Vaulted Roof

[Frank12345]

Having seen other designs I have seen a vaulted roof created by applying a steel or timber structural beam at ridge level to stop the roof dropping.

Instead of choosing this method would the addition of two purlins, at midpoint, splitting the span of the rafters work in the same way?

 

[ree]

There are a number of designs for so called vaulted roofs. Maybe you mean the more or less open vaulted area not a dropped vault? There are various ways of doing that kind of roof but trying to convey the details over the internet is not a safe practice - no reflection on you but there are too many variables even to comment on the two purlins option.

Maybe others with more experience could advise you better.

 

[noseall]

Having seen other designs I have seen a vaulted roof created by applying a steel or timber structural beam at ridge level to stop the roof dropping.

Instead of choosing this method would the addition of two purlins, at midpoint, splitting the span of the rafters work in the same way?

You mean like this one we are currently building....?

Untitled

• noseall
• 15 May 2015
• 1

 

[Frank12345]

Having seen other designs I have seen a vaulted roof created by applying a steel or timber structural beam at ridge level to stop the roof dropping.

Instead of choosing this method would the addition of two purlins, at midpoint, splitting the span of the rafters work in the same way?

You mean like this one we are currently building....?

Untitled

• noseall
• 15 May 2015
• 1

Yes that is right mate. I am not claiming to be any type of expert on this subject but I always understood if the roof was not triangulated, typically the roof was supported at the ridge as it would not be able to spread if it was unable to move downwards.

I know it is a complex subject but by using Purlins at midpoint I cannot help but think the roof would still be able to push outwards.

 

[noseall]

I know it is a complex subject but by using Purlins at midpoint I cannot help but think the roof would still be able to push outwards.

I'm sure there is a pivot point on the purlins, but a good design will counter this.

 

[theprinceofdarkness]

If you stand under a purlin and look upwards, there is equal quantity of roof material on both sides of it (actually the top half of the roof and the bottom half) so the roof will not pivot on the purlin.
The major problem with a vaulted roof is the spreading of the joists at the bottom. The ridge board cannot do anything about this as it is not possible to put any secure fixings into it to resist this force, unless one drills through the edge of a joist , through the ridge board and through the edge of the opposing joist then use a long piece of studding with nuts to pull the joist tightly in towards each other.
I once witnessed a pent house flat being built in Spain with a vaulted roof. The timber for the joists were in the order of 4" X 14" and 20' long. At the apex they did a half lap joint with a bolt with washers through it. I can''t remember if they used glue (they should have!). No ridge board. But at least this form of joint has some ability to stop the joists spreading at the bottom.
Frank