Dip in Roof

[mark_j_k]

I had to replace a few slates on the roof today, whilst up there I noticed that there was a slight dip in the slates over about a 2 foot area up the roof.
Once finished replacing I went up into the loft and had a look to see why the roof is dipped and found this:

It seems stable enough, that brick is wedged in place solid. Any ideas to what should be done (if anything) to sort the problem.

 

[Mark]

looks interesting.

is that some sort of strut between the purlin and the rafter?

Whats holding the purlin in place against lateral movement and whats supporting the rest of the rafters ?

 

[mark_j_k]

If it's what you are refering to, that strut is the nail that holds the rafter to the purlin, it's seems to have slipped out.

The rest of the rafters (to the left) are tied into the valley and are not as long as the ones attached to the purlin.

It looks like the brick that originally supported the purlin has been removed and it has slipped down causing the other brick to tip up and get wedged in place.

 

[biffvernon]

Is TOPLA something to do with topple?

 

[Lime]

Not being able to see the rest of the roof some guesswork has to be involved.
However, the brick pier is there for a purpose.
Is it original?
From what I can see I guess it is supposed to be supporting the purlin.
The angle of the brick (assuming it was originally part of another course) suggests the roof has moved towards the pier, dislodging the brick on which the purlin originally rested.
(As you suggest)
It is likely that the mortar joint was used to hold the lower edge of the purlin in place and this caused the brick we can see to rear up.
Further movement has occurred as shown by the nail coming out of the purlin that was for a time holding the entire roof in place.
This movement could be serious if it is still happening.
I hope it's not.
Does any other part of the roof show signs of movement, bending, twisting, sagging or breakage?

 

[middi]

My interpretation. ( apart from Biff,s clear explanation as to how that purlin was suppose to react ).

The " new" purlin is obviousely an attempt to halt the roof sag.

The angle at which this is positioned would be correct only if the existing brick supporting peers were built at 90% slope to the face of the purlin, hence the movement and brick diplacement induced by sag and inward pressure.

The purlin would only be in contact with the most bowed roof rafters .

Looking at the pictures I would stabilise the roof from further movement by:-

a)........making spacers and/or wedges and stabilise each rafter against the purlin.

b)........Halt the inward displacement of the purling by inserting three trimmers ( to front, centre and rear of the purlin span) to act as counterbalance to the inward pressure from one purlin to the other, presuming there is a left and right purlin.

The side pressure on the brick peers will then be redundant, and only downwards pressure will apply.

This should then stabilise the roof as existing untill it rots away.

I could not fail to notice a nice example of lime mortar " torching" between tiles and battens.

 

[mark_j_k]

Thankyou for the replies so far, here's a bit more:

The brick pillar and purlin are both original as far as I can tell - next door (being a semi-detatched) has the same arrangement and the timber and brickworkm matches the rest used in the roof. The other side of the purlin is held in place by the external wall (gable end)

There are only 2 rafters that are not completely attached to the purlin, the first and second one - second one is only away by about 1/8 inch.

I can't see any other probems with the roof timbers that haven't been fixed yet, we had to have a new piece of timber (about 18inches) on part of the valley board as this had rotted away.

View from the outside of the roof - if you look at the middle of the picture you see a slate held in place with lead, this is roughly where the dip is.

 

[Lime]

Thankyou for the replies so far, here's a bit more:

The brick pillar and purlin are both original as far as I can tell - next door (being a semi-detatched) has the same arrangement and the timber and brickworkm matches the rest used in the roof. The other side of the purlin is held in place by the external wall (gable end)

There are only 2 rafters that are not completely attached to the purlin, the first and second one - second one is only away by about 1/8 inch.

If you have looked at another, similar house with a brick pier how is that purlin supported on the pier?

I am sure that originally all the rafters were attached and the gaps on rafters 1 & 2 demonstrate how much the roof has sagged.
At the very least you need to secure the end of the purlin so further movement is prevented/limited.
The angled brick may be supporting the single rafter and the rest of the roof via the tile battens at present but that is not a healthy situation for the long term safety of your roof.
The brick needs to be removed AFTER the purlin has been supported properly.

Obviously great care needs to be used when doing this work.
Perhaps you need to get professional advice.

If it were mine, I would initially test (gently) to see how easy it is to lift the purlin very slightly (less than a centimetre or so) using a wooden lever between the purlin and the pier.

Unless the purlin moves with ease I would not force it back to it's original position all in one go.
The timbers need time to adjust to any movement.
Perhaps a small vee wedge of wood could be inserted between the purlin and the pier and inserted further in over several days/weeks so that the purlin is restored to it's original position eventually.

 

[Penners]

Like the others who have responded, I'm concerned that the end of the purlin (as shown in your first photo) is unsupported, except by this brick pier. And who ever constructed the pier arrangement really doesn't seem to have had any idea of the angle at which the stresses will act on the purlin (ie: at 90 degrees to the rafters).

I find it difficult to believe that the purlin is original to the building. If it were, it would surely run the full length of the roof and be housed at each end in the gable end brickwork.

I'm no expert, but Middi's solution sounds eminently sensible to me. Particularly as he is advocating a fix for the problem as it stands now, rather than trying the push the roof back out (which could cause all sorts of additional problems).

 

[mark_j_k]

I thank you once again for your replies.
I'm going to have a much better look this weekend in the loft as well as looking at next door's roof - the party wall in the loft is only 1/2 height so I can easily look over it and take some photos.