Will's books

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Sunday, September 29, 2013

Two stories out of one and a half

“Old Chinese Proverb:  Man who say it cannot be done should not interrupt man doing it.”

Back in 2004, a very small, isolated hunting lodge in Western Alaska needed more bed space.  They had a single story 13’ x 17’ bunk house that had a pair of up/down army style bunk beds along the back windowless side wall but could only fit a single up/down bunk bed on the opposing wall since a large 5' picture window and the swing of the entrance door took up the remaining space.  That made for a total of 6 available beds.  There was just one other window and it was located to the side of the entrance door on the near end wall.  The building had 8’ tall walls and the roof was an 18/12 pitch Gambrel roof (barn styled).
They had asked me to enlarge the size of the building in some manner so it would fit an additional 4 beds.  More importantly, they wanted it done in less than two weeks, and “don’t spend much money”.  I would also have to go and get all the material myself.  Luckily there was a good lumber/hardware store not far away.   If you know me, I enjoy challenges so I took the job.  I realized that it would require some very long days to finish within their time-frame but it was mid-summer in Alaska and the days were almost all daylight.  Little did I know then, but I would be required to put in a few 20 hr. days just to get everything done in time.  I would be working solo but my wife would be around if I needed an occasional extra hand.   She was tasked with the most important job of keeping us fed, etc., while I played around with the building amplification.

Studying the building’s construction, I found the lower walls were framed using 2x6s and the Gambrel end's attic walls were framed using 2x4s.  Throughout the interior, the walls and ceiling were covered using 3/8 rough sawn plywood and trimmed with 1x2s (plywood is easier to use in the bush than drywall).  The flat ceiling was framed using 2x6s and there was a single 24”x24”attic access located dead-center of the room.   This access opened to a dark storage area above where a few sheets of ½” plywood supported some boxes of odds and ends.  Inside the attic, I found that the Gambrel’s lesser pitched center roof section measured 67” above the CJs and was about 42” wide before turning sharply downwards on each side.  The rafter bays were stuffed full of insulation and covered with a plastic vapor barrier. 
After some brainstorming, I decided that the best plan would be to convert the small attic space into a second story.  Since it would take too much time/$ to raise the roof, I would need to use the attic space as it was without perforating the roof in any manner.   If you can’t raise the roof - was there a possibility of lowering the attic's floor?  But how to do this without it becoming a headroom problem in the lower floor level was the question.  It would require some real Alaskan “out-of-the-box” ingenuity.   Although no building inspector would ever see this project, I still like to keep everything as close to the uniform building code as possible.  Most of the UBC design regulations were forged over time based on practical common sense experience.  So 7’ min interior ceiling heights is what I would shoot for on both floor levels.  That would be tough to accomplish since the total distance from the first floor’s ground level to the bottom of the center roof section in the attic was just barely over 14’.  I would need to frame a structural floor in the middle of that 14’ that was only an inch thick. 
Another issue was that since the existing first floor interior had no space available to locate a stairwell, I would need to access this new "second story” via the outside of the building.  The bunk house was resting on railroad-tie style blocks that floated on the earth.  There was no formal foundation in the sense that most people are familiar with.  Each spring the building was re-leveled after the frost heaving of the winter had subsided.  It was a common practice to deal with the permafrost problem of the Alaska interior by setting smaller buildings, trailers, etc.directly on the ground versus digging/placing a concrete foundation.  Considering that the whole building was just floating I decided to build the staircase so it had no connection to the ground and was just hung off the side of the building.  That way they both could float around together and the frost heaving would not destroy the staircase.

