Looking for long straight edge to align hip rafters.

[epsilonGreedy]

I cut my first birdsmouth today in a hip rafter and now I need to fine tune the height alignment of the hip rafter before fixing it in position. What is the longest metal straight edge I can buy on less than a 48 hour lead time? It does not need to be a spirit level.

 

Alternatively I could resort to string strung across 3 trusses and then extend the string out to meet the hip rafter.

 

As I type this message I realise than when I fit the hips to the 4m span of the bedroom it will be 2m from the last truss to the lower end of the hip plus another 1.2m to extend over the next two trusses to get a reliable projection of roof height, so this straight edge needs to be 3.2m long to be useful on both the small and mid sized roof.

Edited November 26, 2020 by epsilonGreedy

[ToughButterCup]

Just now, epsilonGreedy said:

I cut my first birdsmouth today in a hip rafter ....

 

Yo!

You're no longer an bird's mouth virgin! How does it feel? Was she easy? Did she wriggle? I did my first one on the ground, but later we did it resting on ther wall plate. Ya wanna try that pphhhh.....

'Ere, I had to cut double birds nmouths  (tell ya more later)

[epsilonGreedy]

7 minutes ago, ToughButterCup said:

 

Yo!

You're no longer an bird's mouth virgin! How does it feel? Was she easy? Did she wriggle? I did my first one on the ground, but later we did it resting on ther wall plate. Ya wanna try that pphhhh.....

 

 

She was easy, cutting off the corner off the facing bricks was harder. I was not happy using the 9" disk cutter at hip height, much safer cutting bricks and blocks on the ground. Think I might hack the other corner with the smaller angle grinder.

 

Anyhow my late lunch is over, time to experiment with the line to judge how much lower the hip seat at the wall plate should to. My desk based trigonometry indicated the birds mouth needed to be 15mm deeper but I took a cautious approach with the first cut.  

[Oz07]

Cut your wall plate corners at 45 to the thickness of your hip. 35/45mm. This will make it work easier in your head. Leave the height above plate the same where the hips meet the 45 corners the same as the height above plate on all your other birdsmouths

[epsilonGreedy]

23 minutes ago, Oz07 said:

Cut your wall plate corners at 45 to the thickness of your hip. 35/45mm.

 

 

I discovered the need for this cut on my first trial offer up then spent a few minutes puzzled why the hip would not seat down fully until I heard the clonk of wooden hip against facing brick on the outside corner. The brickie did ask how high I wanted the last course of facing bricks, the truss rafter eave overhangs clear the facing bricks by 10mm but not so at the corner.

 

27 minutes ago, Oz07 said:

Leave the height above plate the same where the hips meet the 45 corners the same as the height above plate on all your other birdsmouths

 

 

The main roof before the hip end is formed from ready made trusses hence no need for birds mouths there. I did my initial desk calcs based on the height of the truss above wall plate on the inside edge, hopefully this produced a similar result and hence uniform height.

[Oz07]

Use outside edge. In that case plum a line up your trusses where outside of plate is and measure that height

[tonyshouse]

Wall plate is straight and the distance to the top of every rafter including the hip rafter ha to be the same on the outside top corner of the plate. 
 

cheats over cut the birdsmouth a tad and adjust to perfect as the go in 

 

 

[epsilonGreedy]

21 minutes ago, tonyshouse said:

cheats over cut the birdsmouth a tad and adjust to perfect as the go in 

 

 

How can I cheat, a wood shim under the seat?

[Temp]

4 hours ago, epsilonGreedy said:

What is the longest metal straight edge I can buy on less than a 48 hour lead time? It does not need to be a spirit level.

 

How long do you want? Length of angle iron? 

 

 

[epsilonGreedy]

44 minutes ago, Temp said:

How long do you want? Length of angle iron? 

 

 

2.4m would be good, 1.8m seems to the longest normal spirit level available at Toolstation or Screwfix.

 

This 2.4m screeding level from Amazon is of interest:

 

https://www.amazon.co.uk/Faithfull-Screeding-Level-2400mm-Grips/dp/B000Y8HFJW

 

After posting I tried using a string line to project and extend beyond the installed truss tops to the hip corner. This worked well and after taking another 11mm bite out of the birdsmouth my a sight across the hip rafter and across the top of the installed trusses suggested the string method works.

 

I will still find a use for a long level later in the build, I have a 1.2m level at the moment. 

[joe90]

I have an 8ft piece of reclaimed timber that I use, remarkable it’s stayed straight after all this time. I like using “line of sight”, light only travels in straight lines, string can sag a little under its own weight.

[Declan52]

A length of box section is what screed guys use. How long will depend on your budget. 

[tonyshouse]

Wood would do