Groin Ceilings

Here it is!!!!  We have been waiting for this moment for a LONG time.   One of the most exciting features of Villa Costo Mucho will be the Gallery, which runs from one end of the house to the other.  There are actually 5 groin ceilings in total.  One is in the front Foyer, which is where I am standing, the other 4 grace the Gallery and will each be cornered with 4 Cantera columns (12 columns total).  Between each column there is an archway, 18 inches wide, which the arches frame a rectangle, and then up inside that rectangle lies the groin ceiling itself... 

A groin is another name for a "Double Barrel" ceiling, which would be the footprint of two barrel ceilings intersecting perpendicular to each other. 

Now, what is so perplexing to me is how the math all works to make these happen...  First, to keep the arches between columns themselves looking correct, the "rise" needs to be the same.  In our case, this rise is 18 inches (all the other arches in the house are generally 8 inch rise).  So, from the 8 foot column, go up an addtional 18 inches and you are at the top of the column arches. 

One would think, then, that you could frame the groin by tucking in the next set of arches from the 8 foot tall corners, traveling straight up into space a fixed amount, say 15 inches, and then repeat the same arches from below....right???  Wrong....  It turns out that if you use the same radius from below, that the concentric arches from below now look to be at a different radius, and thus are not pleasing to the eye...  So the next arch radius up above has to be adjusted with a larger radius, which means the rise from left to right starts out at a larger number (17 inches in this groin), then decreases at center (15 inches), and then increases again to right corner.  To add great confusion, these groins are not square, but rather rectangles, so the short sides of the rectangle have yet another set of radius' which have to be worked out as well....

Oh, we aren't done yet...  Once these corner points and rise have been figured, the actual framing of the groin requires them to cut plywood arches that span diagonal across corner to corner, and meet up in the middle at the apex of the groin.  These are cut at yet another radius, because the span on these is longer yet.    It all has to work perfectly...

My deal with the carpenters was that they would frame one out, and then call us in for a look before they proceed with the others...  Turns out that day I was in Argentina instead, so my poor wife had to go out and make the call.  She was under great pressure...

Here is the view down the long axis.  You can see from this view why we used a larger "rise" on these arches than in the rest of the house.  Had we not, the groins would have been essentially hidden from view and the sightline down the hallway would have been obscured.  In addition, a shorter rise would have meant things would have looked funny from the sides, by funny I mean the ratio of space above the arches in the room to the space below.

I should add that the dimensions of the column bases were adjusted on the "fly" as we framed this all together.  Originally, we thought that 14 inches would be adequate to fit a 12 inch column and it's base, but this would mean no room for drywall and trim...  So, we had to adjust the column base positions and thus the framing overhead to account for a new dimension of 16 inches, but the rest of the house had to stay fixed.  We also had to do all this while maintaining centerline on the entryway door, the courtyard windows, and the doorway that leads into the study.  We were able to do all this by shifting one of the end walls of the gallery east 2 inches.  Unfortunately, this meant that now the column to column dimensions are not all the same, so the poor framers don't now have the luxury of using the same dimensions from one groin to the next, and have to recalculate each one seperately... 

The framers don't have the luxury of grid paper and a compass to figure all this out, they are using tape measures, plywood, and their intellect to figure this out.  The plywood in this case is 1 1/8 inch decking plywood, which is heavy and hard to cut in a radius.  (by the way, they cut the radius with their circular saw rather than using a reciprocating saw, it produces a smoother radius, and they lube the blade with WD40 as they cut to keep the blade from pinching).

To say I am amazed at their talents would be an understatement...  One day they are lifting a 900 pound beam 12 feet into the air by hand, and the next they are using some pretty tricky geometry skills to lay things out... 

Another view down the gallery.  This one shows the ground so it puts things in better perspective.  All the wooden walkways are temporary, and only the 4x4 posts will remain when they are done.  These posts will be surrounded by the stone columns.

This view is from the living room, looking back towards the dining room and foyer entryway.  You can see here that a more shallow arch would have looked too flat.  This ceiling is 12 foot and pops to 13 above me where it is coffered.  The dining room is similar, 12 foot with a 13 foot pop in a double stepped round.  It's all really quite cool...

Carpenters asked me for a bunch more of these joist hangars.  I just about croaked when I discovered the price of these and it's bigger brother ($57 each for the bigger one, which is special order and not even kept in stock, so Simpson has to make it special...a 20 day lead time)...  Forget it, they say they have something else figured out...

Last shot as I was walking away tonight.  As you can see the garage is not constructed of ICF, and thus looks pretty puny in comparison.  By the end of this week, I think you will see the remaining groins in place and the roof will be on.  They call the soffit material the "cornice", which will be mostly constructed of Hardi Concrete boards... I hate to repair and paint wood, and the Hardi board is awesome.  Doesn't rot, and holds paint a long time...

Yes, the trash pile is growing a little bit.  Thanks to my Dad last week we hauled off some really super NASTY "poly" that was coated in muck.  It was just coated in slop and we got it all over ourselves and my old pickup.  The concrete guys had piled it at the bottom of the trash pile, and it was keeping the whole thing from drying out.  These boards should be easy to get rid of in comparison...

Have a great week...