I am reviewing some lumberyard quotes for a new house I’m building. I see some lumber called out as KD, and some not. I always assumed all construction is with KD. I searched the archives and found some discussions around this topic, and apparently green lumber is used for framing.
What are the pros and cons of using green vs. KD framing lumber?
From building boxes and fitting face frames to installing doors and drawers, these techniques could be used for lots of cabinet projects.
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It is more common on the west coast from what I hear, but not in the east. using green lumber creates another set of problems to deal with
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Thanks. Everything I have read about Building Science suggests that water in building materials is NOT a good thing. Framing with green lumber seems like asking for problems.
alfie
KD lumber has the free water taken out of it, but not usually the cellular water. The KD might have a moisture content of up to 19%. With most softwoods, shrinkage only begins as MC drops below this.
Getting out the free water is realtively easy. Getting out the cellular water takes a lot of time and energy.
The big advantage of KD to the end user is not stability, which is no different from green lumber, but that the surface moulds have been killed. Most people will agree that this is worth the price.
The big advantage of KD to the manufacturers is that they are not shipping as much water as with green lumber.
Ron
Thanks. I have to imagine that "KD" showing on only a couple of framing lumber line items is that some one just happened to enter it in their quote system that way. I'll find out during the week.
There is a LOT to disagree with in all that.First, KD means that it has been surface dried to 19% and that the interior of the wood may be even wetter than that. That is opposite of your def of "up to"I find that green 2x4s will shrink about 1/8" and cause nail pops in the sheetrock finish, along with a few other shrinkage problems. With floor joists, of course, the shrinkage is double for studs, and the building settles around that - a problem at two storey frames sheathed too soon.Since I am in a wet climate, both green and KD can have mildew growth by the time a frame is erected and dried in. So the shrinage factor is greater concern than is the surface moisture content or the surface mold killing. The only place shrinkage is not a problem with using green lumber is in roof rafters, but they have a couple other problems when using green. One is that hot sun hitting them too soon can make them start yanking and twisting as soon as they are nailed up. Another is that they are twice as heavy for the cut man to handle and send up to the guy on the roof.So unless there is a specific reason for me to want green stuff, I spec al;l KD - except for the bottom plates all PT. Now if he were in FL, he would be framing th e whole thing in PT for the termites, I treckopn
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Piffin,
You are right about the surface MC being 19% and that it could be wetter beneath. The objective at the mill is to dry to 19, though, in order to keep down shipping costs.
What I'm saying is that shrinkage will be the same with KD as with green because neither has reached the MC at which shrinkage starts.
The mould and mildew thing really is a big deal, though. I have opened up bundles of green lumber and had to back away from the wave of mould smell. Doesn't happen with KD. Maybe I close in a shell a bit faster than you do so the KD doesn't show mould. (Probably not in reality and I try to stick to ICF's anyway)
As for weight, some of the PT I've seen lately is heavier than the trees it was cut from.
Ron
Can you explain why shrinking studs would cause drywall nails to pop? If the 2x4 shrinks 1/8" overall, that's 1/16th" on each edge and half of that would occur in the center of the board where the nail hasn't penetrated.Is there something going on that sort of squeezes the nails back out?BruceT
bruce
Nail pops aren't necessarily from the wood shrinking away from the drywall. They can be caused by any wood movement caused by shrinkage.
With the SPF framing lumber mostly used in North America, shrinkage parallel to the growth rings is about 3 times the shrinkage across the growth rings. Shrinkage in length is negligible.
The difference is shrinkage rates is what causes wood to cup and bow and twist as it dries. The growth rings tend to straighten as the wood dries.
Ron
Thanks."...shrinkage parallel to the growth rings is about 3 times the shrinkage across the growth rings."Do I understand this right? "Parallel" would be tangent to the growth rings and "across" would be radially, the shortest distance between two adjacent rings?
BruceT
bruce
You got it. And it explains nearly all of the ways sawn wood warps as it dries. To some extent, it is predictable.
Ron
a nail pop ( screw pop nowadays ) is usually because at some point in the surface of the sheet the screw didn't pull the sheet into solid contact with the stud.... usually the stud is bowed or has a hookas the house drys.. the stud moves , the sheet doesn't... and the screw pushes outa lot of times if you walk thru after the sheets are hung, but before they are taped , and you push on the sheet, you can find these areas
the screws will popif you titghten them up , there will be no pop later onMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Mike Smith
I have to concur with you about that.. about the only nail pop's I got in my whole house were places where the nail wasn't properly installed in the first place.. and my whole house was built with green sawmill wood..
Thanks, that explains why it shows up haphazardly.
