Ridge beam,

[CPerth]

Hi there.
I'm building a garden room at the bottom of my garden.

If will be approximately 4m by 3M - with a pitched roof. ( ridge length ways 4 M )

The reason I want it pitched is to block out sight lines of an ugly fence at the back , and It will fit in better to the surrounds. My limit is 4 M high but this would be too high.

Its likely the roof material will be faux slate or similar, but I'd like to have the option of real slate. I also want it ' vaulted ' inside ideally, so when I add in insulation etc, it will have a decent load. ( foundations will be block peer & using 5x2 C24 doubled so span tables suggest heavy load is 'fine' )

I haven't worked out the exact pitch yet ( open to suggestions ) but my general plan is to create a ridge beam ( not board ) using two 9x2 's bolted ( glued?) Sitting raftered on top ..... AND having collar ties underneath these.

Questions on the roof -

- Does it make a difference structurally if rafters are sitting 'on' the beam / or against the beam ?

- i think i need collar ties. But perhaps there is a better way ? I've seen larger projects on YouTube use something similar to a ridge beam but quarter the way up each side. ( all transferring weight to gable end and onto foundation )

- Some of my reasoning for a ridge beam and not a senf supported ridge board is lack of experience mixed with the need to work alone for most of this.

Any advice appreciated.

 

[^woody^]

Siting rafter on the beam is potentially better for loading, but probably not much in it for relatively small roof

You don't need collars or ties with a ridge beam

 

[jake7462]

You don't need to double up the rafters - 5x2 timbers at 400ctrs. would be more than adequate for the size of roof you've got.
It makes no difference structurally whether the rafters are sat on top of the ridge beam or supported from the side on hangers.

No need for ceiling ties or collars with a ridge beam. Bolt your timbers together for the ridge beam with coach bolts and timber connectors.

 

[CPerth]

Superb, thanks both.

I'm still calculating the internal finish ( insulation plus plaster / or even ship lap optinos = ventaltion / possible vapour barrier etc )


but what minimum/max size rafter timber would I use for the timber? Likely yo go 5x2 / or 6x2 - but good to have flexibility. with wither larger or smaller

 

[jake7462]

Either 5x2 at 400ctrs or 6x2 at 600ctrs would be fine

 

[^woody^]

With a 3m span, a rafter is never going to be more than 2m unless more than 40° pitch, but even so a 4x2 c16 will do even at 600 centres.

 

[CPerth]

Back again, thanks for help.

I have been measuring/doing initial dig on foundations and to avoid any question of what the height of the adjacent land is ( and height resections ) and the aesthetic look of the house from the garden / and trying to eliminate the view of flats behind as much as possible.

I've been looking an the option of pitching the roof differently on each side

It means the pitch within eg 1 M of the back boundary could stay under 2'5 ( its already over 1 M away from side boundary's ) but would look well from the front with a steeper pitch. ( height limit 4 M for permitted development - but obviously will be significantly less.

So I'm no looking at moving the ridge towards the front? so It could mean the ridge is eg 1 M from the front , and 2M from the back, as above, all rafters sitting on a strong beam.

After some googling it looks like this is called a 'salt box' style roof ....

baring in mind the ridge beam will be two 9X2's , supported to the foundation , , , would having different length rafters on each side be an issue ? Perhaps I could put a lighter roofing material on the longer side , or more rafters on the front side to match up the weight? Or am I over thinking? because the ridge beam will do the work?

Sorry to be a pain - any advice much apprieciated.

 

[jake7462]

You're overthinking it, stick with the ridge beam as you'd planned and you'll be fine with a different pitch on each slope.

 

[noseall]

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