How to support existing rafters with a new ridge beam?

[minerscottage]

I've got a gabled roof made up of two chunky pairs of rafters, and two dozen much lighter rafters that sit on purlins resting on the larger rafter (and the stone gable-ends of the property).

It looks a bit like the diagram below:

1) Green 'lightweight' rafters
2) Purple 'heavy' rafter (which also has a lateral tie 1/3rd up I've omitted from the diagram)
3) Blue ridge board
4) Pink purlin

The purple rafter is buried into the stone wall, and the green rafters sit on top of the rubble wall, and the purlin. Some of the green rafters are attached to ceiling ties, but most aren't, so the only thing preventing the roof from spreading out is the tie on the purple rafter.

My plan is to turn this roof space into a vaulted ceiling for extra head-space. I've provided detailed measurements to my engineer, and he's produced plans that call for the installation of

1) Extra (large) rafters
2) A ridge beam to hold the weight of the roof, removing the need for ceiling ties. He's happy the span is short enough for a load bearing timber.

I'm currently thinking about how do go about executing this upgrade to the roof, and am looking for insights from those with more experience.

My current thought is to fix collar ties at the top of each existing rafter. This partly to provide extra support to the ridge of the roof, but also to serve as a plate I can rest the new ridge beam under.

Once the existing rafters are supported by the new beam, I would then slide in the new rafters underneath the existing purlin (supported with a birdmouth), and hang them from the new beam with either metal hangars or another birdmouth.

Here's a diagram of what I'm thinking:-

1) Orange collar ties
2) Red ridge beam
3) Yellow new rafter

For further context, here's an image of the inside of the roof colour-coded as above

Thanks in advanced for your thoughts!

 

[blup]

.

 

[Mr Chibs]

I would have thought beam spanning gables, sat on pads, rafters birds mouthed on top of beam or sat in web of beam, then collar ties under beam. My vaulted ceiling was 4.6m long (span around 5m) and from memory was 203mm deep, so you will probably need chunyk timber if you are allowed use this, mine was pocketed into gable walls. I have no purlins.

SE had said if it was longer, it could be broken down into sections and bolted together, although this deflection may be greater as not in one piece, but easier to install (maybe )

Neighbours had a large vaulted ceiling recently, it used a wooden ridge, but it was huge, a glue lam thing, looked about 300mm deep and about 150mm wide, it wasn't even that long, 4-5m.

 

[minerscottage]

I would have thought beam spanning gables, sat on pads, rafters birds mouthed on top of beam or sat in web of beam, then collar ties under beam. My vaulted ceiling was 4.6m long (span around 5m) and from memory was 203mm deep, so you will probably need chunyk timber if you are allowed use this, mine was pocketed into gable walls. I have no purlins.

SE had said if it was longer, it could be broken down into sections and bolted together, although this deflection may be greater as not in one piece, but easier to install (maybe )

My original plan was to birdmouth the existing rafters (small and large) onto the new ridge beam, but the size difference between the "large" and "small" rafter, and the size of the timber beam means one-or-the-other wouldn't be able to touch the other. If I fix a collar to each, I can position them all so they're at equal distance to the beam underneath. There's also the difficulty of trying to pry apart the existing rafters with 100kgs of roof on them.

Seems a lot easier to me to leave them kissing the ridgeboard, and then jack-up the beam underneath them.

Neighbours had a large vaulted ceiling recently, it used a wooden ridge, but it was huge, a glue lam thing, looked about 300mm deep and about 150mm wide, it wasn't even that long, 4-5m.

I've got three spans in total, the longest two are 4m and my engineer has calculated 100mm x 150mm C16/24 timber for the job.

 

[frslam]

I'd like to bring this thread back into life. Doing a full house renovation and installing a 115x495x6355 Glulam beam. Original rafters are 5x2, I want to get rid of the rafter (ceiling) ties and the collar ties and have the Glulam installed right up to the original rafters. I'm also going to glue/screw 45x95 C24 timbers to the edge of the original rafters, making the rafters much deeper. I can't decide whether to birds mouth the top of the new rafter 'extenders' to sit on top of the ridge beam (thickness of beam would only allow a 50 - 55mm bearing on the top of the beam for each rafter - is that enough of a bearing?), OR... have the beam kiss up to the underside of the original rafters (which are fitted to ridge board), just install high wind ties from beam to original rafter, and glue/screw the 45x95 to the edge of the old rafters and plumb cut them into the beam where I would just use some sort of fixing, an 'L' bracket or something like that from the rafter extensions to the beam. Problem I have is, even with the roof at 40°, the new rafter extensions aren't deep enough to be able to use joist hangers (which would definitely be my most favoured option). Does anyone know of any products, hangers or brackets that could work. I have an SE and in touch with B.C.O, they're aware of all of this, SE is happy for plumb cut option and he's happy with the rafters (including extending pieces) to sit on top of the ridge beam (not birdsmouthed). Not being fully convinced, the rafter just sitting on top doesn't make me feel that the roof load is vertical, as it should be, and part of me thinks that it'll put a lot of pressure on the top rafter to ridge board connection. I have loads of sketches that I can upload if anyone replies to this thread. Many Thanks

 

[Mr Chibs]

Morning. Sounds interesting.

What's the span you are dealing with?

As for hardware have you had a look through the Simpson website?

 

[frslam]

Morning. Sounds interesting.

What's the span you are dealing with?

