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Post & beam - green / dry wood - metal fasteners  RSS feed

 
Ionel Catanescu
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Location: Timisoara, Romania, 45N, 21E, Z6-7
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Hi folks.

I'm preparing to start building my strawbale infill single floor house.
It will have a post and beam skeleton, fastened with metal connectors and screws.
The connectors are perforated stell plates and corner connectors like this:


I'm trying to find dry wood which is somewhat difficult to source around here.
Most is green wood and i've been advised not to use it green.
I've been told that screws tightened while the wood is green will come loose once it has dried.

Do you have any experience regarding this ?

All connectors and screws will be galvanized.

 
James Freyr
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I have used many a bracket and fastener like you've described when I used to remodel homes. I've never used much green wood. The closest I think I've come is buying dimensional lumber from the lumber yard or Home Cheapo that still felt kinda wet (it wasn't pressure treated). The only problem with green wood is it is going to move (expansion, contraction, twisting) as it dries, and those movements will also vary from one species of wood to another. Maybe purchasing your lumber needs now and then stacking it all in a manner under a cover so it has a few or 6 months to dry is an option? Maybe using bolts to fasten instead of lag screws is an option. Wood fibers may recede from the threads of lag screws might yield a weak hold, but nuts and bolts will still hold it all in place if the wood wants to move. You may have to go around and snug up the nuts 6 months or a year down the road.
 
Ionel Catanescu
Posts: 174
Location: Timisoara, Romania, 45N, 21E, Z6-7
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I would buy my lumber now and let it dry for a couple months except ... i can't have the property guarded ...
And if i can't have it guarded, that lumber will disappear in no time.

I would use bolts except they would have to be pretty long ... not very practical (long bolts are too expensive) unless i cut them from threaded rod.
And i can use bolts only in a small number of cases.

I'm worried about the shrinking when drying especially for the post / beam connection.
If the post shrinks it's width by 7%, then the metal connectors won't sit tight to it's face but at a distance ...

I can only imagine a situation where the structure is connected minimally until the wood dries enough.
I can put the connectors in place only after this drying.
 
James Freyr
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Yeah unfortunately having supplies grow legs and walk off the job site is a necessary unfortunate we have to deal with. Hmm... Perhaps this may be a solution. Build it using the lag screws, and then in 6 months or a year replace them all with larger ones after the lumber is done drying and shrinking. That will make new tight fastenings, and you will have leftover screws on hand for a new project.
 
Ardilla Esch
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While it isn't ideal to use green wood, I wouldn't worry too much about it.

When we were building our house, the forests in the area were closed to logging due to wildfires.  The forests finally opened right when we needed the timbers so we had to use wet wood.  The visually exposed connections were mortise and tennon and the hidden connections were plates and screws.  The timbers did shrink and check somewhat but didn't seem to create loose connections.  In fact the slight twisting of the timbers during drying seemed to lock the mortises and mechanical fasters tighter.  Not all woods twist when drying however.  With infill walls you can't really re-tighten screws later if the bales are in the way.  I would just do your best on the framing, use more than the minimum of fasteners, and plan to stuff the spaces between bales and alongside posts/beams with cob before plastering.

Also, the finish plaster is most likely to crack over the drying timbers.  You can work reinforcing into the first plaster layers that will help prevent this.  I often use burlap fabric soaked in clay slip to bridge these areas.  Even with dry lumber it helps. 
 
Ionel Catanescu
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Location: Timisoara, Romania, 45N, 21E, Z6-7
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Depending on when i get started, the bales won't get installed until at lleast a couple months after the frame is up, possibly even the next year.
So the wood should have some time to dry.
I really have no idea how green the wood will be when bought but i want to be prepared.
 
Travis Johnson
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Timber frames are "green" when they put them up because wood take 1 year to air dry per inch of thickness. If you are using 8 inch by 8 inch beams, then it will take 4 years for the wood to completely dry at the least if air can get at it from all sides. If it can only get at it from one side, even longer then.

I built my timber frame house green and it is just fine with some checking (cracks), but very little twisting; none of which compromise its structural integrity. As for the checking, that is just wood and why i have a timber frame...no plastic house for me thanks...

Most houses are built using framing that is somewhat green, unless it is specified as "kiln dried", it typically is S-Dry, which stands for Surface Dry. This is actually preferred over kiln dried because the wood is not brittle; drive a nail and it does not split. Then after the house is built, the wood dries and all those connections keep it from twisting. The only time surface dry lumber has an issue is if spray foam insulation is used because after the foam sets up, and the house contracts, gaps are made in the insulating envelop...best to use fiberglass batts in that situation.

