Cut and pitching roofs

[noseall]

What formula do you use for centring commons and jacks?

I just do whatever the SE tells me to do.

My only quirk is 600mm centres. I don't like them. Too far apart.

My favourite is 450mm.

They (SE's) just use span tables and timber strength guides, i.e. C16, C24 etc.

 

[chamfer]

What is SE?

 

[noseall]

Structural Engineer.

A lot of the jobs that we build involve an SE. Not because they are large or important, rather because they involve steel and buttressing and pillars etc.

It is the SE who will cast their eye over a drawing and make the final call, unless a building is simple enough for an architect or designer to use standard span tables.

 

[gregers]

guy i worked with used 'logarithm tables' i couldnt get my head round what so ever.
we done a huge 5 berth garage with over the top 9x3 for the rafters,guy made it into a granny annex .
wish i had done more over the years.

 

[noseall]

wish i had done more over the years.

I have to admit, I like building cut roofs. Probably because (weirdly) I like math's.

 

[gregers]

and yet the guys who put up with my help...sorry hindering them,could not get there heads round kitchens and ironmongery and 2nd fix in general.
whether they found it boring or just couldnt work to the tolerances who knows.

 

[noseall]

and yet the guys who put up with my help...sorry hindering them,could not get there heads round kitchens and ironmongery and 2nd fix in general.
whether they found it boring or just couldnt work to the tolerances who knows.

Second fix is a different animal and a different mind-set. Roofing is 30% planning and number crunching and 70% walloping with hammers and chopping with saws.

 

[gregers]

yeah,once worked on a site where a 1st fixer wanted to try doing the finishing
.OH MY.

 

[chamfer]

Untitled

• chamfer
• 26 May 2015
• 1

I checked rafter span tables and I could go with 600mm centres, but I also don't like 600 centres even on stud work,
I am going to go with 450. How do you approach Jack rafters do you do the maths? or is it another trial and error. I cut my first compound cut, cutting my plumb cut at 55° and my edge bevel at 45°. The plumb cut worked out right edge bevel didn't

 

[noseall]

Untitled

• chamfer
• 26 May 2015
• 1

How do you approach Jack rafters do you do the maths? or is it another trial and error. I cut my first compound cut, cutting my plumb cut at 55° and my edge bevel at 45°. The plumb cut worked out right edge bevel didn't

Jacks are relatively simple. You use the crook of the wall plate b/m as your datum, as the portion of the rafter from the b/m down to the fascia remains unchanged.

Hook your tape over the last full common and mark off 450mm onto the edge of the hip. We also butt the tape against the near side of the common so as to provide a mark both sides of the jack position, onto the hip. However it is the longest mark that you use for measuring.

Do the same marks along the wall plate.

Mark off and cut the wall plate b/m and the fascia plumb cut onto your proposed jack.

Hold your tape measure onto the very corner edge of the wall plate (i.e. the one that sits into the crook of the b/m) and measure up to your (longest) mark on the edge of the hip rafter. Your compound cut should start at this longest point. You need to turn the rafter onto its side to do this and on what will be the longer side.

Incidentally, the compound off-cut of one rafter usually does the other side.