Roof purlins don't go into the walls?!?

[Cmperry]

Hi all,

We live in an 1890's mid terrace. All the houses in the area used to be slate rooves but we're all at some stage changed to normal tiles which are obviously heavier.

Recently one of the houses down the road had there whole roof fall in which has got everyone panicking.

Our roof is level across the peak of the roof but does sag a little I think (it's every so slight) in the middle of the main flat bit.

Upon inspection of the loft there is 1 purlin on each side (approx 1/3 of the way up) of the roof but only 1 of the 4 ends seems to go into the gable walls.

Each purlin is supported by several vertical struts from the loft floor. Each purlin also has 2 angled beams supporting from the centre of the house.

My question is can I support the purlins further without replacing them as they are not long enough to go into the walls at each end?

 

[ree]

We definitely need pics of the inside of the loft and the "little sag".

When you say "gable walls" do you mean party walls?

Do the "several struts" & "angled beams" come off masonry walls? More pics please?

Do you have a reference for or a pic of the roof collapse down the road?

 

[Cmperry]

Thanks for the quick reply.

I'll get some pics of our roof first thing in the morning.

Unfortunately, I don't have pics from down the road and it's all covered with plastic now

When it fell in it looked like the main beam at the roof peak had either given way at one end or come away from the wall.

Apologies if I'm using the wrong terminology. When I say gable walls I mean the walls at each end separating us from our terraced neighbours (is that what you mean?)

I believe the angled beams meet on another beam that goes from party wall to party wall at the loft floor level below our loft boards.

As for the struts I'll also check what is supporting these when I get the photos.

 

[Cmperry]

Here are some pics.

Clearly the first thing is to clear out all the crap the previous owners left us

 

[ree]

I see only two vertical posts - what are these posts, and any other posts supported by? They should push off masonry walls.

There's no context or indication as to where in the loft the pics are pointing?

Are the rafters still securely nailed to the ridge board? Simpson LRU hangers, or L straps, would strengthen the connections at the ridge.
Hold down plates could be used at the wall plate to connect the rafter, and long screws thro the joist and rafter would create a truss effect.
A right angled drill would be needed.

The length of purlin in the pic 139.4KB shows a purlin too lightweight to span and support the rafters/roof. More posts fixed to the purlin would relieve the weight. Fixed with Simpson connectors/plates.
The rafters should be fixed to the purlin.

If your roof spreads or the ridge wobbles then the present set-up wont hold.
How much remedial work, from the lengthy suggestions above, you would want to do is down to you?

 

[Cmperry]

Thanks for your help so far.

The 2 posts are sitting on some wooden lengths that are running across the joists. These wooden lengths are not above any walls or supporting part of the structure.

The posts are at (and towards) one end of the purlin that does not go into the wall at either end. This is also the purlin that is bowed in the 139.4kb pic.

The opposite purlin (not pictured) goes into the wall at one end and not at the other. This side has no posts and is simply held by the wall at one end and then by the 'angled' beams which are also on the first side (139'.4kb pic). It is also the same lightweight dimensions.

Having now been next door it would appear that our roof is the only one not done properly as theirs has purlins double the thickness of ours all going into the wall as you'd expect them to.

Everything seems to be secure at both the ridge board and and wall plate but I'll definitely consider strengthening.

If I were to fix 2x4 across the width of the house vertically under the purlins and then put vertical posts up to the purlins (with right angled cut outs in the top for the purlin to rest in) would this provide any meaningful support if the 2x4's are spanning the joists but are not above a supporting wall?

Long term we'll get the whole place strengthened as part of a loft conversion but we're still a couple of years away from that.

 

[ree]

Leave the purlins/2" x 4" notions to one side for now.

The wooden lengths that run across the joists are plates and you could double up the plates and pack them if/where they cross any walls.

Then secure and notch or mitre the posts to the purlins, & set them on the plates - you will have to do this for the purlins both sides.
So its plates, posts and secure connections.
Bolting end posts to the party walls would help.

Bolting collar ties from front to rear rafters would also help prevent spread.

 

[catlad]

They look poorly constructed roofs to start with and now they have been loaded with tiles well I would advise you to make sure your house insurance is up to date.

 

[TheVictorian]

The roof may once have been adequate with slate tiles (just!) but with concrete tiles I would say it is grossly underspecced. Personally, I would crack on and get this resolved as soon as possoble. If you are looking at a loft conversion then why not get plans done and strengthen the roof accordingly as phase 1 of the project, you needn't finish it with electrics/plastering/fitting out for a couple of years but it saves wasting good money if you are intending to do this in a couple of years anyway.