Roof design

[Uctred]

I am building an extension myself, the walls are going up and I need help with the roof design and timber sizes. The extension walls are constructed from Brick outerleaf, 75mm cavity and Fibolite 3.6 N internal block. I want a usable roof space and would prefer not to use trusses. Can some help me with size of ridge and hip board, Purlins and rafters,
Kindest regards.

 

[joe-90]

If it's big enough to have a habitable roof space then you need plans and building regs.

 

[Uctred]

Thanks Joe-90, the plans are attached, and I believe it is not high enough to be habitable. I think I can construct a traditional roof cheaper than trusses, some of the quotes are close to £2k, that buys a lot of wood.
Regards

 

[catlad]

It may buy a lot of wood, but with trusses you could have a water tight roof at the end of the day. Most old roofs in Lancashire are made with 6x2" ridge 9x3" purlin and 3x2" rafters and are still good today 100 years later, but the wood was better in them days so I would use 4x2" rafters min.

 

[Uctred]

Thank Catlad, C16 or C24

 

[^woody^]

Did you pay to have those drawings done

By the look of things, there is not enough height in the roof. And you need to consider the floor and how it is to be supported

 

[Uctred]

Hi Woody,
I did the drawings myself.
I don't understand why there is not enough height in the roof. All i want to do is to construct a traditional purlin and rafter roof. I don't want to use trusses they are more expensive, the fink shape of truss means I'll have wooden triangles all over the place and access to rear of the extension is limited so I can't use a crane to lift them over the gable end and onto the wall plate.
Regards

 

[^woody^]

If the loft is going to be habitable, then you need a proper floor of say 220mm depth, the roof will need insulating of say another 150 - 200mm depth depending on design, and then you need head room for a fixed stair flight. Take this off the height you have available from those plans, and you don't have enough room in the centre let alone further out into the roof

Then you need to work out where the structural supports need to go

You must be doing this on a building notice, and will need to confirm your proposal with building control

Edit

I think Joe has confused me. If you don't what to to be habitable, then you can probably do a cut roof in 5x2. There are links to span tables via a search of this forum or the building forum. You'll need to consider where purlin post supports will go

 

[joe-90]

He's good at that.