corbelling

[sudbrooke]

I am building a porch ands want to match the corbelling on the gable elevation. What I cannot understand is how do I work out which brick course to begin the corbelling, so that it goes out the right amount to meet the roof timber?

 

[freddiemercurystwin]

Photo? Better off in the Building Section tbh.

 

[ColJack]

I'm not a builder so don't take my word for it

I don't think that you're supposed to overhang more than quarter of a brick each time, so figure out the width you want to come out by, and divide that by the length of a quarter of a brick then round up.. so if it's say 300mm and quarter of a brick is say 65mm ( hey, I did say I'm not a builder, how would I know how long a brick is.. ), then you'd have 4.6 rows, so 5 rows and slightly less than quarter of a brick overhang each..

http://chestofbooks.com/architecture/Modern-Buildings-Construction-V1/Brick-Corbelling.html

 

[noseall]

It is not simple.

We do it by mocking up the wall plate and running a dummy rafter to assume the pitch, bearing in mind that this all needs to be set up whilst the brick-work is still low enough to start the corbelling, i.e. 6 courses or so.

There is no definitive answer as all pitches vary and soffit details too, so your own existing fascia depths and soffit widths will determine how far out and how many vertical straights will be needed.

 

[sudbrooke]

OK I see I can build the inner leaf blockwork up to wall plate level, put on a wall plate and the final rafter next to the gable end, and then build the corbel up to meet the top surface of the rafter.

But in practice, the porch is only 2.1 metres wide across the gable end, so I may not have been able to get the lintel above the door opening in by the time I have to build the corbel. Could be a problrm bonding the brickwork?

Also, do you aim to make the upper surface of the corbel level with the rafter upper surface or slightly higher due to the soffit being raised 30 mm or so above the rafter to lift the tile end?

Thanks

(drawing uploaded here to album if anyone can see it.)

 

[ColJack]

drawing too small, try chopping it up into smaller sections..

once uploaded, click "show my images" under the reply window, then click the picture to insert it into the reply.. simple..

 

[theoldun]

You are on the right track, but falling over half way there. Your lintel over door won’t effect corbels.
Take your inner skin up to top of frame all round. Take face work up to two course below door frame. Each side of frame bed couple bricks two course high to get lintel bearing. Bed your lintel.
Take inner block work up to storey height all round, less thickness of plate and bed, on the two eaves (side walls).
Bed and fix your plate to eaves. Comic is to small to see details, but would say roof is 35 degree pitch. This will give soffit of approx 225 to 250, and depending on up stand for tiles facia of about 200 to 225. At this point you might just as well pitch yer roof. Word of warning, make sure that you have not got to much rise on commons so that you can not get ridge tile and lead saddle to go below centre window above roof.
Set yer drop, set soffit level to the overhang on commons and cut commons to plumb facia cut. If you don’t know how to do any of this, or you don’t know how to work out your plumb, seat cuts and overhang, then you will have to come back.
You now know the depth of corbel and how many corbels you want. Aim for three flats on top so facia tucks into side of them. Corbels can be any where between 30 to 50mm overhang.
Suggest gable, do a fair raking cut 150mm down from top of commons, and run two course flat up verge for tile cloaking to sit on. Looks nice, we often use different brick for corbel and two course op the rake. We also sometimes form arrow slit in gable or diamond shape, to give feature.
Hope I have not confused yer, read it two or three times, go outside and look at it and it will all drop in place.
Best of luck. old un.

 

[sudbrooke]

Thanks for all this advice - it begins to make sense!