Cross-section view of the dropped hallway
So how did I do all this?  I framed in a dropped, 36” wide hallway down the length of building in the attic floor (aka: first floor ceiling).  This hallway was centered under the lesser pitched Gambrel roof center section.   By just lowering the center of the floor space where all the upstairs foot travel would be, the downstairs ceiling to each side of this walkway would remained unchanged at 8’ and allow plenty of headroom for the top bunk beds downstairs.  After the center section of the CJs was removed for the walkway, the top surface of the tail joists remaining on each side would be sheathed with plywood and became the bunk beds for this "second story".  The 16" hallway drop together with a 3-4" foam mattress was the perfect height to access a normal bed. No need for a bed frame or anything. Just sit right down, spin and lay down.  Worked out well.
Before cutting the 36” swath down the center of the CJs for the walkway, I opened up the two lower floor end walls and installed 4x6 posts that would support a pair of doubled 2x12s positioned below the CJs. Not only would they carry the cut ends of the CJs above but they would also form the sides of the dropped hallway.  As such they were to be spaced 36” in-between and centered down the length of the room.  One of these walls had a window located where I needed to place one of the 4x6 posts so I strengthened the existing window header to carry the new additional load by stacking a second header above the first.  I wouldn’t be wasting time tearing out and reframing stuff if it could be avoided.   I made it work out so that the doubled 2x12 floor beam would sit right on this new header.  I would have to build these two built up 2x12 beams in place due to their weight.
3D view of the upstairs hallway and horizontal building truss
Accurate snap-lines on the first floor ceiling were used to cut a 36” wide swath in the ceiling plywood.  Once that swath of plywood was removed those bottom edge snap-lines were transferred to the top edge of the CJs to serve as cut-lines from above.   I located the outside 2x12s from each of the built up beams in place and then temporarily braced them vertically to the floor at several locations.  Before the inside 2x12 was installed, the 36”center portion of the CJs was cut and removed from above.  By only installing the outside 2x12s before cutting the CJs, there was ample space to run a Skilsaw down unhindered from above.  After installing the inside 2x12, I added another 2x12 (that makes 3 now at each side of the opening) as a rim joist to the ends of the remaining 2x6 tail joists.  These two boards were held 3” above the top edge of the CJs to serve as a foam mattress retainer while the extra 3” below the tail joist overlapped and fastened to the doubled 2x12 floor beam.  The top surface of the CJs was sheathed with 5/8“ plywood and nailed off following a typical shear wall nailing schedule.  Not only would this plywood serve as the upper floor's bunk bed surface but it also created a 4’ horizontal truss on each side of the building.  These two trusses would counter the spreading force across the building span that was lost when the CJs had been cut.  To the underside of the floor beams I screwed up 1.125” thick plywood spanning from one side to the other.  3” long screws were spaced at 3”OC staggering between the inside and outside 2x12s of the floor beam.  Now I had my 1” thick floor in place and it was killer strong.                                                                                                                    
No more attic

Framing in the "second story" doorway


Next, I cut an upstairs entrance doorway into the Gambrel end wall at the near end of the hallway and installed a windowed door.   I followed that up by installing an operable window into the Gambrel end wall at the far end of the hallway.  Now we had light and ventilation.  I had other things to do in order to finish up the second floor interior but they could wait until after I had the stairs up.  With the stairs up I could move up/down much faster. 

Starting in on the stairway phase of the project, I found that whoever had built the original bunk house had cantilevered framed the floor joists at the lower level door landing.  This made this landing free-standing and it floated around with the rest of the house.  I planned to start the stairs at the lower floor’s entrance landing, climb them towards an intermediate landing at far end of the wall, turn 180 degrees and climb a few more steps to reach the landing outside at the upstairs door.  To keep the stair load as close to the wall as possible I choose a stair width of only 24”.  Since the width of the stairway dictated the width of the upper stair landing it was 24" but there was space to squeak in another 6” of width at the intermediate landing so it would be 30” wide.

The staircase was narrow and undersized by UBC standards but when finished it was surprisingly comfortable and more than adequate.  I had been up some 4’ diameter circular stairs before and they felt extremely cramped but that was mostly due to a steep riser/ tiny tread size, and that one’s shoulders were boxed in by the center vertical tube post.  Here the tread and riser size was close to the favored 7” and 11” measurements, and there was no confining restriction at shoulder height.  Those two details made all the difference in the world.   Using 24” as the stair width made the staircase assembly’s overall dimension from the wall about 55” including the handrail.  On paper I worked out the rise/run, platform heights, etc., and starting formulating a construction method capable of transferring the staircase load to the wall.  I laid out the staircase and landings on the exterior wall's surface to serve as a visual guide.  The lower level landing length ended up about 12" short of the total staircase width of 55" so I scabbed some longer joists to the existing ones and installed a few more pieces of 2x6 decking to bring it out.  An easy fix.