Myself, having a decent wood lot so I build all my projects straight off the sawmill and to no ill effect. In fact some species like Eastern Hemlock are best green. Try driving a nail in Eastern hemlock if it is dry...or try removing one. The wood will splinter before the tannins and contracted wood let up around the nail. Nailing it in place keeps everything from twisting and bending, just a lot of poping that first year as the wood starts to dry.

But you will be just fine with green wood, and best of luck on your house!!
 
Ionel Catanescu
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Location: Timisoara, Romania, 45N, 21E, Z6-7
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Thanks Travis

I have a little theoretical worry about radial / tangential shrinkage.
Again, not knowing how green the wood will be is a big variable but i think most of it is just surface dry like you said.

Anyway, all the joints in my structure (just a floor level with an uninhabited attic) look something like the attached images.
I don't really care about beams shrinking vertically as all the structure will come down the same amount.

I care about beams and posts shrinking laterally as that will leave all the metal fasteners at a distance.
I thought of putting a vertical peg that will go from the post thru longitudinal beam thru transversal beam thru attic post.
The peg could be galvanized 3/4 pipe and it will reinforce the joint sideways.
For preventing wind uplift, a small vertical strap across all these members should be temporary placed.
After about a year, the metal connectors could be installed at the "final" position, hoping nothing relevant happens after.

But i might be over engineering things a bit ?

Another option is to build the framing as fast as possible and install the bales + plaster.
This way the wood will dry much slower since it will be inside the bales.

I don't know, that's why i need info.
3d.png
[Thumbnail for 3d.png]
3D Jointing
front-lateral.png
[Thumbnail for front-lateral.png]
Front - Lateral view with shrinking
 
Travis Johnson
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In looking at your design I wonder why you might not be able to go with plywood connections in some areas.

I like plywood because it is cheap, easy to work with and does not split. Obviously you can use hand-pounder ring shank nails, but nail gun driven nails with their slender shanks and glue really help hold the plywood to wood. You MUST use plywood though and not regular sawn boards because they split. To get the plywood flush you would just need to route out the thickness of your plywood gusset. Any extra step, but easy and fast to do. In that way, when the wood moves in shrinkage, so does the plywood gusset.

As for the angle bar connections, I used them on my own house using VERY green lumber (felled, limbed, bucked, squared with hand tools and placed into service the same day) and they are holding to this day. It was a quick, fast way to attach horizontal beans onto the main carrying member without cutting out wood that would limit the structural integrity of the main carrying beam.

I don't think you are being overly cautious on this; you bring up very good points, as with a strawbale, you need rigidity that non-existing sheathing will not provide. That means those angle bars must hold. I honestly think it is too weak even strongly bolted. I realize it would be problematic to infill with strawbale, but diagonal supports would be a better alternative. You could do that by using plywood gussets as well. Just cut a 3 foot long 6 x 6 between your beams with the ends cut at a 45 degree angle, then route the ends and insert and nail the gussets.

Many people hate plywood because of the cost, but I have found in using gussets, a sheet pf plywood makes a lot of gussets, so it is really effective and strong. I don't have a lot of interest in building with strawbale, but if I build a WOFATI, it will be with squared timbers and with plywood gussets for strength and speed.
 
Ionel Catanescu
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Location: Timisoara, Romania, 45N, 21E, Z6-7
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Thanks Travis.

The framing will be reinforced with diagonal bracing (4x4's) from top plate to sill plate so there are no problems with racking.
These will be placed in each opening without doors or windows.
Plywood is nonexistent around here anyway ...

The metal connectors are "certified" and the easy route for the structural engineer that makes the plans.
Also, they are very DIY friendly and pretty easy to install but not terribly cheap.
The reinforced connectors offer limited reinforcement, just something to complement the diagonal bracing.

Did you use nails or screws / lag bolts with the angled connectors for your very green lumber ?
I've read some studies that nails driven while wood is green don't hold that well, except helically-threaded ones.
And a screw is very similar to that so it should hold better.
I'm asking because one of the structural engineers said not to use screws with green wood as it will come out by hand after drying.
Of course i went like WHA' ?
 
Fred King
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I build log homes with logs up to 24" so the center of the logs are not dry even months after being debarked. I use lags in many places but never predrill for the threaded part of the lag. That makes installing them harder but even after the log is completely dry they have never loosened. If you look carefully at grain of the wood especially any tiny checks you can often see logs or timbers that grew with the grain spiraling up the tree. These are the ones that will twist when they dry. If they are used in shorter sections the twisting will have less effect. Good luck with your project. I think with care and concern you are showing it will come out well.
Fred
 
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