Trusses or traditional?

[Bodgitnscarper]

To cut a long story short..self build extension, family helping.

"Architectural designer" designs 2 storey extension roof as traditional for planning.

Planning granted with conditions one of which is calcs for roof timbers.

In the meantime builder (relative) sways me towards trusses as they are "easier and quicker to 'throw' up"

So structural engineer didn't include calcs for traditional roof as we had chosen trusses.

Truss designers involved & site visit to measure up.

Then advised we need special adapted raised tie trusses due to existing roof design.

Now builder has changed his mind...they will be too big to 'throw' up.

Doesn't want to wait for trusses, reckons we can't get a crane due to overhead phone lines (although this is debateable in my view, as only our line looks to be in the way telegraph pole at other side of road and neighbours' phone lines don't look that close to me).

Also banging on about a crane permit and road closure but it's a quiet street with an alternate route opposite.

So what are my options? Truss designers reckon ball park figure for weight of trusses is approx 70kg (6" timbers 6 metre span).

No access to rear apart from 1 metre pathway down side.

If I go back to traditional I will now end up paying an extra fee to structural engineer.

 

[John D v2.0]

That's a strange planning condition, will it affect the external appearance?
Anyway you would need calculations anyway unless you can look it up in the span tables.
70kg is a lot to lift up to the roof from a h&s point of view, maybe the builder can't justify the extra risk of having that falling at the wrong moment.
You don't have to use the same SE for the new calculations, and the few hundred quid might be worth it in the long run. Maybe the cut roof would be cheaper on materials anyway.

 

[Bodgitnscarper]

That's a strange planning condition, will it affect the external appearance?
Anyway you would need calculations anyway unless you can look it up in the span tables.
70kg is a lot to lift up to the roof from a h&s point of view, maybe the builder can't justify the extra risk of having that falling at the wrong moment.
You don't have to use the same SE for the new calculations, and the few hundred quid might be worth it in the long run. Maybe the cut roof would be cheaper on materials anyway.

Thanks for the swift response John. When I say planning conditions I mean with regard to the building regs application they wanted further info in the form of structural calculations for the timbers. Had I gone with trusses this would have been provided by the truss manufacturer so, even though the structural engineer would probably have done the roof calculations included in his original price,( we told him we were using trusses so he didn't bother) he will now no doubt want payment for this as additional since I've already paid him.
TBH yes that seems sensible as the timbers will work out cheaper than the trusses. I'm just not sure how it works as the plan drawing shows the ceiling joists going perpendicular to the rafters. Does it not require a tie bar if it has a ridge beam?

 

[Samej1987]

If your ceiling joists are to run perpendicular to your rafters, are you not better to put a collar or tie on every pair of rafters?

My SE just told me to bolt each end of the tie with a spiked washer between tie and rafter. I then used the ties as ceiling joists (although i had a sceiling).

Sounds like you would need the SE to sign off on your size of rafter, height of tie but that does sound easier and cheaper than a crane any day.

I also would think the materials for an on site softwood roof would be cheaper than the prefab trusses (in this example).

Good luck.

 

[^woody^]

I've never heard of a requirement for structural calculations for a traditional cut roof.

All you do is use the correct timber sections as detailed in many published guides such as from TRADA, and just ensure that it is formed and framed "traditionally" and not some whacky design. Whoever did the plans should have designed the roof. Get a refund.