My apologies in advance for such a long winded & unusual topic.
Now im ready to sort the timber out the roof & I’m stuck
The existing roof is to be replaced. It is a gable roof 9.3 meters by 4.5 meters
The angle is at present 30 degrees (same as the other half) but I have permission to increase it to 40 degrees if necessary.
I would like two trusses spaced at 3.1 meters of the simplest design and would like to use peg & hole fixture where possible.
Ill be using round timber for beams and purlins & have paid for some calcs.
These are telegraph poles class C16
According to the work I have had, the calculations can be based on 130mm x 130mm square timber. This being the case I can “square off” the ends of the poles for the purpose of joining.

I have the following (What does it Mean?):
Bending stress 4.6662
Permissible bending 7.2633
Deflection 6.8617
Limiting deflection 6.75
Shear stress 0.8375
Permissible shear 0.8357
Bearing stress 0.23365
Permissible bearing 3.025
But i can’t figure out which is the maximum allowed length for the purlin? Will it manage 3.1 M
To simplify
Would a round timber purlin diameter 178mm (class C16 ) >= sawn timber at 225 x 75mm.
This would be have a maximum clear span of 3.16 meter (which is enough)

I have tried to ask the engineer & have written, but cant get in touch & have had no reply?
I also need to know if I can change the king & tie truss he has designed for a simpler truss?
Pictures are of the present truss
http://www.kindways.co.uk/Hasgot/cottage/photos/18.jpg
Recommended truss and joint:
http://www.kindways.co.uk/Hasgot/cottage/before-2.htm

Things I need to know are:
1. Will the purlin span 3.1 meters? (can I assume this is ok as the beams carrying the purlins span 4 meters)
2. Where the beam sits on the wall in the present design, there is a window/door opening in a brick wall (two bricks thick). This means the weight or the roof is above the lintel. Is this OK.
3. do I have to build pillars (tie them into the existing wall) to support these beams? This could be a problem where doors and windows are situated.
4. Can I replace the middle ironwork and bolts with peg and hole joints?

Thanks
Steve

Steve:
Your questions are very site specific, and because of that you may not get any answers here.
You should again try and contact your engineer as he is familiar with your project and can best answer all your questions.
Your information says that the shear stress and permissible shear stress is the same, therefore any changes made could put your shear stress over the permissible limit. I'd be very careful in making any changes that put you over your limits.
If you are looking for another engineer to help you with your problems, try going to the guild home page, and in the upper right hand corner click on resource guide. Follow the links to the new site of the resource guide and enter "engineer" in the first box, leave the second box alone (so that it will select all that are listed) and select "engineering" in the third box. This will produce a list of 22 companies. Some of them do international work, and at least one of them is from the UK. (I did not screen them all).
You could try contacting one or more of them and see if they can help you with your site specific problems.
Good luck with your project.
Jim Rogers