bco and engineers!!!!!! roof design

hi all,
ill try to make this brief.
my head is in the process of melting with all the crap im getting from bco on a traditional roof i have made on a 3.5m extension.

firstly i will give you roof specs
ridge board 2 9x3 c24 timbers bolted together with m12s and dog tooths
valley rafters 2 6x2 c24 timbers bolted together with m12s and dog tooths
rafters 6x2 c24
floor joists 9x2 c24
purlins 2 9x2 c24 bolted together with mi2s and dog tooths, also put stoothing walls under the purlins with 4x2 c16 and 18mm structural ply.

ridge span is 6m but supported at 2m by 4" block wall and at the end with the gable so longest unsupported span is 3.6m

bco now telling me that the ridge beam aint big enough to support the load and i need to increase it to 12x9 ie 3 12x3 bolted together.

is it just me or does he not have a clue!!
he is making me look bad in front of the client which is my main concern
as i have always had a good reputation.
as far as im concerned iv gone well overboard as i always do.
iv done 5 traditional roofs in the last 3 months and never had bc say anything about any other than iv gone over odds.

if someone out there could give me any advice on what to say to him i would appreciate it
regards
james

In a traditional double pitched roof with purlins, a ridge board does little structurally, apart from giving you something to nail the rafters to initially

And all your other section sized seem well over-board for such a small roof

advancemaintenance1 said:

bco now telling me that the ridge beam aint big enough to support the load and i need to increase it to 12x9 ie 3 12x3 bolted together.

Click to expand...

For a ridge!!!! That's completely bonkers! Something lost in the translation there?

to me its well over odds.
iv checked all the tables and im well in scope.
its the 1st time iv seen this bco, hes only a young pup so i dont know whether or not he knows something i dont or he is just being a bell end. how do i approach this little **** and say retire young cause you aint got a clue! obviously without sounding mean lol

nothing lost in translation freddy! im being serious! even though we may lose a couple of mm in conversion lol. iv never seen a ridge board so big. i literally showed him the size with some offcuts and looked at him stupid.
but theres no movement. hes adamant im wrong! only 17 years as a joiner. damn it i must go back to college

sounds bonkers to me, but I,ve never worked on a wind mill

Time to start talking to his boss methinks!

Well you could ask the BCO why a trussed roof does not have a ridge board

And you can then tell us what is inside this roof, and provide more detail of the design

Are you talking about a ridge board to fix rafters to, or a ridge beam to hold up rafters to prevent sag or spread?

i was thinking the same.
iv worked in my own area for years and know all the bco`s and planning officers. i kind of think i have a professional relationship with them. tbh normally when they come out on a call and see its me they just cast a glancing eye and say all is good.
this job however is out of my normal working area and therefore is a different borough so not quite sure who to call at the moment but im doing my spadework and finding out who to call quietly! dont wanna **** em off if im wrong lol

my apologies woody!! its a ridge board!!! my first post was wrong aaarghh
this weeks stress and tonights stella have taken a great hold in my brain lol. as per design!!!! there is none! i was shown a plan (as on a building notice)
no structural calcs at all!
but i can normally work of them and always go over to avoid this mess.
if you have any input i would appreciate it, i dont want to look like a plonker going to the top if im wrong.


(even the best joiners admit defeat if wrong! "unlike sparks" !
thats a dig at my mate porter projects by the way lol)

Like said above the BCO is assuming the ridge board to be a ridge beam and taking all the loading.. you need to explain its a traditional purlined system where the ridge board is of a non structural nature and the purlins provide all the roof support.

He may well be covering his back and unfortunately might need a surveyor or SE to right a letter to cover the design..
As also said you can go over him all the way to the head of dept..

Here is what we would do. Just to confirm length of roof 6000. Over all plate span 3500, therefore run is 1750. No pitch given so assume 35 Degrees gives a rise of 1225. Length of rafter on pitch line will be 2136 less half of ridge.
Joists. 47x175 C16 will span up to 3750, dead load 0.25to 0.50 KN/m2 and no binder required.
Rafters. Pitch 30 to 45 degrees. 47x100 will span 2500 between supports dead load 0.75 to 1.25 KN/m2. No purlin required.
Ridge board. When working with 47x100 rafters 38 or even 32 x150 will suffice, although we throw a bit of 47x150 up there to give a bit of meat to stitch into.
The above sizes are taken from the 1991 Building Regulations and are exactly the same as present day Trada tables.
If you are high up and in a heavy snow area, then increase rafters to 47x150 and they will take any roof covering that you throw at them. If you use 47x150 as rafters increase ridge to 47x175.
Conclusion. Due respect fellow your spec is way. way over the top for a close couple roof. You only over spec, when you go outside the tables i.e. Couple roof, vaulted, shallow pitch lean to. Otherwise all close coupled roofs can be designed within the tables.
QUOTE. is it just me or does he not have a clue!!
Leave you to think about that one.
C24 timber , if you can source them, they are over the top.
2 no bolted 225x75 as ridge board beggers belief. Ditto 2 no bolted 225x50 as purlins with laminated knee wall below.
QUOTE bco now telling me that the ridge beam aint big enough to support the load and i need to increase it to 12x9 ie 3 12x3 bolted together.
You can get 300x75 nominal but you will have to order it and will cost arm and leg and mean you will have a baulk up there of 300x225, weighing in at approx 216kg that your rafters are not designed to support. Your man is a complete and utter di*khead and has no knowledge what so ever of cut roofs.
Definitions. Ridge beam is a structural member which is designed to support the roof load. A ridge board is a non structural member used to connect the upper ends of rafters. A ridge beam is normally a steel. YOU DO NOT REQUIRE A RIDGE BEAM. YOU REQUIRE A RIDGE BOARD OF 50X175 MAX.
You should be able to pick enough information out of this post to talk your way out, but if no joy with BCI, then tell him you are going to see his superior.
Best of luck. oldun

thanks for that oldun, just wanted to get a bit of advice before i confronted him! hes still wet behind the ears so dont want to scare him too much
as of me going well over spec i must come clean and confess all my sins:
we built a house on the plot next door and i had that much timber left over i thought i would try use as much of it as possible so i didnt have to lug it all on the van and do 3 or 4 trips to the lock up lol. it was already paid for so why not

All the ridge board dopes is keep the rafter ends apart!

Seriously, so long as the entire plumb cut is collected in the depth of the ridge board then i can not see why the bco is speccing such a large section of timber.

They used to use a bit of floor board when fitting 4" x 2"s to Wimpy houses back in the day.

maybe the bco is not even qualified to make such structural comments.
Surely thats why you pay a SE for...