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Author Topic: R Value using Red Pine for Log Cabin build in Northern Wisconsin  (Read 1561 times)

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Offline dgrover13

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I am starting the process of a full round log LHBA style cabin build in Northwestern Wisconsin - as DIY project.

My question revolves around how to meet the energy code R-Value requirements for log cabin construction.

I have read that R-Value does not matter but Thermal Mass is part of the calculation.

From what I have found online in my county - the only requirement they have is a R Value of 15 for walls, and nothing specific or exempt for log cabin construction. 

I am finding that I will be building with Red Pine (White Pine preferred but more difficult to find) - as it is the best available species in northern Wisconsin?

How big of logs must I use to meet the energy codes?

Offline D L Bahler

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #1 on: March 12, 2017, 05:44:23 pm »
I've often heard as a rule of thumb you can figure about r 1 per inch of solid wood.

R value does matter, thermal mass can keep your furnace from running as much because it evens out the cycle, but if you lose air out the wall, you lose it.

It's difficult to make a log building thermally efficient

Offline Dave Shepard

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #2 on: March 12, 2017, 06:38:50 pm »
I have read 1.3 R per inch for pine. Even taking thermal mass into consideration, relying on just the log I don't think you will get enough insulation value. Here it's R21 in the walls, and many high performance systems are much more than that, double even.
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Offline Don P

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #3 on: March 12, 2017, 11:33:06 pm »
It's been awhile since I used it but DOE's website has a program called Res-Chek that does include several log options. The program let's you meet an overall performance target for the building. With log you might need to beef the insulation in the roof and play with the windows to pass.

Yup, if there is infiltration it doesn't matter if there is insulation. It's hard to beat a draft.

There is a table in ICC400-2007, the log home standard (iccsafe.org) that lists minimum average log width across the top of the table and specific gravity of the log up the side. The intersecting point is the r value of the wall, however the table has a stair stepped line diagonally across it that factors in the thermal mass, above the line the combination of R and mass is too light, below the line there is enough mass and R to pass.

Offline starmac

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #4 on: March 13, 2017, 02:06:44 am »
Not too many places get colder than we do here in the interior, and it is easy to heat 8in d logs or 10 in turned logs if built right.

Most natural log house builders around here like to have 14 inch tops.
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Offline breederman

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #5 on: March 13, 2017, 06:06:27 am »
I know when i built my kit house 30some years ago it was the only one that met code for nys. It is 10 inch. Wide white pine.
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Offline Don P

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #6 on: March 13, 2017, 07:57:01 am »
Red pine is listed in the Wood Handbook as having a specific gravity of .46, looking at the table in the log standard, that gives an R value around 7.6 to a 6" average wall thickness which is the minimum average wall thickness below that stepped line. At 8" avg thick the R goes up to about 10. At 14" avg thickness it goes to about R16.5. So that table is giving quite a bit of credit to thermal mass.

White pine has a sg of .35 which increases R but lowers thermal mass. To get on the happy side of the line an 8" avg thickness works and has an R value of 12... 2 more r points than the red but the log needs to be 2" thicker due to less mass, interesting.

Looking for how to arrive at the average width I ended up in the beginning of the standards under "log profile" 302.2.1.4 "The average log profile shall be drawn and dimensioned". Real helpful  ::). This is also the section calling for grading, my state code (VA) specifically calls for logs to be third party graded. Each state is different there.

Offline dgrover13

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #7 on: March 14, 2017, 09:31:23 pm »
It's been awhile since I used it but DOE's website has a program called Res-Chek that does include several log options. The program let's you meet an overall performance target for the building. With log you might need to beef the insulation in the roof and play with the windows to pass.

Yup, if there is infiltration it doesn't matter if there is insulation. It's hard to beat a draft.

There is a table in ICC400-2007, the log home standard (iccsafe.org) that lists minimum average log width across the top of the table and specific gravity of the log up the side. The intersecting point is the r value of the wall, however the table has a stair stepped line diagonally across it that factors in the thermal mass, above the line the combination of R and mass is too light, below the line there is enough mass and R to pass.

I took your advice and found some very good literature that highlights the actual points of R value.  The main point I am taking away is that with thermal mass of logs, you can count on a higher actual R-Value than would would be found through traditional calculations.  Also - the same document highlights you can compensate elsewhere (roof, floors, windows) to increase the overall efficiency and meet requirements. 

It would seem to me it would still come down to convincing your code inspector on these facts and for them to accept them.  Here is a great read - https://loghomes.org/wp-content/uploads/2013/06/EnergyPerformanceWP_2010.pdf

I am pretty much accepting that I will be building with Red Pine - and will calculate 1 R value per inch.  So to attain R Value of 15 - I will need an average width of 15 inch to meet the code - unless I can convince the inspector otherwise.

