
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TexasICF
Advanced Member
Posts:622
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| 10 Feb 2010 06:58 PM |
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Biggreen,
Without boring you to death... the fiberglass is not the best choice since any air infiltration whatsoever results in R-zero (R-value tests are performed in a vacuum as you may know). The 2" of foam will perform much better even if it has the same R-value because it will greatly eliminate convection -- infiltration. This is the problem with fiberglass. Infiltration is absolutely not included in R-value. it's interesting that you note the reduced performance of compressed fiberglass without the air pockets. Since you note that the fiberglass would be easier to install you must have a friend telling you to use foam. He or she is right use the foam. Regards. |
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heatoftheearth
Basic Member
Posts:113
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| 10 Feb 2010 07:53 PM |
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Fill the whole 2" with foam |
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jbaron
Basic Member
Posts:122
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| 10 Feb 2010 10:01 PM |
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Perhaps I'm being naive, but couldn't infiltration be eliminated with a bit of caulking? If infiltration was a problem all of the time, all of the insulation in stick houses would be useless, right?
Jeff |
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glenfotre
New Member
Posts:75
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| 10 Feb 2010 10:08 PM |
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Posted By jbaron on 10 Feb 2010 10:01 PM
Perhaps I'm being naive, but couldn't infiltration be eliminated with a bit of caulking? If infiltration was a problem all of the time, all of the insulation in stick houses would be useless, right?
Jeff
Jeff - I can see that you are catching on quickly! While "all of the insulation" isn't "useless", you are not far from the truth!
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jass
New Member
Posts:6
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| 11 Feb 2010 04:45 AM |
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Try polyurea foam for insulation.It is costly but durable and result oriented. |
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Dana1
Senior Member
Posts:6991
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| 11 Feb 2010 11:22 AM |
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Cutting 2" foam to fit will require endless air-sealing to get it to perform to spec. You're higher-performance options are really 3:
1: 2lb density spray foams (polyurethane or polyisocyanurate), will yield the highest performance (~R12-R13), but at the highest cost per R-value.
2: Half-pound spray foam will be less than half the cost of 2lb foam, but delivers only 2/3 the R value (~R7-8-ish), and still forms a perfect air-barrier.
3: Wet sprayed (if applied when the wall is open) cellulose or fiberglass or dense-packed cellulose (after it's closed up) will deliver a true R7-8 with very low (but not zero) air infiltration. (Cellulose will have lower air infiltration, high-performance blown fiberglass wool will give you about R0.5 more in insulation value.)
Batts will inevitably have gaps, and that R8 compressed value will typically deliver something more like R6-R7 (still WAY better than R-ZERO), and leak air.
The heavy wood construction provides a substantial amount of thermal mass as well as some insulating value. In the shoulder seasons that should moderate heating/cooling loads quite a bit. Going with cellulose would add a bit more to the thermal mass equation. But an important key to overall performance will be getting a near-perfect air-barrier in place, and that means blown or sprayed insulation. Cut-to fit & compressed boards/batts are nearly impossible to make perfect, but sprayed stuff fills in & fits to near-perfection every time. |
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biggreen
New Member
Posts:6
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| 11 Feb 2010 10:30 PM |
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Thank you all for all the advice.
You've convinced me to go with the foam. The rigid boards will be hard to work with but will be less expensive than the sprayed in type. The best price I can find on 2"X 4'X 8' R-10 foam boards is $22.25. I think any small gaps can be filled with fiberglass to stop air flow. I'm planing on adding 1" of foam on the 2nd floor ceiling also that has R-30 in it now and I'll be taping all the seams on the ceiling and walls. |
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Dana1
Senior Member
Posts:6991
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| 12 Feb 2010 10:10 AM |
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Posted By biggreen on 11 Feb 2010 10:30 PM
Thank you all for all the advice.
You've convinced me to go with the foam. The rigid boards will be hard to work with but will be less expensive than the sprayed in type. The best price I can find on 2"X 4'X 8' R-10 foam boards is $22.25. I think any small gaps can be filled with fiberglass to stop air flow. I'm planing on adding 1" of foam on the 2nd floor ceiling also that has R-30 in it now and I'll be taping all the seams on the ceiling and walls.