As for hardware have you had a look through the Simpson website?

Morning! From inside wall to wall is 7.4m, walls are approx 270mm thick, 2 x block plus cavity, it's a good span. I've had a look at Simpson website and Cullen's as well. If I go for the plumb cut of new rafter extenders into the beam, could I just use Simpson A35 brackets? I bought a load of Simpson H2.5A High wind ties which I could use to tie the original rafters down to the ridge beam if the beam just kisses up to the bottom of them, then have the extender pieces plumb cut into the beam, it would lock it all together I think

 

[noseall]

I've got a gabled roof made up of two chunky pairs of rafters, and two dozen much lighter rafters that sit on purlins resting on the larger rafter (and the stone gable-ends of the property).

It looks a bit like the diagram below:

1) Green 'lightweight' rafters
2) Purple 'heavy' rafter (which also has a lateral tie 1/3rd up I've omitted from the diagram)
3) Blue ridge board
4) Pink purlin

The purple rafter is buried into the stone wall, and the green rafters sit on top of the rubble wall, and the purlin. Some of the green rafters are attached to ceiling ties, but most aren't, so the only thing preventing the roof from spreading out is the tie on the purple rafter.

View attachment 293531


My plan is to turn this roof space into a vaulted ceiling for extra head-space. I've provided detailed measurements to my engineer, and he's produced plans that call for the installation of

1) Extra (large) rafters
2) A ridge beam to hold the weight of the roof, removing the need for ceiling ties. He's happy the span is short enough for a load bearing timber.

I'm currently thinking about how do go about executing this upgrade to the roof, and am looking for insights from those with more experience.

My current thought is to fix collar ties at the top of each existing rafter. This partly to provide extra support to the ridge of the roof, but also to serve as a plate I can rest the new ridge beam under.

Once the existing rafters are supported by the new beam, I would then slide in the new rafters underneath the existing purlin (supported with a birdmouth), and hang them from the new beam with either metal hangars or another birdmouth.

Here's a diagram of what I'm thinking:-

1) Orange collar ties
2) Red ridge beam
3) Yellow new rafter


View attachment 293533

For further context, here's an image of the inside of the roof colour-coded as above
View attachment 293535


Thanks in advanced for your thoughts!

Collar ties in a ridge beam roof tend to sit beneath the ridge beam. The higher they go the less useful they become.

 

[Mr Chibs]

Presume you've seen these?

Would this be of any use? Just looked at the tech specs, think they will be to tall for your wood section.

Slope hangers

Maybe this??
Ridge hanger

 

[cdbe]

My SE recommended these from Screwfix, with hindsight I should probably have fixed with twist nails but they're pretty hefty screws.

 

[frslam]

Presume you've seen these?

Would this be of any use? Just looked at the tech specs, think they will be to tall for your wood section.

Slope hangers

Maybe this??
Ridge hanger

I did see them, priced them up, £500 + Veg and Tatties for 26 of them. They want the angle of the bracket slope, not roof pitch. Thought they'd be able to work that out if I gave them the pitch. I can get one to fit, 105mm tall (SAE-250X).
Now I want to birdsmouth the 45x95, am I right in thinking that I can go as deep as 1 third the depth of the timber? (approx. 30mm deep would give a 55-57.5mm seat on top of the ridge beam on each side. Would that be enough? You'd think it would be because the thickness of the GLULAM is only 115mm, though it is deep at 495mm.
I thought the wee ridge hanger could only do up to 30 degree roof pitch? My roof is 40 degree.

 

[Mr Chibs]

With regards to birdsmouth cuts, yes, usually one third of material can be removed.
On the roofs I've see with 45x95 timbers, they are plumb cuts, never seen a birds mouth on that size.

Wasn't aware of the 30° limit on the hangers.

These are meant to be good for up to 45°
LSSR

or these
LRUZ

If your SE is happy with plumb cuts, are you not good to go without hangers?
What about truss clips?

As Noseall had said, you could add a collar tight under the ridge beam connected to the rafter pair. Just means you'll have a flat ceiling.

 

[frslam]

I was gearing up for birds mouth cuts with the trusty self levelling laser this morning then I spoke to my SE. After I told him I could either plumb cut with heavy duty L brackets into the beam or birds mouth the rafter extender pieces to the GLULAM (115x495x6355), I asked him what is structurally stronger and what would be his preference, he said it would be - kiss the bottom of the original rafters with the GLULAM and plumb cut the new joists into the beam with L brackets, the new joists being glued and screwed to the originals (SOUDAL Purocol Express D4 Expanding PU Adhesive and 8 x 180 structural screws)

 

[catlad]

Can you not buy a load of 9 x 1 and make yourself some timber gussets.

 

[frslam]

The SE spec'd 15mm Ply Gussets fixed by 14 nails per member. I'll be using 18mm OSB3 fixed with expanding PU and about 14 nail fixings per member. I'm hoping when he says Ply - OSB3 would do the same job. The rafters have the extenders fitted now, the beam *is* going up and just touching the underside of the rafters, SE said that would be OK too as long as I hurricane tie the rafters to the beam. I am using Simpson H2.5A ties. Bought an auto hammer (HIKOKI) just for fixing the 3.75x30 square twist nails because I'm working inside the ridge there's no space to swing a hammer. Hopefully the BCO will be happy, turned into a bit of an ordeal with backwards and forwards between the SE and Building Control