Split Purlin Helpppp!

[john_smith93]

Hi Community, 

 

I'm buying a new house at the moment and the survey flagged that in the roof, the supporting timber purlin has suffered from a crack to the mid section here and is supported by some additional struts at the moment. Are there any structural engineers here to give an opinion on the damage here?

What's your opinion on the cost (structural engineer survey, scaffolding, fixing) to fix this issue here. (see photos)

Thanks
John

[Alan Ambrose]

Hmmm, I wonder what this might imply besides the need to fix it?

 

+ did some odd load, a tree perhaps, hit the roof, is there other damage?

+ if not, is the roof built so weakly that it's falling apart?

+ did their SE, if there was one, make a mistake?

+ maybe there wasn't an SE, just a builder who made some not very good guesses?

 

In any event, I think you need to ask the seller for a full report by a respected SE, with costings to repair. Also, to take a full look at the house to see whether there's anything else serious there.

 

Alternatively, you could just walk.

[TonyT]

Gus is the man for this!

 

[Mike]

Alan poses some good questions. I suspect that to properly fix it could mean stripping the entire roof to remove the load and straighten out the rafters (I guess that they're out of alignment too?) before replacing or reinforcing the purlin. But I agree that a SE report would be very helpful.

[Russell griffiths]

I could be completely wrong ( but unlikely 🤣🤣) if you look in the pic there are flat boards on top of those rafters, these look like valley boards, there is also a timber directly above the split, this looks like a ridge board. 

I think there is another roof situated resting directly on that purlin. 

Either it is a little gable type roof sitting on top badly designed, or an additional roof has been added like a small extension. 

Either way the purlin has been overloaded 

i think this could be jacked back up, from the opposite purlin or a wall below, then the original purlin could be sandwiched with a couple of steel plates and plenty of bolts, with a couple of better struts going down onto an internal wall. 

Either get them to fix it or go in £10,000 under on an offer. 

[joe90]

2 hours ago, Russell griffiths said:

I could be completely wrong ( but unlikely 🤣🤣) if you look in the pic there are flat boards on top of those rafters, these look like valley boards, there is also a timber directly above the split, this looks like a ridge board. 

I think there is another roof situated resting directly on that purlin. 

Either it is a little gable type roof sitting on top badly designed, or an additional roof has been added like a small extension. 

Either way the purlin has been overloaded 

i think this could be jacked back up, from the opposite purlin or a wall below, then the original purlin could be sandwiched with a couple of steel plates and plenty of bolts, with a couple of better struts going down onto an internal wall. 

Either get them to fix it or go in £10,000 under on an offer. 

+1, or the purlin had a weakness in it to start with and age has found it’s weakness, either way as Russ says above, jack it up and strengthen the area (and negotiate the price), it would not put me off buying it.

[saveasteading]

Well spotted above. Yes @Gus Potter does this stuff. It will help to have a photo from outside.

 

I wouldn't walk away yet.

[Big Jimbo]

I agree with @Russell griffiths. I think there is another roof coming off that. You are quite a distance from the central wall. I doubt it could be jacked right back to where it should be, but you could possibly get it close. A photo from the outside would be good. I doubt those little additional struts are doing much, except trying to push the ceiling down in whatever room is below it. Wouldn't make me walk away, but i would want a chunk of change off the asking price. While you are sorting it, stick a load more fluffy stuff up there. It looks very minimal at the moment. Dont block the eaves ventilation though. That underfelt looks like the old type, so if you are short of pennies make sure somebody has a good look at the tiles on the roof. If the property is 1930's the old tiles may still be doing the job, but will be near the end of life. If you have to do anything on the roof, most of them will break when you start messing with them.

[SteamyTea]

11 hours ago, joe90 said:

or the purlin had a weakness in it to start with and age has found it’s weakness

Hard to tell, but looks like it had a knot in it, and a knot in tension.

Or, a knot, not in compression.

 

Edited August 30, 2023 by SteamyTea

[Big Jimbo]

@SteamyTea or just a naughty knot.

[SteamyTea]

16 minutes ago, Big Jimbo said:

@SteamyTea or just a naughty knot.

In Knotty Ash

[Big Jimbo]

@SteamyTea He was the support act for the Police on Tooting Bec Common, many years ago. Poor fella got ran off stage. Shame as he was actually better than sting and co.

[SteamyTea]

11 minutes ago, Big Jimbo said:

Shame as he was actually better than sting and co.

Probably giving tax advice backstage.

 

Don't stand to close to me with that giggle stick.

Edited August 30, 2023 by SteamyTea

[Carrerahill]

45 minutes ago, SteamyTea said:

Hard to tell, but looks like it had a knot in it, and a knot in tension.

Or, a knot, not in compression.

 

Agreed, looks like it was not ideal!

[Gus Potter]

A lot of good points and observations made here.

 

Yes agree with all it does look like there is another roof framing in which will add a bit of a point load to the purlin.

 

Also as others have noted there is a knot, shake in the timber right at the point of maximum bending stress.

 

The purlin is something that can often be fixed. But you can see the roof must have dropped.. so that suggests that the roof may have spread, including the bit of roof coming off the purlin.

 

I would want to understand if the roof has spread and if so what damage if any has been caused. Some roofs spread and don't impact on the rest of the structure too much.. at times spread can cause havoc = money.

 

Often with something like this you just aim to stop further movement rather than trying to jack things back into position as jacking can often cause even more damage.

 

Sometimes we want to add a bit of prestress to a remedial member. For example if you bolted a new bit of timber to that purlin before the new bit of timber starts to work it needs to carry load thus for load transfer to occur you need more movement... which you are trying to avoid.

 

What you might do here is see if you can get a good length of new timber into the attic that spans nearly wall to wall. Bolt it in the middle where the existing purlin has split then jack the free ends of the new timber.. you pre stress it.

 

Then finish the bolting and use some brackets or equivalent (there are some clever ways of doing this that don't require brackets per say, these work like gallow brackets but much more refined and made out of timber) to fix the ends of the new timber to the masonry.. to take some of the load and help to stop things from twisting. This is a bit of a simplification but hope I have conveyed the principle of my thinking.

 

The main thing is to really examine the rest of the house for damage caused by possible roof movement, if none then it's down to just fixing the roof in a practical and as simple a way as you can find using off the shelf materials.

 

 

 

 

 

 

[joe90]

@john_smith93 we need photos of the outside to understand more. This is @Gus Potter field of expertise. I guess that as that other ridge beam resting on this purlin is so low it might be a false dormer 🤷‍♂️, any bets?

 

I am not sure about spreading as this should be controlled by the ceiling joists 🤔, hopefully only roof joists bowing due to the purlin sagging. I take  Gus,s point about more damage from jacking causing even more damage (if you can find somewhere substantial to jack from!) I still think this is repairable and would not put me off buying (but might get a few ££ off the asking price.) Gus,s suggestion of pre stressing a sistering timber is a great idea IMO.

Edited August 30, 2023 by joe90

[George]

Sometimes see this when clay tiles are relaced with concrete tiles. That, combined with the knot leading to a split.

 

I'd hold off until you get a quote for repair, but once done the roof should be good for a long time. 

[saveasteading]

A lot of effort and good advice here,  but silence from the original poster @john_smith93.

I'm unfollowing.