king post truss repair

[magnet]

I've being putting a new loft hatch/ladder and while up in the loft i noticed one of the struts on the truss where it joins the principle rafter has a pretty big crack in it.Now the house was built in 1938 and i suspect it was cracked when it was first done the base of the king post was loose and used to move in high winds until i spiked it in about 6mnths ago so i suspect it was a friday afternoon job.
So i was thinking of plating up the truss in the area of the crack with a bit of 3/4" ply either side bolted through with a liberal thickness of epoxy.
Would this be the best way to proceed or are things best left well alone any thoughts/advice appreciated

 

[mike os]

pic would help... more likely to want 10-12mm steel than ply, epoxy is probably not needed

 

[ford34/2]

I would weld up a Metal strap, one for both sides, and bolt through. This the Strut from the pricipal rafter to the strut --just under the roof tiles??. I have put steel on the principal /tie beam joint,(the one in the eves corner) and on the king post to tie beam,(the one in the middle) never done the strut at the principal rafter end though, It wouldnt do any harm, hopefully the birds mouth notches are still tight. If the two timbers are the same thickness I would go with steel maybe 2"" X 1/4 or 3/8" is a bit overkill, depends whats available, Me personally I wouldnt use ply.If the two timbers are different thicknesses fill the void with a packer, Ply or timber. We slipped corrugated washers in any timber/timber joints that were bolted through, some 1/2" bolts be nice.

Stan

 

[Kent]

Gluing with PVA and screwing on structural grade ply is often specified in building structural std walls, never seen it for repair of a rafter. I have replaced joist ends stepped "do one, miss one" then "do the missed ones". Pva screws then coach bolts.
Building control need talking to if in any doubt and I think you will find its required

 

[magnet]

I would weld up a Metal strap, one for both sides, and bolt through. This the Strut from the pricipal rafter to the strut --just under the roof tiles??. I have put steel on the principal /tie beam joint,(the one in the eves corner) and on the king post to tie beam,(the one in the middle) never done the strut at the principal rafter end though, It wouldnt do any harm, hopefully the birds mouth notches are still tight. If the two timbers are the same thickness I would go with steel maybe 2"" X 1/4 or 3/8" is a bit overkill, depends whats available, Me personally I wouldnt use ply.If the two timbers are different thicknesses fill the void with a packer, Ply or timber. We slipped corrugated washers in any timber/timber joints that were bolted through, some 1/2" bolts be nice.

Stan

Stan that sounds like a plan i think its been cracked since the year dot but a bit of reinforcement wouldn't go amiss if it was going to fail it would have by now Hitler and his Germans couldn't manage it so i dont think i need worry 'bout a bit o wind. Nice to hear from a fellow Northumbrian we're practically neighbours i'm in Stakeford

 

[magnet]

Gluing with PVA and screwing on structural grade ply is often specified in building structural std walls, never seen it for repair of a rafter. I have replaced joist ends stepped "do one, miss one" then "do the missed ones". Pva screws then coach bolts.
Building control need talking to if in any doubt and I think you will find its required

Cheers Kent i haven't got to the spar feet yet no doubt there'll be an issue there too so i may need to do one and miss one thanks for the reply.........Magnet

 

[magnet]

pic would help... more likely to want 10-12mm steel than ply, epoxy is probably not needed

Mike i think i'll go for the steel thanks for your reply..............Magnet

 

[malcolm]

You've got principal rafters? Mine were removed years ago which is proving to be a bit of a hassle. I've just ordered a lot of steel for operation wall spread.

Pictures would be good for a better guess. 10-12mm is twice as thick as the stuff I've ordered and mine will be doing more work.

 

[magnet]

You've got principal rafters? Mine were removed years ago which is proving to be a bit of a hassle. I've just ordered a lot of steel for operation wall spread.

Pictures would be good for a better guess. 10-12mm is twice as thick as the stuff I've ordered and mine will be doing more work.

my God it sounds like you've got your hands full there Malcolm, so is it just the purlins holding it all up?

 

[ford34/2]

Nice to hear from a fellow Northumbrian we're practically neighbours i'm in Stakeford
small small world, 6MM will be fine, at least 2" wide, If the roof was built correctly with then right joints, as the weight increases as the roof is built, all the joint self lock under compression, the steel is an extra, but hundreds and hundreds were built with 6" nails, right up to the 70s when Gang nailed trusses took over. Study barns and old buildings if you ever get the chance, Japanease woodwork where the contruction is made with joints interlocking and using compression to lock them all in. drilled and dowelled, you`ll not see 6" nails in their roofs.

You've got principal rafters? Mine were removed years ago which is proving to be a bit of a hassle
I`m guessing you have a Purlin,whats supporting the Purlin and the roof rafters.??
Or indeed whats keeping the roof up???, The wall plate and ridge board !!!, and the roof rafters.? I wouldnt like to be sleeping in any rooms underneath your house roof. If your walls are pushing out, the weight of the roof is being tranmitted onto that wall, and on down the brickwork, lack of Tie beam allows the wall to buckle outover. the wall plate should be on the inner leaf.
Many Barnes are contructed as a single skin of bricks/blocks/stone and the roof contruction is almost just dropped on top the walls and the use of tie beams doesnt allow buckling of the wall.The roof contruction does not allow the rafters to spread , the structure is locked together, and all the weight is transmitted down, if the rafters start to creep outwards due to the downward weight, then the consequences are the walls, and the wall plate, move outwards creating the bend/buckle. If thats the case time for some serious investigation and remedy.

Note:: we always brought the struts down to the stub Mortice and Tennon joint of the Kingpost and Tiebeam, nowt as fancy as this diagram

 

[Kent]

I must say some of you guys might love to see my roof structure calcs and drawings. it includes some "interesting bits"

 

[malcolm]

Would be interesting to see. We ought to have a building section on here. Probably get much more sense from members here than from your average structural engineer.

My faulty roof is in the barn. It still has tie beams but they are not secured to the wall plate. Steel is for that and ply boarding to take diagonal load from the rafters to the tie beams. An over engineered approach. 1mm by 25mm strip has been doing the job surprisingly well for 30 years.

 

[Kent]

Yeah, the issue is there is a bit more to it than it seems. It cost me over 3k in fees but each job is specific to that job! Its impossible to say what is right and wrong without a guy who tries to drive a 911 down a dirt track apparently (no it didn't end well for his underneath bits)