Offline Brian_Weekley

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #8 on: March 14, 2017, 10:52:44 pm »
Northern Wisconsin is climate zone 7/8.  In my opinion, R15 is inadequate for walls in your climate zone (regardless of the minimum code requirement).  “Thermal mass” of the logs does not have anything to do with R value.  It simply means that the logs will absorb some of the heat (and will give some of that heat back when you turn the heat off).  However, once the building reaches thermal equilibrium, the heat loss through an R15 log wall is no different than any other R15 wall.  Heat will always move from hot to cold (2nd Law of Thermodynamics).  R value is simply a measurement of heat transfer through a given medium.  The fact is more heat will be lost through any surface with a lower R value than one with a higher R value.
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Offline Don P

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #9 on: March 15, 2017, 01:07:02 am »
Build 2 boxes of identical size and R value. One of typical insulated lightweight construction, the other of solid timbers. Put a thermostat in each set to the same comfort zone. Change the outside temperature 30 degrees. Which thermostat kicks on first?

Set back the thermostat in both for the night. Which thermostat will go longer into the night without kicking on the heater?

 These standards are based on performance more than building by the numbers. The performance of mass assemblies has been tested, the cites are in the link dgrover posted. I'm not entirely disagreeing though  :)

Offline breederman

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #10 on: March 15, 2017, 07:24:36 am »
All i know is that my log home is more comfortable at 65 degrees than my lady friends stick house is at 72.  :)
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Offline timberwrestler

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #11 on: March 15, 2017, 01:31:40 pm »
I've always wondered about this myself, so I read through most of the pdf.  Reading it critically, it's pretty vague about the thermal mass effect.  Which I would suspect, because it's hard to beat physics/thermodynamics, as Brian pointed out.  It all comes down to Figure 4 (p. 20), and there's no explanation of where that magic came from. 

My thought experiment with thermal mass in an exterior wall is, what if the wall was concrete or stone, something very conductive with very little R value.  If it's warm inside and colder outside, you're heating the outside air for free through that wall.  Now logs have a higher R value, and are less conductive, but it's the same principle of heat moving towards cold.   

And breederman, I wonder if the difference between the two houses has more to do with they type of heat, or draftiness?  I'm curious.

Offline ChugiakTinkerer

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #12 on: March 15, 2017, 03:18:27 pm »
Not sure if it's any help, but the Alaska Housing Finance Corporation has a publication on log homes.  It's a 20 mb download so may take a while.

https://www.ahfc.us/files/5613/5716/0253/log_construction_logmanlo.pdf
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Offline Brian_Weekley

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #13 on: March 15, 2017, 05:21:54 pm »
Build 2 boxes of identical size and R value. One of typical insulated lightweight construction, the other of solid timbers. Put a thermostat in each set to the same comfort zone. Change the outside temperature 30 degrees. Which thermostat kicks on first?

Set back the thermostat in both for the night. Which thermostat will go longer into the night without kicking on the heater?
  :)

Don P, I agree with your example, but I don’t think it tells the whole story.  The thermal mass is like a battery.  Suppose you have two boxes with identical R15 insulation containing two guys peddling stationary bicycles running generators, and each guy needs to continuously generate 100 Watts to power a light bulb (representing the heat being lost to the outside).  However, one bicycle is also hooked up to a battery with some capacity to store extra electricity (representing the log thermal mass).  On day one, the guy with the battery is going to burn more calories keeping the 100 W output and using extra energy to get the battery charged up—not unlike the energy it takes to bring a cold log cabin up to temperature.  However, once the battery is charged, the guy on the bike with the battery is free to take rests and bathroom breaks, while using the battery to keep the 100 W light on.  The thermal mass makes this guy more comfortable at times.  Unfortunately, he will still have to work harder later to recharge that battery again and the net energy usage will be the same between the boxes.

Consider if one guy chose to increase the R value of his box from 15 to 20 (reducing the watts he needs to supply from 100 to 75).  He’s going to expend a lot less calories in the long run (with the battery or without).  The minimum insulation codes are meant to save energy (which is good for your pocketbook and the planet).  In cold climates, insulation is much more important than thermal mass when it comes to saving the fuel you burn and the BTUs needed to keep your house at a given temperature.  If we were forced to ride bikes to heat our homes, I bet a lot more people would care about the insulation value!   :D


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Offline breederman

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #14 on: March 15, 2017, 05:52:22 pm »
Brians example is my experience.  I am away  from home several days a week and electric  heat is set at 55 degrees. I come home and livht a hot fire in my indoor furnace, it warms up fairly quickly  as long as the fire keeps the blower on . If the blower shuts down it feels cold within a few minutes.  After a couple hours when the logs get warmed up it just takes a slow fire to maintain temp with the forced air blower rarely  oming on..
 I dont know the science but am happy with real life experiance of 3o years.
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Offline Don P

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #15 on: March 15, 2017, 10:25:41 pm »
I agree with a good bit of that, somebody used the term "thermal flywheel" one time. The coldest weekend you will spend is in a cold log cabin. When you leave it is comfy for 2 days.
 I'm not saying I am entirely in love with that standard. From my small perspective of what I've seen I do agree with Res-Chek and the table in the standard as good minimums though, which is what they are. I also think a 2 or 3 high log wall would be cool. I sort of predate the standard. We did use Res-Chek for permitting several times.

