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mx2
millennium club
Joined: 18 Jan 2006
Posts: 1966
Location: Miami, Florida
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 Posted: Mon Jun 04, 2007 4:41 pm Post subject: |
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I don't know how to interpret your remarks...they seem quite pointedly sarcastic in reference to a serious proposal. I have never seen them either but I noticed that they've been presented on many sites that were pushing for energy efficiency and th article I quoted explains rather well as to their value, and in context to what I was saying before, it works well with the wall system by insulating the cover plate itself, rather than trying to build an entire wall that would essentially still allow air to infiltrate through the outlets. Are we on the same page or did I miss something here?
mx2.5
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*Art of Architecture: The conscious use of skill and creative imagination in the production of an aesthetic building.
*Science of Architecture: The calculated use of technical skill and knowledge in the construction of a functional building. |
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Mon Jun 04, 2007 6:55 pm Post subject: double wall construction techniques |
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mx, forgot you were from Florida. Those gaskets are pretty popular up here and I thought you were jokin around about finding out about them.  |
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mx2
millennium club
Joined: 18 Jan 2006
Posts: 1966
Location: Miami, Florida
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| Posted: Mon Jun 04, 2007 7:57 pm Post subject: |
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Ah! I get it now...yes, we don't spec them down here, BUT I will start doing so because, as we've determined here in this on-going thread, insulation is not only about keeping the heat (or cold) out but also about air and moisture AND keeping the heat (or cold) INSIDE!
Well you seem quite accustomed to local methods, and I noted you've not remarked about the foam fill in the outlets either, so is that also a common method up north? Prhaps it would be easiest to custom build and insulating "box" around the junction box before putting up the drywall (extend into the space & cut back to face of sheetrock)...or somehow insulate the box before installing them. Heck, you may even get a patent for insulated outlet boxes...you're free to run with it. 
mx2.5
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*Art of Architecture: The conscious use of skill and creative imagination in the production of an aesthetic building.
*Science of Architecture: The calculated use of technical skill and knowledge in the construction of a functional building. |
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Wed Jun 06, 2007 6:39 pm Post subject: double wall construction techniques |
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mx, I haven't mentioned the insulated/foamed electric boxes because as I have previously mentioned, I am really trying to avoid that energy detail. It's a good idea, and if all else fails, I will be using that detail. btw, there is a Canadian company that makes them.
Here is the construction scenario for the super-insulated, double wall with the vapor air/ barrier in the center. Theoretically, this wall should be able to dry to the interior and to the exterior. ( i am waiting to hear back from a couple of sources that may be able to shed some light as to what are the vapor/dew point/ condensation etc. etc. issues inside such a wall.
Now, you just finished raising the 2 x 6 outer wall...... the roof is on, the 5/8 cdx sheathing is installed, the housewrap is installed....all seams carefully taped and sealed, the windows are in. You take the R-21 cotton batt insulation in your hands (you don't have gloves or a mask on because you don't need them) and you carefully install the batt in the 24 inch bay. Now aside from a few wall penetrations (bathroom vent/oven vent) , there are no other obstructions in these bays, none. After installing all the R21 insulation, you seal up those bays nice and tight with 1" foam board, probably adhesive caulked so as to not make any holes in this air/vapor barrier. Think about that exterior wall ( R-27 with no penetrations, no wires, no obstructions, just full insulation). Now you frame up your 2 x 4 interior wall, 16 or 24" on center(your choice). Next, the electrician comes in, drills the crap out of that 2 x 4 non-structural interior wall. There are electric wires, speaker wires, security wires, but no plumbing because we don't want that in any of the exterior walls. Now when all that roughing is done, we carefully insulate these interior wall bays with the unfaced R13 cotton insulation batts. Again, no gloves and no mask, so we can really do a good job splitting the insulation to go behind and in front all of the wires strung across each bay. After we get the ok to close up the walls, 5/8 sheetrock is installed, rotozip around each electrical box and we are pretty much done. We can foam around each electric box, but its not that critical because the interior wall is well sealed up with an air barrier and R-27 insulation, against the outside elements.
