calvinml
New Member
Posts:7
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| 02 Jun 2011 04:35 PM |
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We have talked to several builders in San Antonio Texas area about an ICF home and they all seem to think that for this climate ICF walls are not worth the extra cost. The attic insulation is what really matters. We were told ICF can add as much as 25% to the total cost of the house
We are now considering building with an unvented attic with spray foam insulation on the roof. Then framing using the advanced wall framing method with 2x6 24" oc with spray foam insulation and using the EFIS stucco exterior finish
Can anyone comment |
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Ray Gladstone
New Member
Posts:97
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| 02 Jun 2011 04:48 PM |
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ICF will maybe add 5% and your new house will not blow down with the next tornado. Why would you build with wood 24" on centers? Did your grandma never tell you the story about the three little pigs? They have a term for that: "Flimsy". Remember Joplin/Tuscaloosa. |
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Peter Jackson
New Member
Posts:29
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| 02 Jun 2011 05:05 PM |
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If you're going to sell the house in five to ten years, go ahead and build with sticks and foam. You have to remember though that a wood house these days is built with a lot of OSB which delaminates when it gets wet and stays wet, especially here in Texas. So essentially your wood house will require a lot a vigilance as your outside finish begins to age. If you're going to be in the house for longer than five or ten years, wood = rot, wood = termites, wood = mold. wood = fuel for a fire, etc. |
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Peter Jackson
New Member
Posts:29
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| 02 Jun 2011 05:06 PM |
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And yes, wood = tornado chow.
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Dana1
Senior Member
Posts:6991
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| 02 Jun 2011 08:08 PM |
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An advanced framing house with open cell cavity fill, no exterior foam comes in at a whopping R15 for a typical whole-wall R, which is ~R2 less than the minimal 2" EPS per side ICF. Of course, an inch or two of exterior foam (rigid board or sprayed closed-cell) brings it into the 20s pretty cheaply. It's generally more bang per buck to put the and inch or two of closed cell foam on the exterior, since it air seals more reliably, and you can then fill the stud bays with cheap fiber.
A 2" shot of ccSPF on the exterior, with a wet-spray cellulose or R21 batt cavity fill comes in at around R25 for whole-wall performance, for similar money a full cavity fill of open cell. An inch of exterior rigid XPS taped & sealed, and fiber cavity fill comes in at ~R19. Detailing the structural sheathing and stud plates as a primary air barrier using acoustic sealant costs peanuts, and can be as air tight or better than a cavity fill of spray foam.
With even an inch of exterior closed cell foam (rigid or sprayed) it's R value relative to the cavity fill keeps 100% the structural wood above midwinter dew point of interior air, so moisture drives from the interior are essential zero (assuming you ventilate and air condition the place.) And with the ~1 perm or less rating of 1" of ccSPF and even lower EIFS summertime moisture drives don't touch the structural wood. As long as you don't put up interior vapor retarders (not even kraft face batts) the wood stays nice & air conditioned-dry all summer, and with the exterior R keeps it from gaining moisture in winter. The only other paths to wood for moisture are related to flashing details, and the foundation sill . A good sill gasket makes an excellent capillary break, a copper-flashing capillary break extending beyond the foam on both sides is a termite-proof sill gasket It won't rot from moisture unless you're sloppy.
It's easy to buy a LOT more thermal performance per dollar going stick built. ICF's thermal performance related to it's mass has been oversold, as has it's ease of air sealing, but it doesn't really add up to all that much- the mass works much better when it's full inside the thermal envelope rather than wedged in the middle, and unless the rest of the house is detailed to be air tight, it's not dramatically tighter than any pretty-good stick built with only modest air-sealing details (like taped seam housewrap). The real advantages of ICF are mostly structural, fire resistance, and sound-proofness, all of which are good things, but if thermal performance is your goal it's cheaper to get there with other methods.
BTW: 24" o.c. AF 2x6 construction has the same structural capacity of 2x4 16" o.c. old-school stick build but beats it's thermal performance by ~50% even before enhancements like exterior foam.
Both 5% and 25% are exaggerations of the cost of going ICF compared to stick built of equivalent thermal performance. But an R20 ICF is pretty pricey compared to a 2x6AF fiber-fill + 1" exterior foam approach. Still, price it out.
Beyond ICF vs. stick built...
If you're REALLY serious about thermal performance you'll be very selective about window size, orientation, and type, since in an R20 wall the windows will dominate the heat gain/loss. Going with 25-30% less glazed area taking the minimum-reasonable for daylighting and view is cost-negative (smaller is usually cheaper.) Push-out casements & awnings seal better than double hung, single hungs, & sliders, and offer more egress cross section per square foot of glazing where bedroom egress code must be met. Fixed windows are even tighter. Designing both overhangs and window placements to minimize summer gain, yet allow for some winter gain can also be huge.
Air sealing as you go during construction is the single-most cost effective efficiency measure that can be taken. Define the primary air-barrier for the entire envelope during the planning stage, and make sure it's executed at each step. It's a lot easier to get a good seal with a bead of acoustic sealant under the stud plate BEFORE it's nailed down than anything you do to it after. Spray foam makes air-sealing easier, but like ICF it's not guaranteed.