BruceT
alfie,
This is a subject that Piffin and I disagree on.. the differance is both in the details and the end result..
I'll try to skip the details and deal with the end results..
I've built my home with basically "green" timbers. The vast majority of high end timberframe homes are built with "GREEN" timbers.
If you build with KD you have just about the same chance of problems as building with "green" Both will shrink as they dry out and you risk warping, bowing, bending, nail pops, etc..
To be really fair I'd need to know where you intend to build and when..
You can build with all KD wood and if it's exposed to enough rain etc. during construction you'll have just as much of a risk of problems as green wood does.
The one thing you need to understand is that KD really doesn't mean what most people think it does.. sometimes those studs etc. simply go through a kiln on the way to the railroad car. If they are sawing wood that has reached a certain level of dryness already either because they are harvesting windfalls, standing dead or the logs have been in the sawmill yard long enough the kiln doesn't even need to be on..
Always good to see robust debate.I am building in Connecticut, and expect to be framing in mid October. It will go fast, and get covered up quickly. Of course the best laid plans of mice and men ....
alfie...KD is relatively new it wasn't prevalent around here 10 years ago...
mostly KD studs
we usually framed with DF #1 &2
then that disappeared and / or became special order
next up was Hem-Fir #1 &2...again, not KD
now most of the yards are stocking SPF KD #2 & Better
so...the species are declining in quality and the lumber companies are making up for it by switching to KD...
i like KD, but it means you usually get SPF ( Spruce-Pine-Fir )... sometimes, if you are going for long spans, you need HF....or DF
or go to engineered framing...like I-joistsMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Thanks. The quotes do specify Doug Fir. I am using TJIs for all floors, layouts designed by the manufacturer. The lumber is for walls and roof.
"KD is relatively new it wasn't prevalent around here 10 years ago...mostly KD studs"Holy cow Smitty!
The only times in 35 years of this that I have worked with green was building cabins way u[p in the woods and it was cut on site.In FL, in CO, and now in Maine where I have been for 20 years now, KD was never uncommon to find on jobs.and they call me backwards...sjheesh!;)
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in RI, the snob factor kept SPF out until DF & HF got scarce & expensive
the only KD i see here is SPFMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
As a boy learning from my dad in the late 50s I never saw a stick of green framing lumber. Mind you, I can't swear it was KD; it might have been air-dried. But dry it was; driving 16d commons into that stuff was work for a skinny little 8-year-old. When Dad wasn't looking, I used to snitch the bar of paraffin he used for screws to rub on my nail....
OTOH, when I moved up here in the mid 80s, I found most of the guys routinely framing with green lumber which surprised the heck out of me. A typical comment back then was, "KD? Forget it. Damned stuff is unworkable. Can't sink a nail in it; all twisty and warped, too. Gimme the green stuff." (Since nailguns have become as common as chopsaws, though, opinions have changed somewhat, LOL.)
In '95, I framed most of my own place with green lumber because it was still common practise here then and it saved me about 15% over the cost of KD. Which means I learned about screw pops and so forth the hard way.
But now, if I wanted some green framing lumber for a specific reason, I'd have to special order it. The big yards have gone over to 100% KD for SPF (which constitutes 99% of 2x production); the only thing still sold green is rough hemlock and I gotta drive 60 miles each way to get it.
Dinosaur
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we aren't in disagreement at all.Totally diffent ways of building.You are going so slow that things have time to dry as you build so you don't end up hanging drywall on new gree studs before they shrink.And timberframing is totally different way of building than is stick framing.And you have admitted elsewhere that your frames moved quite a lot, adding 'character' to your house.Also, you had some idea what the wood would do and were able to compensate for it.
But I assume if this OP has to ask about the difference, he knows none of those tricks.
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Piffin,
What you say is true enough about the timbers moving.. Some moved dramatically and since most didn't move the differance was really noteable.
However you forget that timbers aren't all I used in the construction of my home.. Floor joists and subflooring are just two examples of green wood I used.. Now granted all my green wood was hardwood.. Tamarack, Hackberry, Basswood, etc.. were all used. But since those woods are considered "trash" wood locally they were cheap.. much cheaper than plywood etc..
For just a brief look of what I'm talking about my subflooring would have cost me $3600 if I'd purchased 3/4 inch T&G plywood. Instead I spent $700 and wound up with a sub floor of 2 inches (actual not nominal thick hardwood)
That's a savings of $2900 on just the subflooring alone..
For the record the subflooring was laid down green and now up to six years after it was laid down only a few nails (less than a dozen of the thousands that were installed) are proud of the wood.