That dead air space won't do you any good unless it is virtually airtight, other wise it's just a path for drafts.
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That dead air space won't do you any good unless it is virtually airtight, other wise it's just a path for drafts.
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Hence the "Dead" part of dead air space.
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Nicely put,Originally Posted by Larry Edgerton
Mac
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Not sure why would use 2x4 outer walls in new construction. ??? Sure when selling some buyers will probally wonder same thing.
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Common with spray foam insulation as I've already noted. The major reason for the general shift to 2x6 walls is space for insulation and with closed cell foam coming in at R7.5 per inch, the extra cost of the thicker walls isn't necessary and helps to balance the cost of the insulation. But with fiberglass or other materials, I agree with you...no way would I accept 2x4 walls.
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The most expensive tool is the one you buy "cheaply" and often...
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Spray foam and typical 3.5" stud wall will give you fairly noticeable thermal bridging (in ~9% of you wall :: 1.5"/16"). IIRC studs have R-value of ~1.5/in. For full benefit of foam you need 2x4 wall studs staggered in/out on 2x6 plate - or something equivalent.
Also, keep in mind that with improved insulation and air-tight windows/doors, you can get indoor air quality issues. Today, its relatively easy and (sorta?) economical to insulate to the point that you'd need makeup air blower with air-to-air heat exchange on it.
There will always be a balancing act between costs: installation vs energy use vs live-ability (health).
Last edited by Malcolm McLeod; 03-05-2018 at 3:50 PM.
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I'd be curious too. Where did that idea come from. See, the whole point of insulation such as fiberglass is to create lots of small, disconnected, dead air spaces. Large dead air spaces are actually quite prone to convection air currents.
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Pat, this house has all kinds of unconventional thinking. The dead air space is inside 3 1/2" of polyiso foam, and serves two purposes. One a disconnect between the outside insulation and a path for wiring so that the outside envelope does not have to be compromised except where boxes are routed in. It allows 2" of foam behind boxes. Also the air currents do not make any difference as each individual section is sealed and so the and so air is not taking a part through the wall cavity but rather just moving around.
I have been doing dead air space ceilings for years with a sealed layer of 1/2" polyiso HD, 3/4" strips, all caulked in and then drywall. The results have been amazing and no problems with trapped moisture. This is the first time I have done it on walls, but this is an experimental house, so why not experiment? I have to admit the wiring issue was the catalyst but I am curious by nature. I have probes installed in the wall that allow me to keep track of the temp and humidity of the air in the airspace in the wall.
If no one tries anything new, nothing changes.............
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We did a deep energy retrofit on our 1950 garrison colonial that was an energy hog and added a 1000sf addition built to modern specs. The list of things we did was long, but included wrapping the old part of the house in 2" of blue foam, sealed and taped zip wall sheathing and insulating the 2x4 walls with cellulose, new windows (not "replacement" windows), spray foam in the attic and rim joists. and foam, 2x4 walls with fiberglass in the basement. The addition was panelized construction with 2x6 studs 24" oc, spray foam inside, rigid foam outside for thermal bridging, blown cellulose in the attic. We were fanatical about air sealing. Heating is a conventional inexpensive forced hot air furnace with zoned dampers. We installed an ERV for air quality and used sealed combustion furnace and water heater to prevent backdrafting.
This wasn't the "passive haus" level of cost or complexity, but seemed a reasonable compromise. Doing it again I'd probably go with staggered doubled 2x4 walls with cellulose rather than the spray foam for the walls.
The house is incredibly comfortable, with no drafts or cold spots. Our biggest complaint is that it won't cool down to a comfortable sleeping temperature at night, so we end up opening a bedroom window in midwinter.
Bottom line is it works; here's our energy report from a rather cold month (a week of near zero):
Screen Capture.jpg
Last edited by roger wiegand; 03-06-2018 at 12:27 PM. Reason: spelling
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I agree that experimentation is often the best way to confirm a new idea. On the other hand, there is quite a lot of published data related to insulation. A quick search yielded this for example ( http://hyperphysics.phy-astr.gsu.edu...es/Rvalue.html). This shows the R value of 3.5" of air as only R=1, contrast that with the R10/13/15 you can get by filling that same space with fiberglass insulation and you can see the dead air is not energy efficient. On the other hand, you have valid reasons for wanting the air spaces, such as for wiring, maybe sound deadening, etc and you may already have enough R value with your construction methods. The problem is coming up with data for your situation. I hope it works out well for you and your customer.
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We built a 1600 sf low tech, passive solar house in 1980. In 2007, we added a 1312 sf addition to it to the West. The original part has decent insulation 19 & 38, but nothing special.
The addition has double 3" exterior walls, 1" polystyrene on the outside between 1" nailers for the White Oak board on board siding. I think the outter part has 13 in it, and the inner paper faced 15. There is a 1" space between the two 3" walls with three horizontal spacers fastened to each 3" section. Walls are 10 feet.
The ceilings in this part are flat. Underneath the ceiling joists is 1" foam board. The 2x8 joists have R30 in between them, and then a layer of unfaced R30 running perpindicular across the tops of those. When the inspector looked at it, he said,"You know, code only calls for an R30 minimum". I said, "I don't care what the minimum is. I'm going to insulate the hell out of it."
The floor is R30 with the thin, fanfold foam board, like is sold to go under vinyl siding fastened underneath the floor joists, mostly to hold the insulation that I laid in there when we framed the floor-never liked those wires.
