Cracked roof truss

rocky_robin · 1 Nov 2008

Hi all.

I'm needing a bit of guidance on who to solve this issue!

It's the roof of my 19th centry steading and as shown has a nice crack on one of the trusses.
My boss told me to get a hold of one of those long structural jacks, drill 4 holes through and bolt on 2 thick plates either side (i.e like sistering).

Now as you will see, trying to jack up the angle will be difficult, but I could lay the jack at an angle and place a very heavy object at the base of the jack.

Any other suggestions?

Thanks in anticipation,
Robin.

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JohnD · 1 Nov 2008

I would be inclined to try to fix a block to the floor (big nails or something)else put a block there, and a piece of timber bracing the block against the wall that it will try to slide towards.

If you can shape the block so that its bottom surface is flat on the floor,and the top surface is angled to the bottom of the prop, it will be less inclined to slip out.

Take precautions that it cannot slip out and shoot away while you are working.

^woody^ · 1 Nov 2008

You will have a terrible job trying to jack that back up to anywhere near where it was all those years ago - it just wont go back now.

Just strengthen the rafter to prevent further movement.

rocky_robin · 3 Nov 2008

Thanks both for your replies.

Would a steel plate either side of the truss do the job?

In the case of bolts, obviously I don't want to drill too big a hole into the wood, incase I weaken the damn thing more! What size of bolt is commonly used in this case?

Thanks.

mrcrow · 3 Nov 2008

steel plates i thought were better and less bulky...the gripper type will take out any shear and so the bolting wont have to bear on the timber under the released load

noseall · 3 Nov 2008

i tend to agree with woody.

it may be wise to take some of the load, whilst work commences, by moderately jacking the trusses either side of the effected one.

datarebal · 3 Nov 2008

I have seen this same problem before. The rafters have started to basically snap at the connection of the collar ties . It was caused by spreading movement of the masonary walls.. check it out

Deluks · 4 Nov 2008

datarebal said:
I have seen this same problem before. The rafters have started to basically snap at the connection of the collar ties . It was caused by spreading movement of the masonary walls.. check it out

Which in turn was probably caused by the rafters themselves pushing out the walls, due to them being undersized in the first place, or maybe the ties were moved up at a later date?

If it were me I'd be bolting new 50mm deeper rafters to every other truss.

^woody^ · 4 Nov 2008

The problem with a steel plate either side of the rafter is that the collar is preventing a full plate on one side of the rafter, so effectively only one plate will be doing the strengthening.

So this one plate should be suitably thick, or you could just double up the rafter - at least for part of its length

If using timber then, use some spiked timber connector washers between the two and large square plate washers on each side. m10 or 12 coachbolts at say 500mm centres

Is the visual aspects of the repair important? Although it does seem that there is a section of doubling up of this truss in the background

Have the other trusses been checked for similar problems?

mattylad · 4 Nov 2008

If the visual aspect is important, use the steel plates & cover them with a wooden boxing in a matching wood ?

stuart45 · 4 Nov 2008

Its difficult to be sure from the photo, but the collars look a bit high to be effective against roof spread.

rocky_robin · 5 Nov 2008

Thanks a million for all that replies!

The steading is dated back to the mid 1800's, so the wood has done not bad. According to my records of the steading, the only repair that was done was at the left side of the rafter (in the 1st pic above). The slates were damaged during the hurricane storm in 1983 and was replaced, hence the difference in slates.

This rafter in question is the only one that has cracked. Thankfully, as many has noted the collar is holding the crack together.

The visual aspect of the repair is not important. What is important that the roof doesn't come down! I've got 2 precious cars under that roof and will be a tad upset if anything happened.

The other side of the rafter is beginning to sink slightly too, as if they are both bowing inwards.
That wood that is nailed into the rafter in the background seems to be doing nothing, but I'm not even chancing taking it off.

Time to buy a pair of structural jacks!

Deluks · 5 Nov 2008

You can hire acro's for a few quid per week. You'll only need 'em for a day.

rocky_robin · 6 Nov 2008

Yeh, I think I will be hiring! To eck with paying that price for a once only use!

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Cracked roof truss

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