That's my idea of a fairly environmentally friendly, R-40 wall, that should drastically cut energy consumption for a systems integrated active solar house. Open to discussion....... |
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Wed Jun 06, 2007 6:48 pm Post subject: double wall construction techniques |
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| Btw, the whole house is radiant floor heat. Another question to wrestle with is : what effect would floor heat directly under each insulated bay have on the wall cavity? |
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tfurry
Joined: 13 Jul 2007
Posts: 2
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| Posted: Fri Jul 13, 2007 11:19 am Post subject: |
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I'm new here, so go easy on me. My dad built the first earth-insulated house in the area about 30 years ago, and I guess I inherited his miserlyness.
I find myself in a two-story home built in the 60's in Kansas, U.S. It has 2x4 exterior walls with lapboard siding. The fiberglass batt insulation, from my initial pokings, was poorly installed into the wall cavities. I've kept a diagram around of a double wall construction method (there was no vapor barrier in it, however) hoping to build my own house someday. Now I'm thinking about retrofitting this two-story monster with a double wall retrofit...rip out the current drywall, replace the old batts with the new R15 batts, build a non-structural interior 2x4 wall in front of that, move the electrical etc. into the inside wall, and insulate it with the R15 as well. Debating whether to put the vapor barrier under the new drywall (full inside) or between the two walls (no cavity). But this should give me a near-R30 wall in an existing house where the monthly utility bills are climbing to around $300. Existing single-pane-with-storms windows would be replaced with low-E double pane windows (debating on vinyl or aluminum clad, we've got one exposure that faces SW directly into the evening sun).
Interested in what you guys come up with...looks like several good ideas are already on the table. |
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Sat Jul 14, 2007 3:11 pm Post subject: double-wall construction techniques |
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welcome to the forum, tfurry, you have an ambitious project .....good for you. I will toss out a few ideas and see what sticks. This topic brings up many questions (and a lot of opinions including my own) without an equal number of answers. As you have previously read, I have built several double-wall projects with good success and so far (about 14 years) no negative consequences. I wanted to improve the design and R-value with the vapor barrier (one inch foam board in the center of the wall, but hit a deadend with the question of potential condensation problems. (but I'm still workin on it)
As previously noted, the as-built design was as follows:
cedar siding, tyvek, 5/8 cdx plywood, R-19/21 stud wall, 1inch air space, R-11/13 stud wall with foil faced vapor barrier and 5/8 sheetrock to finish.
I wish i could tell you if it would be better to place the vapor barrier in the middle of the wall or behind the sheetrock but it seems to be safer to place it behind the sheetrock. Through practical experience, I prefer the center wall vapor barrier idea to isolate wiring, etc. in the non-structural interior wall and deter air infiltration around electrical boxes and other penetrations into the outer wall.
The more research I did, the clearer it became that even the experts are wary of recommending a one size fits all approach. One family living in a super-insulated home could be fine for 10 years and another family moving in could experience problems due to excessive humidity production or higher interior temperatures. A hygrometer and an air-to-air heat exchanger should probably be standard equipment. The vinyl clad windows may conduct a bit less cold than the aluminium clad but if they are wood core it may not make much difference (great idea to use non-expanding foam around the new windows). Also I am not a big fan of foam in the walls but others may tell you why it's better than double wall insulation. Most likely I will be using cotton insulation because of it's non-toxic nature. Another idea to consider is to install 1/2 or 3/4 inch foil faced foam board under the sheetrock and leave the cavity insulation unfaced. This method makes it a little harder to install the sheetrock but I am leaning towards this as an alternative vapor barrier material. Hope this helps for a start. |
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csintexas
millennium club
Joined: 06 Feb 2006
Posts: 1771
Location: USA
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| Posted: Sat Jul 14, 2007 5:01 pm Post subject: |
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Hi tfurry,
I don't think doubles walls would be a good investment in your case.
Three hundred doesn't sound bad for a house that age. That would be a big job and the wall is just one component of the house. Just moving the wiring out 3.5" would be a real pain with wiring that old.
Get insulated window frames, insulated doors, use spray in place foam in the attic. If you plan on having to re-sheetrock the exterior walls already than just rip off the existing sheetrock spray in foam cover with (a layer of extra foam if you want) and then sheetrock.