Attic insulation matters, but designing the mechanicals to be completely inside of the thermal boundary is more important, and makes air-sealing the ceiling boundary & going high-R on the attis insulation much easier. The cost and thermal performance hit of adding a foot of height to the R20 walls to accomodate bringing the ductwork & air handlers indoors is minimal, and the performance gains significant.
First air-seal to under 2 air changes per hour @ 50 pascals pressure (ACH/50), insulate the slab edge to R5 or more (you can skip center-slab in San Antonio unless you're going all PassiveHouse on it), take it up to R15-R20 for whole-wall R on the walls, R50-55 ish in high-density fiber (14" of cellulose, 12" settled depth, not low-density fiberglass at any rated R-value) in the attic, use CRCC rated "cool roof" materials on the roof and keep the roof pitch 4:12 or higher, and be VERY picky about window size, type & placement. That can all be done reasonably affordably with or without ICF, and you'll have half the energy use or less of a typical code-min house.
Spray foam at the roof deck is a ridiculously expensive way to even make code-min, let alone high-R. If going that route consider putting 3-4" of rigid foam (any type) above the roof deck, air-seal the interior of the roof deck with an inch of closed cell foam, and doing the rest as cellulose or high-density new-school fiberglass like JM Spider blown-in-blanket at the rafters. With 3" of EPS you'd have to derate it's R to R10 or so during the summer, the inch of ccSPF would be ~ R6, so you'd then need ~10" of fiber to hit a whole assembly R of R50. That's cheaper than all-open-cell but more complicated to build, and still way more expensive than raising the walls a foot or so & keeping the ducts inside the insulation.
Consider this: Open cell foam on the roof deck R50 would cost you an unaffordable ~$6 per square foot of roof area. With open blown cellulose on the attic floor at R50 would be on the order of $1/foot (often less). Open cell at a code-min R30 would still be 3x the cost of R50 cellulose. Factor that into the performance picture of adding a foot of height to bring all the mechanicals indoors. An extra foot or so of wall height is a tiny fraction of the cost of a truly high performance sealed attic approach (or even a code-min sealed attic.) The primary advantages of spray foam are air sealing, and in some instances adjusting the vapor permeance for better moisture contro, in others, for thermal breaks on timbers, etc.l. Once you have the perfect air seal (attained by any method), it has no further advantage in a high-R assembly- let the cheap stuff do the heavy lifting on thermal control. |
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robinnc
Advanced Member
Posts:586
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| 02 Jun 2011 10:50 PM |
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Dana......have you ever thought about writing a book?.....seriously. You know a hellava lot about this stuff!
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Peter Jackson
New Member
Posts:29
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| 03 Jun 2011 12:11 AM |
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BTW: 24" o.c. AF 2x6 construction has the same structural capacity of 2x4 16" o.c. old-school stick build but beats it's thermal performance by ~50% even before enhancements like exterior foam.
50% is a really big number. Why such a big difference? |
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Ray Gladstone
New Member
Posts:97
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| 03 Jun 2011 08:31 AM |
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"Wood = Tornado Chow". I love it. I'm going to use that Pete, and I will attribute it to you the first three times. Then it's mine. |
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ICFHybrid
Veteran Member
Posts:3039
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| 03 Jun 2011 10:39 AM |
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50% is a really big number. Why such a big difference? Doesn't it have something to do with 2 X 4 construction having a 3.5" insulation cavity and 2 X 6 construction having a 5.5" cavity? (5.5-3.5)/3.5 = 57% deeper alone. Dana1 probably has the details on thermal bridging ratios, etc. |
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Dana1
Senior Member
Posts:6991
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| 03 Jun 2011 11:03 AM |
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Posted By ICFHybrid on 03 Jun 2011 10:39 AM
50% is a really big number. Why such a big difference? Doesn't it have something to do with 2 X 4 construction having a 3.5" insulation cavity and 2 X 6 construction having a 5.5" cavity? (5.5-3.5)/3.5 = 57% deeper alone.
Dana1 probably has the details on thermal bridging ratios, etc.
