birdsmouth cut advice... potential cock up

[Oscar Mike]

Hello all,

New forumite here... I have been using these valuable resources for some time to plan a shed build and got underway last week.... after spending hours studying how to do a birdsmouth cut correctly, drawing it out and taking a day off work to sort it, I think I’ve cocked up. No, I know I have. #-o

A picture says a thousand words so it would be appreciated if you could confirm that this is the case and I will tear down and start again. (With a heavy heart and much lighter wallet)

(for what its worth, the rafters are 47x172 and the cut depth is approx 50mm)

Cheers
Mike

 

[Oscar Mike]

Sorry, I didnt really give you all the info did I... basically both of the vertical cuts have been made on the INSIDE of the structure. I think I know whats coming next.

Thanks for taking time to look at the post.

Mike

 

[Rorschach]

If my understanding is correct, downward load on the roof will push the walls outwards with the cuts this way.

 

[Oscar Mike]

Thank you for the response Rorschach, i think you're right.

I dont think it makes any difference at all but its a mono-pitch roof (and I am clutching at straws).

Gutted isnt the word, what a plonker...

Thanks again
Mike

 

[johnnyb]

I get it now I think. It won't make a difference. Both are attached to the head plate solidly. Ie neither will be moving when built. It's important to tie the 2 rafters together if your roof is going to be heavy. The smaller the structure the less it matters.
Interestingly old tongue and groove shed roofs always sag . But single sheet roofs are better. Think about the way a t and g roof spreads the load which allows spread in the centre of the walls and therefore ridge sag.

 

[Oscar Mike]

Hi there, thanks very much for the response. I have been a bit light on info so apologies for that.

Dimensions wise its a low pitch mono roof with a span of approx. 3.6m and pitch of approx. 7 degrees.

I was going to be fixing them with additional hurricane ties and also the usual noggins inbetween the rafters (2 sets)

I am not sure what you mean by tying them together though... I'm not planning on another rafter spanning the two ends and connecting them together as want that additional roof height.

Roof wise, its 18mm osb, membrane and then onduline/coroline on top so pretty lightweight?

Any additional thoughts are appreciated as I'm almost ready to cut it all up for firewood :wink:

Cheers
Mike

 

[Kieran62]

Afternoon Mike.
Not sure which way you have cut the birdsmouth; is it
A or B?
If it is A, you don't really have a problem, you can attach a firring piece to the top of each rafter to produce your fall.
If it is B, simply use truss clips https://www.toolstation.com/shop/p76165?r=emarsys[/url] to attach the rafter to your wall plate and secure with shearadised nails.
Hope that helps.
Kieran

 

[Oscar Mike]

Hi there Kieran62, thanks for taking time to respond in my hour of need

I couldn't see the options that were in your post - something about not having permissions - maybe because I am new I guess.

To help describe further I have sketched a quick drawing - its not to scale obvs but will show you what I have done (the wind ties in red and there will be one either side).

Re those truss clips, i guess that they go on the inside of the building to keep the walls from pulling apart?

Thanks again
Mike

 

[topchippyles]

I have cut thousands of roofs mike all shapes and sizes,Your top cut is correct and the bottom cut is wrong but its not a major issue on a shed,Just skew nail down through the sides of the rafters directly into the wall plate and what i would do is cut back the rafters on the bottom flush with the outer finish and then put a deeper fascia board on the outside screwed on so in effect it will lock both walls in place and create what a birds mouth rafter will do.As for the depth of birds mouth cut it is around a third so you are correct with that.

 

[Kieran62]

Hi Mike,
If you are using the wind ties, you won't need the rafter clips.
I presume you are going to have a fascia board across the rafters; if you add a longitudinal section behind the fascia it will prevent the rafter from moving.
Hopefully you have enough posts to see my pic this time.

Kieran

 

[Kieran62]

Beaten by Topchippyles.
I think he explained it better than I did.
Cheers
Kieran

 

[Oscar Mike]

Hi Mike,
If you are using the wind ties, you won't need the rafter clips.
I presume you are going to have a fascia board across the rafters; if you add a longitudinal section behind the fascia it will prevent the rafter from moving.
Hopefully you have enough posts to see my pic this time.

Kieran

I can see the pictures now Kieran - certainly better than mine

Ok this is making sense now, all is not lost which I can tell you is amazing!

I like the idea of using the fascia to give some additional 'hold' on the bottom rafter - I will do that for sure.

You have saved me from a sleepless night so thank you very much to all who have contributed 8) Just an amazing forum.

Cheers
Mike

 

[topchippyles]

Beaten by Topchippyles.
I think he explained it better than I did.
Cheers
Kieran

Thanks kieran62 ,Thats why i am topchippyles,These eyebrow roofs are my speciality. (homer)

 

[Kieran62]

Topchippyles, excellent work!
That eyebrow dormer is very impressive.
Thanks for showing it; I wouldn't have a clue how to start it without some VERY detailed drawings and someone with your experience passing on their knowledge.

Thanks
Kieran

 

[Oscar Mike]

Hello, its me again...

SO as I have got the birdsmouth cuts arse about face I then started worrying about the depth of the cut vs rafter size etc as I am guessing that now the load is in a different place?

I have tried to draw a little better this time and my question is where should I take the 'max birdsmouth cut depth' from on my configuration? A or B or X? I am also assuming that the touted 1/3 of total width. (50x175 timber used).

Cheers for helping (again)
Mike

 

[topchippyles]

From point A which is the smallest point

 

[Oscar Mike]

From point A which is the smallest point

Thanks for the reply - just measured and all looks good 8)

Success snatched from the jaws of defeat!

Thanks for the help once again

Mike