Hi guys. I hope to cut some hemlock for the construction of a sawmill shed as well as sill beams and floor joists for a cabin.
I have heard that hemlock twists bad and is prone to ring shake. It is used extensivley here in northern Ontario for dock cribbing and is said to last when used in this under water application.
Is hemlock rot resistant enough to be used for sills and joists?
Can I saw as many 6" x 6" timbers from a log as I can or should they be sawn one 6" X 6" per log with the heart boxed?
Hi, Buck! My experience with Hemlock is that it is rather brittle when dry and prone to splitting while nailing. I wouldn't hesitate to use it for sill and joists, however, so long as you are up off of the ground in your construction, i.e. air circulation underneath. It's very wet and heavy when cut green, hence the twisting if it dries too fast. That's as far as I can go, except that most woods resist rot well underwater, as there is no insect infestation, and low oxygen levels. Rot needs oxygen AND moisture. Keep that cabin floor a good 15" off the ground, on blocks or a below-frost-line foundation, and I think it will out live you, 'less you're a five -year old :)
I'd saw as many as I could out of each log, but that's only one guy's opinion.
If you have plenty of logs to get your 6 by 6s blocking the centers will produce a more stable hunk o' lumber.
Most of our mill is built from hemlock. We used it for trusses and for siding. We used post and beam construction. Posts are black locust, the beams are white oak.
Our siding goes to the ground, and have no rot, even in areas covered in wet sawdust. That doesn't mean it won't ever rot, but, we are having pretty good luck.
I have seen hemlock used as posts. I was at one mill where the posts were used next to a debarker. The roof drained right onto the posts. I cleaned the bark away, and found them to be in excellent shape after 30 years of service.
Hemlock is rated as low in decay resistance, prone to distinct warping, and shrinks quite a bit. But, if kept dry, any wood is rot resistant. I saw lots of it for construction lumber.
I would box the hearts. There will be less problems with ring shake.
Thanks Guys! Your help is greatly appreciated.
Buck Saw
If you use green lumber for floor joists you shouldn't expect a "quiet" floor. Re-nailing or screwing down the sub-floor will probably be necessary because of shrinkage. Use the shortest fastener that will do the job. For example, I would use a 2" screw or ring shank nail to fasten down 3/4" subfloor if the joists are green. The amount of the fastener that the joist is gripping is key. If you were to use, let's say, a 4" nail for 3/4" plywood, 3 1/4"of the nail would be in the green joist. How much is 3 1/4" of green hemlock going to shrink? Maybe up to an 1/8 of an inch (guessing). That's how much the nail will be sticking up above the plywood when the joist dries. You see this on drywall sometimes when a homeowner does a job. He thinks that if 1 1/4" screws are good than 3" screws will be GREAT. After one heating season some one leans on the wall and "pop goes the sheetrock". The screw head pokes it's ugly head through the surface.
You could use some deck adhesive like Lumber Lock or Liquid Nails as well. It should stick to green lumber. Some manufacturers make an adhesive for wet or frozen lumber.
Cross bracing of "bridging" between the joists will probably help to minimize twisting. I used 2x4 bridging on my house but most codes call for 1x3. You might have to tighten these up as the joists shrink. Shrinkage is why I don't like solid blocking for bridging.
One last bit about shrinkage while I'm blubbing. I built a 1 1/2 story house (cape) with a center chimney. I used all KD SPF lumber and the house shrank about an 1" to an 1 1/2" from sill to peak. I could see it in the chimney flashing. I am positive that the chimney didn't settle. The first floor joists were 9 1/4" when installed. I can go downstairs right now and measure them at between 8 15/16" to 9" even.
When you add up
2 sills 3 1/8
1 deck 9 1/4
3 plates 4 5/8
1deck 9 1/4
3 plates 4 5/8
2x10 rafters 9 1/4
Total 40 1/8
This is the horizontal members only which do most of the moving and kiln dried stock. Anyone have any percentages for shrinkage for green wood to dry?
Try this calculator from our friends over at www.woodbin.com
The Shrinkulator (http://www.woodbin.com/calcs/shrinkulator.htm)