DIY extension - roof

[pixiepoo]

Hi

We have just had our planning permission granted for two storey extension and will be building by notice.

Quite a few family members are in the trade including my husband so will be doing all the work (apart from the bricklaying) ourselves.

I am trying to do all the research/prep work but I am struggling to work out how we design/plan for the roof structure.

We need to decide between a cut timber roof (my husband is a joiner) or roof trusses. But who actually decides the measurements/design?

At the moment we have worked out the roof pitch, gradient and length etc from our scaled architect drawings and I assume a roof truss company will be able to design some for us based on that. But...if we go with a cut timer roof (probably with the need of a steel beam or two) where do we even start on that? Do the Building Regs inspectors come and tell you what they expect first?

Our roof will incorporate two dormer windows and the first floor rooms will sit some way into the roof with sloped ceilings.

Sorry for all the questions, its the one bit of the build that is baffling me!

Many thanks

 

[freddiemercurystwin]

If it is baffling then respectfully maybe building on a Notice is not the best way forward.

 

[ban-all-sheds]

 

[pixiepoo]

Yes i totally agree... specifically because Im a control freak and like a plan to stick to - unfortunately the others don't agree and feel confident doing it by notice, which hasn't help with our architect actually pushing us to do it by notice as well.

anyway, my reason for asking on here is just to get my own head around it.

To simplify it - is the roof structure ultimately determined by architect, structural engineer or building inspector (beforehand)?

Many thanks

 

[ban-all-sheds]

the others don't agree and feel confident doing it by notice,

Then surely they know exactly how to design the roof, and have completely justifiable faith in their abilities not to get anything wrong.

which hasn't help with our architect actually pushing us to do it by notice as well.

Why on earth is he advising that? Are you going to be paying him a day rate for project management?

is the roof structure ultimately determined by architect, structural engineer or building inspector (beforehand)?

Not the latter, and if you go the Building Notice route then they won't check the design either.

And I would suggest not the former, as your architect sounds a bit of a fool.

 

[freddiemercurystwin]

For a cut roof, in an ideal world, a designer (whoever that may be) will draw up and design and propose sizes and positions and spacings of any timbers required including the pitch ensuring that the roof will work and flashings will fit under windows or eaves will line up with the existing etc etc. Building Control may expect some calcs if the roof is a beast. A joiner will then have enough info to cut and build the roof structure.

If a trussed roof then again, in an ideal world, a designer (whoever that may be) will draw up and design the roof including the pitch ensuring that the roof will work and flashings will fit under windows or eaves will line up with the existing etc etc. The truss supplier will supply any calculations to Building control as part of their appointment. The joiner or builder must measure the existing walls once they're built and the truss supplier will make the trusses to suit.

Without a designer you will have to do this yourself, you just need to think where does my fascia want to end up or where does my ridge want to end up and then work it all back etc.

Your architect must have too much work on.

 

[theoldun]

Hi
Do the Building Regs inspectors come and tell you what they expect first?

No.
On a building notice application it is their job to either accept it or reject it.
If they reject if, they will tell you why, and possibly you will have to start all over again.
No body is going to be able to give you any advice whether roof should be trusses or cut on the scant information posted, nor is a truss company going to be able to help you without some decent drawings.
Regards oldun

 

[pixiepoo]

Thank you for all your replies, they really are very helpful.

I want to push to get full drawings done, I too was surprised that our architect suggested building by notice, freddymercurystwin – you are probably right and maybe he has too much on.

The only thing I don’t want to do is pay the £700+ for the full plans just to get the information on the roof, hence me wondering whether we can get someone to design it on its own. The rest of the construction (walls, openings, floors, insulation, foundations) I find pretty straightforward, if a little laborious, after poring through the building regs documents.

We have the structural engineer working on the calcs for a beam for the first floor and a beam for the roof.

I understand that people won’t be able to provide any advice on whether we choose timber cut or truss but is there an advantage to either? As our roof will sit at a higher pitch than the roof it is adjoining along with two dormer windows my simple mind assumes that a timber cut will be more flexible.

 

[freddiemercurystwin]

You could ask your SE to do it, he may or may not want to get involved, he will certainly be able to size it all up and be used to drawing up a cut roof layout for example. But he will need some knowledge of how the detailing will work at the junctions which he may or may not have. There are some SE's out there who will do detail drawings though I don't recall not seeing an SE's drawing that didn't have a disclaimer or note on it saying waterproofing by others

Dormers can be easily be incorporated into a trussed roof. All in all a cut roof seems to be about about the same as a trussed roof cost wise. A cut roof will be more labour intensive to fit, but then a trussed roof will cost more to supply etc

Or you could approach A.N.Other to draw up the roof.

 

[tony1851]

architect actually pushing us to do it by notice as well.

architect is pushing you to do it on a building notice because he couldn't be bothered to do detailed construction drawings for the job.

My guess is that he did cad drawings at 1:100 for your planning application, with a few cut-and-paste notes on them, and with some pretty trees and a few people on the drawings to tart them up.

And I bet his name is blazonned across the bottom right-hand corner so that it becomes the most important item on the sheet.

 

[freddiemercurystwin]

architect is pushing you to do it on a building notice because he couldn't be bothered to do detailed construction drawings for the job.

Or doesn't know how!

 

[pixiepoo]

we got 1:50 but unfortunately no pretty trees or people

 

[tony1851]

we got 1:50 but unfortunately no pretty trees or people

1:50, 1:5 or full-scale - makes no difference if you can't build from it.

 

[pedantician]

I would advise getting full construction drawings done and submitting a full plans application. The Building Notice procedure (although legally acceptable) isn't really suited to anything more than small extensions and minor alterations.

If you do go with BN, building control may help you with timber sizes, etc. They aren't really supposed to, and some inspectors definitely won't, but I used to take the view that it was no skin off my nose to do it, unless the roof was very complicated, in which case I would push people in the direction of a structural engineer.

If the roof is straightforward, you may be able to work it out yourself from published span tables. You can buy these from TRADA amongst other places. If you do this, ask building control to agree to the design before you start ordering materials. If they won't look at it you are back to the str eng (or trussed rafters).

Good luck

 

[freddiemercurystwin]

Or just download them for free http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_1992.pdf