Do i understand my roof structure correctly?

[padstar]

I would like to construct the roof structure to my extension myself before getting a roofer into re tile and install the leadwork. I am confident in my carpentry skills and like the idea of the challenge.

Before i go and order materials for this job is the below correct. I know i need more ?jack? rafters but couldnt draw them correctly but i am sure you get the idea. I have tried to get how i think it should work clear on the drawing. I hope it makes sense.

The 49 degree pitch on the right hand side is set as it must tie in with the existing roof above it. I have drawn the extension section (left) with a 35 degree pitch. I would prefer a 30 degree pitch to this area but am not sure if that is acceptable?

 

[noseall]

I have drawn the extension section (left) with a 35 degree pitch. I would prefer a 30 degree pitch to this area but am not sure if that is acceptable?

If you intend using plain tiles, then it's 35 degrees minimum.

Before i go and order materials for this job is the below correct. I know i need more ?jack? rafters but couldnt draw them correctly but i am sure you get the idea. I have tried to get how i think it should work clear on the drawing. I hope it makes sense.

Yes - jack rafters are the compound cut diminishing fellas that rake up a valley or hip end - as opposed to full length common rafters.

When you cut the compound cut for one side of the hip blade, the off-cut will have the correct splay for his mate on the opposing side.

Your hip blade (rafter) will need to be deep enough to collect the whole depth of the compound cut.

Your valley board is actually a lay board. We use a scaffold board for this and they are ideal thickness and width.

We tend to locate the pitching plate or pole plate beneath the rafters and notch the rafter end onto the pitching plate, but it's ok doing it as you have shown. It may result in you having to double batten if you need to locate a short course batten right at the top of the rafter.


Restraint straps is in reference to gable straps. Yours are actually correctly known as holding down bent straps.

Don't forget a dragon tie in the corner of the hip. Also, we trim the very corner tip of the wall plate flat so that the plum cut on the hip rafter b/m sits against something flat as opposed to a pointy corner.​

 

[padstar]

With regards to the yellow beam, i had planned to hang it from the external wall using built in joist hangers but looking at it to do this if i had 2 hangers side by side they would hold the 2 outer timbers with a 4" gap between. Am i best to do this and bolt 2nr full length 2x6 timbers between the 2 on hangers essentially making a 10x6 beam or just fitting noggins between the 2 joists.

What would be stronger and acceptable to the BCO

 

[noseall]

With regards to the yellow beam

It's taking the weight and thrust from two roof elements. I'd be inclined to get this checked by an S.E. to be sure. Logic suggests a 152mm x 89mm with a 4" x 2" bolted to it and built into the masonry. If a composite timber beam will suffice, I'd build this in too, rather than suspend it off HD hangars.

What is the span?

 

[catlad]

Why dont you just leave it as a flat roof over the garage then it could be used potentially as a fire escape. You can also position a skylight better for the porch.

 

[padstar]

It's taking the weight and thrust from two roof elements. I'd be inclined to get this checked by an S.E. to be sure. Logic suggests a 152mm x 89mm with a 4" x 2" bolted to it and built into the masonry. If a composite timber beam will suffice, I'd build this in too, rather than suspend it off HD hangars.

What is the span?

The span is only 1.5m. I need (Planing) and want the roof pitched rather than flat in this area. Surely it is only picking up the pitched roof from 2nd floor level. The extension Pitch is loading on the external wall?

Would a wall plate Chem fixed into the masonry with 3 6x2's nailed into that and bolted together suffice.

If building into the masonry do i just stitch drill a hole slightly larger than the timber into the masonry slide in the timber then fill in with mortar. Sorry if this is a stupid question.

 

[padstar]

I am reluctant to build into the masonry as its very busy in this area with openings and lintels etc close by. Is the below acceptable, and BCO compliant. The beam will be supporting 5nr rafters that are circa 4m long holding 6m2 of roof tiles so not a huge load. The image below shows what i am thinking. 6x2 wall plate fixed with either chem fixed rods or concrete bolts with 3nr 6x2 timber beams sat on top (spanning 1.45m), fixed down and bolted (this will then have a wall plate on top for sitting the rafters on.

This area will sit within a cupboard space so it wont be seen (Wall plates will sit below ceiling level)

 

[^woody^]

Crap idea with the ledger plates.

How are rafters going to sit on that when it's lower than the wall around it?

 

[padstar]

It's only holding the rafters dropping down from the main roof (turquoise ones in the model in OP) which will form the valley with the extension pitched roof.

Top of beam will be level with the wall plate on the external wall .

How else can I do it. I want to crack on with it this weekend just dont know how else to do it

 

[^woody^]

Why don't you just put a valley rafter in?

 

[padstar]

Why don't you just put a valley rafter in?

So make the blue Valley board a valley rafter and then ground the rafters to the existing roof into that?

So would the valley rafter fit from the wall plate on the existing wall (Pink) down to the wall plate on the new wall (Red) at a 45 degree angle?

That may challenge my skills further but makes sense.

 

[^woody^]

You're fitting a hip rafter, so it not much different skill wise to fit a valley rafter.

You's just need to allow for a suitable depth to accommodate the compound rafter cuts, so 8 or 9" deep.

 

[padstar]

Ok so if i am using 6" common rafters then should a 9" valley and hip rafter be more than deep enough for the compound cuts.

I must admit i find it strange that the valley and hip rafters are strong enough to carry the loads but maybe i am over thinking how much load actually goes through them. It has always been something that i found bizzare.

 

[^woody^]

then should a 9" valley and hip rafter be more than deep enough

You'll need to work it out before you order the timber! I don't do refunds.

 

[noseall]

I must admit i find it strange that the valley and hip rafters are strong enough to carry the loads

The thrust is transferred down to the wall plate. New scaffold boards often double up as ideally sized roof timbers (ridge, layboards etc).