Extension vaulted Roof

[crxdave]

I'm currently planning a single storey rear extension, and would like to know if my idea for a vaulted ceiling would be prohibitively expensive/difficult.

Essentially, it's a dual pitched roof with a 7m span, 4m length, 18deg pitch. With a steel ridge beam in place, this puts the rafter span at approx 3.8m - even at 400mm centres, I presume I'm looking at some fairly hefty timbers to span this? Is a possibility to run a purlin halfway along this span, or at a 4m length would I be looking at another 2 steels to support the rafters?

I can upload some drawings if necessary.

Thanks,
Dave

 

[freddiemercurystwin]

Its all do-able, whether you think its prohibitively expensive we cannot answer.

The span tables suggest a 150x50 will almost do it so it won't need to be much bigger.

A purlin would of course half the span but for me I'd sooner avoid a purlin. If timber they'll be something like 75x250. Or a couple of steels.

 

[crxdave]

Thanks for the reply, I'm very keen to avoid purlins, as this would spoil what I'm trying to achieve. A closer look at the span tables shows that this should be achievable with some readily available timbers.