crack in my lower front purlin

[jaysta]

Hi guys,

Another question but this time it's about a crack that I have spotted in one of my purlins.

The property is an 1880s mid-terrace house. The roof is a slate roof. The rafters are 3" x 2" and meet a ridge at the top (not sure of the dimensions of this unfortunately). On each side of the roof there are two purlins. One lower and one upper. Each purlin is 3" thick and 10" high. The length goes straight from party wall to party wall. Each purlin is also angled at the top all the way along to accommodate the rafters being at an angle.

The front lower purlin seems to have a crack in it. I'm unsure as to if the crack is continuing to grow further along the purlin but what should I do about it?

I will post pictures of the purlin later but I'll describe briefly here. The crack starts from one end of the purlin (party wall) and continues about a third of the way along the purlin inward. I'd say the crack is about 1cm in depth in some places and the crack is both visible from front and back of the purlin.

My initial idea was to put another purlin alongside while I gut the main bedroom (existing bowed joists will be coming down as well) but I'd like to know what you guys think.

I'd rather get the job done properly while the opportunity is there and I don't want a building surveyor pointing out that this needs to be rectified before selling the house in future.

Again, thanks for your time and any advice would be appreciated.

Jay

Edit: pics are now added below -

Lower purlin 1

• jaysta
• 5 Feb 2010
• 1

Front part of roof with upper and lower purlins. Lower purlin being the culprit.

Lower purlin 2

• jaysta
• 5 Feb 2010
• 1

The crack in more detail.

Lower purlin 3

• jaysta
• 5 Feb 2010
• 1

Start of crack

Lower purlin 4

• jaysta
• 5 Feb 2010
• 1

Middle of crack

Lower purlin 5

• jaysta
• 5 Feb 2010
• 1

Towards the end of crack

Lower purlin 6

• jaysta
• 5 Feb 2010
• 1

The crack is .25" or 1cm in depth

Lower purlin 7

• jaysta
• 5 Feb 2010
• 1

This is the crack from the back of the lower purlin

 

[PrenticeBoyofDerry]

Metal straps, should sort it out.

 

[jaysta]

Any advance on metal straps?

For metal straps... would I then have to somehow compress the purlin first before fastening metal strips to the purlin or just bolt metal strips to the purlin as it is now?

What spec should the metal strips be?

I've emailed local BCO about this and attached same pictures but he's not got back to me yet.

 

[denso13]

I don't think there's much of a problem there. There is an obvious 'crack' showing but no sagging of the purlin.

I'm pretty sure the original purlin was oversized by today's standards and if there are no other problems, like sagging on the roof finish, then I wouldn't worry about it.

 

[Burnerman]

They sure knew how to overdo things in those days......a splendid roof thats lasted well.
Perhaps you'd consider capping the purlins with 1" WBP ply, and bolted through with coach bolts?
John

 

[Deluks]

I've emailed local BCO about this and attached same pictures but he's not got back to me yet.

He won't care. If anything he'll ask you what you intend to do about it.

For strapping, get some light restraint straps. All the sheds, screwfix, builders merchants do them. Fix the right angle end under the purlin, fix through the holes with some 35mm screws, hacksaw off the long end to the same length as the purlin depth beforehand. All probably unnecessary but will give you peace of mind for under a tenner.

 

[jaysta]

I don't think there's much of a problem there. There is an obvious 'crack' showing but no sagging of the purlin.

I'm pretty sure the original purlin was oversized by today's standards and if there are no other problems, like sagging on the roof finish, then I wouldn't worry about it.

Thanks denso. That's one thing I haven't checked. I'll check the roof from outside to see if there's sign of tiles being lifted or indeed sagging.

Perhaps you'd consider capping the purlins with 1" WBP ply, and bolted through with coach bolts?
John

What does capping mean? You mean all four purlins?

One thing that has been mentioned to me as an idea, which I'm wondering if John is talking about is to get a length of 7" x 2" or 6" x 2" length and bolt this alongside the purlin. But then I'm thinking that if the purlin was to crack any further then it would split the length of wood as well.

John, is your suggestion of WBP ply better then because in plywood one layer the grain is going one way and then the next layer's grain is going perpendicular so it's stronger?

Thanks again everyone

 

[denso13]

The property is an 1880s mid-terrace house.

I think that's the important bit. It's been there for 130 years and your pictures look better than many modern houses.

There are tweaks you can do for peace of mind as others have mentioned but if it was going to fall down it would have happened a while ago!

I wouldn't worry about it any more, hard as it may be

 

[perrybond]

The purlin spans from wall to wall, working as a simple beam. The largest bending stress is in the middle, (That's why you can notch a beam at the ends.) taking one tenth of the depth of the beam for a third of it's length would not affect it's structural capacity in the slightest (assuming it's just holding up the uniform load of the roof and no point loads like a chimney!)
I would suggest the crack appeared as the wood dried years ago and that if you inspect the crack carefully with a torch, there will be no light wood visible, the timber colour is the same as the surface. Mark the end of the crack and if it gets bigger, I'll come and fix it myself.

 

[noseall]

I'm pretty sure the original purlin was oversized by today's standards .

[/color]They sure knew how to do things in those days

When was the last time you two built an all timber roof "these days"?

The timber sizes for a modern cut roof are astounding and are becoming prohibitively large. The latest roof i built includes huge steel pulins and makes the roof that is joins onto a joke.