Log home R value

Brad White

That is something I gave to my students:

"When you have a wall structure with a lot of variations in thickness, do the thicker parts add R value or do they act as "fins" of increased area exposed to the weather?"

I would take the net core of wood (7 inches as you say). Anything thicker is just a bonus and incalculable to my thinking.

Softwoods such as pine, cedar and fir have a per-inch of 1.25. Hardwoods fall in about 1.0 by the way. No harm in being conservative unless it triggers an over-sizing of the boiler.

Infiltration: Absent a blower door test, it is just a guess. 1.0 ACH? Good a guess as any. Is there a full basement or is it a crawlspace? Attic? General condition? Can you get a blower door test done?

I remember about 20 years ago there was a log home system with integral neoprene gaskets fitted into grooves in the logs. I have to imagine those held back the wind well. Anyway to tell what they have?

Simply Rad_2

log home R values

I have a remodel coming up. The home was built in 1990 and its in good shape. I am looking to figure in an R value for my heat loss program. THe wall consists of full rounds that are 12" in diameter. Then at the chink line they are 7" wide. I believe that wood has and R-value of 1 so do I us R 12 or R7. I also know that infiltration plays a part of this and I have bumped that to 1 ach. What do you think.

Thanks

Jeffrey

Ken_40

Brad's right...

But, you might consider doing a fuel use analysis vs. degree days?

Log homes are notoriously dificult to do heat loads on - accurately.

Sometimes working backwards is easier (and safer) than doing it the normal way.

Of course domestic hot water needs to be extracted, but DD calcs are given for almost every major city in the US in the NOAA archives.

If you have the time, do it both ways!

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Paul B_5

I know the ACH is definately higher. As brad says pine will be 1-2 per inch. Studies have shown that spring and fall the Log home will outperform a stick home due to the beneficial effects of Thermal mass. And in the dead of winter the heating will be comparable.!!! Paul

mtfallsmikey

I did several

Hydronic BB jobs in log homes back in the '80s, and Brad's way is the way I (sort of!)approached it..(with the help of a now Dead Man hydronic design guru). Everything went well, customers were satisfied. Most of the log homes have splines and foam/rubber gaskets between the logs, and in all of the ones I have seen have been good and tight, little infiltration.

[Deleted User]

You can't get the log home manufacturers to committ...

All they want to talk about is the internal flywheel mass affect of the logs... Yeah, right. And when it doesn't heat, I'll call you and talk mass...

I've successfully used the mean R value. Infiltration can and will change over time as the logs shrink. If the HO is not doing a good job of chink maintenance, you may end up with a piece of Swiss cheese.

CYA. Get a blower door test done and note the noted infiltration rate on your contractual proposal. THat way, when it changes, your butt is covered in paper.

ME

robert carey

R values of log construction

i'm in mid-michigan and have used R values for 6" insulated walls for a number of years with good results. hope this helps. bob

Steve Ebels_3

My method

I take the average thickness and use that at a value of 1 per inch. So a wall as you describe would be figured at 9.5 (12+7 =19 / 2 = 9.5)

I'm with Mark when it comes to the "mass" factor. I've never seen any numbers that validate what the log home guru's say. Some of the European literature I've read will refer to the mass of the structure as having a mitigating effect on heating/cooling loads but they're talking concrete or brick, not wood. The bottom line is that when it's my "mass" on the line, I cover it well in the absence of any firm data to make a judgement with.

Brad's suggestion of 1.0 ACH is what I usually apply also. If it's a newer log home with tight fitting machined logs and "gaskets" I'll drop to .8

Mike Thomas_2

I was asked to do a blower door test on a brand new log home for a heating contractor. He had done the calculations just as you guys are describing, but couldn't get the home over 42 degrees on a cold day (10 degrees). The place leaked like an old barn. It wasn't the walls, but the ceilings. They had tongue and groove wood on the ceilings, and no vapor barrier, vaulted ceilings and vented the roof and eaves. Used fiberglass insulation in platic bags and thought that would do it. Air went right around the bagged insulation and out the roof. The Equivalent Leakage Area, (add up all the little holes) was equal to a 4 foot by 6 foot hole in the wall. When I dropped that bomb on the homeowner while the log home salesman, the general contractor and the heating contractor were present you could hear a pin drop if it wasn't for the wind whistling through. The lady of the house stated she wasn't living in a *&^#$%^ barn, and then left.

Darin Cook_5

Sprinkler System

Mike, I saw the same thing in a log home that I installed a steel panel radiator system in. The beautiful tongue in groove ceiling had no vapor barrier in it ( the paper backing on the fiberglas insulation is not a real vapor barrier). The ceiling had air moving through it due to the buildings stack effect like nobody's business. The problem being that it carried all of the buildings moisture with it which condensed on the bottom of the roof and soaked all of the fiberglass insulation in the joist bays and proceeded to drip back into the home through the tongue in groove ceiling. They did not own enough pots and pans to catch all of the "rain". The builder tried to blame us and said the heating system made "too much" heat!!!! WHAT!!!???? ACH what's that?? The real shoe to the homeowners cashews was when they removed the ceiling ( the builder had turned his back and walked away ) BLACK MOLD EVERYWHERE!!!!!!!!!!! What a nightmare.












Darin

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Ken_40

Please cite...

the "study" that showed thermal mass is superior to an equal thicknes of high R-value.

I gotta see this...



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