Roof pitch for lean to

[howy1]

Hi all , I am looking to put a pergola off my bunglelow , it will be approx 4.5 metres out , can you tell me what is the least fall I can get away with as I haven't a great deal of height to play with coming off the wall plate .
I have read that 15 degrees will be ok but how does that equate in drop from back to front , thanks Howy
Sorry forgot to say it will have shingle roof on it .

 

[palaceray]

The manufacturers say 15 degrees is ok but I still think its too shallow.

 

[hardmetalking]

Perfect for zinc

 

[noseall]

4.5m pergola? Who is designing such a behemoth?

Are you aware of the design criteria for an open structure of this size i.e. posts, rafters, wind and snow load, diagonal stiffening etc?

It will certainly be an interesting project.

 

[howy1]

Hi noseall , its just a lean to roof to cover a dining table area , do you think it needs an architect

 

[theoldun]

A pergola is normally open top, but see no reason why you can not put a lid on it.
To answer your question 15 degree on 4500 span the drop will be 1206 on the pitch line.150 for HAP and 225 for timber bressmur. Total approx 1580 below bottom of wooden bressmur and top apex of rafter on bungalow wall.
Have you considered an awning blind.
Regards oldun

 

[howy1]

Thanks oldun , I think that might have blown it out of the water , I have not got enough height to get 1.5m drop over that length it would be to low at the front , what to do
Howy

 

[noseall]

Hi noseall , its just a lean to roof to cover a dining table area , do you think it needs an architect

Once you stick a lid on this thing it becomes like a sail in the wind.

Also, a 4.5m span will need some pretty serious timbers to prevent sagging.

I don't believe it needs an architect but it does need some thought to prevent it becoming a lethal weapon in next years' gales or heavy snow.

As said, you would be better off with something retractable.

 

[theoldun]

what to do
Howy

As suggested. providing you have sufficient height above top of frames and underside of soffit then consider awning blind. You can get them up to 4000 in depth and up tp 6500 wide.

Or consider a flat EPDM, roof. Snow load will be no problem. C16 47x200 joists will suffice. Can not comment on wind load without knowing your post code, but can not see a major problem.
Regards oldun

 

[howy1]

Well thanks to this excelent site and the information i have gathered from you guys i am back to the drawing board , i cant get that pitch in the height and space i have , i had a chippy who i know look at it to see if he could come up with any ideas and he suggested flat roof with felt , cant say i am to keen on this but food for thought .
Thanks again.
Howy