Unsupported cavity wall, how high?

[fox33]

I’m building a gable end, from wall plate height (the unsupported ‘triangle’) is 10m wide by 5m high.

The roof construction is steel purlins (two per side) and a steel ridge beam, with rafters supported on these.

I’m up to first purlin height now, but I’m concerned it’s getting high and until the roof construction is complete the wall is unbraced.

I’ve looked online but can’t find anything, does anyone know a safe height I’m able to work to? The wall is two skins of 100mm dense block with a 100mm cavity, so 300mm in total thickness.

 

[^woody^]

I use this formula

(h x 1.5m) x (weather forecast for the days after it's built)

 

[noseall]

We built this fella....

Raisedtie1

• noseall
• 15 Mar 2019

on a windy day but with the roof in place. There is no way I would build one the size of yours without the ability to stabilise it whilst the mortar cures.

 

[garyo]

There is no way I would build one the size of yours without the ability to stabilise it whilst the mortar cures

How would you do it if it wasn't trussed, and you couldn't get any rafters in until the wall is built hight enough to seat the ridge steel in place? I did one last year where the only way I could think to stabilise it was a 45 degree joist coming out of the floor and then bolted into the wall.

It was still pretty uncomfortable though (3.5M tall from the floor joists)

 

[noseall]

You should be able to construct a ridge beam roof using the rafters and props to stabilise the beam until the wall is built.
Or...
Fix stabilising timbers to the walls below allowing them to extend beyond up to the proposed gable and use these as stabilisers. Fine as long as there is no big opening below.

The best you could do is build both leaves in unison - i.e. so many courses on each leaf and then walk away for the day.

 

[Tigercubrider]

Just to cheer you up
When I was a kid in the mid 70's a house was built opposite us by a firm of builders, with one of their directors as the client. About 10 at night there was a massive bang and the entire gable end fell down.
It's always windy when you don't want it to be

 

[garyo]

construct a ridge beam roof using the rafters and props to stabilise the beam until the wall is built.

I like the idea of it, not least because it allows for building around the gable ladder as you go along, but it doesn't seem much less precarious than an unsupported wall.

Let me check I understand you: You hover the ridge steel in place using a crane, or temporary scaff, then get ~3 pairs of rafters in so that you know it's in the correct final position. Then get four or five 'king post' style struts underneath to take the weight, maybe spreading their weight over the first floor joists using scaff boards?

 

[noseall]

I like the idea of it, not least because it allows for building around the gable ladder as you go along, but it doesn't seem much less precarious than an unsupported wall.

Let me check I understand you: You hover the ridge steel in place using a crane, or temporary scaff, then get ~3 pairs of rafters in so that you know it's in the correct final position. Then get four or five 'king post' style struts underneath to take the weight, maybe spreading their weight over the first floor joists using scaff boards?

Yes, that would be it. Or just build the whole roof whilst supporting the ridge beam until the gable is constructed.

Not so easy on tall roofs I admit.