New extension hip roof design

[derek777]

I am planning to build a single storey rear extension approx 6m x 6m on permitted development. I would like a three sloped hip type of roof that abuts the main house at one end with skylights on all slopes. I am unsure on how the framing arrangement should be designed to restrain the rafter feet from moving outwards on the hip slope, as the collars for the other rafters running at right angles. Also, is it necessary to have a verticle post at the junction of the hip rafters and ridge to support the hip rafter, and if so what would it need to bear on? Does the hip roof need to be designed by a structural engineer?
I would greatly appreciate any advice and an outline design so I dont have issues with BCO.

 

[noseall]

Are you personally designing this extension?

If not, let the person you are paying to design it sort it out.

Your designer may need to run it past his S.E. depending on the complexity of the roof.

 

[derek777]

Yes, I will be personally designing the extension. I have some knowledge of standard pitched roofs but not hips.

 

[noseall]

Yes, I will be personally designing the extension. I have some knowledge of standard pitched roofs but not hips.

What does 'some knowledge' mean?

Are you going to be building this roof also?

The thing is all roofs are different and there is nothing more quirky than a hipped fella.

 

[Dextraneous]

I'm with noseall on this. You really need to get an experienced SE on this to draw up the designs and specs. Cost you a few bob but it's the safest way.

 

[tony1851]

You also need to make sure you can keep the ridge height below 4m to keep within permitted development.
As per the others, designing and building an open hipped roof is not for the faint-hearted; the words 'roof' and 'spread' come to mind.

 

[catlad]

Have I missed something or is the new permitted development 6m x 6m I thought it was more like 6m x 3m

 

[tony1851]

Have I missed something or is the new permitted development 6m x 6m I thought it was more like 6m x 3m

Maybe his house is 6m wide and he is extending across the back and going out 6m?

 

[catlad]

Well yes that is what I was questioning permitted development going out I thought was 3 metres after that I thought you had to apply for planning.

 

[derek777]

Recent regulation changes allow for extensions 6m deep on terraced houses.

 

[theoldun]

OP,
With due respect, you know nothing whatsoever about cut roofs.
Leaving aside all the other PD conditions, then on a detached house. under PD you can come out 8metres . On all other dwellings 6metres is your limit, with a 4 metre max ridge height.
A 6x6 metre full hip will give you a half span of 5800 and a rise of say 1500 will give you a pitch of 13.6 degrees and a slope of rafter (Run) of 5867 plus your overhang of 450.
As a 47x195 rafter supporting concrete interlocking tiles will only span 3970 between supports, this will mean that you will need a wrap round purlin which will be supported at the moment by fresh air until you design your steelwork and joists to support purlins.
Good luck in finding an old school SE to sort it out, if it was ours we would go to a truss manufacture and go either a loose hip construction, standard hip end or possible girder hip end.
Suggest you change your roof design depending on your back first floor windows
Regards oldun

 

[tony1851]

@OP,

At 6m overall width,(?) you would be struggling to get the ridge in at under 4m and at the same time, maintain a pitch of at least 15 deg.
This is the minimum pitch acceptable for Velux roof lights, and if you are going out 6m, you will need rooflights to get light into the inner part of the room.

As above, you will also find it difficult to get an open hipped roof. Most SEs wouldn't consider doing it without some sort of tie-wire arrangement.