Offline D L Bahler

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #16 on: March 17, 2017, 07:02:28 pm »
The thing with thermal Mass is that having massive walls is not actually that terribly efficient. Yes it does store a good deal of heat like pointed out, in theory allowing your heater to run less often and to somewhat negate the loss of efficiency heating heating system. But major issue with thermal mass and walls is that not all of the heat stored in those wall is radiating back into the living area, in fact energy will have a tendency to want to move towards the low-energy side of things that is the cold side of the wall. Thermal mass is a lot more useful when it entirely contained within the living space, like an interior stone or brick wall, or a masonry heater of some sort. You really better off forgetting about the thermal mass of your walls and treating it as just normal insulation, and wrapping the inside of your walls with an insulating barrier of some sort if r value in insulation value and efficiency is your primary concern. Of course this has the disadvantage of hiding your log walls on the inside of the building. This is however the solution arrived at in the traditional log building regions in Europe.

Using Brian's battery example to further illustrate the point, a good battery might have 70% or so efficiency rate. That means nearly a third of the energy you create is lost somewhere in the process. The same is true with thermal Mass but in a different way. As a pointed out your walls are going to bleed a lot of their stored heat to the outside because they don't really insulate very well, and the cold side of the wall has a greater demand of energy.

The advantage of thermal mass lies in the fact that any heating system you have has an inefficiency. Exhaust for example, and the fact that it requires significantly more energy to raise the temperature of something then it does to maintain something at a certain temperature. So that's the basic idea of thermal mass is leveling out the temperature between the times when your furnace runs and trying to negate some of that inefficiency by leveling out the temperature listening heating system has to put into the air each time it runs.

Offline ScottCC

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #17 on: March 17, 2017, 09:01:13 pm »
Here is what I know, if you take two identical structures in a r-value sense (one log one stick) and heat and cool them for a year to the same comfort level ultimately the log structure will be cheaper to do this for a year.  Why, thermal capacitance I believe is the term.  The mass of the logs makes the air temperature you are heating to cooler and vice-versa.  Thus overall cost to achieve exact same comfort level is less.  Anyone with in-floor radiant would tell you this to be true.  Air temps above 72 are hard to tolerate.  Time to open a window in winter.  Try that in equivalent stick house.  Next, when doing res check it is not average wall thickness but minimum thickness you put in equation.  Your only as good as your weakest link.  Now drafts are drafts and go to workmanship not construction type.  An igloo can keep out a draft.  Lastly, kind of, a home is a system and needs to be thought of that way especially for insulative purposes.  You can and should increase performance of other structure components to compensate for some weak points.  Now, want to see the kicker, try my solution.

Notice the spline, adjust according to your needs.  Now when doing res check area with spline represents a percentage of wall with extra r boost from spline and rest of the wall now has a thicker minimum width to be plugged into res check calculations.
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Offline dgrover13

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #18 on: March 30, 2017, 11:05:48 pm »
UPDATE

I am moving forward with Red Pine for the cabin build.  I was able to hand pick 20 trees from a property about 3 hours away.

All were 18-20 inch butts - with typical taper calculation gives me about 13-14 inch tops at 33 feet.

Hoping to achieve a 15 inch average for my walls - which should keep me above a 15 R value.

Not digging or starting yet (will start foundation next summer).

I just wanted to get some logs laying on my property in preparation.  20 sticks will get me started, I can get 25 more next year.  Now my next step is to figure out how I am going to move them or raise them around my property.  Where do I find a used log loader or lift or tractor or crane that can lift 35 ft long logs?  ;D

Offline bucksnort

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Re: R Value using Red Pine for Log Cabin build in Northern Wisconsin
« Reply #19 on: March 31, 2017, 08:03:09 am »
UPDATE

I am moving forward with Red Pine for the cabin build.  I was able to hand pick 20 trees from a property about 3 hours away.

All were 18-20 inch butts - with typical taper calculation gives me about 13-14 inch tops at 33 feet.

Hoping to achieve a 15 inch average for my walls - which should keep me above a 15 R value.

Not digging or starting yet (will start foundation next summer).

I just wanted to get some logs laying on my property in preparation.  20 sticks will get me started, I can get 25 more next year.  Now my next step is to figure out how I am going to move them or raise them around my property.  Where do I find a used log loader or lift or tractor or crane that can lift 35 ft long logs?  ;D
My ford 545 loader backhoe will lift and move 50 foot pine logs with a 22 inch butt. I got it off craigs list for under 10 k