Green oak, post/beam joint.

[gee69]

I'm replacing a wall in my cottage with an oak beam and post (nicer to look at than a plasterboard clad RSJ) and have a question regarding the joint between the two.
The beam will have the roofs pitched rafters bearing on it, and has been sized by a SE. Post 150x150 and the beam 200dx100w. Span is approx. 1.8m

I was originally planning to tenon (with as small shoulders as I can get away with) the beam centrally into the post with pegs holding it. Top of post and beam flush so an open topped mortice in the top of the post... I'm sure there is a proper term for it.

Since then (due to complications with the pad stone location for the post) it will be necessary to have the post approx. 300mm in from the beam end. SE says this is no problem regarding the rafter over the cantilevered end.

What would be my best choice for this joint? i.e. a 100mm thick beam passing over a 150mm post?
It has to not look 'odd' as it will be very visible, I will also have to plaster around it all where it meets the sloping ceiling both sides, which made me wonder if keeping the beam flush to one side of the post would be an option?

I'm no carpenter, but can turn my hands to most things.

Picture to show the wall in question. Beam will run the length of it (sat on brick the far end), post about 300mm in from current wall end.


Any advice would be much appreciated.

 

[MikeG.]

Just don't have a beam which is narrower than the post. It was never, ever done. If you have a 150 square post, then your beam should be at least 150 wide. Anything else will look dreadful. Don't forget, the engineer's sizes are a minimum, so make it a 200 x 150, or 200 x 175, beam. So a proper mortise and tenon, and stopped chamfers to the exposed underside of the beam.

 

[gee69]

I had wondered about that but was concerned about the increase in weight of the beam by at least 50%.
Thanks.

EDIT:
Oh also, regarding the stopped chamfers, is there a 'rule' as to their size, position of the ends etc..?
What would be the best treatment of the exposed cantilevered end?

 

[MikeG.]

Stopped chamfers, so long as they stop clear of any junctions, can be however you want them to be. I generally set mine back about 6 inches from a junction, but in some circumstances this can be as little as 2 inches. The stopped end.....chamfer the edges boldly (I usually do 25mm), but only on those edges that will be open to the air rather than up against plaster.

The self-weight of the beam doesn't matter, as it adds strength as well as weight.

 

[AJB Temple]

100% agree with Mike. I have lived in a few old timber framed houses, and re-erected a few old oak barns, and built a few from green oak. If you look at old buildings, the beams can sometimes be double the cross sectional area of the posts. I have one exactly like that in the master bedroom of our house. God knows how many men it took to lift it as it is 11 yards long and 18" deep top to bottom - not sure how thick not is but at least 12". Posts are just transferring weight downwards to the foundations (not that all (very) old buildings had foundations...).

 

[gee69]

Okay. Thanks both.
I shall look into a wider beam, it would make life easier in most regards.

 

[El Barto]

This video is a useful intro to timber frame mortice and tenons, though you can see the joint is slightly too tight. Mortice and tenons in timber framing aren't the same as in cabinet making - you want your tenon to fit easily, even loosely into the mortice, due to the size and weight of the timber and difficulty moving it - you want to be able to pull the joint apart for reassembly and adjustments.



Timber of this size is often out of square so unless you plan on squaring it all up, be mindful that you may get gappy joints where you haven't accounted for the out of square timbers.

Traditionally, stopped chamfers tend to be quite wide but there aren't any rules. If your cottage contains other timber framed sections then perhaps look to match those.

 

[gee69]

Funnily enough I was watching that this morning. Thanks.

Nothing to match here. 1852 cottage that was robbed of all it's character in the 70's. I'm hoping to put some back in, even if not totally original.

 

[Lightning bolt]

You can't go wrong with any of above advice. I'm a professional timber framer & that's the exact advice i'ld give. They've hit the peg on the head...

 

[gee69]

You can't go wrong with any of above advice. I'm a professional timber framer & that's the exact advice i'ld give. They've hit the peg on the head...

Thanks for that.

Out of interest, roughly how heavy is a 150x200x2100mm green oak beam going to be? I need to work out how I'm going to get it up our tight stairs.

 

[MikeG.]

Heavy. You'll need two people. It's easy enough to handle on your own on saw horses etc, but getting it up some stairs is going to be a trial if you attempt it alone.

 

[gee69]

As long as me and MrsG can manage it. Social distancing aside, there's not room for many people where it's going.

 

[AJB Temple]

Green oak weighs about 75 pounds per cubic foot. 35kg for a 300mm cube. So you are looking at approx 82kg. I can lift posts like that easily enough vertically on my own, up onto a plinth say, so could get it upstairs step by step, but it feels seriously heavy when you have to shift it horizontally. If you are going to be positioning it as a beam, at above shoulder height, then you will need to arrange slings or props to get it up safely. Get your act together on that (including a couple of trestles in the room) before you try to get it into place. Make sure you have test fit posts and beams beforehand, as you do not want to be adjusting in situ.

My wife (who is slender and tall) helps me move seriously big lumps of oak around. We have various trolleys and so on to help, along with ropes and winches. I make sure she wears gloves and steel toe capped boots and we take it very steady. I hope it goes well.

 

[gee69]

Bit of an update on this, been removing the wall.
Got the timber a couple of weeks ago, beam is now 150 wide to match the post.
Started work on the joint today, tenon on top of post up into the beam.



First time I've done anything like this so was pleased with the end result .... Fingers crossed I've done it right.

 

[AJB Temple]

Well done,. Personally I would have made the tenon a third of the thickness - you have gone much slimmer. But in this application it will be fine. Well done.

Before you erect it, drill your peg holes very slightly offset (so that the tapered pegs draw the joint tight) and get a belt sander or ROS to get a better finish on visible faces. Doesn't take long. Nice job so far - you should be proud.

Adrian

 

[MikeG.]

........First time I've done anything like this ........

Fun, isn't it?!

 

[gee69]

Well done,. Personally I would have made the tenon a third of the thickness - you have gone much slimmer. But in this application it will be fine. Well done.

Before you erect it, drill your peg holes very slightly offset (so that the tapered pegs draw the joint tight) and get a belt sander or ROS to get a better finish on visible faces. Doesn't take long. Nice job so far - you should be proud.

Adrian

Cheers. I do have a newly acquired belt sander ready to go.

Fun, isn't it?!

I have enjoyed it so far, and already have been thinking about a few more oak structures.
I've never been a great fan of carpentry really, I get by (Father is a retired carpenter so I should be better), but I really could get into this chunky stuff

 

[MikeG.]

......Cheers. I do have a newly acquired belt sander ready to go........

Use 40 or 60 grit belts. No point in anything finer.

 

[OrangeFive]

Yes rougher the better on the sandpaper really

 

[gee69]

Well a number of hours (days!) later and I have this.
All chamfers cut with hand tools as I hate routers, or at least my inability to control them! The slower pace of hand tools minimised the risk of a disaster.
Don't know that it's 'correct' but I'm happy.