The whole-wall R of a perfectly installed R13 2x4 batted (or spray cellulose @ 2.5lbs density) studwall comes in at about R10 after the thermal bridging of the studs, sills, plates headers, and band joists are factored in. A 2x6 AF perfectly batted or spray cellulose studwall comes in at a bit over R15 after framing factors, a 50% boost in R. OK, that's really only a 33% improvement in U value, not 50- mea culpa! (Gettin' sloppy in my senescence!  ), so you really DO have to add R5 in exterior foam to pull the real 50% inprovement in U value. A decent comparative study of R values in mid & high-R assemblies (including ICF) can be found here. See Table 3 on p.9 for the quickie view of whole-wall Rs by assembly type. (Compare assembly 2a to assembly 1a & 1bii. Then compare 7a & 7b to 2a.) |
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Peter Jackson
New Member
Posts:29
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| 03 Jun 2011 04:18 PM |
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Well 33% is a pretty big number too, and you're saying that's mostly from the difference in thermal bridging. That's a pretty astonishing difference when you isolate it like that. And thanks for the link! |
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Ray Gladstone
New Member
Posts:97
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| 03 Jun 2011 04:27 PM |
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Yes, thanks a lot for that link. I have downloaded it and look forward to reading the entire whitepaper. |
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Dana1
Senior Member
Posts:6991
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| 03 Jun 2011 05:10 PM |
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BSC has similar discussions about high-R foundations & roof assemblies on their site as well. They're pretty readable for stuff written largely by nerds with PhDs. ;-) I find this one a useful guide for what might be long-term cost-effective in different areas, depending on the approach taken:
http://www.buildingscience.com/documents/reports/rr-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones
They've done a bunch of studies for the US D.O.E. as well, some available on the Oak Ridge Nat'l Labs and Lawrence-Berkeley Nat'l labs sites. Some are readable, others showing the real math, & less digested data targeted toward engineers & scientists. |
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mike morrison
New Member
Posts:18
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| 05 Jun 2011 12:36 AM |
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R values are only part of the picture K value is a bigger one I beleve Dana only quoted icf foam R value not as a system .and we can vent roofs with sray foam on the pitch of the roof with R 50 we also use tech sheild roof sheeting we see a 20 degree diference measured at open framing |
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ICFBdr
Basic Member
Posts:232
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| 06 Jun 2011 02:56 PM |
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Not at all related to energy efficiency, but the big problem of advanced framing in my mind is the 24" o/c studs (rather than 16" o/c standard) gives very little support for drywall. If you have any kids/grandkids, they seem to be rather rough in a house and seems like the extra spacing between studs is asking for damaged drywall. I realize this is designed to minimize thermal bridging, but I would hate to be patching drywall every 2 months. |
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The Sipper
Basic Member
Posts:264
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| 06 Jun 2011 03:59 PM |
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Of course, there is one other major building system that should be brought into any discussion such as the one that is the subject of this thread. However, there is another forum here that offers a more appropriate place to discuss that system. |
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| The Sipper |
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Dana1
Senior Member
Posts:6991
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| 07 Jun 2011 11:30 AM |
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Posted By mike morrison on 05 Jun 2011 12:36 AM
R values are only part of the picture K value is a bigger one I beleve Dana only quoted icf foam R value not as a system .and we can vent roofs with sray foam on the pitch of the roof with R 50 we also use tech sheild roof sheeting we see a 20 degree diference measured at open framing
As a system ICF is only buying single-digit percentage improvement in thermal performance compared to low mass wall systems of equivalant U value, in most US climates it's a LOW single-digit improvement. I was talking only "whole wall" R, not center-cavity R. The relevance of the K value of the center-cavity insulation compared to that of the framing diminishes rapidly at cavity insulation K values less than 0.25. (R4/inch) due to the miserably high 1-1.25K framing. Low-E roof decking is only meaningful in places with high sensible-cooling loads. It can make a real difference in low-moderate R attics, but it's not always commensurate with cost in a higher-R attic. It makes the most sense when ducts & air handlers are in the attic, outside of the insulation. Going unvented and thermally breaking with R15-R20 rigid or spray foam on the EXTERIOR will make a bigger difference in your exposed-framing temps. High-E/low solar absorption roofing materials and keeping roof pitches 4:12 or higher can make as much or more difference than low-E vented decking. |
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jonr
Senior Member
Posts:5341
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| 08 Jun 2011 09:01 AM |
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I haven't had any problems with 24" (vs the 16" used for interior walls) OC drywall. I wouldn't worry about it even with kids. |
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ICFHybrid
Veteran Member
Posts:3039
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| 08 Jun 2011 10:00 AM |
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I haven't had any problems with 24" OC drywall. I wouldn't worry about it even with kids. I've viewed a large number of houses recently that were built during the "irrational exuberance" of this last decade. A number of them were larger homes than the builders were probably used to building or maybe, they were just forced to use the drywall subs that they could get, but combining large, soaring walls with 24" OC framing can make for some pretty poor results. In most cases, these homes were billed as high-quality construction, but the poor results are visible for all time. A new homeowner-to-be should at least understand how the quality of the framers and the drywallers go together with big walls and AF design so they aren't surprised when their dream home comes out looking like something less than what they were shooting for. |
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BrucePolycrete
Advanced Member
Posts:524
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| 08 Jun 2011 10:15 AM |
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24" OC drywall is a cheap and cheesy way to build. I do not understand why anyone would want to live in a cheap cheesy house. Lots of floor space, but flimsy construction that will fall down in a high wind. Plastic hollow-core doors, cabinets that are stapled together with nary a dovetail in sight, molded EPS trim, vinyl siding, bouncy floors, yech! I made a pact with myself 25 years ago: No more cheap sh*t. I decided that if I couldn't afford high quality, I would do without. It's a policy that has served me well. |
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insuldeckflorida
Basic Member
Posts:157
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| 08 Jun 2011 10:37 AM |
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no argument with you academic types and other experts here on R value, K value, whatever...... BUT: what about sound transmission, floor to floor or external? (airport approach noise in my case) fire? tornado? maybe even hurricanes? termites? insurance? do i dare add re-sale value in 20 years? for almost 10 years now we live in an icf house with icf concrete floors and roofs (edited/added: plus some interior cmu and loadbearing icf walls) and a few huricanes under our belt.... whenever we visit our neighbors in their 2 story wood framed house house i realize how much i miss the house shaking when someone slams the front door, or the sound of kids trampling upstairs, and oh, that sweet sound of flushing toilets, creaking stairs or squeaking floors... just my 2 cents of sarcasm.... [email protected][email protected] |
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jonr
Senior Member
Posts:5341
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| 08 Jun 2011 10:52 AM |
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BUT: what about sound transmission, floor to floor...fire Don't forget room to room - those interior walls should be concrete too. |
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lzerarc
Basic Member
Posts:423
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| 08 Jun 2011 02:33 PM |
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and the sound transmitted through doors and windows. Doors and windows should also be concrete. |
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insuldeckflorida
Basic Member
Posts:157
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| 08 Jun 2011 03:12 PM |
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2" solid core lumber doors with 1" steel armor plating both sides should do the job...
or hollow core metal doors filled with molten lead....
who needs windows anyway?