Personally I would leave those walls alone unless that they are in such bad shape that they had to be refinished. A geothermal heat pump would probably be a better investment.
that's my 2cents
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Sun Jul 15, 2007 5:25 am Post subject: double-wall construction techniques |
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Just a few additional comments..... I agree with chris that if the walls are in good shape and other components are basically ok, it may not be the best idea to rip everything apart to build the double wall plan. But that being said, if the house is in need of renovation, here are some reasons why I might proceed. Please note: I am not advocating everyone adopt this method, but I have used it, like it, and each person can make his/her decision as to its usefulness........
First, my financial breakdown would look like this:
(Btw, obviously the plan may make more sense for folks who are the diy type. It makes less economic sense to hire a contractor to do the extra framing and insulating, but if you do it yourself, the cost is not that great.)
To use an example of a 2 story, 2400 square ft. house with 1200 square ft. on each floor equals 140 linear ft of exterior wall on each floor or a total of 280 linear feet of ext. walls.
This translates to approx. 300 (2x4 studs) and 900 lf of plates. Total of
3300 linear ft. of 2x4 at (.35) per ft. equals $1155.
R-15 insulation for approx. 2400 sq. ft. of exterior wall cavities should cost about $1000.
Also, add about $250 for additional window and door jamb material for jamb extensions.
To keep the numbers simple, the cost of adding the extra interior wall
( if you do it yourself) is approx. $2500.
I am leaving out other costs of sheetrocking/ taping/ electrical etc. because the decision has already been made that these items needed upgrading and for new house construction, these items are a constant.
Next, a conservative savings per month (I think it would be more) might be $100 or times 12 equals $1200 per year. This leaves us with a payback period of about 2 years. If you hire a contractor to do the extra work for $4000 or $5000, the payback is still only approx. 7 years.
Furthermore, the additional advantages are as follows,
Once the initial investment and payback has been made, the owner pockets approx. 1200 a year, every year, but gross energy savings are
$24000 over a 20 year period. Also, with energy prices accelerating almost every year, the savings should be even greater.
$24,000 over 20 years didn't go to the utility companies and OPEC.
$24,000 in greenhouse gases were saved.
The added insulation makes the home quieter and more comfortable with the exterior walls having warmer surface temperatures.
Now of course, one may argue that foam or other insulation materials could be used, but I like the idea of not encasing all the mechanicals in a wall of foam.......(just a personal preference). Also, adding a ground source heat pump or other energy saving mech. equipment is a great idea. Extra rolls of unfaced insulation in the attic, insulated windows/doors, caulking and other energy detailing are critical parts of the total picture. In areas of very high energy costs (ie. Northeast) the savings are even more dramatic. |
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csintexas
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Joined: 06 Feb 2006
Posts: 1771
Location: USA
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| Posted: Sun Jul 15, 2007 7:40 am Post subject: |
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I do agree doubling the walls will eventually pay back.
I don't know where you are getting the 100 dollar saving figure from and I would question the accuracy of that (particularly in Kansas). Most energy loss (especially in a house of that era) is through poorly insulated and sealed attics, windows, doors and air infiltration in general. A typical house of that era can have the equivalent of a door left standing wide open in air leakage or more. Also the air conditioning system is probably not nearly as efficient as new systems. Often older duct works placed in unconditioned space leak and have little insulation. The quality of attic and floor insulation has much more effect.
Although I would guess that the payback on wall insulation increases as you move north and in your case birgco I think the double walls are a good idea.
I still can't figure out why you insist on a vapor barrier in the center though. Do you believe the experts are wrong?
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Modern Texas Home Project |
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csintexas
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Joined: 06 Feb 2006
Posts: 1771
Location: USA
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| Posted: Sun Jul 15, 2007 7:50 am Post subject: Re: air as an insulator |
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| arch*tect wrote: |
If air as an insulator is not good, then cavity walls would not be around as much as today.
As most would agree that cavity walls are constructed accordingly to the context of a site, for instance environmental conditions.
Would you not try this type of construction in your area? Maybe it worth to experiment it. |
I don't see cavity walls in use other than with masonry wall systems and that is a different case.
P.C. is correct, air stops being a good insulator when convection is allowed. That is why air by itself is a bad insulator and air trapped within insulation is a good insulator.
