Simple Question Re. the Orientation of Half-Lap Joints

[Ernest T. Bass]

Hi all,

There are several areas in our vertical-log-cabin-to-be where we will need to use quite a few end-to-end splices in horizontal runs of logs. The half-lap is the most common, but I always see the lap positioned with the "seam" running through the wall. That is, with one log lapping "on top" of the other, with spikes pounded down through the splice. It seems that this configuration would be harder to weatherproof, as you have the seam running straight through the wall to the outside. Why couldn't the half-lap be turned "on end", with lag bolts installed from the outside to secure the joint? Wouldn't this joint be much more weather tight, and possibly more forgiving (aesthetically) of a poorly fitted notch? Wouldn't the joint also be stronger when it is  positioned over a support post, as in the case of a sill beam on a pier foundation?

The bolt heads on the outside of each joint might not be the prettiest things, but these joints will only be needed on the sill and header beams in our situation, and could be plugged.

It seems like a silly question, but is there a good reason for making the splices the traditional way?

Thanks,
Andrew

[Redoverfarm]

Ernest at first glance I would say there is no reason that the seam cannot be run verticle vs. horizontal.  The fasteners would be visible unless you cut wooden plugs. But then I got to thinking that unless the joint was extra long you could loose some structural intergritiy with the forces outward agains the wall. Try an experiment. Take two pieces of 1/4" X 2" stock and nail them together.  Now take your knee and try to break them with the edges toward your knee. Tough huh. Now take the same piece and put the flat part against your knee and try to break. Watch for splinters. See where I am coming from.   Not a very good example at least that was close to what was in my head for simplicity.

[Ernest T. Bass]

That's something to consider, but our sill beams will be tied together by the floor framing, so I don't expect there would be any of the stress you describe on the joints. The cap logs, where we will also be using splices, are going to be tied together as well.

[glenn kangiser]

I think a couple vertical rebars driven in  from above and into the log below would take care of any problems with strength

[PEG688]

 

The half lap should be done horizontally not vertically . The way I see it the pressure downward and the pin lock the joint together , the vertical joint doesn't have that downward pressure that make the joint stronger.

I'd recommend doing your laps on a angle , sort of like a dovetail , I guess I'd call it a ramped half lap , they could all be done to shed the water to the outside . 4 or 5 degrees would be all it would take.

 

[glenn kangiser]

You always seem to make the most sense, oh wise one.

[PEG688]

You always seem to make the most sense, oh wise one.

Yes , scary init

[Ernest T. Bass]

What would be the best way to seal the joint and prevent any air infiltration? Lots of caulk?

[glenn kangiser]

I'd vote for some of the round foam crack fillers then maybe chinking or caulk of your choice.  They use the foam in tilt up concrete buildings then Sikaflex over it.

[PEG688]

I'd vote for some of the round foam crack fillers then maybe chinking or caulk of your choice.  They use the foam in tilt up concrete buildings then Sikaflex over it.

That would be a good idea , have some on hand and place it just before the top log is set. Should have some "spring back" for when the log shinks as it drys. I wouldn't rush to caulk either , maybe a year even if the logs are sold as "dry" they will shink for a few years , move , twist , check ,etc. If they are green it will take longer. The foam "rope" in the joint should help , even if in the long rn it just become "backer rod" for the caulk.   

[Ernest T. Bass]

Those sound like good ideas...

One more Q on the lap orientation.. The sill beams (6''x10'') will be bearing a lot of weight from the vertical-log walls, and will be supported by piers where they splice as I mentioned before. Is there any concern that the notch will weaken the end of the beam? It seems less likely that the joint would shear off in a vertical lap configuration vs. horizontal.

I guess another factor would be, how much is a good amount of overlap for the joint? 4''? If so, than the beam would probably be fine as 2'' of un-notched beam-end would still bear on the 8'' diameter piers.

Hope I described that well enough...

[glenn kangiser]

Figure that wood has a fiber stress (before crushing or damaging the wood) allowable of around 900 to 1000 psi - I round it to 1000 when I want to figure what I'm doing to the wood.  Not an exact answer but it will give you an idea of things that may or may not work.  Note that I'm not an engineer -- I just like to know some of their stuff to keep my rule of thumb projects working.

[glenn kangiser]

...and I think 4 inches would work.

[Redoverfarm]

.  Note that I'm not an engineer -- I just like to know some of their stuff to keep my rule of thumb projects working.

Sort of like Glenn on this part. Oh God I hope not. Anyway I try to make comparison and regarding the lap of the sill  I would opt for a little large than 4".  Imagine joining a rim joist with a 6" scab. Now increase it to a 2' scab.  Seems a litle more substantial to me in that respect. The weight of the wall will be resting on the sill. IMO the more joint the better the weight distribution would be. 

[Ernest T. Bass]

Perhaps adding some corbels under the splices would help strengthen things up?



They might help "balance" the cabin better, too, as I could lower the piers a bit... Though, the corbels may have to be PT or cedar or something...

[Redoverfarm]

Like the joint. Could be a real PIA to cut. How many are you talking about? 

[Ernest T. Bass]

8 + 4 corners... Yes, it sure looks time-consuming. Don't see any cheap way around it though... 

[PEG688]

 

Ernest T. I like the block under the lap I'd make it about 18" long , beyond the shoulder joint and put two re-bar stubs or bolts in it  ,so a  total of 5 ea.   per block . This may seem like "over kill" BUT the foundation , which essentially is what we are talking about in a post and pier foundation , is no where to skimp, IMO . YMMV.   

I'd also say tilt those laps toward the exterior  as well as the plane / angle your showing IF weather proofing is your goal , which is what you originally asked about. And maybe you have them sloped that way and it just doesn't show in that view.

[PEG688]

8 + 4 corners... Yes, it sure looks time-consuming. Don't see any cheap way around it though... 

I think once you cut a few of those a system / way of doing it / jig setup will be revealed / show itself  and the rest will be "cake" as we say , as in piece of   

[Ernest T. Bass]

Here's hoping... I plan on giving my fine chainsaw carving skills a run for their money.

And, if all else fails, there's always really thick caulk-backing rod.. 

When you suggest making the corbel 18'' long beyond the lap, do you mean 36'' total? I don't mind a little overkill down there, especially since they will also help support the log walls better.

They would probably be about a foot off the ground.. You think it would be necessary to use something rot-resistant like cedar?

[adawgk]

  haha Trust me Four inches works, im on my 3rd kid :p

[PEG688]

When you suggest making the corbel 18'' long beyond the lap, do you mean 36'' total? I don't mind a little overkill down there, especially since they will also help support the log walls better.

They would probably be about a foot off the ground.. You think it would be necessary to use something rot-resistant like cedar?

Yes and yes or treated . Don't want bugs in your "foundation " either eh.

[Ernest T. Bass]

Prob. w/ treated (besides $$) is the difference in size, dressed lumber vs. our rough-cut. I guess it wouldn't matter too much in this situation, but it would be ugly...

[PEG688]

Prob. w/ treated (besides $$) is the difference in size, dressed lumber vs. our rough-cut. I guess it wouldn't matter too much in this situation, but it would be ugly...

Either would work.

  But  Cedar not what it was 20 years ago around here , not much old growth and the newer faster growing / grown stuff is very weak as well as open grained , less decay resistant.

[glenn kangiser]

Shut up, Aaron.