# Blimey the hardest job I've done so far...

Discussion in 'Carpenters' Talk' started by alwaysworking, Jul 31, 2007.

1. ### alwaysworkingNew Member

Hi Chippys,
Spent the day trying to build a pitched roof over my porch 35 degree pitch, how many cuts did I have to do to get it right...god knows.

What is the best way to work out the angle of the cut for attaching to the ridge board and cutting the Birds mouth.

I've done all jobs from bricklaying, electrics, plastering and so on, but this has beaten me.

Any advice other than pay a chippy would be really good.
AW

2. ### Â­New Member

> Hi Chippys,
Spent the day trying to build a pitched roof over my
porch 35 degree pitch, how many cuts did I have to do
to get it right...god knows.

What is the best way to work out the angle of the cut
for attaching to the ridge board and cutting the
Birds mouth.

I've done all jobs from bricklaying, electrics,
plastering and so on, but this has beaten me.

Any advice other than pay a chippy would be really
good.
AW

For a 35 degree pitch the ridge cut is 55 degrees (90 minus 35). Cut this first.

You then need the rafter length from the top of the ridge cut to the outer face of the wall plate. For a 35 degree pitch you multiply the run (half the span) by 1.221. So say your run was 2 metres then the l/o/r would be 2.442 metres.

This is to the back of the birdsmouth.

Birdsmouth plumb cut is 55 degrees and seat cut is 35 degrees.

Birdsmouth plumb cut should never be more that one third of the length of the plumb cut line. So say you're using 47 x 100 timber the plumb cut line at 35 degree pitch may be about 120mm so the birdsmouth maximum cut should be about 40mm in this example.

Leave rafter long enough for eaves overhang which is often cut in situ after the roof is pitched.

Simple eh? :^O

3. ### -chippy_johnNew Member

You've answered your own question really, the plumb cut at the top is 35 degrees, the plumb part of the bird beak cut also has to be 35 degrees and as you are sitting it on a square plate the seat cut on the bird beak will be 55 degrees, (35 + 55 = 90).

4. ### alwaysworkingNew Member

Oh right, I think I must have been overcomplicting things.....................
...........................
...........................
...........................
...........................
...........................
...........................
...........................
...........................
...........................

5. ### -chippy_johnNew Member

ecm is probably technically correct but if you're using a speed square or a chop saw, set it to 35 degrees for your plumb cut,(not 55) and if it's just a lean-to roof don't halve the span before multiplying by 1.221.

Try googling roof calculator,I think you will find the plumb cut is 55degrees

7. ### TrogNew Member

Chippy John is right though.

Chippy John is right though.

What do you mean "always right" So the roof calculator is wrong

9. ### chippie244Super Member

35 deg and 55 deg are the same thing but approached from different sides. This probably won't help.

10. ### -chippy_johnNew Member

Chippy John is right though.

What do you mean "always right" So the roof
calculator is wrong

He didn't say *always right*, (but in this instance I am).

The angle used to mark out a rafter cut depends where you are marking it from, in practice we are marking from the finished plane of the roof not from a vertical perspective.

Why else do you think it is that a jack rafter is always cut at 45 degrees when cut on a chop saw and yet is marked at a totally different angle when marked out by hand?

11. ### Â­New Member

If you are using a chop saw then the ridge cut angle to set the saw is 35 degrees because the saw is already set at 90 degrees to the timber. (in other words, even if you set the chop saw to 0 degrees, you will still get a 90 degree cut)

The angle you will get on the timber will be 55 degrees.

That's because 55 and 35 add up to 90.

If handcutting (I know, I know...) you mark 55 degrees on the timber.

12. ### dirtydeedsNew Member

some idiot above has never hit a nail with a hammer, let alone framed a roof

the FIRST lesson in pitching a roof

the plumb cut is the same as the pitch

13. ### Â­New Member

Plumb cut the same as the pitch? You're having a laugh!

This is only true on a 45 degree pitch.

Let's take a shallow pitch, say 20 degrees. The ridge cut (plumb cut) will be 70 degrees. The two always add up to 90 degrees.

I'll be back with a drawing.............. :^O

14. ### dirtydeedsNew Member

he cant work out his roof from first principals, so he spends money on a calculator then comes here to proove it

15. ### dirtydeedsNew Member

the plumb cut on a 20 degree pitch roof is 20 degrees

extremely clever man you are the second person on this topic who has clearly never pitched a roof in his life

16. ### dirtydeedsNew Member

mr vercleverman, the whole world is waiting for you

you will be the first person in the history of this planet to have pitched a 20 degree roof with a 70 degree plumb cut

18. ### Â­New Member

Calm down dirtydeeds. You're misunderstanding how we're explaining it.

***!

19. ### dirtydeedsNew Member

very clever man

pythagoras is waiting for you to proove him wrong

20. ### Â­New Member

In fact, take a look in a ready reckoner. It will explain it all for you there.