Log Size

[sekoutdoors]

I wanted to know what log size would provide good "insulation", what are "standard" log sizes?

[Shark]

Depends on your area, how cold it gets etc, but it seems most people don't go less than about 9 - 10" average diameter.

It's not as much about the actual R-value of the log, but the thermal mass that the logs provide.

[StressMan79]

Thermal mass only matters if you have a big swing in temperatures. If it is cold and stays cold, thermal mass will help you zero. That being said, I agree with shark that you wouldn't want to go below 9-10", but I would say minimum, rather than average diameter. The scale of the home also comes into play. if you are building a 14x14 ft starter cabin, smaller logs may be appropriate. if you are building a massive 50x50 cabin (a la skip) you'll want larger logs. Skip used ~24" tops. Those logs are huge.

-Peter

[sekoutdoors]

I am just learning about log homes. I understand the that I am looking at thermal mass. I was looking for a minimum size, and what may be to big to work with. I have seen one foot diameter logs, and thought they are a nice size, but I live in NE Montana, and wasnt sure it would be thick enough for some of the bone chilling weather here.

[sekoutdoors]

The cabin I am looking at is 48X27

[Klapton]

Are you talking about an existing cabin? Or a design to build your own?

If you are looking to build your own, a 36' x 36' square design will get you the same square footage, but will cost you less in materials for your foundation and roof, and ~40' logs will be cheaper than the 50' ones you would need to build 48x27.

[Yuhjn]

The cabin I am looking at is 48X27

My first piece of advice would be to take the class. In it you'll learn a whole list of reasons why you probably want to build a square house. I dont want to get into all the details but I will list a couple for you:

First of all it will cost a lot less to get the same square footage. Because of some rules in geometry (that I'm not getting into here) a square area maximizes your internal area relative to your perimeter. So for you, a 48x27 gives you 1296 square feet. But if you build square you can get that by building a 36x36 (also 1296 square feet). This will make your logs a LOT cheaper because you dont need 53 foot lots for your long dimensions.

You're also worried about heating. Well the more extrenal surface area you have, the faster your house will cool down. If your house is square you have minimized surface area realative to your internal square footage.

There are MANY other reasons to build square.

But really my main point is that if you take the class you'll learn more in 2 days that you can imagine about how do properly build a log home.

[sekoutdoors]

About the class, it sounds great, any held in Montana? I also like the 36x 36 idea. But still curious about log diameter for my area of Northeast Montana.

[Yuhjn]

About the class, it sounds great, any held in Montana? I also like the 36x 36 idea. But still curious about log diameter for my area of Northeast Montana.

I live in Bozeman and just drove to Seattle to take the class. Missed some work but it was well worth it. Unfortunatley classes are only held at Skip's ranch outside Seattle WA. This is kind of important though, at least for me it was.

Several times you are told things in the class that seem to good to be true or somewhat incredible (no settling, only chink once, etc), especially if you have already gotten an "education" from the kit guys. It makes a whole lot more sense when Ellsworth says "yes, it will work, that's what we did on this house... see for yourself that it worked." when you are sitting inside Skip's 7000 square foot log mansion. If he came into your living room and said those things, it would be harder to believe.

When Skip says "In my opinion this is the best way to build" it has a lot more impact standing in front of a MONSTER example of what he's teaching.

Having those real world examples all around you (including buildings built in styles other than BnP) really helps with the learning.

[TOMGION]

THE CLASSES ARE HELD IN MONROE WASHINGTON.
ASKING THIS QUESTION STIRS THE WRATH OF THE GODS.

[sekoutdoors]

Well, that would be nothing new to me, seems I do that and dont even know it! I don't mind the travel to Monroe, sounds like that is the place to be, I know I could'nt have gone to the east coast for it, so I wanted to ask.

[kahle]

I thought SKip's house was 6000 square feet. Has it grown?

Wood generally provides a resistance to heat transfer (R value) of about 3 per inch. So a 12 inch log is about R-36 at the thickest part. Of course the thickness of the log varies butt end to scale end so the best you're going to come up with is an average. The largest logs go on the bottom of the wall, and then they get smaller as you go up. If I had a rule of thumb to suggest, I would look for logs approx 12" diameter on average. Bigger ones for the bottom of the wall, smaller at the top. The thinnest part of your wall will be at the chinking points which may get down to as little as 6 inches or even less. However, the combination of thermal mass with a medium R value makes a log cabin the best possible structure for these cold climates. I disagree that it only works when the temperature outside fluctuates. A log cabin would not work well in Hawaii where temperature runs from 80 - 90. But in Montana even if you get one of those weeks when it hits -20 and stays there day and night, you have sunlight in the daytime that adds heat to the structure and (hopefully) a roaring fire inside the house during the day. Thermal mass will help retain and distribute the heat from both of those sources.

