Scarf Joint Question

[Clive McF]

A while back on this very forum I'd asked about the best way to join bearers lengthways, and was advised that a scarf joint was the way to go. Simple novice question: which is the best way to cut the joint for maximum strength - option A or B on the attached sketch? And for bonus points, how long should the joint be? Bearers are 190 x 45 F7 treated pine, notched into 90 x 90 TP stumps. Thanks in advance, Clive.

[sleeping-wood]

Have you considered other types of scarfe joints?

[ausdesign]

For your application I would prefer a butt joint with 4 galv. bolts & a check in of 25mm.
a scarf joint & vertical scarf joint [ carrying loads ]are only suitable for situations where there is full support of the bearer & with whichever one is used the cut should be such that there is still full depth of the timber supported on the stump.
i.e. I would consider sleeping woods pic as borderline in quality.
Thats only a personal opinion & others may not agree.

[Vernonv]

I would consider sleeping woods pic as borderline in quality.

Hi Peter,
Just out of interest - are you saying that joint was poorly done? or are you saying it's not really suitable for the application?

How could the quality be improved?

[silentC]

Definitely not A. B would be OK if it's checked into the post, wouldn't it Peter? It's got full support from underneath. The diagram is a bit misleading because it shows the bearer hanging off the side of the post, but he says "Bearers are 190 x 45 F7 treated pine, notched into 90 x 90 TP stumps"

Otherwise, if there is no support underneath, I'd go a step further and use an offcut to lap the butt joint and get 3 or 4 bolts into either side.

Actually, if I was going to do a splice, I would use an end lap instead of a scarf because I think they are easier to make.

[Ben (TM)]

Hi Peter,
Just out of interest - are you saying that joint was poorly done? or are you saying it's not really suitable for the application?

How could the quality be improved?


I came up against this very situation putting the joists down for my front verandah. I my (absolute amateur) opinion, the joint should look something more like the attached - which I think is what Peter was saying...

[Vernonv]

Thanks Ben.

I was kind of thinking the same thing, but was not sure.

Funnily enough I also has the same situation with my deck. I ended up making the 75mm steel posts with a flat plate on the top. This gave me much more area to play with and also allowed me to bolt up into the bearers.

Needless to say, I always made sure that both bearers were seated above "solid" post.

[ausdesign]

Yes Ben. the ends of the bearers are being supported through their full depth. Not so critical with the bearer with the halved joint at the bottom but the top bearer if not sitting on the stump has had its strength reduced by half [in simple terms] With sleeping woods joint the top is supported but i'd like to see the bottom one in further - if that makes sense. Around 30mm support.
The benefit with a halved joint on a concrete stump is that the wire contains both bearers.

Yes silent - as you would know used commonly with fascia beams & if checked in 25 odd mm would be fine. I'd still be using 2 bolts in each' espec. if being used with a high deck. It may seem like an overkill but its not much effort to make sure.
The main problem I see with vertical scarf joints is the chippies lining up the outside line of the mitre cut with the centre of the post [to make it look pretty] which doesn't leave much sitting in the checkout.

I wouldn't document the ' A type' scarf joint on any designs but if it was necessary for some reason the slope should be around 1:12 .

[Clive McF]

Thanks everyone: sorry about the sketch but you're quite right: the bearer is notched into the post, I just omitted the notch for clarity (hah!). So am I right in thinking that the consensus is that a butt joint notched 25mm into the post is the simplest and strongest option, as per the attached sketch? I'd be very happy with this. And if so, would say M10x100mm coach screws be the way to go, or should I bolt straight through the bearer and post? Thanks, Clive.