SUBS#6:
Goof Proof Roof

400 years ago, people built houses from trees with a buck saw, an axe, and a hammer.   Shingles and shakes were a brilliant solution to the problem of how to make a waterproof roof with the simple tools and materials available.  The drawbacks were: it takes a huge amount of material and labor; you need a steep roof pitch to shed water; it requires a lot of maintenance or it leaks like a sieve; and you have tons of kindling nailed on your roof waiting for a spark.  The single huge advantage was no other common useable system existed.

[Some people also split rocks to make slate roofs, which are comparably laborsome to shakes but far superior, because they are fireproof . . . and during earthquakes become gratis tombstones.]

Now that far superior roofing materials are available, it is absurd to use shakes.  It's still done because people like how they look and architects still specify them.  We also have the further absurdity of compositon roofing, which is MUCH better than shakes, chopped up into little "three-tab shingle" hunks slashed with grooves to let in water and make it LOOK like shingles or shakes.  You need multiple layers so the grooves don't leak, and the tabs still break off.

Along with rethinking framing, we need to rethink roofing.

FLAT ROOFS:

Since SUBS is naturally oriented to right angles, the easiest roof to build is perfectly flat.  "Every ceiling is a roof."   Aside from being good pigeon toilets, most roofs are a total waste of space.   A flat roof you live on or otherwise use is an "extra" floor at little or no extra cost.  On a one story house that Doubles your square footage and Halves your cost per foot.

A flat roof can be treated in several ways.

The easiest is simply to cover it with EDPM, torch down rubber roofing, or other continuous membrane.  Flat roofs are a guaranteed-to-leak nightmare with traditional small piece multiple layer roofing materials, but a perfectly viable option with the very durable continuous membrane materials now available.

For sun belt applications, frame a 2x4 flat around the edge of the roof, lay your membrane, and fill with water, creating a 1.5" deep roof pond.  [Thank you, Nick Pine.]  Many mini-trickle leaks onto sun heated walls would cool them too.  You could probably throw away your air conditioner and have fire protection too.

If you want, build a roof top swimming pool or fish pond.
Don't shed water; catch it, keep it, and use it!

You could also pour a lightweight concrete roof pad.   If you want runoff on one side, start 1/4" thick and run 1/8" per foot to make a small slope.  A 20' span would be 2.75" thick on the high side, or less than 1.5'' average thickness.  A gutter on the runoff side or a slope into one corner would allow easy water collection.  This would create a durable fireproof waterproof dance floor.  Proper SUBS panels can easily support concrete, band and dancers.

RIGHT ANGLE PEAK, DOUBLE PITCHED ROOFS

Pitched roofs are desirable for many applications, and customary for heavy snow loads.  SUBS will do them also.

In a stick-built house, the most complex framing is usually the roof.  If you have many chopped up roof surfaces meeting in hips, valleys, dormers and so forth, the geometry quickly gets abysmally complex.   You wind up with every stick a different length, difficult compound angles on every board, cheek cuts, bird's mouth notches with vee cuts [?how DO they cut those things?], complex framing tables, large piles of scrap material, and other carpenter's nightmares.

If you want rube goldberg gothic gimcrack roof surfaces, it's complex to build no matter what your method, and it would take so much time to design "modular" panels you wouldn't save much, though it would vastly simplify removing and replacing the roof to add an extra story.  You could build a "modular" house and stick whatever "normal" roof you want on top [as loathsome as that would be].

On the other hand, if you are content with simple roof planes and vertical gable ends, SUBS works splendidly for pitched roofs.

The easiest roof to build with SUBS is a 12 in 12 pitch 45 degree angle, because two such pitches meeting at the peak make the normal right angle of the system.  Square connectors and metal flashing with a plenum for wires or fire sprinkler pipes would be the roof peak and also provide bolt-in anchoring for ladders, scaffolds, safety lines, equipment hoists and so forth.

The trick is to match the standard floor and roof panels with the proper floor dimensions so the roof geometry works without wierd panel lengths that don't conform to the universal geometry standard and are therefore useless for anything but one particular roof design.

The obvious basic lengths for floor and roof panels are 8', 10' and 12'.  Joined at the peak with 6" square connecters, they make equal right triangles with inside dimensions of 11.31', 14.14' and 16.97'.

An attic floor plane bolted to two roof planes makes an immensely strong triangular sheet truss covering the entire bulding: not widely spaced flimsy two dimensional trusses supporting roof sheets, but ONE ENORMOUS 3D TUBE TRUSS as long and wide as the building itself!

The question is how to bolt the three planes together into one unit.

8 FOOT ROOF PANELS

To demonstrate, take the basic 8' panel.   It spans 8' from floor-bearing wall to floor-bearing wall, allowing a room 8' x N'.   If we use two 8' roof panels for a right angle peak pitched roof, the attic floor hypotenuse of our triangular roof truss is 11.31'.  The gable walls sit on the floor-bearing wall connectors, and the roof span touches down on the OTHER two walls.

See the Alpine Cabinette elevation for a typical geometry.

The floors panels reach TO the floor-bearing walls but do not sit on them.  They are hung by bolts from the connector sides.   The rising Edges of the roof panels [which are oriented across, not parallel to, the floor panels] reach TO the gable walls, but do NOT sit on them.

Two 4' wide roof panels equal the 8' length of the floor panels, so that geometry is perfect.  The rising roof panel edges bolt to connectors on the gable walls.  The 6" wide gable wall top [the outer edge of the roof] is covered by sheet metal flashing resting on standard square ring connectors.   The roof covering is simply laid over the metal flashing like the rest of the roof deck.

