want to make exposed trusses from hardwood. Need advice.

[lakeman]

Morning Forum,

Just found this site and joined straight away! From the quick scan through so far this looks to be a gold mine of building information for the owner/builder.

I want to make trusses (rafters?) for the small cottage i am building.

The building is 14m long x 5m wide divided in the middle into 2 separate rooms, each with their own doorways to get into the room from outside.

I would like to build exposed trusses from the nice Rosewood hardwood we have locally. The problem is the longest length of timber i can get is 3m. I need to span at least 6m. That would be to allow 5m for the room itself plus at least a short overhang.

What style of rafter would i have to use to be able to do this? I am presuming i will have to join sections together to do this (somehow).

Any advice? Any urls i can go to to look at examples?

With thanks.

lakeman

[Don_P]

If you put a conventional gable roof on it with a ridge down the center and locate the top of the ridge about .5m above the wall top it would use about 2.5m of your 3m rafter leaving the rest for end trimming and overhang. So at a low slope there should be enough rafter for that to work. To get ties across the bottom with that length material it would take 4 pieces at each rafter pair to make it look good. Can you get something else that comes in a 5m length?

[nailit69]

Check out YouTube for "Traditional Japanese timber frame builders"... some of these guys are making 40' beams and trusses out of 8' timbers... amazing work.

[UK4X4]

Truss wise you can make larger spanning distances out of smaller pieces, but then you need engineered plates to join it all together.

Think along the lines of mechano. and their short pieces and all the triangular gusset plates.



If you have snow loads to contend with , why not do standard scissor trusses for the structural and simply build some non load supporting trusses to visually see below

[lakeman]

Can you get something else that comes in a 5m length?

No unfortunately not. It would make life much easier if i could but its almost impossible. The size cants coming out of the forests these days are much smaller then in days gone by. I went out to the forestry area the other day to take a look at what size lengths the timber companies are using right now and the longest i saw was 3.2m. But there were not that many 3.2m lengths - mostly 3m and down.

So to make sure i can actually make something from plans i get drawn up (when i figure out how to do this) i decided i should work with 3m lengths - just to be on the safe side.

The wood in question;

From: The Wood Explorer:
Common Name(s): African Rosewood
Scientific Name: Guibourtia coleosperma
Distribution: Central and southern Africa

I am in South Central Africa in a remote area, so its not easy going. Skilled workers very hard to almost impossible to find, so its going to have to be me. Yikes!

http://blog.cifor.org/24491/chinese-timber-companies-in-zambia-few-jobs-but-more-outlets-for-local-loggers#.VW6G3c-qqko

http://thewoodendimensions.blogspot.com/2012/03/know-your-wood-african-rosewood.html

[lakeman]

Check out YouTube for "Traditional Japanese timber frame builders"... some of these guys are making 40' beams and trusses out of 8' timbers... amazing work.

Thanks - will check it out.

[lakeman]

Truss wise you can make larger spanning distances out of smaller pieces, but then you need engineered plates to join it all together.

Yes - this is what i was thinking - but was not sure if it could be done and if it could, what to call it technically - you can tell i am not a builder !

I think this is my answer. Because then i can just buy the timber in the dimensions i want - get the timber milled to the correct dims and smooth finish and build it all onsite. Thinking something like 6"x 2" - or maybe 6" x 3" ? - but this is HEAVY as its solid hardwood. I was thinking about changing my building plans i have so far which has one ring beam around the top of the brickwork to having a ring beam run around the building above the window/door height and then another ring beam on the top layer of brickwork for the trusses to sot on. There would be about 7 or 8 courses of brick between the bottom ring beam and the top ring beam.

Thinking 2 ring beams made of 1:2:3 concrete and rebar will add the strength to carry the weight of these trusses (rafters) and generally stiffen everything up.

Would these be a plate that goes on each side of the beams and use bolts to connect them? or would it be possible to have some sort of U channel bracket made up for the joined pieces to sit in + bolts ?

I want it to look visually attractive. I would want to have the plates - how ever they get done - plated in either brass or copper and use the alternate metal to plate the bolts for contrast. Ie, Brass plates/Copper plated bolts or Copper plated plates and Brass plated bolts. Should look nice with the nice reddish colour of the Rosewood.

Grand aspirations eh ? I also want stained glass windows but i've never done stained glass before and being in the middle of Africa its not going tobe easy to find someone who can do them. Might have to offer working holidays to those who can.

[lakeman]

If you have snow loads to contend with

I am in the rift valley - no snow. Actually its winter here now and day time temps hit 35 degrees Celsius and night time temps are 26 degrees celsius. My biggest problem is staying cool !

[UK4X4]

Rift valley, thinking Kenya rather than further north, hot dry and wet seasons, not a code in sight !