:-))))) |
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Dana1
Senior Member
Posts:6991
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| 08 Jun 2011 03:53 PM |
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Structural & sound transmission aspects are all valid reasons for paying the ICF premium. I like ICF construction (I really do) but the thermal mass dynamic-R aspect of ICF has been over hyped- it's a secondary aspect. When going for truly high-R structures it gets to be pretty expensive (yet still worth it, for some.)
High mass homes perform a lot better when the thermal mass is NOT behind R8+EPS + foam & finish-wall. High-R counts for a lot more than high mass, in both comfort and energy use. At equivalent whole-wall R there is but a marginal (sub-10% energy use) advantage to ICF, that all but disappears if the interiors are designed with a modicum of thermal mass (slab floors, fat wallboard, etc.).
24" o.c. studwall construction doesn't have to be cheap in look & feel, or particularly noisy just because it CAN be in it's lowest-cost implementations. My in-laws built a 2-story w/full basement with dense pack cellulose in the cavities behind metal-lath hard plaster finish walls & fiber-cement clapboards, with gypcrete slab radiant floors (putting thermal mass fully inside the thermal envelope where it belongs.) It looks, feels & performs pretty good, and performs. Sure, it's less hurricane & tornado resistant than ICF, but to hit the same thermal performance (~R25 whole-wall R with the 2" XPS factored in) with ICF would have been a budget buster (and it WAS considered.)
It's been a good half-dozen years or so, the plaster hasn't cracked and the place hasn't fallen down yet, but give it time- I'm sure it'll feel "cheap" when it gets dead-centered by a tornado. ;-) It is at the top of a hill, and the wind-stresses are substantially higher than most in that town- if it were going to have issus they probably would have seen something by now. But you can't hear kids, or traffic outside without the windows open, and the coyotes are only evident when howling in the yard.
Squeaks & creaks in timber framed is usually a fastener problem- screwing rather than nailing critical components like subfloors (and using engineered joists for planar flatness & rigidity) can make a real difference.
Or you could just go with the absolute min-spec joists & subfloors, slam it all together with nail guns with the minimum allowable fasteners for the squeaky-creaky trampoline effect, and go with a vinyl siding over an inch or three of EPS, low density batts & half-inch wallboard and still get decent thermal performance so long as you've air-sealed it, but with a very different feel (and price-point and performance/$.) But you don't have to. Most custom-builds are done much better than that, because the buyers value more than mere thermal performance, even when they DO demand thermal performance. |
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galore
New Member
Posts:40
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| 08 Jun 2011 07:27 PM |
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Why is R25 using EPS with a concrete core a budget buster? I paid $0.25 per 1 inch thick EPS per SF. Type II EPS is rated at R4.5/inch so it takes a bit more than 5 inches of foam to achieve R25. Is $1.25/sf of wall space a budget buster? |
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jonr
Senior Member
Posts:5341
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| 08 Jun 2011 07:59 PM |
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Interior mass is only slightly better than middle mass. Factor in thermostat setback and I'll take middle mass (like ICF). All of this varies with climate.
I've heard people complain about concrete floors being harder on the feet - I think they like a little give.
But sure, same price for ICF + concrete floors and I'll take it over traditional stick framing.
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insuldeckflorida
Basic Member
Posts:157
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| 08 Jun 2011 08:15 PM |
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agree on the concrete being harder on your feet...
but also cooler in warmer climates, whether raw, stained, tiled or marbeled....
for comfort in colder climates add radiant floor heating (into the mass) or use carpet and good padding...
also workes well with real or laminate wood floors...
in the end you get what you really want and are willing to pay for... |
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insuldeckflorida
Basic Member
Posts:157
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| 08 Jun 2011 08:21 PM |
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Posted By insuldeckflorida on 08 Jun 2011 08:15 PM
agree on the concrete being harder on your feet, and colder in the cool months...
but also cooler in warmer climates, whether raw, stained, tiled or marbeled....
for walking comfort or colder climates add radiant floor heating (into the mass) or use carpet and good padding...
also workes well with real or laminate wood floors...
in the end you get what you really need or want, and what you are willing to pay for...
all you really do is spend most of your free time in it... |
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Peter Jackson
New Member
Posts:29
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| 09 Jun 2011 12:29 AM |
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I'm personally convinced that in central and west Texas that simply keeping the sun off the house with solar sails or trees would probably be as effective as any amount of additional insulation over say r-10. I'm going to prove it one day too =8^] |
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jonr
Senior Member
Posts:5341
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| 09 Jun 2011 08:07 AM |
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You have a point - 30% savings on cooling costs is common when shade trees are added.