Thicker is better as far as keeping the structure hot in winter and cool in summer but cost and ease of construction count for something. Ultimately, as Skip said, the best logs to build with is the the logs you got.

[Yuhjn]

I thought SKip's house was 6000 square feet. Has it grown?


Skip's house is quoted to be 7000 quite often. I believe the actual square footage is like 6750 or so? (I dont remember the exact number).

So I think it's more a matter of if you want to truncate the number or round it off.

I'm also fairly sure I heard LHBA staff quote it at 7000 as well.

(Edit: I've actually just googled a bit and found links to Skip's personal info page as well as the old LHBA page that both quote the size at 7000)

[Klapton]

Well, that would be nothing new to me, seems I do that and dont even know it! I don't mind the travel to Monroe, sounds like that is the place to be, I know I could'nt have gone to the east coast for it, so I wanted to ask.
Apparently Tomgion posted a similar question in a couple places, and one or more of the posts was deleted because of redundancy or something. Anyway, he's a little annoyed that his posts got moderated. I do hope he'll lighten up a bit, and find his capslock key. But yeah... the class is held at Skip's house. Donna and I flew out from PA, and it was WELL worth the time and expense.

As for log diameter, basically bigger is better. I know that's a pretty simple answer. 12" is definitely big enough to get as good or better R-value than anything stick built. The number, size, quality, and placement of windows and doors will probably have a much larger effect on your heating bill than 12" vs 14" logs. More and bigger windows = more heat loss. Cheaper, single-pane windows = lots more heat loss. Crappy installation of those windows can = TONS of heat loss.

[sekoutdoors]

We have looked at placement, of and type of windows, we aint going cheap, want a real tight house! I am thinking that 12 to 14 inch logs will be checked out. Thanks!

[StressMan79]

Sek,

Dunno how "tight" you want to go. You definitely want to keep the weather out and the heat/AC in. Consider moisture, however. You'll either want to have plenty of ventilation (vents, fans, etc) or maybe not make the outside quite so "tight." Anyway, you can get surprisingly good windows for cheap/free. I have 7 large brand new vinyl double pane windows that I picked up for free.

The only reason I can see to "not go cheap" would be for the reason that paul had: He didn't want vinyl windows in a log home, so he had some wood ones made. They are beautiful, but I think they cost ~25% of the overall cost of the home.

It's your choice.

-Peter

[Klapton]

If you use mortar for your chinking rather than the slick synthetics, you won't have the problems that you might get with a super-vapor-barriered stickbuilt home. Of course, opening your windows periodically to get fresh air is a good idea no matter what kind of house you live in. But I think by "not going cheap" on windows, the main thing is to at least have double-paned windows. Also, window manufacturers publish technical stats on their engergy effeciency. So, balancing energy efficiency with price is something that one should consider. In any case, proper installation to avoid drafts is important.

[sekoutdoors]

I want a tight house, no drafts, but understand good venting as well. I was interested in the chinking, and we are looking at double pane, and don't have a lot of them to worry about.

[Rowjr]

What size of log would you use using 26x38 dimensions for a cabin in West Virginia

[Klapton]

What size of log would you use using 26x38 dimensions for a cabin in West Virginia
The general rule is that bigger is better. The greater the diameter of the log, the fewer logs you will need to achieve the desired height, and the greater insulation and thermal mass the logs will have for energy efficiency. Plus big logs are just beefy and kewl. Also, the straighter the logs are, and the less taper they have, the better. (Douglas fir is one of the best species for log homes for this reason.)

If you are going to build a house that isn't square, you will have more difficulty accounting for taper. The logs on the longer side will get skinnier at the far end compared to the shorter side, etc. Also, you could build a square home and get more sqaure footage for the same size and number of logs. For example 35 x 35 = 1225 sq ft per floor, but 26 x 38 is only 988. This would enable you to accquire all the same size logs (minus cap logs and ridge pole, which would have to be longer), and have less difficulty with levelling your corners due to differing amounts of taper.

[Rowjr]

I guess I should be a little more descriptive, I meant what size log should you use for the ridge or peak of the roof 36' feet long say I'm going to use 12" logs for the wall and rafters...probably going to need a center support along that 36' length ? Or one large log...