To avoid having bolt heads poking up through the roof surface, install the top flashing First but don't bolt it down.  Then bolt the side [fascia] flashing in place with the 2" leg lapping OVER the top flashing.   [Normally, you would expect to put the fascia flashing on first and then the top piece overlapping it for drip control, but the roof surface covers both flashings and they won't leak.]  This allows you to remove the side flashing for pipe or wire maintenance without removing the top flashing and the roof surface.

8' long floor panels with 8' long roof panels dictate an 8'x10' floor area.  To make this, use one 2'x8' panel in each floor, ceiling and long wall surface of the room.  [Two 4'x8' panels plus one 2'x8' panel equals one 8'x10' floor or wall surface.]

The roof Ends touch down ON TOP of the connectors on the two roof-bearing walls [the Other two walls relative to the two floor-bearing walls].  The 10' floor length plus two 6" thick walls means the inside corners of the roof arch must span 11'.

Conveniently, the attic floor hypotenuse is 11.31', which means we have .31' or 3.72" extra width in our roof arch.  This gives a soffit gap of 1.86" [about 1 7/8"] between the outside edge of the wall top and the inside corner edge of the roof panel.  This can be screened and left open for ventilation, or blocked with 2" PVC pipe lengths.  The 6' square plenum can be insulated or not to suit.

The roof panel ends are connected to the roof-bearing walls with roof connectors made from 6"x12" steel plate 1/4" thick, with one 45 degree bend and two 1/2" holes.  They bolt on top of the square connectors on the roof-bearing walls, and to the outboard end of the roof panels, which become outward leaning fascia boards.

The same bolts which fasten the outer end of the connecters to the roof panel fascia can also hold gutters.  It is simple to file notches 1/4" deep and 6" wide in the lower corner edges of the roof panels to accomodate the roof connectors without distorting the geometry.

The roof connectors cantilever the roof panel ends out about two inches past the supporting wall.  The weight of the panel tries to bend the connector down.  If it were flexible, it would bend down at 45 degrees, dropping the roof edge about 1.4" [minus the 1/4" thickness of the roof connector] and resting the panel joist on the connector.  A 4'x8' roof panel weighs under 200 pounds with typical roofing material and there are two supporting connectors, so you have a dead load of around 100 pounds per connector.  The 6" wide 1/4" thick steel plate is overbuilt for 100 pounds across a 2" span.  It would take quite a lot of live load to bend it.

The triangular geometry of the tubular truss roof is not as "perfect" as the right angle geometry of the walls and floors, but by choosing the proper standard panel and floor sizes we can make it close enough to be completely workable.  The "imperfect" gaps are easily converted into useful soffit ventilation or sealed up as desired.

Each roof panel length requires slightly different placement of the bend and holes in the connector because the soffit gap varies, but they can all be made from the same 6" x 12" piece of 1/4" plate using a heavy vise, a small sledge hammer, and a drill press.

If the lower roof edge tries to sag in the middle [the gables support it at the ends] with longer roof panels or heavy snow loads, you simply trade up to a thicker and more rigid connector.

This example uses 8' roof panels and 8' floor panels for an 8'x10' room.  We could also build a 12'x10' room using 12' floor panels and 8' roof panels.  The roof would simply be three panel widths long instead of two.  The triangular geometry and the soffit gap would be exactly the same.

10 FOOT ROOF PANELS

With 10' roof panels, the attic truss span is 14.14'.  This means the floor will be 13' feet wide [remember the two 6" thick walls] so we need to insert one 1' wide panel in each wall, floor and long wall surface.  The roof arch is .14' beyond the floor+wall span, giving smaller soffit gaps of .84" (about 7/8").

The easiest room sizes to build with 10' roof panels are 8'x13' and 12'x13' because they are two and three 4' wide roof panels long, but you can build 13'xN' floors by adding narrow roof panels to suit.

12 FOOT ROOF PANELS

If we go to 12' roof panels things get VERY easy because the attic floor span becomes 16.97'.  Subtracting the 1' for the two walls, you get 15.97', an error of only .015" on each side.  This means you can build an 8'x16' or 12'x16' peak roof room using ONLY 4' wide panels.  You can bend the roof connector right in half and drill the bolt holes dead center in each face and it will bolt right up.  This eliminates the soffit gap, so for ventilation just replace some of the metal fascia flashing with screen and have as much air as you want.

See the Alpine Cabinette elevation geometry.

Gable end walls require special panels to match the roof line.  For 8' roof panels these are simple triangles cut from 4'x8' ply. For 10' or 12' roof panels you can either cut truncated rectangles or stack triangles on rectangles.  Since there is very little load on the gable walls, it probably doesn't make much difference.  The gable panels can have windows for attic light and ventilation.

If you want to use the fully floored attic for a room, 8', 10' and 12' roof panels provide peak headrooms of 5.67', 7.09' and 8.51' respectively.  A hatch panel in the floor provides access.

OTHER ROOF DESIGNS

Other roof peak angles than 90 degrees can be used.  A 6" equilateral triangular connector at the peak would give you 120 degrees between the two roofs sections, or a lower roof pitch of 30 degrees.  I don't know if 6" triangular tubing is a standard industrial commoditiy, but it could certainly be made cheaply in large enough quantities.

Square tubing posts at the corners and edges of a flat roof deck could support a flat or pitched "flying" roof deck that could overhang the building as much as desired.

Universal geometry dormer systems to bolt into flat roof planes could be designed.

Much longer roof panels could also be built.   There is so much you can do with the monolithic shorter ones I haven't bothered to think through the geometry for larger spans.

I have hardly started to explore the subject of SUBS roofing.  I have simply worked through a few very basic examples to show the amazing versatility and some of the vast system possibilities.

Bill Dur <billdur@net-prophet.net>

modular.systems * Simple Universal Building System * "Superior By Design"