Does Douglas fir maintain the board shape better than Hem fir?

[ponderosae]

Some information I was reading about lumber grading says that Douglas fir has 'comparative freedom from warping, cupping or twisting'. But I wonder if you get relatively dry lumber that is not warped, cupped, or twisted, would Hem fir be more likely to change its shape afterwards, or is it more like you get a better selection of well shaped boards if you look at Douglas fir (of the same grade)?

Personally, I haven't noticed that Hem fir changes its shape, but they say that joists, for instance, need blocking between them to prevent that (twisting, at least with the taller dimensional lumber). So if single pieces were invloved for some other purpose, without lateral supports, I'd imagine the Douglas fir might not get bent out of shape as much, perhaps due to being somewhat stronger, as they say that Hem fir is 'straight grained, stiff' and 'distinguished by its strength' as well.

[Stuart Caruk]

Hemlock shrinks more than fir and the local big boy mills have to run it through the kiln before selling it at home stores, hence they prefer to cut fir, as it's lets cost to produce a finished product. I build saw guides for a lot of mills and the hemlock guides are thicker across the body to make thicker product than fir.

[ponderosae]

That's interesting. Lately I've seen more boards that look like they were cut with a warped saw blade than ones which are planed smooth on each side. Usually one side has a ridge on it (more often with the Hem fir, but sometimes on the Douglas fir too). Is that supposed to happen? Somehow it keeps happening...

[DMcCoy]

I have never understood the 'Hem-Fir' marking, why not just call it 'Hem'.  D. F. does hold it's shape better - not that it can't twist, cup, and bow like any lumber.  
Hemlock on the other hand is a PITA.  Mostly I see it used in making P.T. lumber and you need to install that stuff wet and nail it down before it goes haywire.  In the out door lumber yard they store it wrapped in plastic and out of the sun to keep it wet.  I've got a P.T. 2x4 I should take a picture of- it bows 24" in 8' or less.  I used 10 pieces of Hem Fir for studs while building my house and ended up replacing every one.
I use D.F for cabinets in my shop. It works great and is does weep pitch.
The insert panel is 5/16" T and G - all D.F.


 

[Don P]

We lump some woods that regionally grow together and have similar strength characteristics into species groups for construction use grading purposes, SPF, spruce-pine-fir is probably the most common species group we've all seen. The lowest strength species in that group determines the design values of that group. Sometimes there is also a single species design value for one or more members of one of those groups if it is graded and stamped alone  There is a stand alone grade "Western Hemlock". The species group Hem-fir contains these species- Western hemlock, California red fir, grand fir, noble fir, pacific silver fir, white fir.

The ridge and hit or miss planing you are seeing on lumber is probably from a slightly mis aligned top saw in a mill.

Cupping, bowing, twisting, those types of wood movement are related to changes in moisture content. The best way to avoid those troubles is to use wood that is at the in service moisture content. Kiln dried construction lumber is dried to 19%, in service the equilibrium moisture content is generally closer to 8-12%.

[DMcCoy]

Thanks Don for the grading explanation. 

[ponderosae]

I have never understood the 'Hem-Fir' marking, why not just call it 'Hem'.  D. F. does hold it's shape better - not that it can't twist, cup, and bow like any lumber.  
Hemlock on the other hand is a PITA.  Mostly I see it used in making P.T. lumber and you need to install that stuff wet and nail it down before it goes haywire.  In the out door lumber yard they store it wrapped in plastic and out of the sun to keep it wet.  I've got a P.T. 2x4 I should take a picture of- it bows 24" in 8' or less.  I used 10 pieces of Hem Fir for studs while building my house and ended up replacing every one.
I use D.F for cabinets in my shop. It works great and is does weep pitch.
The insert panel is 5/16" T and G - all D.F.

Thanks for sharing your experience with those. What I noticed with pressure treated Hem 2x4s was that when the fresh pallet at a hardware store was wet, the lumber had a lot of mildew on it. I had to find one burried in the back to get a dry straight piece that didn't stink (that was the stuff treated with Ecolife for above-ground use). But yeah, I think the dry pieces generally showed more warp too. I'll probably skip using treated lumber in the future (unless it's absolutely necessary).

[Bruno of NH]

When I was building I noticed more lumber was getting shipped with mold on it.
I would tell my supply house I wasn't building with pond soaked lumber or if they charged extra for the pond soaking.
They didn't like it.

