Fixing to beam

[Neversaynever]

Hi all, please excuse my ignorance if this sounds stupid. I’m looking at options for a single storey dual pitch roof (dual as 5m out from house)

 

When constructing a traditional cut roof with a steel beam, is it possible to fix the rafters to the steel itself rather than having a timber on the top? If so, how can the ridge tile be sat then - more timber? Or is there an actual structural reason as to why the rafters are attached to the timber above? 

 

Reason for question, I am really really tight on the bedroom windows so every mm counts! But I can’t lower the pitch less due to tiles.

 

also, what is the advantage/disadvantage of using raised tie trusses over a cut roof? 

 

Thanks!

[Russell griffiths]

You can cut your rafters INTO the sides of the steel instead of on top, look at my pic

i tried to find a pic as I find it hard to explain sometimes 

 

can you substitute the steel beam for an LVL or a GLUELAM ,could make fixing easier

you basically fit two timbers either side of the steel so it turns it into a box instead of an i shape

then plumb cut your rafters to fit to the sides instead of on top

 

regarding ridge tiles you can probably run a roof batten down the centre to pick up the fixings for that. 

[Russell griffiths]

@Neversaynever

better pic. 

[Oz07]

You'd need a hanger of some kind if going onto side of ridge beam. Weight has to be supported from underside rafts without ceiling joists as ties 

[Neversaynever]

Thanks Russell that’s how i

imagined. I see that the rafters can attach inside the face (?) of the beam - is this ok structural wise? If it is okay to fix that way then that would save me a few inches at least where the timber would usually go on top of the beam. I have also been quoted for a glulam beam but it is 200mm deeper than the steel 

 

so oz07 are you saying hangers inside the face of the steel that the timber is attached to then rafters? Or just hangers then rafters to the hangers? Sorry not getting what u say about ceiling Joists as ties? 

 

Obvuously im not doing any of this! Just trying to guesstimate dimensions without paying ££ every time I have a question for the architect!! 

 

How does a steal beam compare to raised tie truss?

[Russell griffiths]

You need to answer this. 

Are you having ceiling joists or is it a vaulted ceiling like the pictures 

as @Oz07 said the the ceiling joists act as a cross tie to prevent the roof spreading

if it is a vaulted ceiling with no cross ties then the rafters need to be fixed securely to the ridge beam, otherwise when you load them they can physically slide down the face of the ridge beam. 

Just look at the angle you will cut on the end and you will see how this can happen

you should go back to your designer and find the correct way of connecting 

[Neversaynever]

Thanks Russell that’s how i

imagined. I see that the rafters can attach inside the face (?) of the beam - is this ok structural wise? If it is okay to fix that way then that would save me a few inches at least where the timber would usually go on top of the beam. I have also been quoted for a glulam beam but it is 200mm deeper than the steel 

 

so oz07 are you saying hangers inside the face of the steel that the timber is attached to then rafters? Or just hangers then rafters to the hangers? Sorry not getting what u say about ceiling Joists as ties? 

 

Obvuously im not doing any of this! Just trying to guesstimate dimensions without paying ££ every time I have a question for the architect!! 

 

How does a steal beam compare to raised tie truss?

[Neversaynever]

The architect has only drawn a raised tie truss, but the SE suggested a steel beam cut roof as an alternative. I don’t know what the pros & cons of each are. 

 

what I gather it will be slightly vaulted where the rafters go up & then a flat section in the ceiling where the ceiling rafters are 

[Russell griffiths]

Basically the flat section of ceiling will have ceiling joist in it, it’s these that tie the two sides together 

if you take these out and have a fully vaulted ceiling you need to stop it spreading 

that’s why he had them on top of the steel

but if you want to drop the ridge height you need to design in a method to keep the rafters connected to the ridge. 

[Oz07]

A ridge beam won't add any height if you keep ridge at same level. Then you could cut rafters over top of beam then either drop some collar ties below this or expose if you choose an engineered timber product might look nice. Raised tie trusses might not solve the problem if you want big vaulted ceiling area nevermind price. Think ceiling tie can only be 1/3up from bearing wall plate level and still stop wall spread

[Neversaynever]

15 hours ago, Russell griffiths said:

Basically the flat section of ceiling will have ceiling joist in it, it’s these that tie the two sides together 

if you take these out and have a fully vaulted ceiling you need to stop it spreading 

that’s why he had them on top of the steel

but if you want to drop the ridge height you need to design in a method to keep the rafters connected to the ridge. 

 

Thanks, just to clarify if there are ceiling Joists (flat area) then the rafters CAN be joined to the face of the steel rather than on top of the steel? 

[Neversaynever]

I don’t think a big vaulted ceiling will be possible Oz due to the bedroom windows above. Being a dual pitch is making it difficult to get a nice height internally but still keep it lower than the bedroom windows externally 

[Oz07]

Correct if you have ceiling joists. The question them becomes though why do you even need a steel. Timber ridge board 25mm thick. 

[Neversaynever]

1 hour ago, Oz07 said:

Correct if you have ceiling joists. The question them becomes though why do you even need a steel. Timber ridge board 25mm thick. 

Hi Oz, sorry I’m completely lost now? Extension is single storey. 5m out from existing house, 9m wide. Dual pitch roof as mono pitch would be too steep up back of house. Trouble I’m having is keeping it below the bedroom windows above. Been told raised tie truss or steel/glulam beam with rafters are the only options? Thanks 

[Oz07]

I haven't seen it but if you send your sizes to a truss company they should be able to quote you