Structural ridge beam & gable end roof design

[TOMPARKER44]

Hi all,

I am designing a roof for my new extension which is 5m out from the end of the existing 2 storey house and 4m wide. The extension will be single story and built under permitted developement and a building notice.

Where can I find span tables for the structural ridge beam and rafters please?

The roof will have a 20deg pitch, tiled with Redridge concrete tiles and have 2 x sky lights either side.

Regards - Tom

 

[noseall]

Are you designing the whole structure?

The reason, i guess, that you pay a designer for structural drawings is he has the privilege of having paid for his span tables, so i doubt they are gonna give them up easily.

You will also need an S.E. on board to design the beam and possibly the connections and the subsequent calc's that will need to be submitted to B.C.

It may pay you to get the S.E. to design the whole roof. This may or may not be simple and could depend upon the design of the walls and foundations below.

 

[noseall]

P.S. who will be building it a pro or diy?

 

[theoldun]

Hi all,

I am designing a roof for my new extension which is 5m out from the end of the existing 2 storey house and 4m wide. The extension will be single story and built under permitted developement and a building notice.
Regards - Tom

5 metres out, would suggest you check out your PD rights and then come back.
Regards oldun

 

[TOMPARKER44]

Hi chaps,

Thank you for your replies.

From 1st of October the PD regs change and I can extend twice that of before without PC so in my semi detached it's now 6m.

I appreciate the additional load from the roof will have a direct impact on the wall and foundation design but I have those calculations in hand.

I will employ an experienced brickie to build up from the foundations and I'll do the rest.

I'll be calling on my brother in laws who are carpenters and roofers to help build the roof. The rest I will do on my own.

I have a degree in industrial product design which was 50% engineering and covered electronics, thermo fluids and solid mechanics. It's been a while since I used those skills but am confident I can design the structure with the right resources and am happy to use software for complex calculations as I am qualified to issue calcs to BC.

All assistance much appreciated.

Regards,

Tom

 

[^woody^]

From 1st of October the PD regs change

Are you posting from 2008, or do you know something which no-one else knows?

 

[tony1851]

I have a degree in industrial product design which was 50% engineering and covered electronics, thermo fluids and solid mechanics. It's been a while since I used those skills but am confident I can design the structure with the right resources and am happy to use software for complex calculations as I am qualified to issue calcs to BC.

All assistance much appreciated.

Regards,

Tom

If you can do the 'complex calculations' and are 'qualified to issue calcs to BC', then why do you need span tables for your roof timbers?

There isn't much use for knowledge of electronics and thermo fluids when building an extension; as you have been advised, your time would be better spent reading the permitted development rules.

 

[chickenlips]

Well based on the dimensions given and dependant on actual velux size,
rafters should work at 2 x 6 (600mm centres) held up by a piece of 315mm Glulam for ridge.

Doubtful you would need to get a strutural engineer to work out the rafters or structural ridge beam, most roof truss manufacturers should be able to design and supply the rafters and ridgebeam ... shouldnt they ? ?

 

[TOMPARKER44]

Hi theoldun & woody - my initial statement of the PD rules changing on 01/10/12 is incorrect, this date is the end of the consultation period for the proposed changes.

I am fully aware of the current PD rules.

I spoke to my local Planning Officer and he said that the changes could take affect at anytime from 01/10/12. The government want to introduce the relaxed PD rules by the end of the year, see below link for information.

http://www.guardian.co.uk/money/2012/sep/06/building-rules-what-changes-mean-homeowners-extend

Hi tony1851 - although I am capable of doing the calculations on the beams in order to do it I need to have the relevant information to do it, none of which I have access to anymore. The simplest way I could see was to look it up on a span table and go from there.

Hi chickenlips - thank you for your helpful post, much appreciated I will look into the span/load of Glulam beams. I assumed (often a mistake!) that as the ridge beam is structural it would need calculations to back up the size and construction. I will though speak to my local BCO and see what the say and take it from there.

 

[TOMPARKER44]

Hi chickenlips - thanks to your helpful suggestion of using Glulam I found the below straight away and it is just what I was after.

http://www.glulambeams.co.uk/hres/roof beams loading.pdf

Thanks again

 

[chickenlips]

Hi chickenlips - thanks to your helpful suggestion of using Glulam I found the below straight away and it is just what I was after.

http://www.glulambeams.co.uk/hres/roof beams loading.pdf

Thanks again

If you decide to use glulam, then whoever you buy it off would be able to size it up and supply calcs for BC. Providing they offer that service, so it may be best to check before hand.

 

[tony1851]

Hi tony1851 - although I am capable of doing the calculations on the beams in order to do it I need to have the relevant information to do it, none of which I have access to anymore. .

Hi Tom. If it's any help, you have, or can easily obtain, the info. you need to do the calculations for the timber roof rafters.

You know the span of the beams, and the slope;
You can easily work out the dead loads of the tiles, battens, insulation etc.
You can look up the live load for your area (will be either 0.75 or 1.0 kN.m2)
Knowing the loads and the span, you can work out the bending moment on a rafter, and from that figure, and knowing the bending stress of the grade you are using (usually C16) and applying the appropriate 'K' factors, you can work out the 'Z' value required, and from that choose a convenient section-size. Oh, and don't forget to check for deflection as well. Hope this helps.

 

[TOMPARKER44]

Hi Tony - thank you that does help and I can now work out what I need and satisfy the BSO.

All I need now is for the PD rules to be relaxed soon so I can get started!

 

[theoldun]

Hi all,
Where can I find span tables for the structural ridge beam and rafters please?

The roof will have a 20deg pitch, tiled with Redridge concrete tiles and have 2 x sky lights either side.

For future reference, either 1991 Part A Building regs, Trada Span Tables 2nd edition or Trada Eurocode 5.

Redridge Concrete Roof Tiles. Never heard of them, never used them. Suggest you check that they go down to 20 degree pitch.

If PD is relaxed and you go out to 5metres you will be struggling to get a 20 degree pitch in, without a lot of additional work.

[Quote from chicken lips.] based on the dimensions given and dependant on actual velux size, rafters should work at 2 x 6 (600mm centres) held up by a piece of 315mm Glulam for ridge.

With all due respect to this gentleman, would not pay to much attention to this as it would appear he has not read your original post correctly.
Regards oldun

 

[chickenlips]

[Quote from chicken lips.] based on the dimensions given and dependant on actual velux size, rafters should work at 2 x 6 (600mm centres) held up by a piece of 315mm Glulam for ridge.

With all due respect to this gentleman, would not pay to much attention to this as it would appear he has not read your original post correctly.
Regards oldun

LOL, I read the OP perfectly, I was merely pointing out other alternatives for a Ridge. Since the OP was wanting to try and calc most of it himself, I offered a viable alternative to having to spend a few hundred on a SE sizing up an RSJ.

I should of maybe quoted the post below the op, where he was mentioning using a SE.