[RockEngineer]

The ridge pole size depends on a variety of factors.
Snow load, length of supported rafters, span between supports, log species and log grade. That's where the engineer comes in. If you are going for ridge pole envy for the most massive ridge pole, then the logs own weight can be a big factor.

[cntrydan]

Paul, everything I can find from various sources suggests wood R value is considerably less than what you quote. Even with an adjustment for so-called "mass" effect, the number is still much less than what you state.

Can you clarify or guide me to understand the difference??

Thanks

dl

[ChainsawGrandpa]

Where are you located in Montana?
I know of lodgepole pines that are 22" ABH.
Might be worth a look or could be way to far.
Montana is a big state.

The larger the logs, the less you will chink.

-Rick

[2 cents]

I'm quoting the following from the Enertia site, which uses a building envelope in their design, but the same applies to solid wood walls, ie log homes.

DELTA T
All architects and engineers work with the Heat Loss Equation. Heat loss equals the temperature difference (Delta T) divided by resistance (the familiar R factor). All modern attempts at energy efficiency have focused on the "R" factor - i.e. more and more insulation into a thicker wall. But reducing Delta T has the same effect - why not look at that? While insulation is necessary to increase "R" factor, Delta T can be reduced by natural means.

SOLID WOOD
In 1981 the National Institute of Standards and Technology constructed six test buildings in Gaithersburg, Maryland and tested them for energy efficiency. Much to their surprise, Building 5, with walls made of solid wood, was the most energy efficient. This was attributed to "thermal inertia," a phenomenon where the solid wood walls stored energy during the day, and released it during the night. Actually the energy efficiency of solid wood is well known in the Scandinavian countries where it is the prevalent method of building. (Its long life is well known too. When interviewed during the 1994 Winter Olympics, a Lillehammer couple casually remarked that their solid wood home had been built in 1406!)

THERMAL INERTIA
The use of daytime heat at night, and nighttime cool by day, is made possible by Thermal Inertia, and the engineered Lag-in-Time is a property of the thickness and Specific Heat of the solid wood walls.


http://www.enertia.com/Science/HowItWorks/tabid/68/Default.aspx

[cntrydan]

With all resepct, I would be a bit careful about quoting and using information from a commercial website, particularly conclusions, without considering the details of how those conclusions were obtained. Particularly a kit-built site. The principals of Delta T over R, (usually referred to as uADelta T ) are pretty well used and accepted as tried and true. That's not to say I don't plan to build a LHBA home, And that's not to say thermal mass doesn't have an effect on energy consumption, under certain conditions. A fire-warmed rock in a sleeping bag is an old campers way of using "thermal mass" to keep warm. But the R value of that bag, and the delta T between the interior and exterior, play a significant role in how long those feet stay toasty. Thermal mass or not. A log wall does not change "T". "T" is what it is. If ambient temp is greater than the log, or the sun shines on it, then it warms to approach ambient or absorbs the suns radient energy. If ambient then drops, the log releases that energy in the form of heat as it cools to approach the new ambient. No magic. Just thermo. If it was a warm day, or the sun shone bright, good for you. The logs will help keep you warm on a 20 degree nite. If it's been 20 degrees for 3 cloudy days, I have a feeling uAdelta T will be the driving force on how often you go to the woodbox or how much your fuel bill is.

All that said, and noting I have not been to the class yet, I have the distinct feeling that the construction methods taught by LHBA go a long way to minimize the other factors in the energy equation, inflitration for example, so that when complete, and when the benefits of thermal mass, whatever they might be, are experienced, the resultant home maximizes the effort such that R-value of the walls is somewhat less importanat than it might otherwise be.

[StressMan79]

Thanks, 2cents for that (albeit somewhat plagarized) scientific discussion. The phase shift in delta T does work this way, but like I said in an earlier post, for sizing your systems, you should use quasi steady state values. That means neglecting thermal mass benefits and using R and delta T. You don't want to be unable to heat your house if the temperature got to -10 and stayed there for a week (negating any effect of temperature lag). You may be able to make the case of not rounding up (say you need 82,000 BTU/hr, you might be able to use a 80k, rather than 100k heater).

However, Thermal mass WILL significantly cut your heating bills.

[Bronco]

Thermal mass -delta T - R value,To me it dont much matter I have 12" top's ,My son lives in fairbanks Alaska were it is -50*all most ever winter for a short time , They only have 10"to12" bottoms and if they have any air leak's they get big "glob" of ICE that will plug the hole tell spring, when they open the door it make's fog.I guess if I lived up there I would want as much of everthing I could get mass "T"s mass"R"s and "mass "mass's" Jim