purlin length

[gasmanuk]

anyone know how big a timber purlin would have to be to run 5.5m un-supported on a roof carrying slate???

 

[jeds]

Current approved documents don't go up to 5.5m so you are looking at an engineered solution there.

As a guide; the longest purlin listed in the documents is a 75x225 which gives a max length of 3.63m.

 

[gasmanuk]

thanks jeds would a truss roof be better then as i can span the width better

 

[Static]

How big is the roof in total (widthxlength) and what pitch? Is it a new roof or a replacement to existing? on house or garage? more info please

 

[jeds]

Truss roof might solve the problem gasman. Alternativeley you might be able to design the purlin out by upping the size of the rafters. What span and pitch are you looking at?

 

[gasmanuk]

ok I am extending the house at the rear on two storeys i have a wall that runs through the centre of the house width ways (the house is wider than longer). This is 600mm towards the back of the house from the ridge. My plan was to bring the roof out in a double dormer type (M shape if you like) because i dont have much height so i have to have the roof like this to achieve the pitch. The proposed roof size would be 11m wide and 5.5m long not in cluding the front of the house that is from the mid wall.


if you need a rough sketch let me know.....

 

[Static]

I need a sketch

From the sound, its quite complicated thus i would say a truss roof would be the answer.

 

[jeds]

If a hand cut purlin roof is the easiest option perhaps look at a steel beam purlin. You would need calculations but steels are quite cheap so it might work out more economical than a truss roof.

If I were you I would get a cost from Minera for your trusses and then compare that with the cut roof option including the steel purlins and calculations. Trusses are not usually that expensive but you sometimes need a crane to get the up.

http://www.minera-rooftrusses.com/newsite/index.html