Think again. Fiberglass has many nice properties, but it is about the LOUSIEST insulating material for blocking air flow. (Air filters are often made of fiberglass!) The small gaps are best filled with foam if you want the assembly to perform. If you have a lot of it to do (and it sounds like you do), invest in a 100-250 board-foot 2-part foam kit. If you have smaller amounts (which you don't) 1-part foam in the 20+ ounce cans with purpose-made foam guns are a lot cheaper/better than the cheezy li'l cans (Dow Great Stuff or similar) with the plastic trigger-nozzles you get at box stores. The sealant guns waste less, and the volume cost of the larger cans is much more cost effective. At $22/sheet for 16 square feet, 2" deep, that's $22/32= $0.69/board-foot plus sealants plus labor. (If you can get out for under a buck a board foot total you're a genius.) Half pound foam is typically $0.40-0.45/board-foot, installed price. 2lb foam is typically $1.10-1.20/board-foot installed price. By the time you've factored in the labor value and sealant costs you'll be at or over the 2lb foam cost, with a result that underperforms it in both air-infiltration and R-value. About the only time you can get the price/performance of rigid board to work in your favor over spray applied is large flat surfaces. It can sometimes work in cut'n'cobble situations like yours if you're using heavily discounted factory seconds or recycled goods (InsulationDepot.com or similar.) |
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TexasICF
Advanced Member
Posts:622
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| 12 Feb 2010 10:50 AM |
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Thank you Dana1 - very nice summation. Regards. |
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Bruce
Basic Member
Posts:142
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| 12 Feb 2010 03:45 PM |
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The $22.25 cost was for a 4'x8'x 2". That is 64 board feet at a cost of approximately 35 cents per board foot. |
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smartwall
Veteran Member
Posts:1209
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| 12 Feb 2010 08:03 PM |
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Blowin cellulose would be the best choice. The amount of overspray with poly will drive the cost up. It would be impossible to spray that small an amount and get a complete cavity fill. You would have to spray 4" inorder to get it to blossum into the complete space. |
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jonr
Senior Member
Posts:5341
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| 12 Feb 2010 10:01 PM |
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Where can I find the quantities of 1/2 lb two part spray foam at those prices?
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Dana1
Senior Member
Posts:6991
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| 15 Feb 2010 10:35 AM |
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tb1472000: Mea culpa! (I was reading that a bit fast- thought it sounded a bit high.) At 35cents/board foot you're at about the price/performance of half-pound foam after sealants, if you discount your labor to near-zero.
smartwall: 2lb foam isn't supposed to be sprayed more than 2" at a time (and usually isnt'). The excess volume would be near-zero, and the R-value more than 50% greater than with blown cellulose. Experienced installers can hit 2" lift practially in their sleep. It's a bit harder to be consistent at 2" with half-pound foam, but double the volume? (I don't think so.)
jonr: Almost all local foam installation contractors near me quote half-pound foam in that range under normal economic conditions, and many are discounting below that at the moment. SFAIK there aren't any half-pound foam kits out there- TigerFoam, Fomo-Foam, Froth Pak, etc are all much higher density stuff (1.5-3lb/ft^3) and the retail for about the same or more as the installed price as 2lb foam from the pros in my neighborhood. Unless it's a very small job
Two pound foam is a premium product at a premium price, but in an otherwise uninsulated cavity 2" is almost always cost effective from a 10year present value analysis on projected fuel use compared to the alternatives. Many foam installers used to go on about how "2" is all you NEED", but that was largely distortion/mis-interpretation of where the cost effectiveness argument takes a sharper pencil. When going for high-R layups it can get to be quite expensive, but when 2" is all the space you have to work with, it's the only way to go IMHO. The difference between 2lb foam and cellulose or half-pound foam will be EASILY measurable in the utility bills. |
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LarryT
New Member
Posts:84
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| 15 Feb 2010 12:18 PM |
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At $22/sheet for 16 square feet, 2" deep, that's $22/32=$0.69/board-foot plus sealants plus labor.
Dana,
Am I missing something? The price /board ft is 1/2 the way i calculate. He is talking $22/ a 4x8 sheet. that's 32 sq.ft, or 64 board feet for a 2" panel.