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Dana1
Senior Member
Posts:6991
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| 09 Jun 2011 06:46 PM |
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Posted By galore on 08 Jun 2011 07:27 PM
Why is R25 using EPS with a concrete core a budget buster? I paid $0.25 per 1 inch thick EPS per SF. Type II EPS is rated at R4.5/inch so it takes a bit more than 5 inches of foam to achieve R25. Is $1.25/sf of wall space a budget buster?
Show me Type-II EPS that's rated at 4.5/inch. (Seriously?) It may approach R4.5/inch or so for the exterior third of the EPS in a very cold climate, the interior third is only going to average ~R4/inch. When it's 100F out that exterior third is going be averaging something like R3.75/inch- even less under sun-baked 115F+ siding. See: http://www.transconsteel.com/products/ultraframe/docs/Other_Properties_of_EPS.pdf (Type-II EPS is ~1.55 lbs/ft nominal density) And of course ICFs never get dinged, chipped or compressed in installation and experience no separations at the seams, so it really IS a perfect insulating plane with no defects...  Overstating R values by 12-20% I'm not sure what weight to apply to the rest. I can make all sorts of systems appear to have premium performance if I'm allowed to add 12-20% of fantasy-R. Type-II EPS is going to run ~R4 per inch, seasonally averaged, maybe a bit less in TX, and maybe bit more in ND, but it's not R4.5 anywhere south of Fairbanks AK. The cost delta issues for in my in-laws' place were timber framing vs. concrete (distance from the plant matters), and the cost of mostly-cellulose vs. all-EPS insulation package. YMMV And R25 whole-wall R wouldn't be considered "high-R" in US Zone 5, but it's above code-min. At R30-35 it would be, but even that isn't considered "superinsulated" by any means. (R50+, now you're talking, and they DO exist.) A gut-rehab project on a 115 year old building I'm consulting on right now is going to end up a hair under R30 for whole-wall R (full dimension 2x4 w/spray cellulose, 3.25" iso on the exterior), but that's not very extreme compared to some houses in the area.
jonr: I'll grant that the difference in dynamic R between interior mass vs. ICF isis pretty neglible in fairly temperate climates like
Seattle or strongly heating-dominated climate zones 6 or
higher. But in places with high
sensible-cooling loads and huge diurnal temperature swings in summer it can be almost
twice as effective to have the mass on the interior rather than an ICF. See: http://www.ornl.gov/sci/roofs+walls...e5.pdf
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galore
New Member
Posts:40
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| 09 Jun 2011 07:45 PM |
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So add another inch for $0.25/sf. Still negligible cost wise unless you are building above your means. |
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Dana1
Senior Member
Posts:6991
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| 10 Jun 2011 03:52 PM |
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An inch of Type-II EPS purchased as is only 25 cents a foot, or ~6 cents/R/foot?
Installed cost of Type-II EPS as sheet goods is about 10cents/R/foot, so a 1" would be more like 40 cents.
Is it somehow much cheaper to install ICF foam than sheet goods?
I can sometimes get used Type-I EPS for about about 3 cents/R/foot ( at which it's at rough parity with spray cellulose). Raw cost to me for virgin Type-II sheet goods is usually more like 7-8cents/R/foot, not 6.
Could it be that this is a 12-20% fantasy price discount that goes along with the magical R-value up-rating?
It's about half the installed cost per R/foot as EPS. At R25 it's not as big a deal as at R50, but it's still not nothing.
I suspect it was the concrete more than the EPS that would have broken the budget on their house (not that I saw all the quotes, which I surely didn't- it wasn't my project.) |
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TexasICF
Advanced Member
Posts:622
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| 11 Jun 2011 12:18 AM |
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Jonr said:
"Interior mass is only slightly better than middle mass. " I agree with this statement -- it is definitely true in the lab.
I've read at least most of the ORNL material on DBMS - Dynamic Benefit for Massive Systems (like the link Dana1 provided).
In digging through this data I found some interesting stuff.
DBMS charts comparing interior mass and ICF are based on R-17 ICF --- I don't know of any ICF on the market that has this low of an R-value so we can call this a hypothetical ICF at best. Not such a big deal since the entire study was about isolating the benefit of thermal mass. But if you read the small print you'll find that in order to extract the benefit of whether or not the mass is better inside or out -- both mass and R-value have to be the same for each of the computer models. Makes sense, if you vary r-value or mass for any of the systems you really can't isolate the benefit of the thermal mass.
So if you take your typical real life ICF with 2 1/2 inches of foam on each side of the 6" concrete core -- then the interior mass model has to use the same amount of foam and the same amount of mass in order to prove anything. Therefore, the interior mass system has to have 5" of foam to the exterior and 6" of concrete to the interior. I'm sure it did - in the computer model. Although it would be easy enough to accomplish -- this is a rare wall system in the real world -- I'll call this system a hypothetical competitor.
This report is often misquoted by folks trying to sell that internal mass is better. You might say that someting like CMU is better if you put 5" of foam on the outside. But CMU has a small fraction of the heat capacity of solid concrete. Then when you look at these systems you will usually find that they usually have less than 5" inches of continous insulation (LESS R value) and they don't have anywhere near 6" of heat capacity (LESS MASS).