Most buildings I saw during my last trip into that area used tin roofs and either light weight metal or wooden poles rather than milled timbers for the roof spans.


Making solid wood trusses out of short lengths will be a fun project, what were you thinking for roof materials
as this would majorly effect the weights involved.

Were you thinking inner planked woods and tin outside ?

I'm guessing you'd want more like a timber frame truss seperated by about 2 - 3 meters outside the planked seen roof lining a bunch of horizontals to hold the tin down.

Splices on the short lengths are best over a support location with a staggered joint

[Don_P]

The 3m length works for the rafter, or top chord, of the truss. The 5m long bottom chord is actually a tension member, it restrains the rafter bottoms from spreading, it can be a steel rod, a cable or chain.

A kingpost is also a tension member, it is essentially a rope or chain thrown over the peak and dangling down to help support the bottom chord.


I couldn't saw the bottom chord of these trusses in one piece so I interrupted them at the kingpost and passed a spline through the king and tied each side to that spline.


A schematic of that truss during design.

[lakeman]

Rift valley, thinking Kenya rather than further north, hot dry and wet seasons, not a code in sight !

Making solid wood trusses out of short lengths will be a fun project, what were you thinking for roof materials
as this would majorly effect the weights involved.

Were you thinking inner planked woods and tin outside ?

I'm guessing you'd want more like a timber frame truss seperated by about 2 - 3 meters outside the planked seen roof lining a bunch of horizontals to old the tin down

Actually down South in Zambia on the lake. Hmmm codes..... sorta. Things are changing and i do need approved plans stamped etc. But not terribly strict in any real sense - not like i'd find at home!

[lakeman]

Making solid wood trusses out of short lengths will be a fun project, what were you thinking for roof materials
as this would majorly effect the weights involved.

Were you thinking inner planked woods and tin outside ?

Hmm fun? Well i guess, sorta. I can turn my hand to a lot of things but becoming a chippy is not one of them ( you are from UK right? So you know what a chippy is, not sure what they call a carpenter in the states)

The join in that photo looks real nice. Not sure where i could get that done here, but the photo really helps as i can show various people to see if i can track down someone who could do that.

For roofing i would like terracotta tiles. If that becomes too hard to organize i will fall back to IBR color bond roof sheets.

[lakeman]

Hey Don,

You must be a master at this !

This is getting way over my head. So i could use some sort of decorative wrought iron rod for the bottom chord? Hmmmm......

Ideally i would like to go longer then the 3m for the top chords. I would like a decent overhang outside the brick work as it really really rains here. So some sort of joint would be sooooo nice. The joints in your picture look real nice.

How hard is it to do those joints? For a chippy i guess its nothing, but for a novice i'm guessing it wont look nice.

I like the idea of joining members with plates. As mentioned i think the plates, plated with some sort of metal (Copper, Brass, Chrome, Pewter etc) could look nice...ok i dont think i would go for chrome, but you get the idea.

Any photos of nice plate work ?

Thanks

LM

[Don_P]

I guess chalk up another one for the wonders of the internet, I learned what a chippy was when they showed up on construction forums.

Yes, a wrought iron tie would be appropriate... early iron truss bridges used cast iron for compression members and wrought iron for tension members. Modern commercial heavy timber construction often uses cable or rods for tension members.

I had a pic, was looking at it awhile ago and can't find it at the moment, it was clunky large solid plates but did the job. Go to the architectural products group at strongtie.com to see one manufacturers products.

scroll down to these folks free standards downloads, they do get into plate and bolt layout and design a little;
http://www.aitc-glulam.org/Shopcart/index.asp

The connections calculator at awc.org has bolt capacities, I believe they included the tables for various steel side plates as well.

One way to do the overhangs is to build a braced corbel with the roof angle on the top, bolted to the wall.

Can you sketch what you are proposing? My brain is old, ornery and hardwired for feet and inches, if you can convert back and forth faster than me please do so.

[lakeman]

yes the wonders of the Internet...... like finding this wonderful site.

Thanks for the links. I will take a look.

Braced corbel sounds like a solution if the lengths don't work out.

Yes converting..... i get lost in the feet and inches. I really struggle with what 5/8ths is for example.

When you say sketch what i am proposing, do you mean the trusses or the building overall? I am not sure what i am proposing so far. All i know is i decided (after having the original plans done - which are really simple anyway, so no big problem to change the roof now) that exposed trusses would look nice. Its only for aesthetics, but then i guess in 95% of cases exposed trusses are only for looks, right?

I've got a stack of photos on my phone of what i have done so far, but cant find my cable to connect the phone to the laptop. As soon as i do i'll get some photos up.

[lakeman]

Don,

Strongtie.com ...... that was THE place i was looking for.

Thank you so much

LM