I like sundog's use of 3.5" studs in place of the 2x6 studs as long as the codes will allow them to be placed on 24" centers.
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Modern Texas Home Project |
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Sun Jul 15, 2007 5:08 pm Post subject: double-wall construction techniques |
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Hi Chris, I am not forging ahead with regard to attempting to place the 1 inch foam board in the center of the two walls but I honestly have not been able to find any authority who addresses the issue of a vapor barrier in double wall construction. As I have mentioned previously, the great attraction of possibly placing the foam board in the middle of the two walls, is that it virtually seals all electrical outlet boxes, wiring and other mechanical lines from the 2 x 6 outer wall. A 99.9% sealed outer wall is a potentially huge energy saver. Also, having personally experienced both standard R-19/21 wall insulation and R-38 + wall insulation, the later provided approx. 50% energy savings over the single wall. Without any active energy systems, the boiler size was reduced to 120,00 btu's from 240,000 btu's in a 3600+ sq. ft. house. The walls in these type houses are dramatically warmer and allow for additional reduction of thermostat settings because the walls are not wicking warm air. It is similar to radiant heat because occupants "feel" warmer because wall surfaces are warmer.
It's hard to fathom northeast energy costs. They are considerably higher than the rest of the country with several area utility companies currently applying for 17% and more increases. The northeast sucks the most energy of any area in the country and is closely watched by energy traders for indications of colder winter weather. I forgot to mention the codes will allow for 2 ft. o.c. placement of the studs which helps a little for material utilization. If you know of anyone who can definitively address the vapor barrier question I would appreciate letting me know. Most of the government sites and BCS only address 2 x 4 and 2 x6 single exterior wall construction. |
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csintexas
millennium club
Joined: 06 Feb 2006
Posts: 1771
Location: USA
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| Posted: Mon Jul 16, 2007 5:22 am Post subject: |
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I still think you can look at is as being no different than a 2x6 wall (just thicker) If they say no vapor barrier is needed in your climate zone for a 2x6 wall than it stands to reason no vapor barrier would be required for a 2x12 wall either. That just means that the foam board you chose should be permeable but it will still stop air infiltration. Also since no air space is present (I assume) foil would not be effective.
I would suspect that other factors where involved in the reduction of heating BTU's required. In other words, if I had two identical houses (except one had thicker walls) I would not expect a 50% reduction in energy consumption. Just off the top of my head I would guess 10-20%.
I suppose that it would be easy enough to calculate if one wanted to know for sure.
Tight sealing is possible with any thickness of wall so I don't consider that a great advantage of your system.
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Modern Texas Home Project |
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Antisthenes
Joined: 28 Nov 2006
Posts: 593
Location: Phoenix
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| Posted: Mon Jul 16, 2007 1:55 pm Post subject: |
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build it tight ventilate right
i like air walls with hard shells personally
or a perfect amount of mass for variable thermal lag
or a good mixture of the 2 mass:insulation
every location and orientation will be different, even the different sides of the structure.
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birgco
Joined: 01 May 2007
Posts: 302
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| Posted: Mon Jul 16, 2007 4:19 pm Post subject: double-wall construction techniques |
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Vapor barriers are a hard and fast code requirement for the New York metro area. They can be kraft paper fiberglass, foil backed fiberglass/ foil backed foam board or even foil backed sheetrock, so attempting to change the location to the center of a double-wall design is kind of a big deal.
One thing that makes it easy to underestimate the effectiveness of the double wall is the theoretical versus the real world application. At the risk of repeating myself (sorry about that), when standard 2 x 4 or 2x6 walls are insulated, they are seldom done correctly. There is so much crap in the average wall today, wiring etc., that unless you encase everything in a wall of foam (not my favorite insulating material), achieving advertised R-ratings is virtually impossible. The separate, non-penetrated R-21 - 2x6 exterior wall of the double wall is the workhorse of the system. I also believe that when you consider the average house has about twice the exterior wall exposure versus 2nd floor ceiling exposure, it's not a stretch to see how cooler wall surfaces would make an interior feel less comfortable (like radiant heating in reverse). We may have to agree to disagree but any discussion that helps to further the goal of energy conservation is worth the effort.
Btw, i would like to hear more about air walls with hard shells??? |
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