Ridge Sagging - jack it up?

[slimj]

Hi,

I have stripped the rear elevation of my roof to rebuilt it completely. The previous owners took out a purlin and built a dormer which over the years has caused the ridge to sag...

I have put in a new steel purlin and will also be putting in a steel ridge beam (under the engineers instructions). I have now got the ridge beam up there and in place and the extent of sagging can be seen...

As you can see, the new ridge beam is nearly touching the ridge board in the middle (right of the picture) but it some 3" off the board on the left hand side.

I will be re-roofing the other elevation but not for a while as I have plenty else to do first, so I need to get the ridge to a point where I can work from.

What I am wondering is if I am OK to jack this up? My thoughts were to get some acros under each end and move these up by about 0.5'' per day? I wouldn't envisage I will be able to get the ridge back to perfectly straight, but anything would be an improvement on what is there now.

Any thoughts appreciated. Cheers.

 

[catlad]

I can't see any sense in not stripping the roof and then building your new roof.

 

[ree]

As above.

If we are looking at the rear elevation (with the dormer) in the pic - then no way has it or the other roof elevation been stripped & rebuilt.

The collar ties have been cut - this could lead to the roof spreading - and there's no double trimmer framing or double rafters in the pics.

The dormer is sinking and will continue to sink until the R/S 2" x 4" common rafters split and pull loose.

How the dormer has been framed up - on what support - we cannot see.

When a purlin is cut precautionary measures must already be in position.

Your RSJ is resting on what?

I should stop what you are doing and get a SE in to advise. I'm not a SE but i would advise you to strip both roof planes, and re-do the whole roof and dormer.

 

[slimj]

The elevation with the dormer has been stripped back to the rafters. I put this photo on so you could what it was like before and also some of the roof sag. The photo with the steel has been taken as if you were stood under where the dormer used to be. The blue 'tinge' is because it is covered with tarpaulin.

I have cut the collar ties until I get the ridge beam and new rafter in, I can then install new. Ideally I would like to do the roof at once but I am leaving the other elevation until I have finished other works. It will require planning and I need the time.

I have heard about successful jacking so I will very carefully give this a go to try and improve it a bit. If the whole ridge lifts (rather than it straightening out) I will pack it and build from there.

 

[tony1851]

I suspect the whole ridge might rise, as timber deforms under long-term loading (known as 'creep').

 

[catlad]

I can't understand why you want to jack it up if you are going to have a new roof ?

 

[ree]

OP,

With respect but you dont know what you are doing.

The odds are you dont have the appropriate insurances, and you could be putting passing pedestrians or vehicles at risk of falling slates etc.

If your roof spreads, even by a 10 - 20 mm's you've got big problems.

If you lift the whole ridge by jacking you could tear the common rafters from the wall plates - wall plates that in themselves will not be strapped down.

I'm still curious as to whats happening with the "padstone" arrangement for the RSJ?

 

[jontop]

Try it, take it easy with little steps, see how it goes.
The ridge board is in two pieces so there might be movement there.
I personally wouldn't , probably a waste of time .
1/2" a day will take 4 days for 2"........ could pitch it and slate it back in in that time

 

[ree]

Good spot - i missed the ridge board splice.

That splice was possibly the start of the sagging difficulties.

The splice actually makes the whole jacking effort more perilous. Its already moved ie. begun to fail.

 

[jontop]

No, the sagging difficulty started when they cut the purlin out

 

[catlad]

That ridge looks like a piece of floor board to me so that would not have helped when the purlin was taken out.

 

[slimj]

To update, I sorted this today. In the end I trimmed around the ridge board so the new ridge beam sat under the rafters. I then fixed an acro under each end of the ridge beam and slowly jacked it up. It now nice and level to work off.

Thanks for help and comments.