Low pitch roof - needing some advice

[jambikesalot]

Hi there, i'm new to the forums. I'm going to be putting a low pitch roof over an old flat roof, and the span of the rafters is going to be just over 3900mm.

Am I right in thinking this is too long of an unsupported span? I'm planning on using 6x1 or 8x1 and 400mm spacing for the rafters. If I need a purlin what size does it need to be for this roof? The roof is 3000mm wide, and I'll be putting in a skylight. Also how could I hide the purlin if I need one? Would I just have to bring the ceiling height down inside?


Thanks for any help,

James.

 

[noseall]

What sort of pitch are we talking about?

It is likely that you will need to use say 175mm x 50mm at 400mm c/c in an unsupported span.

Installing a roof light will mean doubling up the rafters each side of the opening.

 

[jambikesalot]

c/c?

Pitch will be less than 22, more than 15 degrees.


Thanks for the reply.

 

[noseall]

c/c?

Pitch will be less than 22, more than 15 degrees.


Thanks for the reply.

c/c = centre to centre.

15 degrees, that's virtually flat!

There are only a limited number of tiles that will cope with 15 degrees. Do not skimp on the tile head-lap or the roof membrane when fitting to that pitch. You may need to double the felt or at least tape the laps.

 

[jambikesalot]

Yep, quite flat, can't bring pitch up much, if any more because of power line on the side/back of house. What tiles would you reccomend? The existing house is slated.

Also I'm thinking of using celotex insulation as that end of the kitchen is always really cold, even with rads, any reccomended way to use? I was originally thinking in between and on top of rafters, but i might be able to increase the pitch if just between.



Thanks again

 

[Leadman]

I know wessex tiles go down to 15* marley make them i think but only in brown or grey, also there more expencive,£1.20 each i think.
Good luck
Dave