Rafter seating on wallplate

[Welderpaul]

I'm fitting new rafters, 5x2"s, sistering up the trusses for a loft conversion. This is how they end up. The Engineer noted on the calcs that the new rafters are to sit on the wallplate.
Due to the geometry of the roof, this is as far as they will sit on. Top of the new timber is tight against the slate battens.

Is it good enough or how can i improve this?

 

[Agroshield]

Make half of the offcuts into 2 1/2" x 2 by ripping along their length and glue and screw to the back of the rafter so the wall plate is covered.

Being offcuts, the chamfer angle will already be correct.

 

[addjunkie]

As it will be fixed to the adjacent truss, the fixing to also transfer the downward forces into the wall plate. You will always get some over hang as the wall plate looks like 4x2 and joist 5 x what ever cut at an angle.

 

[KaneH]

Bearing is never really an issue on a typical rafter / joist end supported on a wall plate so the ~50mm bearing you have (assuming 100mm wall plate) will more than suffice.

Unless your rafter is 50m long that is..

 

[dan treg]

on some raftes the joist is bird nested or notched so the bearing face isn't dissimilar to that

 

[mtt.tr]

When cutting a rafter the bird mouth would be 1/3rd of the depth of the joist, so i would say it looks fine from the picture.

However you could ask the engineer

 

[Pigeon_Droppings2]

However you could ask the engineer

As above...ask the structural engineer.

I doubt it's an issue as it is though....assuming the two are tied/connected correctly on the other side.

 

[Erie Fred]

As this is a welding site, how about a angle bracket to run up the side
of the rafter (with bolt/screw holes) and same on surface sitting on the wall plate ?

 

[mtt.tr]

As this is a welding site, how about a angle bracket to run up the side
of the rafter (with bolt/screw holes) and same on surface sitting on the wall plate ?

Why, its over complicating something that doesn't need to be over complicated.

We've been cutting roofs like this for a long time

 

[Welderpaul]

Thanks chaps, that is a fair point about the depth of a birds mouth being the usal bearing area. With it being bolted to an existing truss as well i think i will leave it alone and sleep easy. Ta.

Another question - Velux structural opening sizes. (it's a GGL PK04) Nothing in the box with it, and google seems to give various answers, much of it AI lead.
Concensus seems to be frame size plus 40-60mm on the width and plus 45mm on the height. Does this sound right?

 

[JimmyS]

I got Fakro rooflights and pretty much made the openings just the frame size. Providing its square it should be ok but you might want to think about your roof tile or slates and where they are going to end up when the rooflight is in. Only problem I had were the flashings. I got the slate flashings but they didn't seem to work for a roof with sarking boards. I ended up having to make lead flashings for ours.

 

[addjunkie]

https://wattsroofing.co.uk/wp-content/uploads/2019/03/installer_handbook-1.pdf

Velux instructions

 

[Welderpaul]

https://wattsroofing.co.uk/wp-content/uploads/2019/03/installer_handbook-1.pdf

Velux instructions

Found it. All the pertinent dims are in the flashings section, not the window fitting section! I had to print all 90 odd pages to find it. Thanks @addjunkie

 

[addjunkie]

Found it. All the pertinent dims are in the flashings section, not the window fitting section! I had to print all 90 odd pages to find it. Thanks @addjunkie

We fitted one here from the inside, dont remember it been that difficult though very fiddly with the flashing etc, though the guy who was assisting me had done 3 before in his own place.

 

[Welderpaul]

We fitted one here from the inside, dont remember it been that difficult though very fiddly with the flashing etc, though the guy who was assisting me had done 3 before in his own place.

There's a couple of good YT videos so I'm happy enough fitting it, I just couldn't find for certain the opening sizes.

When you Google things now you get given the AI version first. It is a bit harder to try to find more credible results. It even says after the AI bit, 'This may contain inaccuracies'
It was certainly giving me the wrong info.

 

[Blobber]

The last Velux windows we did were simple enough but the flashing kit was a right faff, a lot depends on what style of tile you have and with ours im still not happy how it looks externally but its done correctly!

 

[Welderpaul]

The last Velux windows we did were simple enough but the flashing kit was a right faff, a lot depends on what style of tile you have and with ours im still not happy how it looks externally but its done correctly!

We have pan tiles on our roof, so the bottom flashing is like a skirt which moulds to the tiles. Looks like I need to trim the top of the tile profile off so it all seats correctly. I have another day or so of breaking my back working round the trusses to essentially build a roof inside a roof before that stage. I'll let you see how mine turns out (If it looks ok)

 

[Blobber]

The flashing is nice and big all around but once you start cutting pan tiles up they don't sit very well, I think I might have had to stick the little pieces down one side of the window, I may even have done it all wrong!

 

[Welderpaul]

Very similar to my set up

 

[roofman]

Cut the tiles close up to the window and don't be tempted to "glue" the bottom tile with mastic as pics above...can hinder water getting down and out from secrete channels, this then promotes the breaching of the perpendicular side flashing.