Wood R Values

[HDARTY]

Does any know the R-value (insulating value) of southern yellow pine and poplar? I am trying to decide which one to use in my next cabin project. I am considering using 4x6 or 4x8 walls and am not sure if 4 inchs is thick enough to adequatly insulate it.
Thanks
Hugh

[Ellsworth]

Hi Hugh,

Some folks will estimate the average R-Value of softwoods as 1.25 per inch. I believe that Southern Yellow Pine is a bit closer to .95, and Poplar around 1.13 per inch.

With a log home usually R-Value isn't the important issue, but rather one is concerned with thermal mass. Of course the thicker your walls are the more thermal mass you have -- and as a bonus you end up with a little higher average R-Value too :)

Regarding cutting your lumber to 4" thick. I'd go much thicker to gain the advantages of more thermal mass. Personally I would not cut them at all, I'd just leave them a nice natural round shape, but then I'm a log home builder :) If I were to cut logs into boards for a wall, then I'd go for at least 8"thick -- it would give you a lot more thermal mass.

BTW: If your walls are going to be load bearing then typically your lumber has to be a minimum of 6" thick to qualify your structure as heavy timber construction. Heavy timber construction is type IV construction (e.g. a properly built real log home), and does a lot better in regards to fire safety than a stick frame home which is type V. So if you want load bearing walls I'd at least shoot for a 6" min thickness.

Of course if your walls aren't going to be load bearing and you wanted to meet heavy timber requirements then all you need to worry about is doing your columns, girders, floor, roof and deck properly.

[Fred]

That's actually a caveat I have to add to log building, which I think Skip (at least in my class) was little glib about.

Keep in mind this is not based on actual experience, and I'd love to hear my theory disproved.

Log Buildings are good insulation, if the logs are thick enough, but not great.

If you assume about R1 per inch and a 12" diameter log you have a Maximum of R12...at the thickest point. The log is usually round, and worse, you have those mortar chinks backed with insulation. I'd be amazed if you could get R-10 out of the chinking. There is a lot of chinking surface.

The good news is that if you live in a climate that's mild, the thermal mass of the log structure (which can be thought of as the time it takes for the cold to penetrate) can accomplish wonders by smoothing out the highs and lows. So if the average temp ( in degree hours) is ok, you'll need only mild heating.

The bad news is that if you live in a part of the world where it gets cold, and I'm thinking daily highs that are sub freezing for weeks on end (if you think ice-fishing is normal, snow sticks and accumulates for several months, your foundations have to go 3+ft down to avoid heave, and you've driven your car across a lake, you are there) then the thermal mass becomes much less important, and the R value becomes critical.

As I mentioned above, the R value of the walls is no great shakes (unless you have massive logs). Certainly it's lame compared to a modern, well insulated, house wall you'd build in that sort of climate. (R20+, and excellent sealing)

Now this isn't a deal killer for log construction. If you can save a lot of money spring and fall, a couple of weeks of high heating season won't kill you, especially in smaller homes. It helps if you wear a sweater too and, don't mind a house than can get a little chilly once the heater turns off.

But is is something to bear in mind if you build in places with serious winters.

Or you can do like people who live in those old large (uninsulated and not really heated) homes in europe and elsewhere, and retreat to a heated subsection of the house in winter.

[spin05]

Here is it pretty cut and dried srticle i read awhile back about thermal mass VS r- value I think it explains it pretty well www.biglog.com/HTML/LogEnergy.html

[JeffandSara]

Interesting article, Spin. Thanks for posting it.

Fred, I'll be interested to hear any discussion on this-- though for us it's a moot point since we built with large logs in a southern hot summer/cold winter climate with good passive solar opportunities, and oriented the house to take good advantage of winter sun and summer's prevailing breezes.

Sara
:D

[HDARTY]

R-9 is the usual factor in stick built walls in my area in Alabama. So a 4 inch wood wall of poplar should be close to a 5 R factor. So if you figure mass into the equation it might compare with the stick built R-9. My main concern is summertime heat, as this cabin will be located on the riverbank and will be used mostly in the warmer months for a fishing camp.
The advantage to the 4 inch walls is availability. Four inch heart center cants are cheap and plentiful. A little router work on the edges with s3s, (surface three sides) stacked butt and pass, fastened with log screws, and chinked with a latexed chink should look fairly rustic.
As for the loadbearing part, my county as no building code. A tin roof with styrofoam sheathing (3/4 inch) over 2 inch kd poplar t&g shouldn't affect the walls.
My main concern is settling. On my old cabin I left 3 inchs of open space over the doors and windows and it had settled 1.5 inchs or more in a couple of years (It was flat saw logs top and bottom with an average thickness of 7 inchs). The logs had been kiln dried to less than 15% moisture content before use. The poplar I may use will be the same moisture content, so should I do the doors and windows the same?
Hugh

[Fred]

The other point is that heat flows *both ways* for you southern types.

Of course a lot can be accomplished with landscaping too, good shade trees and windblock plantings ( or in warm places wind directors) can do wonders for your microclimate.


At the risk of bringing the wrath of the Ellsworth's upon my head, has anyone insulated a log home? While it might compromise some esthetics ( and I suppose, the manageable risk of condensed water, bugs and animals), adding some insulation on the outside of a log structure might be very helpful.

There's lots of log structures in Scandinavia and places like the Ottawa Valley that were later "covered up" with stucco ( and close relatives), or boards or what not.

Some times for esthetic reasons, Swedish manor houses often wanted to look like stone structures, for instance, and in the Ottawa valley settlers wanted to make things less rustic too, but also I would assume to protect or better insulate.

I suppose one could insulate inside too, but then you "lose" the mass.

[JSanfilippo]

http://www.eere.energy.gov/consumerinfo/factsheets/ca8.html

I found this link on log home efficiency on the U.S. Department of Energy website.. interesting.

[JSanfilippo]

Some folks will estimate the average R-Value of softwoods as 1.25 per inch. I believe that Southern Yellow Pine is a bit closer to .95, and Poplar around 1.13 per inch.

Does anyone know of a link to a R-Value table for species of Wood?

Oops, found one... http://www.loghomeliving.com/document_display.cfm?document_id=86

[gregorama]

Since we all know the government is here to help us, I found a energy calculator from the ICC (International Code Council) and others at

http://www.energycodes.gov

The program is called ResCheck; you basically put in the area of all parts of your building envelope, with ratings for R- and U- values. Just shooting in the dark, I found that a 2-story 18' high log bldg 40x40, 14" logs and R-38 ceiling and floor will meet code with as much as 25% window area (U .35).. BTW, U=1/R, R=1/U.. And that's in Juneau, Alaska. In Seattle, it's 22% over "code requirements".

The interface is surprisingly easy to use, and will print out a "compliance report" for your inspector.

[KakarotMF]

Ellsworth,

This is a late question, but are there any other benefits that you (anyone) knows of when building under type IV vs type V? I was thinking of code-issue benefits, but any would be good. Does it play a role in property assessment/insurance rating?

[Ellsworth]

Just a lot safer: and by that I mean a properly built log home is MUCH safer when it comes to fire danger and fire damage than a stick frame home.

As far as I'm aware of there's no real 'insurance advantage' for home owners, if there is please let me know... cause it means my family has been overpaying for years LOL.