Which Type of Roof Truss

[suts89]

Hi,

I,m in the planning stages for a new rear extension.

The build will be 6m wide with a standard pitched roof at 17.5 Degrees.

My plan was to install a number of velux windows in the roof and have a kind of open/cathedral type ceiling.

Is this achievable with such a low pitch??

Thanks in advance for any advice.

Suts

[Shytalkz]

At 17½° it won't be very cathedral-like....

A ridge beam will allow you to have a sloping ceiling though. This won't be trusses, just loose timbers, order of 50x150s at 400 centres, miss out where you want a velux trim either side with doubles. Ridge beam size dependent on span: can be either steel or flitch.

[suts89]

Hi Shy thanks for the response.

Yeh i realised the cathedral look was out when i found out the low pitch
Slight slope is fine, the main criteria is the extra light offered by the Velux,s

So if trusses are out, does that mean i need a structural engineer to design the roof?

If was to get the trusses from a truss manufacture what kind of truss would i ask for. Or would they just design me one to suite?

Oh yeh, whats Flitch ?

Thanks again

Cheers

Suts

[Shytalkz]

If you want a sloping ceiling, you won't be using trusses. SE can design rafters and ridge beam for you, shouldn't cost you more than £150 plus VAT off-plans.

Flitch is gnerally a steel plate sandwiched between two timber beams, although there are variations on a theme.

[suts89]

Whats the story with a scissor truss then??

Thanks for your valued input by the way.

[Shytalkz]

You could theoretically use a scissor truss, but at that slack a pitch, it almost becomes a ceiling tie and you're back to normal type trusses. Don't forget these trusses would be at 600 centres too, so hardly the effect that you are seeking, viz sloping ceiling.

ST is not the answer you're looking for.

[suts89]

Ok i see what you mean.

In your opinion do think its going to look out of place installing velux,s in this configuration of ceiling/roof?

Thanks for all your input.

[freddymercurystwin]

suts89 wrote:

In your opinion

Your opinion is the relevant one regarding the suitability of rooflights or not, not someone else's off a forum. Whats wrong with rooflights in a low pitched roof anyway? Seems an odd question to ask.

[suts89]

Yeh i understand that.

I,m just finding it hard to visualise what the finnished ceiling will look like.

Thanks again

[hotrod]

suts89 wrote:

I,m just finding it hard to visualise what the finnished ceiling will look like.

Likely to be Scandinavian in style, I'm thinking possibly yellow pine matchboard cladding.

[noseall]

We built a vaulted 15 degree pitch roof extension a while back with a bank of four velux window in a row. The flashing kit was a special and needed to be ordered six weeks in advance.

There was a total of six velux in the roof.

The underside however required celotex insulation across the underside of the rafters so exposing them was not possible.

[suts89]

noseall wrote:

We built a vaulted 15 degree pitch roof extension a while back with a bank of four velux window in a row. The flashing kit was a special and needed to be ordered six weeks in advance. There was a total of six velux in the roof. The underside however required celotex insulation across the underside of the rafters so exposing them was not possible.

That sounds great, we didnt want to expose the rafters anyway.

So did you need a SE to design the roof? or were you able to use a truss manufacture?

I dont suppose you have any pictures available??

Thanks all this feedback has been a great help.

[noseall]

We built a cut roof, piece of cake.

Steel ridge beam with a pair of mid-span steel purlins. Rafters were 150mm x 50mm. at 600mm c/c.

The four velux were sized 980 x 550 and sat between the rafter spacings so no need for trimming.

All designed by an S.E.

Incidentally, the building was 10m wide giving each rafter span (clear span) about 5.3m