I've found that the more I dig into this subject the more I realize that we really just don't know that much about it. Regards. |
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galore
New Member
Posts:40
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| 11 Jun 2011 12:26 AM |
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The $0.25 per inch per sf is what I paid for Type II EPS for my house. It wasn't a fantasy price discount but the actual amount I was billed by the foam factory.
My wall assembly is actually siding + 1" air gap/drainage plane + 7" EPS Type II + 8" concrete so I didn't purchase ICF blocks but used EPS foam panels inside conventional concrete forms with the goal of having the thermal mass inside and all insulation outside. I thought that the foam was exceptionally cheap so I was a bit puzzled by the statement that it was a budget buster... I would think that ICF forms would track similarly, price-wise. |
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toddm
Veteran Member
Posts:1151
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| 11 Jun 2011 07:52 AM |
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Ah yes, TexasICF. Insulation is good and more insulation is better. Or is it? Look at Fig 8 at the very end of this paper http://www.ibsadvisorsllc.com/_library/ORNL_Thermal-Mass_Energy_Savings_Potential_in_Residential_Buildings.pdf
If you used Logix blocks to built a house in Phoenix and I slipped 2 inches of EPS in a concrete form and poured 8 inches of interior concrete, which house would perform better? Cost less?
That R17 ICF doesn't exist today is neither here nor there. ORNL did this work in the '80s by comparing test buildings. (One suspects that R17 blocks did exist then.) Then the lab developed a computer model and tested it against the performance of these buildings. Hypothetical? Yes. Wrong? Well, construct your test buildings and prove it.
The fact remains that high mass houses have worked for centuries with zero insulation. It takes the right climate: dry, big extremes in daily temps but a comfortable daily average. I was amused to read that the builders of the Tucson zero energy house say that their approach to thermal mass needs more work. (R14 EPS over CMU filled with concrete.) Surely there are hundreds of adobe houses in Tucson that have worked just fine for decades.
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jonr
Senior Member
Posts:5341
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| 11 Jun 2011 11:41 AM |
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the interior mass system has to have 5" of foam to the exterior and 6" of concrete to the interior... this is a rare wall system in the real world Good point. And I suspect that most people will cover a poured or CMU interior concrete wall with an air gap + drywall - which makes it "nearly interior" mass. CIC (often thinner concrete sprayed over foam) looks to be pretty good and is capable of values all the way from R5 to R25. Last but not least, the savings from high mass can also be achieved with active systems - heat pumps or radiators + water storage tanks. Might be cheaper, more even in temperature and save more; definitely if there are off-peak utility rates involved. Galore - do you have more info on the cost for forms in your design? I wouldn't be surprised if it came out better than ICF. No problems with the foam floating upwards? |
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arkie6
Veteran Member
Posts:1453
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| 11 Jun 2011 01:16 PM |
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Posted By galore on 11 Jun 2011 12:26 AM
My wall assembly is actually siding + 1" air gap/drainage plane + 7" EPS Type II + 8" concrete so I didn't purchase ICF blocks but used EPS foam panels inside conventional concrete forms with the goal of having the thermal mass inside and all insulation outside. I thought that the foam was exceptionally cheap so I was a bit puzzled by the statement that it was a budget buster... I would think that ICF forms would track similarly, price-wise.
Do you have metal form ties protruding through your EPS insulation? If so, doesn't that effectively negate some/much of the insulation value provided by the EPS? Is your foam continuous on the exterior or are there areas where the concrete flowed to the surface? How did you attach your siding to the structural wall through 7" of EPS foam? |
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jonr
Senior Member
Posts:5341
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| 11 Jun 2011 03:50 PM |
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Here is what Certainteed does. One would hope that their R value specs are whole wall.
http://www.certainteed.com/resources/Fnd_ThermaEZE-Brochure_40-96-02B.pdf
Any foam joint can be glued to prevent leaks. T-Roc also looks interesting. Drywall + foam is installed in the forms, so combined with a textured pattern or thin stucco layer on the outside, the wall is almost finished right out of the forms.
http://www.greenstreak.com/subpacks/Stone_Pattern_Flyer.pdf
http://www.specformliners.com/Hack/PDF/SheetsPDF/1205.pdf |
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galore
New Member
Posts:40
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| 11 Jun 2011 07:30 PM |
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jonr - The foam is held by temporary form ties and doesn't float up. I have my own set of forms (about 200) that I built for about $3500 (HDO plywood) before I started construction. I used them on my basement (completed) and am now getting ready to pour the first floor this month.
I find ICF a very cool technology (that's why I'm reading this board) but was intimidated by the prospect of pouring myself. This whole building project is my main hobby (I totally love doing it) and thought that wood forms would be more forgiving w.r.t. blow-outs (especially using an internal vibrator). I also found it easier to embed conduit and plumbing in "traditional" forms but this may be easy to do with ICF. I don't know if ICF would have been cheaper. Apparently I am getting a good price from the foam company for EPS panels (and that company is also really easy to work with and delivers within 3 days (I purchase the foam for each floor, which is about 1500sf per order)).
arkie6 - I won't have metal form ties protruding the EPS and the foam is continuous on the exterior. The siding (4 ft x 2 ft glass panels) will be screwed to a steel frame that is attached to the top of the house (flat roof) and rests on the bottom (brick ledge) so there are no thermal bridges through the EPS. It's a contemporary house.
