Holy *!!@ my roof is falling off

[StoneTheCrows]

OK,

I've got a rafter, joist, ridge and purlin roof. Gable end, standard pitch. The rafters are 3 x 2's, the purlins are massive 12 x 4 hunks. the span of the purlins is 5 metes the length eaves to eaves is 8 metres with a load bearing wall in the middle.

I noticed a tapered vertical crack developing between a first floor internal wall abutting an external wall. the ceiling has also got a crack where the external wall has pulled away from the plasterboard.

Having pulled off all the surrounding plaster and bathroom tiles I've discovered the external wall is bowing out from the centre of the external wall and has pulled away about 25mm from the internal wall. It has pulled out most at the wall plate height and tapers back in to the internal wall about 3 foot lower. the ridge of the roof appears, from the outside, to have sagged too

So I've clearly got some roof spreading going on.

I've re nailed all of the ceiling joist at the centre overlap and I've crawled into the eaves to have a look at how the rafters are attached to the joists and to my surprise I cannot find any trace of the rafters being originally nailed to the joists. In fact I can slide a saw between the rafters and joists and it slides in and out, up and down without any hindrance so I m pretty sure there are no nails there

the rafters have the normal 'birds mouth' cut to sit on the wall plate.

Is it normal not to have the rafters nailed to the joists? they surely must be attached somehow??? so perhaps the rafters are nailed through the top of them into the wall plate and the joists are perhaps also nailed into the wall plate and so the wall plate is the thing tying it all together albeit not very well!

There is a slight tapered twist movement in the purlins apparent in the mortar where they bed into the wall, nothing massive though only maybe a 1mm twist. I would have expected more given the amount the wall has bowed but maybe the rafters have just slipped off the purlins, again, if they are not nailed.


So in my mind I need to nail the rafter to the joists and create the triangles in each pair of rafters and joists to give the strength required to prevent deflection and strap the external wall back to the internal wall to tie it back together.

any other thoughts?

I'm particularly interested to know if its normal in roof construction not to nail the rafters to the joists and just nail them both to the wall plate as appears to be the case here.

cheers

 

[tony1851]

Lots of older houses don't have any direct connection between rafter and ceiling joist.

Over time, the outer wall will gradually move out at the top as the rafters bow under long-term creep; a ceiling casually nailed to the wall plate (or in many cases, just nailed to a bearer plugged to the wall) will give practically no restraint.

To prevent any further spread, you really need to consider putting timber ties in front-to-back, as low as possible.

 

[StoneTheCrows]

cheers fella,

the house is about 44 years old, if that adds any info.

"timber ties in front to back" - do you mean in effect new joists goings eaves to eaves and nailed to the rafters at both eaves?

The ends of the current ceiling joists are all snug against the rafters, which is why I can only get a saw blade between them. The fact that they are snug was why I was so surprised not to feel any nails in between, seems obvious to me that they should have been nailed, anyhow....

Because they are snug, could I not just nail these current joists to the to the rafters.

what do you think?

 

[StoneTheCrows]

Also when I decide what I'm actually nailing what size and type of nail should I use?

I've read not to use screws as they are prone to snapping upon any movement whereas nails can flex a little.

is that other people experience too?

cheers

 

[theoldun]

Before giving any possible reason or remedial works, would like to clarify the following.
House built early 1970, so assume cavity wall with roof plate and rafters on interior wall?
You say average pitch, could you be more precise?
What is present roof covering and has it been changed in last 5 years?
Regards oldun

 

[hairyfingers]

House built 1972. Yes cavity wall. Yes house has cavity wall. Yes joists and rafters sat on interior wall. I'd say pitch is about 35 degrees. Roof covering is concrete tile. Original covering. The only roof work done is we had a dry ridge fitted 18 months ago.

Cheers

 

[ree]

Why not, if its accessible, screw the rafters to the joists at the wall plate. Use a right angled drill and nut-setter to drive in hex headed screws. Do likewise where the joists meet over the interior wall.

Check Simpsons catalog for various kinds of clips that would enable you to tie in the rafter-joist-wall plate.

Any gaps between a rafter and a joist can be packed before screwing together.

Sheets of 3/4" ply screwed down into the joists will act as tremendous tie-ins but getting them into the loft is the trick?

Also check and see if galvanised restraint straps have been used to tie the wall plates into the masonry below. And that the rafters are nailed to the purlins.

I've never encountered such lack of nailing as you describe - surely the joists would have bounced when the plaster board was nailed up, and been prone to deflection when anyone walked in the loft?

Just a thought, is the wall plate definitely on the inside skin?

Anyway, you should take a shed load of pics (some external) and post them on here, and perhaps a scanned sketch of the upper floor footprint?

 

[StoneTheCrows]

I think I've now identified that the joists ARE nailed to the wall plate, each one with a single nail going from the tip of the joist diagonally down into the wall plate. If a scrape my hand to the back of the joist I'm pretty sure I can feel a nail head. I cannot see any nails on the rafters but I would guess then that these have been nailed from the top of the rafter down into the wall plate.

So in effect they are tied by each using the wall plate.

perhaps some of these nails have deteriorated hence the slippage.

good call on the right angled drill I tried getting my drill into today and was impossible.

there are no restraint straps going from the wall plate down the wall

I'll get some pics up tomorrow

cheers everyone for taking the time to input.