I think the biggest thing I did to help is the way I did the ends of the ceiling joists, where that space communicates with the ventilated soffit. I cut plywood bulkheads to take all the space, but fitted around baffles that let the air get from the soffits into the attic space. On the inside of those baffles, I used scraps of the 1" foam board, and sprayed foam around them to completely seal the ends of that space.
My Wife wanted a heated floor in the new bathroom, so it has one, but we can't use it. If we warm the floor up enough to feel warm to the feet, the room gets up to 90 degrees.
I had put ducting in that addition to work for a 2 ton heat pump, that HVAC contractors figured we needed for the addition. That's the size we've had forever in the original part.
I never thought that it would take that big of a unit, so we decided to live with it for a while, and see how it did.
Long story short, it never needed any additional heating or cooling, other than what it got from the original part. I ended up tying the return ducts together, and even though the ducting is now way oversized for the old 2 ton unit, it works just fine.
We built another 440 sf kitchen out the North side the same way. Still didn't need to add any more heat or cooling. We're in the process of building a 1068 sf gym on the East end, that will balance out the first addition to the West. We may put a mini-split in there, but we're going to use it first, to see how it goes.
Last month was the coldest since we've had the additions, if I'm remembering correctly. We have subpanels off of subpanels to the barn and shops, all off the home panel. There are two heated 16 gallon horse waterers, a couple of chicken waterer heaters, a heated bed for the outside cat, heat lamps in the hen house, a heater in the room in a shop where all the paint, and finishing supplies are kept, small refrigerator and water heater in the barn,boats, tractors, mower, and anything that has a battery but doesn't get used over the Winter much has a Battery Tender on it, and a couple of miles of 9 ga. aluminum hot wire along the top of the horse fencing, and probably something else that I forgot. Our electricity bill last month was a few dollars over 200. That's the first time it's ever been over 200, or even fairly close to it.
I never calculated anything. I just insulated the hell out of it.
[OP]
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It is any old house. The keys are to not include the wasteful options;
No sliding glass doors
No fireplace
No tall ceilings
No skylights
It is also critical to have good windows and doors properly installed.
Gas forced air heat burns about $600 in gas per year. 1300 sq ft plus full basement. 68 degrees at night, 72 in the daytime.
As an HVASC salesman / engineer long ago, I made load calculations for a number of buildings. The heating loads from largest to smallest are usually;
1. infiltration
2. window and door transmission
3. ceiling transmission
4. wall transmission
so spend your money and effort at the top of the list.
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I agree with your list with an exception on tall ceilings. I would agree that you are indeed heating more space, but the typical hot air at the ceiling, cold at the floor can be pretty much mitigated by paying very close attention to rule #1. If cold air can not come in and settle at the bottom pushing warm air to the top temperature differential is very minimal.
I will use my current house as an example. My main room, 26'x32' has 11' ceilings yet the temp differential between the floor and ceiling is always around 2 degrees. This is a copy of a schoolhouse that I owned in the seventies, and I can tell you that the temp differential on that place was about thirty. No hard facts but the loft was almost unbearable, and your feet were always frozen when on the floor. I always loved that place so I built a copy, but super efficient.
I studied Canadian methods of conserving heat years ago as an efficient home is good for repeat customers. They were doing pressure tests long before we started using them here. Another good source is Joseph Listbureks "Building in Northern Climates".
I use some of his principals in my houses, and have added some of my own. The "Thermos Bottle" ceiling I incorporate was an experiment on my own house that worked out amazingly well for example.
I bought a trashed after divorce house that needed a lot of work, but did not want to tear down the old ceiling because of the old rock wool in the attic, so I retaped the drywall, added 3/4" furring strips, then drywalled again, making sure that all electrical boxes were sealed. There was 5" of rockwool above, tops of the ceiling joists were still showing, and yet I could heat the house and hot water for under $100 in the coldest months, and I am above the 45th parallel.
In my current house I used the same principal but as it was new construction my first layer was 1/2' HD polyiso foam as is used under EDM roofing, sealed, furring strips crossing the trusses, all caulked in so if one section is compromised it would not affect the adjoining space, and again, all electrical outlets sealed, then 5/8" drywall. Some areas have wood ceilings, but there is a finished drywall layer under the wood.
This house, 1340 feet with 26 large glass windows/doors and 11'ceilings in about 2/3 can be heated for under $100 a month in the cold months. If I was not a claustrophobic and had a lot less windows it would be substantially less, but that is a price I am willing to pay. I now have a wood furnace in the basement with gas as supplimental and heat the house on 8-9 face cord a year I cut off of the property.
Last edited by Larry Edgerton; 03-09-2018 at 9:52 AM.
I built my house in MI in 1975 and thought I was being efficient by sheathing the exterior in 1" foam, then standard r-13 walls with 6" in the attic with vinyl windows. Code is so much better now. Last year I helped my son re-side a flip house with vinyl. In order to pass inspection, we had to completely wrap the house with Tyvek and tape it to the window and door frames to seal against leaks. Something I wish had existed 43 years ago. I have since added new aluminum clad wood windows and an additional 8" of cellulose insulation in my attic as well as insulating the garage and adding insulated doors there (I keep it at 42 degrees in the winter with a small unit heater). Also added a bunch of ridge and soffit vents and a 95% condensing furnace. House is still not very tight. I did have to have a fireplace though. Always shut the damper the morning after having a fire. I just totaled my gas bill for the last 12 months, it was about $550, not complaining. 1530 sf ranch with a walk-out basement.
NOW you tell me...
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"dead air space", sounds good in theory, very hard to execute and keep that way.
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