Cut and pitching roofs

[chamfer]

Untitled

• chamfer
• 24 May 2015
• 1

I have been trying to teach myself cut and pitching using Google sketchup. I have managed to work out how to measure up for common rafters using trigonometry and reading stuff on the internet, but now I am now stuck as I cannot get past hip rafters.

I have read and watched plenty on using imperial framing squares and speed squares, but I would really like to know if there is a maths formula I can use.
Should I forget the maths and just get a square and use tables?

I have uploaded a picture of the model I am working on, would appreciate any feed back

 

[^woody^]

What are you trying to learn - construction or drawing?

 

[chamfer]

What are you trying to learn - construction or drawing?

Construction

 

[^woody^]

A rafter square guide may help with the principles
http://www.irwin.com/uploads/documents/97_RafterInstructionManual.pdf

 

[noseall]

We "trial and error" our hip rafters into place.

First we cut the corners off the edge of the wall plate junction so that it is no longer a point but a 50mm wide 45 degree edge.

We then cut a pair of short (opposing) hip end jacks and temporarily site them close to the edge of the wall plate junction on opposite elevations. These are butted together and fixed.

We then lay the (uncut) hip blade onto the top of this pair of jacks and rest it on top of the peak of where the two last full commons meet.

You now have the plane of the hip blade, albeit on the underside of the resting hip blade. You can now use the bevel and a short level to gauge the plumb cut and set it on the bevel.

You then do the 45 degree bevelled end cuts which will be the top cut on the hip blade. You need to do a bottom cut also even if it means leaving the hip blade long. This is so you can use a level on it on the next step.

You then remove your temporary jacks and offer the hip blade into place. Obviously, until you have cut the bottom wall plate b/m, the top cut of the hip blade will sit high in the crook of the last two commons. You fiddle with this height whilst siting a level on the bottom cut and until the level reads true.

Once your level reads upright you can then mark off the bottom b/m cut. The depth of which will be determined by how much the top of the rafter is sitting above the crook of the commons.

Simples.

 

[gregers]

gosses ready reckoner had mine for over 25 years was given it by an old chippy,DUNNO why still dont understand the blooming thing.

traditional roof= work of art.

hence why i stayed mainlydoing 2nd fix

 

[ajstoneservices]

gosses ready reckoner

And a Stanley roofing square you're in business.


http://www.matchatile.co.uk/roofing-calculators.html

 

[noseall]

gosses ready reckoner had mine for over 25 years was given it by an old chippy,DUNNO why still dont understand the blooming thing.

Hip blades are quirky things to get spot on, always have been. Whilst I use math's exclusively for setting up commons etc, I use the practical method for the hip blades. There can be inconsistencies within the measurements i.e. like the existing building being out of plumb etc, to be able to accurately rely on the math's.

A few mill out and the hip blade ends up low or with that much gouged out of the bottom b/m, that you may as well scrap it.

 

[chamfer]

We "trial and error" our hip rafters into place.

First we cut the corners off the edge of the wall plate junction so that it is no longer a point but a 50mm wide 45 degree edge.

We then cut a pair of short (opposing) hip end jacks and temporarily site them close to the edge of the wall plate junction on opposite elevations. These are butted together and fixed.

We then lay the (uncut) hip blade onto the top of this pair of jacks and rest it on top of the peak of where the two last full commons meet.

You now have the plane of the hip blade, albeit on the underside of the resting hip blade. You can now use the bevel and a short level to gauge the plumb cut and set it on the bevel.

You then do the 45 degree bevelled end cuts which will be the top cut on the hip blade. You need to do a bottom cut also even if it means leaving the hip blade long. This is so you can use a level on it on the next step.

You then remove your temporary jacks and offer the hip blade into place. Obviously, until you have cut the bottom wall plate b/m, the top cut of the hip blade will sit high in the crook of the last two commons. You fiddle with this height whilst siting a level on the bottom cut and until the level reads true.

Once your level reads upright you can then mark off the bottom b/m cut. The depth of which will be determined by how much the top of the rafter is sitting above the crook of the commons.

Simples.

Untitled

• chamfer
• 25 May 2015
• 1

Have i got it right Is this what you mean? when you say

We then cut a pair of short (opposing) hip end jacks and temporarily site them close to the edge of the wall plate junction on opposite elevations. These are butted together and fixed.

We then lay the (uncut) hip blade onto the top of this pair of jacks and rest it on top of the peak of where the two last full commons meet..

 

[noseall]

Untitled

• chamfer
• 25 May 2015
• 1

Have i got it right Is this what you mean? when you say

We then cut a pair of short (opposing) hip end jacks and temporarily site them close to the edge of the wall plate junction on opposite elevations. These are butted together and fixed.

We then lay the (uncut) hip blade onto the top of this pair of jacks and rest it on top of the peak of where the two last full commons meet..

Spot on!
The underside of the temporarily positioned hip blade is, what will be, the top side of the proposed hip. Irrespective of this, the hip is now in plane which means that an upright level on the side of that hip will provide you with the correct plumb cut.
Transfer this to a bevel and you have your plumb cut secure.

 

[noseall]

P.S. your image shows a rather large 45 degree cut on the wall plate corner. The cut only needs to take off enough material as to allow a 50mm flat section. Or greater should the hip blade be thicker.

Take this into account when screwing the wall plate corners together as to not leave any screws clashing with the handsaw!

 

[noseall]

Don't forget to add a bottom cut onto the jacks as well. this is so that you can pop a level on the bottom plumb cut and make sure they are upright.

Laying a heavy hip blade upon these may cause them to dip slightly so take this into account when securing them.

 

[^woody^]

I cheat and either move a cut rafter to the corner to work out the hip cut, or run a line across from some fixed rafters to work out the top line of the hip.

 

[noseall]

or run a line across from some fixed rafters to work out the top line of the hip.

My method works in the absence of any commons, i.e. when the hips virtually meet at the top.

Believe me, we have tried all ways and the one I have described is the most reliable.

 

[noseall]

P.S. your image shows a rather large 45 degree cut on the wall plate corner. The cut only needs to take off enough material as to allow a 50mm flat section. Or greater should the hip blade be thicker.

Also, with deeper section hip blades, you often need to clout a wee bit off the corner of the masonry too.