A nail - holding up the rafters?

[CrawfW]

Hi,

Is it likely that the lower ends of roof rafters have been simply nailed to the wall-plate?

Picture A shows the general appearance, Picture B the nail.

I was expecting something like a Bird’s Mouth joint, as I can’t see anything else serving the function of a tie-beam.

The room is 2.5 metres wide, and the roof has an elevation of 1.0 metre and a thus a pitch of 21 degrees.

In more detail -

1. At the top of the roof, the rafters (must be) fixed to a wall-plate which is itself attached to the (cob) wall. I cannot see how this was done.​

2. At the base of the roof, the rafters are attached to a wall-plate, with the timber held in place by the outer skin of the breeze-block cavity wall.​

This attachment looks like it has been done with a single nail for each rafter; there is no sign of a bird’s mouth type joint (Picture B).​

3. Short vertical posts do not transfer weight from the roof, but instead support the ceiling joists below them (Picture C).​

4. The horizontal beam at the right-angle base of the wall supports the ceiling joists, and rests on breeze blocks at each end.​

5. There is an intermediate horizontal which is built into the breeze-block wall at one end, but the other end is unattached. As such, it cannot be preventing lateral spread.​

Hopefully the pictures make this all a bit clearer…..

Finally, before people tell me this is a job for professionals, I do have a structural engineer coming. The aim is to see if we can remove the ceiling joists, but thought I’d try my luck on here – keen to understand as much as possible…..

Any comments appreciated!

Cheers,

Crawf


Picture A

Picture B

Picture C

 

[CrawfW]

Perhaps Birds have smaller mouths than i realised - could this be such a joint, with a nail straight through it?

 

[CrawfW]

Hmmmm. Now i see that a Birds Mouth probably isn't structural - even though if gives a vertical bearing to the load. In which case, i am struggling to see what is holding the ridge up......

 

[tony1851]

What's the problem? Countless thousands of older properties have the rafter/wall plate joint with a simple 6" nail like that.

 

[^woody^]

And yet the roof is still on after all these years. Strange.

 

[CrawfW]

Like you guys, I'm a big fan of time - if it has lasted 50 years it can't be too bad. People on another forum are telling me it cannot possibly be standing and that it must be taken down and replaced.

Having said that, given that there doesn't seem to be a tie beam, I guess the chances of removing the ceiling joists aren't high?!

 

[skenk]

leave the joists but clad them and fit out up to the roof... mezzanine storage, rooflights or dormer etc. You'll still get the height, there will just be some (nicely finished) joists in the way. Or else there will be some way or other to do what you want, at a price.

 

[CrawfW]

So, just in case anyone wanted to know the answer, the structural engineer reckoned i was fine to cut the ceiling joists. I've done so, and all is still standing.

He said the combination of the nail and the wall-plate seemed to have been doing fine for the last 80 years, and that the ceiling joist wasn't doing anything to prevent spread.

He did, however, suggest we double the rafters - they were marginal size for their length. Actually quite a satisfying job to do!

Onwards.....

 

[KenGMac]

So, just in case anyone wanted to know the answer, the structural engineer reckoned i was fine to cut the ceiling joists. I've done so, and all is still standing.

I trust you got that in writing? and signed on headed paper?

Ken.

 

[skenk]

If the joist's aren't (weren't!) tying the roof together, what is? How much of them have you removed (a photo would be great)?

 

[garyo]

Remember that this is a lean-to roof, so the rafters are probably birdsmouthed on to a ridge/wall plate that's bolted in to the wall.

 

[catlad]

Wow! were did he study, looks like a lot of timber used for no
apparent reason then.

 

[RonnyRaygun]

If the joist's aren't (weren't!) tying the roof together, what is? How much of them have you removed (a photo would be great)?

It's a lean-to roof - I know I will probably have to keep saying this but rafters on a lean-to roof do not need tying, never have, never will. See below.

Lean-to Roofs

• RonnyRaygun
• 10 Nov 2015

Proving Lean-to roofs do not exert a horizontal thrust.

There is a chance that the rafters need support from the vertical members onto the ceiling joists (creating a truss) but as they are only spanning 2.5m it's unlikely that is the case. 50x125mm rafters would do the job without any truss action. Your SE should have carried out a check on this.

 

[catlad]

I also don't see any birdsmouth on the rafters so they will be relying on the ceiling.

 

[noseall]

A solid wall takes the place of a ridge beam in terms of roof spread, regards a lean-to roof.