Roof purlin shrunk and so not supported

[trevorbayliss]

From the photos you should be able to see how i have built my extension. It is a box spanning 7m wide.

I have 4 oak purlins holding up the roof structure.

I was about to do some caulking around plasterboard where the purlins sit on the block walls (its been 2 yrs since this was finished).

I have a spine wall dividing up the span, so the purlins only span 4.5m max in the main room. This is where i can see the purlin in question is not touching the block wall. You can see from the photo the light into the utility room on the left side of the purlin. The camera cannot show what the eye can see, but you can also see fully underneath the purlin by 10-15mm.

This was the worst purlin they sent and it was bowed as well, but we used it.

All seems ok still elsewhere.

What should i do ? Do i cut the plasterboard back so i can pack under the purlin with a cement mix ? Do i leave it ?

Its the purlin above the step ladder.

 

[^woody^]

That's saying that the rafters are staying up regardless

Slide a tile or something in, then just caulk it. Don't mess about disturbing plaster

Or maybe intumescent mastic depending on the location

 

[tony1851]

Although tough and durable, oak - particlarly if installed green - can be subject to twisting and bending. It's not an ideal timber for incorporating into neat, precise designs. It was often said to be 'not for the faint-hearted'.
Just fill the gap at the left, and pack cement mortar underneath, and forget about it.

 

[trevorbayliss]

Ok great thanks. I will see if i can do a smallish repair with slate, maybe compo.

Because its the spine wall it also means the purlin is strong enough spanning 6.5m, rather than the 4.6m as intended. So happy that the oak is showing it is quite strong.

There is cracking to be caulked up, but not that bad. I think this was a dodgy purlin they sent. The other ones are mush more straighter and solid looking and the shrinkage around them is much less. I used air dried and not green oak. Just depends how long they were dried for in real terms.

 

[tony1851]

The cracks are called 'shakes' - very common in oak. They can look alarming but are usually not a structural problem.

 

[trevorbayliss]

Sure, but around where the plaster board touches the purlins there are shrink cracks which need filling.