Thread: Mgp 12

My plans state that my roof truss should be 190 x45 MGP 12 at a max span of 5m

What other choices do I have f17 ?? Lvl and what is the cheapest option


Ta

What sort of roof ? Skillion ?

Yes Skillion

190 x 45 MGP 12 will do it, so will 200 x 45 H3 LVL's. F17 sizes are getting up there and you will pay around $ 18 / mt for it. I would say the MGP 12 would be the cheapest option but I would use H3 LVL's @ around the $ 13 - $ 15 /lm. I just assumed that you are using a standard sheet roof ( tin ) and no ceiling when putting the numbers into my program.

would hardwood 190/35/ F17 K/D Beams be ok to replace the mgp12 190x45 with

use i beams easy to lift and cost less than soild timber, 200 i beam is around $8.00plm 190x45mm pine is about $7.50 so not much price difference

As long as the info is correct ( no ceiling and tin roof and a single span of 5 mt, rafter and batten spacing of 900 ctrs and a pitch od 12 degrees) then yes, 190 x 35 KD F17 will do it ( can also use 170 x 45 ). Gaza, I have not seen I beams used in a roofing application before - could be interesting. Just for the record, my hyne program says to use either a 200 x 90 or 245 x 90 I beam

Originally Posted by ringtail

As long as the info is correct ( no ceiling and tin roof and a single span of 5 mt, rafter and batten spacing of 900 ctrs and a pitch od 12 degrees) then yes, 190 x 35 KD F17 will do it ( can also use 170 x 45 ). Gaza, I have not seen I beams used in a roofing application before - could be interesting. Just for the record, my hyne program says to use either a 200 x 90 or 245 x 90 I beam

we did for the first time maybe 7 or 8 years back only done it a few times since but works ok, i just email Hyne the details of the project and they come back with a design and engineering certificate within a few hours. only issue is if you want exposed rafters on the eves you have to laminate on soild timber with a decent back span,

on my mates garage we saved about 5k going from soild LVL to I beams plus lighter to lift.

Sweet. Have to keep it in mind for future

Originally Posted by ringtail

As long as the info is correct ( no ceiling and tin roof and a single span of 5 mt, rafter and batten spacing of 900 ctrs and a pitch od 12 degrees) then yes, 190 x 35 KD F17

Thanks for that is there any drama if the roof is Skillion and 5 degree pitch

One of the reason I like the hd is that I want to expose the rafters internally its also 8 $ m compared to 16 $ a m for the LVL

Nah. 5 is the minimum for custom orb sheet though ( corro) so dont go any less. Also bear in mind that some KD timber is not durable and not suited for external use unless heavily sealed. Make sure you put some form of sarking on top of the battens before the roof sheeting goes on otherwise you will get bad condensation drips everywhere. I normally use the heavy duty type used under tiled roofs. Cheap and very effective, knocks the heat out pretty well too.

Ta
What I meant was exposed internally and then run luan ply sheets between the rafters

Regarding pitch one side is 2.3 the other side 2.7 is thaT 5 deg

Still not sure about how to join the rafters to the top plates as I said before plans state birds mouth but they seems time consuming still looking for the right bracket

" Regarding pitch one side is 2.3 the other side 2.7 is thaT 5 deg "

Ummmm, what ??

Sorry about that

The lower side of the frame on one side is 2300 High
and on the Higher side it is 2700

Does that make sense

Makes sense now. Geez thats close, but I make it about 4 degrees. To get 5 degrees you want 2300 and 2800.

Would a builder inspector pick that up ?

Probably not, unless he is having a crap day and wants to get narky - which can happen. Ive never seen one get out any form of level and bevel to check the roof pitch. Its not ultra critical on a skillion flyover roof but if the roof cuts into a existing roof it can be a drama. If you are putting flashing / capping on the uphill side of the roof make sure you turn up the valleys of the roof sheets with a shifter.

438mm (rather than your 400mm) difference in wall heights will give you 5 deg over 5 m span.

5000 x 5deg tan = 437.4mm -->> Scientific Calculator

You could also use Trimdeck instead of Orb. Trimndek goes down to 2 degrees.

You could take the risk with things as planned (with Orb etc), but be concerned if your particular inspector gets his digital spirit level out of his boot. Distracting him with fresh coffee and warm muffins is a priority technique then

Pfffft. calculator. Puts me to shame with my ruler

x 2 on the coffee and muffins

remember the 5 degrees is to stop leaks, not just keep the inspector happy, picture a downpour with a wind up the slope, all of a sudden the water starts coming between the laps!

cheers Pulse

Originally Posted by ringtail

Pfffft. calculator. Puts me to shame with my ruler

x 2 on the coffee and muffins

First time I've used that calculator. I was determined to find one online this time

Using the calculator, mullfitz's roof will be a tiny smidge under 4.6 degrees.

Pulse, agreed, of course.