As an aside, a few years ago I designed and built two massive trussed beams to fit into an existing trussed roof space in a roof extension for Denise’s brother. They were 32 feet 6” long and 6 feet 6” high, with the upper and lower chords in twinned 2” x 9”s, linked with 5 sets of doubled 2 x 4 struts at 45° set out in 'X' patterns with vertical end and mid ties. No timber was longer than about 10 foot; I jointed the chords too with bolted cheek plates. Joints were with M12mm stainless studding and 60mm diameter spiked timber connectors at every joint, timber to timber, with ¼” thick square plates under the nuts.
Each assembly was 12” minimum thick, 6 timbers meeting at every joint, 3 studs per joint. The timber was 'SS' grade air-dry Douglas fir. I built them on my shop floor, marked each member in best medieaval carpenters method, then dissassembled them for shipping to Maidenhead. On site, we pulled the whole lot up in pieces through the loft hatch- my sister in law is so house-proud we were banned from bashing any holes in the structure!
The beams were assembled along the roof as the extension ‘walls’; we painstakingly wound up an endless stream of long studs with an air wrench normally used to take truck wheels off, taking it in turns to be the sap crammed into the eaves space with the ring spanner. At the end walls the shear loads were transferred to the existing masonry by oak plates set on concrete beams cast into the inner leaves. When in place, after 2 weeks of solid graft, sustained with several hundred mugs of builders’ tea and endless bacon sarnies, we wedged them up to the existing truss upper chords with oak sprags and wedges. Then, with the original trusses ‘unloaded’, we began to saw out the original ties and struts with a sawzall! As each one parted, the roof settled about 1/8” with a groan, quite unnerving! Once they were supporting the roof, we nailed collars at 8 ft head height as ceiling members and fitted floor joists on hangers on the bottom chords, leaving the ceiling below independantly hung to avoid cracking the plasterwork, then cut in the stairwell. I made a bespoke staircase with Pirana pine, a timber I have never used since, as it stinks to high heaven! The upper chords of the original trusses now became the common rafters.
Result: A room, in a trussed roof structure, the full length of the house and about 13 feet wide.
The stressing out took me weeks- not least because the local Building Control Department had to hire in a structural engineer in to check my calculations, as no one on their staff knew how to do the math. Not surprising, the last folks to use 'Wilson’s Method' probably built pole bridges for American Railroads! And check it he did, fair play, we went through every sum, every theory, every line of the calculations in detail, the moment, force and shear diagrams, the specifications of the studs, the connectors Standards, the lot, over 5 days in the Windsor B.C. office. No fee and free tea!
And of course it was vital to get it right - the trussed beams support a huge tiled roof and all the floor loads below.
Several times he expressed the notion that steel I beams would have been easier: True, but then he didn’t know my sister in law, did he?! [ Actually we just couldn’t get RSJs in- the houses each side were too close for a crane.]
Alan
![[Linked Image]](https://www.electrical-contractor.net/ubb/smile.gif)