[Don P]

It is becoming less common but do look at the grade stamp. If the stamp reads KD19 it was kiln dried to 19% moisture content prior to surfacing. S-GRN was surfaced green and shipped. With anything what happened after it left the mill can certainly change that moisture content. I see building supplies regularly storing kiln dried lumber out in the weather. Generally speaking though Dougfir is a better behaving, stronger and more handsome wood.

[ponderosae]

When I was building I noticed more lumber was getting shipped with mold on it.
I would tell my supply house I wasn't building with pond soaked lumber or if they charged extra for the pond soaking.
They didn't like it.

Was that any kind of lumber? I'm not sure if one molds easier than another, except I think the moldy lath I was looking at was SPF, which is pretty much any kind (where I see building materials grouped together). I've read that cedar and other woods may be used in place of treated lumber, so maybe those don't mold as easily either.

[ponderosae]

It is becoming less common but do look at the grade stamp. If the stamp reads KD19 it was kiln dried to 19% moisture content prior to surfacing. S-GRN was surfaced green and shipped. With anything what happened after it left the mill can certainly change that moisture content. I see building supplies regularly storing kiln dried lumber out in the weather. Generally speaking though Dougfir is a better behaving, stronger and more handsome wood.

I haven't worked with either of them enough to say how much of a difference it makes, but a couple of things about the Hem fir that may be advantages at times are that it seems to be lighter weight, and much easier to shape with a rasp (because Douglas fir maintains its shape better that way too). I'd imagine the denser wood might wear out more saw blades, so I can see why people would prefer the Hem fir sometimes.

[Gilman]

Hemlock can be a real pain.  Here's some lumber from a log I sawed.  Every board was like this.  It wasn't the blade and it wasn't from poor blade guide alignment.  The fir log prior to and after this one sawed fine.  My uncle "loved" this lumber.  He used it to build his corral.  I asked him why and he said, "This way I get to laugh every time feed the cows."



 


 

An advantage of Hemlock over Douglas Fir is it has fewer knots.  The lumber is more brittle than Douglas fir, thus the limbs snap off more frequently. 

Hem fir is used for PT because it has a lower pitch content.  The local PTers started PT douglas fir recently.  To PT douglas fir it has to be heated ~130-160 degrees (I don't remember the exact temp) prior to pressure treating.  

[BradMarks]

Green doug fir will bend, twist, warp like any wood. Nail it up green, don't wait. That's why it is worth it to buy KD when building about anything. Maybe it's just local but the other day I was able to get DF 8' 2x4's KD for 3 cents more than green. Still wasn't a deal at $2.97, but just saying.

[ponderosae]

Green doug fir will bend, twist, warp like any wood. Nail it up green, don't wait.

Really? I've read about leaning houses, and that's one reason it happens, at least with oak...

The Crooked House of Windsor

"The house was built with such haste that unseasoned green oak wood was used. As a result, the structure soon noticeably buckled and shifted. The Market Cross house from then on became known as the Crooked House of Windsor... Moral of the story: season your wood before building, otherwise, your house might last for 400 years."

Supposedly it was reinforced, since then: "About thirty years ago when the house was refurbished, enough steel for a second Forth bridge was inserted and then carefully hidden"...

There's also a note about this in a book chapter about choosing lumber for framing: "Select lumber that is seasoned or dried. Green lumber can cause problems as it shrinks."

[ponderosae]

An advantage of Hemlock over Douglas Fir is it has fewer knots.

I've noticed this with the SPF 2x2s, where it seems that the denser fir ones are most often warped because of a knot.

[Ljohnsaw]

I've read that cedar and other woods may be used in place of treated lumber

When I filled my foundation blocks with concrete, I had cedar headers bolted to the inside of the top course.  The inspector asked why didn't I use green stick.  I replied, "Cedar is what the plans called for".  He said, "OK".  I didn't tell him I drew the plans...;)

[Stuart Caruk]

Green doug fir will bend, twist, warp like any wood. Nail it up green, don't wait. That's why it is worth it to buy KD when building about anything. Maybe it's just local but the other day I was able to get DF 8' 2x4's KD for 3 cents more than green. Still wasn't a deal at $2.97, but just saying.

Less than 56 cents a board foot for a 2 x 4 and you are complaining? Honestly I can't figure out how they make a buck. I can't buy my raw logs on a landing for that, much less saw the log into boards.