Curving Collar Tie

[Wondering_Aloud]

Hi All,

Had a water tank problem and while fixing it, noticed that one of the collar ties in our loft has a proper bend in it. The house is a 1990's new build and is at the end of a row, so the roof slopes at the front, back and at one side.

Roughly half way across the loft space is a post that comes from the downstairs up, but unlike a full queen post (that's what diagrams on Google images called it anyway), which would go to the full height of the roof peak, it meets up with a collar tie to form a T shape. From the point where the post passes the ceiling joists, there are 2 diagonal beams that go out from it at an angle of about 30 degrees, that meet up with the collar tie and the rafters. The overall form is that of an inverted triangle made up of of 75mm x 50mm timber with a vertical beam bisecting it, the whole plot being held together with hammered in steel spike plates.

The two diagonals which transfer the weight of the roof to the frame of the house, are both dead straight and in line with each other, but the collar tie seems to have bent to the point where the centre of it is deflected from straight by about 40-50mm. It almost looks as if the horizontal beam is too long.

What would the wise action be here? Is two inches too far deflected? If you push the collar tie in both directions, it returns to the point that it's sitting at, suggesting that it's in some kind of equilibrium state rather than fighting increasing compression. There's no visible sagging in the roof, the steel plates are all fully hammered home so I'm not expecting it to collapse at any moment but being outside of my comfort zone, I'm not sure what the next step is.

Any advice would be greatly appreciated.

Cheers.

 

[^woody^]

Collars are to stop spread, not compression. But 3x2 collars commonly sag to the extent you describe as the roof initially loads, dries and settles, and the fact that they are often too slender for this function.

If the roof is otherwise OK then it can be left as is. If it's an issue you can put a 4 or 5x2 on the other side of the rafter or nail a 4x1 to the collar, or drop a vertical 4x1 hanger down from the rafter near the ridge to the collar.

If the roof is compressing, then a post is needed below the collar, or two angled struts

 

[Wondering_Aloud]

Nice one, thanks Woody. Like I say, I'm out of my comfort zone on this one and do have a tendency to worry unless I know enough about what's happening. The roof looks fine, hasn't sunk as far as I can see, so I'll monitor it for the time being and if it stays as is, then I'll leave it. If it worsens, it's up to Wickes with the roof rack on to pick up some timber.

Thanks again.