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jonr
Senior Member
Posts:5341
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| 11 Jun 2011 09:23 PM |
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The glass siding will collect solar heat?
I suppose one could stagger foam seams with multiple sheets to avoid any leaks.
For some hypothetical small single level house walls, might be $3500 for forms, $3000 for foam and $3000 for the concrete. ICFs might be $4500 + concrete if you can get them for $3/sq ft. Sounds like a wash at two stories, ICF wins at one. As far as I can tell, renting forms is outrageously priced. |
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toddm
Veteran Member
Posts:1151
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| 12 Jun 2011 09:45 AM |
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TexasICF writes, 'The interior mass system has to have 5" of foam to the exterior and 6" of concrete to the interior' to be comparable to ICF, to which I answer, bogus point.
You can get to the same place by increasing mass rather than insulation -- to the point of skipping insulation altogether in the desert Southwest. Add too much insulation, in fact, and the dynamic benefit stops working. Mass provides time shift -- a thermal lag that means that intense afternoon heat won't be felt inside until early morning. (Actually, heat rarely penetrates adobe or European-style high mass structures, but, rather, ebbs and flows in a diurnal flux.) Insulation increases thermal lag. Judging by ORNL's modeling of ICF in Phoenix's climate (see earlier link), its foam sandwich increases thermal lag to the point that it no longer buffers heat and cold there on a 24-hour basis. Afternoon heat that manifests itself on the following afternoon isn't getting you anywhere. Add to this ICF's interior insulation, which is like queuing up Augie Meyers on your CD player and then tossing a quilt over the speakers. The result for ICF is a modest bang for major bucks if energy savings is the criteria. That would not necessarily be true of hybrid ICF systems like Apex, Rastra, Durisol, or of AAC, except perhaps for the major bucks part.
Here is a good explication of high-mass dynamics: http://home.vicnet.net.au/~oversite/house.html
As the article suggests, mass offers little benefit in places like Minneapolis or Miami, where the thermometer rises or plunges to uncomfortable levels and stays there day after day. UCLA has a free tool called Climate Consultant 5 that will help you sort through a hundred years of San Antonio weather and come up with an appropriate energy strategy. http://www.energy-design-tools.aud.ucla.edu/ But if you read the fine print, CC5 is making assumptions about what constitutes high mass that could skew your analysis. Super insulation is more predictable and usually cheaper. Truth be told, mass is a gimme only in the high desert unless you have bigger goals in mind, like passive solar. Start with your local weather in any case. One suspects that cooling matters a great deal more in San Antonio than heating, such that ICF with night-time setback may recover its premium in, say, 100 years. |
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TexasICF
Advanced Member
Posts:622
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| 12 Jun 2011 03:05 PM |
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I do appreciate your opinion and the link to the report from a few posts back.
I contributed 15 Texas houses to the recent MIT study. MIT reported ICF buildings to be 20% more efficient than conventional. I believe this 20% better number is low (at least for Texas).
Why? (1) Many of our customers regularly communicate their utility bills. (2) I’ve lived in an ICF home for several years myself and know approximately what neighbors are paying and (3) About half of the Texas ICF houses contributed were built with conventional BAT attics.
All 15 Texas homes I provided to the study had sealed foam attics. Why? Because as most of you know, ICF is not ‘nearly’ as effective without taking the attic or roof into consideration. Imagine a screen door on a submarine.
I believe mixing these different ICF construction approaches knocked the final data down to 20%.
Regarding the link provided to the ORNL report from ten years or so ago. Why does the ORNL report say that ICF performs less than half to one third as well as the 20% just reported by MIT?
1st this ORNL report is actually a compilation of several reports and if you’re not careful you might read a section and think it’s talking about another area of interest. For example directly from the report:
“The steady state R-value traditionally used to measure energy performance does not accurately reflect the dynamic thermal behavior of massive building envelope systems. “
And they continue…
“Since the majority of U.S. residential buildings are built using light-weight wood-framing technologies, all energy performance comparisons in this paper are made against light-weight wood-framing buildings. “
Clearly, this report is a compilation of several reports…
“An overview of several historic and current U.S. field experiments are discussed. These experiments were performed in a wide range of U.S. climates utilizing several building sizes and shapes. Theoretical energy performance analysis is presented for a series of four wall assemblies. “
Is the report now talking about ICF and the other three mass walls types at this point? No.
“Burch built four one-room test huts at the National Institute of Standards and Technology (NIST) to compare seasonal energy performance of wood-framed, masonry, and log construction.”
“It was observed and documented that heating and cooling energy in massive houses can be far lower than those in similar buildings constructed using light-weight wall technologies”
At this point they’re still talking about wood-framed vs. mass.
Often misquoted, the portion about Burch’s research says: “Significant energy savings were noted for the house with a higher internal thermal mass”. Are we talking about the four theoretical mass walls at this point? Any type of ICF? No, although this statement establishes the superiority of mass walls we are not yet talking about internal and external mass just mass versus low-mass.
The report continues:
“Robertson and Christian investigated eight one-room test buildings that were constructed in the desert near Santa Fe, New Mexico, to determine the influence of thermal mass in exterior walls. The buildings were identical except for the walls (adobe, concrete masonry, wood framed, and log)”.