I remembered that on many big Tutor style homes in CA, we had sometimes attached exposed false plate beam assemblies at the outside corners of the Gable ends to carry the lower end of a beam fascia.  These assemblies were preassembled on the ground and consisted of a horizontal piece (the false plate beam) sitting upon and connected to the end of a somewhat longer vertical post piece (as in an upside down “L”), and having a 45 degree angle brace fitted between these two.  To install the assembly, the vertical member of the assembly was then lagged or thru bolted to the building corner.   I figured to apply this same methodology to support the staircase.  I would use 3 separate large angle braced 4x4 moment frames (for lack of a better name to call them) as my structural supports.  They would be attached to the wall using 5/8” thru bolts and thick washers.

"moment frames" supported the staircase
The first moment frame was preassembled on the ground and bolted thru the end wall to the 4x6 post used to carry one of the doubled 2x12 floor beams that was installed just to the right of the lower floor entry door.  It had both a top horizontal piece that would form one end of the upstairs landing and a bottom horizontal piece that would support the lower end of the stair stringers.  Both horizontal pieces had handrail posts attached via a notched connection to their ends.  

 The second moment frame was also preassembled on the ground and was bolted to the double king studs at the right side of the operable window (I doubled the existing single king stud in the wall to create a post).  It had a single horizontal piece that would form the near edge of the intermediate landing.  It had a handrail post connected to the end of the horizontal piece and a second handrail post connected in the middle that ran down to the angle brace for rigidity.

The third moment frame was the identical to the second unit except it lacked the middle post.  Being located at the building corner came with the added benefit that a metal strap could be run along the back side of the top horizontal member to overlap and nail to the rear wall.  Since the vertical members of the second and third moment frames did not run down to the bottom of the wall to butt against the interior wall’s bottom plate like the first moment frame did (I could have done that but didn't think of it until it was too late), I installed a 2x4 band at the lower end of the vertical piece to help dissipate the inward force evenly across a greater section of the wall length and serve as base unto where I rest the lower end of the moment frame while I worked to connect it to the wall.

While, the little hardware store lacked the fancier metal connectors, it none-the-less had some A35 clips, which I installed on the “in wall” framing members that supported the moment frames.   These clips would help the vertical wall framing members resist the pull/push shear forces caused by the weight of the staircase straining to yank them loose.  I ran the clips on each side of the posts (or doubled studs) at the top and bottom plate connections.  I also ran some MST straps and A35 clips from the posts to the doubled 2x12 floor beams thereby locking the moment frame's in-wall supporting members to the two building length horizontal trusses.  Remember these trusses were fabricated at the top of the side walls when the CJs forming the second story bunk bed surface was sheathed.   The weight of the stair assembly would have a tough time now distorting the outside building wall.

The staircase skeleton in place
Finished staircase (sans paint)

With the moment frames up in place and braced side-to-side to the end wall, I installed 2x12 stair stingers (for open style hung treads) from the lower horizontal arm of the first moment frame to the intermediate landing moment frame.  No stair angles were available so I used 2x2 cleats instead as the supports for the treads.  Because the downstairs window by the entrance door was located below the far end of the upper landing there was no way to install a wall mounted moment frame to carry that load so I chose to support it using a long handrail post that sprung from the lower left stair stringer.  With that post in place and everything well connected, I ran the short stringers from the intermediate landing to the upper landing.  Now I only had to run the 2x6 decking on the landings, install the 2x12 stair treads, and put up the handrail.  The landings were designed so that no joists were required, only the outline framing.  That helped keep the staircase weight to a min.

Landing at upper doorway
Upstairs all  finished (sans paint)

 Now we could finally see the light at the end of the tunnel but I still had to hustle to finish the finer details: I installed a few new breakers in the electric service panel and ran separate lighting and an outlet circuits upstairs; I installed 3/8” plywood paneling to the bottom of the upstairs rafters;  I trimmed out the rakes, the door, and the window.;  I framed up some gear lockers to define the 4 individual bunk bed spaces upstairs and while I was at it I built a few lockers for the downstairs as well.  Finally I gave everything a quick coat of paint and headed back to Anchor town (Anchorage for you foreigners) before the boys arrived.  It had been a tough challenge but through it all I had thoroughly enjoyed the adventure. 

Lower level of bunk house as seen with center hallway drop ceiling

Copyright 2014 by Will Holladay