Other than that, I would agree with what you have said. Last thing I want to do is to piece in rigid foam and then seal.
LT |
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LarryT
New Member
Posts:84
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| 15 Feb 2010 12:19 PM |
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Whoops,
Didn't get to the next page.
Already said.
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biggreen
New Member
Posts:6
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| 15 Feb 2010 11:38 PM |
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Posted By Dana1 on 12 Feb 2010 10:10 AM
invest in a 100-250 board-foot 2-part foam kit.
Can you give me some sources for a 2-part foam kit? and how would I find a good installer in my area if I don't do it myself? I may give it a try for at least part of it. |
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Dana1
Senior Member
Posts:6991
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| 16 Feb 2010 02:05 PM |
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Posted By biggreen on 15 Feb 2010 11:38 PM
Posted By Dana1 on 12 Feb 2010 10:10 AM
invest in a 100-250 board-foot 2-part foam kit.
Can you give me some sources for a 2-part foam kit? and how would I find a good installer in my area if I don't do it myself?
I may give it a try for at least part of it.
Grainger carries kits, but it's usually significantly cheaper to buy direct or online if you have the time to wait for shipping.
TigerFoam
FomoFoamDow FrothPakTo find a foam insulation company in your area do a web search from the usual sources, or try this website. Be clear about what you're asking for- it's alternately called two-pound foam, closed cell foam or other things, but you want something that's ~R6 per inch or so. Half-pound foam is also called open-cell foam and is about R3.5 per inch of thickness. There is a continuous range out there though- some are formulated at 0.7lbs/ft^3 , 1.5lbs/ft^3, 3lbs/ft^3. R-value pretty much goes up with density to a max of about R7ish per inch for 3lb foam. There are probably a half-dozen brand names for closed cell ~2lb foam, and I can't say I can really tell much difference between them (other than some have interesting green or blue coloring agents. :-) ) Most are polyurethane base, some are polyisocyanurate, all are good, but only as good as the installer. It's a big chunk of change- get references, and go look at the work if you can. If it looks good, it usually is good, if it looks sloppy/lumpy/full of gaps that need to be touched up, keep looking. Get multiple quotes as well- some contractors are hungrier than others right now. |
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biggreen
New Member
Posts:6
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| 16 Feb 2010 10:50 PM |
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Dana1, Thank you for all the great advice. I calculate that I need about 3200 board feet of insulation (1800X2"). So that's well over $3000 for spray foam. The board foam is around $1000. I've done some already with the board foam and it is turning out quite well. The ferring strips on the walls are quite consistant so that helps, but they are 2 1/2" wide so I am covering them with 1/2" R-3.3 foam. The lower 1' sections where the wiring and outlets are I think I will use the spray foam. I tried to upload a couple pictures to show what the project looks like but the files were to large. I turned down the resolution of the camera but they still were to large  |
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Dana1
Senior Member
Posts:6991
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| 19 Feb 2010 10:10 AM |
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Posted By biggreen on 16 Feb 2010 10:50 PM
Dana1, Thank you for all the great advice. I calculate that I need about 3200 board feet of insulation (1800X2"). So that's well over $3000 for spray foam. The board foam is around $1000. I've done some already with the board foam and it is turning out quite well. The ferring strips on the walls are quite consistant so that helps, but they are 2 1/2" wide so I am covering them with 1/2" R-3.3 foam. The lower 1' sections where the wiring and outlets are I think I will use the spray foam. I tried to upload a couple pictures to show what the project looks like but the files were to large. I turned down the resolution of the camera but they still were to large
You absolutely need to seal it all with spray foam to get the performance out of it, and XPS will underperform 2lb foam in R value by ~18-20%. You need to add the (not insubstantial) cost of the spray foam sealants to your estimates as well- if you're lucky it'll be just one 600board-foot DIY foam kit (at $700, by the time you've added in shipping and extra nozzle tips, etc.) If you value your labor at zero you'll do OK, but even at minimum wage cut-cobble & seal adds quite a bit. If done perfectly with cobble & seal you end up with an average R-value of a bit under R10, compared to R12+ if done in 2lb foam. It doesn't sound like much of a difference, but when the R-values are that low the 5 or 10 year fuel cost difference still works out in favor of the more expensive insulation job. |
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