So ICF wasn’t included in part of this part of the study? No. It wasn’t. The section on Robertson and Christian continues…
“This study demonstrated that on small windowless massive test huts, energy consumption can be up to 5% lower than in a light-weight building. It is important to point out that during this study, the massive walls had about three to four times lower R-value than the wood walls (wood-framed wall R-value was about R-13 vs. R2 to R5 for adobe, concrete masonry, and log walls)”.
Just in case you missed that, the report continues…
“This gives a completely different meaning to the 5% energy savings that were reported.”
One might make the claim correctly at this point the internal mass is better but the report is talking about adob, concrete masonry and log walls, not ICF (not yet). At this point we’re still taking about adobe, concrete masonry and log walls compared to wood-frame.
Then the report discusses the 1999 NAHB study: “This suggests that most likely thermal mass related energy savings during the NAHB ICF study were in the neighborhood of 11%.
MOST LIKELY? Interesting? The report continues:
“Masonry or concrete walls having a mass greater than or equal to 30 lbs/ft2 and solid wood walls having a mass greater than or equal to 20 lbs/ft2 are defined by the model energy code [MEC-1995, Christian 1991] as massive walls. “
What? Solid wood wall that has mass of 20 lbs/ft2 is considered a mass wall by this study?
“They have heat capacities equal to or exceeding (6 BTU/ft2 F). The same classification is used for this work.”
This is a very low heat capacity to define a mass wall since the average density of concrete is 133 lbs/ft2 with a heat capacity of well over (20 BTU / ft2 F).
Regarding ORNLs BTC 1995 Dynamic Benefit for massive systems model (DBMS). According to the report: “DBMS should be used only as an answer to the question: What wall R-value should a house with wood frame walls have to obtain the same space heating and cooling energy consumption as a similar house containing massive walls?”
There is some groundbreaking work here but putting it into one mixing bowl has confused the intent of the research and causes many to misquote it. And folks continue to misquote the report. Take Bakersfield (figure 7), for example, sometimes used to say that the report says you only get a 10% improvement with ICF over conventional construction. What this chart actually says is that you will get a 10% savings with ICF over a conventional wall built to R-25. Not too many walls are conventionally built to R-25. Furthermore, regarding mass, if 15% of the density of concrete is considered a mass wall by the report what might we learn if we did a study with a higher standard for a mass wall? Put another way, how much better is ICF if you use a mass value of 130 lbs/ft2 – 140 lbs/ft2 and then compare it to today’s actual conventional construction of R-13?
Remember the computer simulation for the four different mass wall types including ICF used the same mass and the same R-value for each. My hats off to galore as he did not miss this point at all and built a custom system that exceeds what’s presented in the report.
The last statement in this report implies that the report was much more about ICF than most of its content and says: “It was found that for ten U.S. locations, ICF walls … the average potential whole building energy savings (ICF house vs. conventional wood-frame house) can be between 6 an 8%”.
MIT came up with a huge difference in favor of ICF and I believe it too is low. If you doubt it, just ask a neighbor living in an ICF home. Regards. |
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toddm
Veteran Member
Posts:1151
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| 12 Jun 2011 07:58 PM |
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Well, yes, TexasICF, but the Mad Hatter offended Time, as he explains to Alice, so he can no longer ask for it to be dinner at any point during the day, which explanation confuses Alice even more. "What if I'm not hungry?" she asks.
I am also disappointed in the work on thermal mass. ORNL's aim was to develop a multiplier so that consumers could calculate an effective R value adjusted for thermal mass and compare high and low mass walls correctly. Then the lab pretty much quit.
But the parties with skin in the game pressed on: "The Energy Performance of Log Homes" http://www.crockettloghomes.com/Pdf/Technical%20Library/The%2520Energy%2520Performance%2520of%2520Log%2520Homes1.pdf; "Thermal Performance" http://www.rastra.com/ThermalPerformance.html: "Thermal Performance for AAC Block" http://www.safecrete.com/products/techmanual/pdf/thermal.pdf
So where is the study from the ICF industry showing that ORNL had it all wrong?
One drawback is that an official number, even if it improved on 6 percent to 8 percent, would be a serious letdown from the wild claims ICF types have repeated for decades. The contractor who installed my ICF stem walls in '09 insisted that the effective r value for Arxx blocks was 45.*
The MIT study is a joke. It compared ICF and stick built in Chicago and Phoenix, but it was measuring much more than dynamic benefit. Its leading conclusion states (duh): "The advantages of higher R-value and lower thermal bridging enable ICF homes to deliver energy savings in heating, cooling, and ventilation compared to conventional wood-framed construction." http://web.mit.edu/cshub/news/pdf/BuildingsLCAsummaryDec2010.pdf It was funded by the Portland cement and ready mix industry trade associations. The 20 percent savings figure is vs. "code compliant" stick built in Chicago. I believe I have made the point that climate is everything in the dynamic benefit of mass. Others here have held forth persuasively on the notion that code compliant is not necessarily a high bar.
So, TexasICF, the answer is sitting right there. You know who to call at MIT. You'll want to ask for multipliers that correct R value for the dynamic benefit of mass in ICF walls in sample U.S. climates. Post pub date, I'll shut up.
* R45 on 30 random days each year during which the meteorological stars are perfectly aligned.
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