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I need info on where to buy, or how to design an adjustable post base for a 14″ round column. It will support about 25,000#, so one of the little deck supports won’t do it. It’s for a log wall house, and I need to accomodate the shrinkage of the walls without holding up the roof. Someone told me they’d seen an ad for such a thing in FHB, but I’ve scoured through old issues and can’t find a thing. Any help?
Tom Laing
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Replies
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Tom, Is this thing going to be visible in the finished structure or is it going to be sitting on a footing below floor level somewhere? It sounds like you only have to be concerned about lowering the column over a period of time... is that correct? What is the 14" column made of?
*The plan for now is to install it at the base of a round log post, approximately 14" in diameter. It will carry a ridge beam which bears down on the log walls at both ends and on this post near mid-span. Because the ridge rests on the logs, the post will have to be adjustable to accomodate up to 4 or 5" of potential shrinkage over a period of a few years years. As the logs shrink, the ridge and all the framing above the walls will lose elevation, too. The post will rest on the main floor, and there will be another post in the basement, carrying the weight down to a footing under the slab. The adjustable base could be either at the bottom or the top of the post, but for convenience of making adjustments, I figure the base is the best, so the owner wouldn't have to be working off a ladder. It could be visible, as an architectural feature, or could be hidden by some type of removable baseboard trim. So that's the plan. Any ideas or comments would be appreciated. Tom
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Tom,
Joseph Fusco
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Joe,
Yes, some type of screw jack is exactly what I had in mind. I'm just not sure how to design it to carry the intended loads. I'm sure this would be an easy one for our engineer friends, but since it's not made of wood, I'm not so comfortable with it. And yes, shrinkage in a log house is a given...the amount depends on the dryness of the logs. Standard procedure is to leave a gap at the top of windows and doors, stuffed with fiberglass insulation, and covered with a wide head trim. When the shrinking stops, you can foam in the remaining gaps. Another dilemma, is how to anchor the tops of interior partitions in such a way as to keep them from holding up the upper floor or roof as the logs shrink, while keeping them rigid/vertical. No wonder people invented stick framing!
Tom Laing
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Hi Tom
If I had my drudders, I would install it in the top of the post but there's no structural reason that it couldn't go on the bottom.
Just buy a steel extension post assembly, remove the screw and plates. Drill a hole into your wooden post to accept the screw shaft.
Buy two steel plates the size of your post top,(the reason for this is that the collar and plates that are supplied with most telepost are too small to adequately spread the load on the wooden post you want to use) one with a hole drilled though the center the size of the screw diameter and the other plain.
The one plate with the hole would go on the top of the post and the screw assembly with the threaded collar would slip into it. The other plate would be fastened to the underside of the beam. This would give you an adjustable, screw jack for your structure.
If the load exceeds the recommended loading of the telepost that you have in your area, you can substitute a commercial forming jack screw for the assembly. The amount of loading you are anticipating seems high to me for a log structure. 12 tons is a lot of weight. Normally in a properly designed structure the main loading is transfered to the outside perimeter onto the foundation on completion. You should have an engineer check the loading for you. Just bring in your drawings and they should be able to work it out for you.
You can of course reverse the process to have the jack screw on the bottom.
Hope this helps,
Gabe
*Go to Alta Vista and type "log home screw jacks" or "panel fasteners" I saw these things all over the place when I was looking for 6" Insulated Panel Fasteners.-Rob
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These screw jacks are commonplace in log homes and I've had a lot of experience with them. Gabe's description was accurate. For an application such as you describe I would suggest 1-1/4" allthread. Whether you make it yourself or have it made be sure to account for the thickness of the nut, plates and the weld so you get a full 5" of operable stroke. When drilling the post make the hole an eigth inch larger and plenty long enough to accept the allthread when fully screwed down. As far as the location goes, there are two main considerations, convenience in adjusting and ease of concealment. Sometimes there can be tremendous pressure accumulating and you need a cheater bar or a sledge hammer (or both) to get started adjusting. Try that standing on a step ladder. It's much easier to do on the floor with the screw jack under the post. However, the nicest looking detail is to extend your log post past the floor with the screw jack in the crawl space/basement. Hope this helps, Greg
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Gabe & Greg, sounds good.Don't forget either anit-sieze or some moly grease on those threads and interface surfaces. MUCH easier to start things turning....
S.
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Good point, Sam. Another thing that helps is to use a washer between the nut and plate. Typically the 1/4" plate is mild steel and can score and gall against the nut. Greg
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I need info on where to buy, or how to design an adjustable post base for a 14" round column. It will support about 25,000#, so one of the little deck supports won't do it. It's for a log wall house, and I need to accomodate the shrinkage of the walls without holding up the roof. Someone told me they'd seen an ad for such a thing in FHB, but I've scoured through old issues and can't find a thing. Any help?
Tom Laing
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1) there was an OLD FHB article about a log house , I think with some timber frame sections, built by some architecture students. I think they used a screw jack type arrangement at the top of the post. The advantage there is it's carrying roof load but not wall and intermediate floor loads.
2) the Hometime TV crew (what's his name and the girl of the season) did a log house and used a window and door jamb system with slots chain saw cut in 2x lumber and lags into the logs so the jambs would compress as the logs shrunk around them. There must have been compression room at the heads. They must have been pretty confident in the system because the house was big and there were lots ($$$) of Anderson or Marvin windows and doors.