6 metre Lintle / RSJ advice please?

[geraint]

I agree with static gerraint is not substantiating his claims, if headroom was critical perhaps a 254UC might do the trick. Though it might be wise to leave returns which will reduce the span and ensure that the structure is still stable. I'm afraid you will have to pay a good structural engineer to get a defintive answer that is safe as houses.

so you dont know....

end of...

 

[mikric]

Come on then Geraint hit use with your calcs and sizes if you can ??

 

[deanomy]

clue for gerraint

m=wl2/8 (for a udl) and don't forget the partial safety factors!

 

[geraint]

well you are so clever....

you tell me.... still waiting for answers to my earlier questions...


and no clues...

keep it up gang....

 

[hammerswinger]

As far as I can see the design of the roof of the house is such that the gable ends appear to support the majority of the roof weight.

What makes you think this?

The gable ends support little weight if it is a typical roof construction. It is the other 2 walls where the weight is transferred due to the coupled roof design.

Therefore your steel beam would need to support half of the total roof weight.

I may be wrong with this but the front elevation of the house only has brick pillars at each side, the middle is hung tile. The span between the brick pillars is approx 5 meters and the windows span the whole distance.

Inside there is no supporting wall in the middle of this span, there is a wall but that is made of plasterboard, actually I think it's called Paramount board, 2 plaster boards with cardboard ribs inside.
If the beam spanning the front is taking the weight of half of the roof I guess it would have to be pretty substantial.

Here's a couple of pictures of the structures in the loft, these structures span the whole width of the house from gable to gable, they are about 1.7 meters in from the front & rear walls of the house.

The top timber is 7" x 3"
The bottom timber is 6" x 3" (could be 7" x 3" as it's hard to measure with all the insulation)
The diagonals are 4" x 1½"

 

[wavetrain]

Is that a trussed purlin I see before me?

You need to show more pictures for us so we can be sure of the direction of the ceiling joists.

 

[hammerswinger]

More pictures, that's just about impossible as there is a LOT of stuff stored in the loft, I know as the loft has just been insulated and we had to empty it to have it done....then put it all back

I can tell you that the celling joists run from the front of the house to the back so at 90° to the trussed purlin.


Thanks.

 

[wavetrain]

In that case if you can just check and confirm if the ceiling joists are tied to the rafters at the eves.

If they are and there is a continous run of joists from front to back (joists can be overlapped and joined togehter), then you have a coupled roof which means the ridge is not taking any load. If the ridge was taking any load it would be constructed like your trussed purlin. Is it like them?

 

[hammerswinger]

Checking that the celling joists are tied to the rafters at the eves will be a hard job also, you nigh on need to be a contortionist to get through the spaces in the trussed purlin. The other half can fit through but only just.

Ok then just for you here are some more pictures

....I managed to find a bit of loft space that isn't full of shi....stuff!

The Ridge:

A clearer picture of the "Trussed Purlin":

The celling joists & another beam:

The celling joists (yellow) are doubled up giving a measurement of 4" x 3"

The Green beam is 4" x 2" and goes from gable to gable.

Thanks.

 

[wavetrain]

Now I am no expert, in fact I claim to know little more than you do , but my hunch is your rafters are 'balanced' on the trussed purlins with them taking the weight of the roof with that load being transferred to the gable ends just like you said at the beginning. Without doubt however, the ridge beam does not carry the weight of the roof.

Now wait for the expert regulars such as 'noseall' and '^woody^' and other gents (and ladies) to say if I am near the mark or not.

I heard a rumour that TV celeb Tommy Walsh is a regular on this forum...

Nice insulation BTW

 

[hammerswinger]

Thanks for your input, its very appreciated

As soon as I saw what I now know to be the Trussed Purlin I thought that it was a strange set up.

I take it if the weight of the roof isn't resting on the front and back walls of the house that this will effect the size specifications of the steel that would have to be used ?

I'm just trying to arm myself with a bit of knowledge as I don't want to be told by the SE that I need a 10" steel if it's not necessary. I know that may not happen but I'm wise enough to know that not everybody always does their job properly and advising an over specked steel may be an easy option rather than doing the bespoke calculations.

Yeah lets see what the other guys think...


Thanks.

 

[geraint]

you could always try a 203x100 uc....

it works.. but getting a supplier might be difficult..


does that answer all you quiet ones....

hiding again....

 

[Deluks]

I heard a rumour that TV celeb Tommy Walsh is a regular on this forum...

OK, who's gonna own up to it?

 

[RonnyRaygun]

Yeah lets see what the other guys think...

I think - even allowing for the small amount of roof load and the fact that there is no brickwork for a large proportion of the span, you are still going to need something like a 254 UC 73 to span 6 metres.
You are probably envisaging flush walls through from your existing house to your extension, but as Jeds said in an earlier post, a frame with columns, or brick piers are the only way to guarantee lateral stability. By removing the end wall you lose all lateral stability to that end of the house, and the SE should think about ensuring stability is maintained.
A frame might also mean a base beam along the existing footing.

 

[hammerswinger]

So is that how the roof set up I have works... with very little load on the front & rear walls ?

Does this roof design have a name ?

I did think that if we wanted the walls flush that there would have to probably be some sort of frame, I've heard of this before, maybe seen it on the TV or something.
I understand that there will be returns to sit the beam on, that's ok, I just don't want to have to have (and pay for) a beam that's loads bigger than I actually need.


Thanks.