Construction of exterior raised tie truss in larch

[Halo Jones]

Hi All,

I am building our shed/workshop at the minute and plan on having a little porch area on the side that faces the house. I am going to make an external end truss out of 100x100 heartwood larch (can't afford oak ) As the eave height is only ~1.9m I want to make a raised truss. Looking at green oak construction techniques it seems that people use either pegged mortice or pegged lap joints for raised trusses but I haven't found anywhere to explain which is best. The truss is going to be largely decorative and will not carry much weight so I'm not too concerned about it not supporting the roof. I just wondered what would look best / be least likely to warp or cause problems.

Thanks for reading,

Halo

 

[Dibs-h]

I don't think 4"x4" is going to look right - I'd be tempted with 6"x4".

When you say a raised truss - do you mean one where the "collar" or bottom chord is not at the bottom but higher up. Like the letter "A"?

Cheers

Dibs

 

[Halo Jones]

Hi Dibs,

Hopefully I have uploaded a (bad) sketch-up image showing an unfinished skeleton of what the shed will look like, obviously missing the roof and internal trusses.

It is the end truss that I am trying to work out the best construction methods for.

I had been tempted to do 6x2 but 6x4 seem a little overkill and may look way too chunky.

Thanks for looking,

Halo

 

[Dibs-h]

What's the distance from the door to the outer edge of the porch and what's the roof covering?

Cheers

Dibs

 

[Halo Jones]

The overal dimenson of the shed plus porch is 12 x 18 feet.

There will be about 4 feet from the door to the outer edge of the porch. The roof covering will be felt tiles.

I am actually just modifying a wooden garage that we bought second hand, putting it on a decent base and tarting it up a bit as SWMBO is keen on her garden and wants to see something a little nicer than bog standard wooden garage staring at her when doing her gardening.

Cheers,

Halo

 

[Dibs-h]

The overal dimenson of the shed plus porch is 12 x 18 feet.

There will be about 4 feet from the door to the outer edge of the porch. The roof covering will be felt tiles.

I am actually just modifying a wooden garage that we bought second hand, putting it on a decent base and tarting it up a bit as SWMBO is keen on her garden and wants to see something a little nicer than bog standard wooden garage staring at her when doing her gardening.

Cheers,

Halo

Halo

Sorry for not replying earlier. If the end truss is 4' from the door - is there a truss (or 2) between the 2? A 4' gap between trusses seems on the large side.

Cheers

Dibs

 

[Halo Jones]

Hi Dibs,

The original garage was 18' long. There are four roof sections split into 9' sections with 5 or 6 purlins on each side of the apex. Overall there were only 3 internal trusses. Each roof section was sitting on one gable end an internal truss and then sharing the central truss with the other roof section (the central truss is double thickness). That means the tursses in the original garage design were every 4.5'. If this is unclear I will endevour to finish the sketch-up!

As far as I can tell a purlin type construction uses less trusses. I'm not too concerned as I don't suppose a company would want to release an unsafe design, plus I was planning on putting in another couple of internal trusses in anyway.

Thanks for you concern about the overall construction but my main worry (apart from the gales blowing outside) was getting the aesthetics of the visible external truss correct.

Cheers,

Halo

 

[Dibs-h]

Hi Dibs,

The original garage was 18' long. There are four roof sections split into 9' sections with 5 or 6 purlins on each side of the apex. Overall there were only 3 internal trusses. Each roof section was sitting on one gable end an internal truss and then sharing the central truss with the other roof section (the central truss is double thickness). That means the tursses in the original garage design were every 4.5'. If this is unclear I will endevour to finish the sketch-up!

As far as I can tell a purlin type construction uses less trusses. I'm not too concerned as I don't suppose a company would want to release an unsafe design, plus I was planning on putting in another couple of internal trusses in anyway.

Thanks for you concern about the overall construction but my main worry (apart from the gales blowing outside) was getting the aesthetics of the visible external truss correct.

Cheers,

Halo

Hi Halo

The reason for asking about truss spacing was to get an idea of its likely loads and therefore get a ballpark idea for the dimensions and the type of joints that would work.

From what you are saying - with only 3 trusses and purlins, these are effectively Principal Rafters

"Principal Rafter - Generally, an inclined timber in a roof truss. May support purlin(s)"

in which the the construction is generally beefier than those cases where the trusses carry the roof directly as opposed to via purlins, and are at spacings more equitable to "normal" rafters - i.e. 16" or so centres.

Most of the Raised Collar (Tie) trusses that I have seen - and I've seen perhaps way to many during my research when designing mine - all have reinforcement below the rafter-tie joint. A picture make it easier,

http://www.oakmasters.co.uk/gallery/images/12310 couldn't link this image directly.

You could leave the main building as it is and then have the external visible truss, but would require at least 1 if not 2 intermediate trusses - with the roof on them in the traditional manner as opposed to using purlins. You could get away with 2" thick timber. But this puts the final (and intermediate) trusses on show.

This might give you a better understanding regarding the joints\types\location of them,

http://www.carpentersfellowship.co.uk/f ... p/t87.html

HIH

Dibs

 

[Halo Jones]

Hi Dibs,

Thanks for all the advice. I can see that truss design is way more involved than I appreciated when you want to use traditional joinery techniques. And, according to the last link you gave, it gets way more complicated if you want to use a raised tie!!

I clearly need to do a bit more reading, what books/articles can you recommend for truss design? I would be especially those using traditional designs?

Thanks again,

Halo

 

[Dibs-h]

Hi Dibs,

Thanks for all the advice. I can see that truss design is way more involved than I appreciated when you want to use traditional joinery techniques. And, according to the last link you gave, it gets way more complicated if you want to use a raised tie!!

I clearly need to do a bit more reading, what books/articles can you recommend for truss design? I would be especially those using traditional designs?

Thanks again,

Halo

Hi Halo

ChestofBooks is awesome, might be a start - http://chestofbooks.com/architecture/Co ... Beams.html

Tredgold's work is quite informative - http://chestofbooks.com/architecture/Bu ... tling.html

Also my thread might be useful - Simon was very helpful with my trusses and referred to a few good books, https://www.ukworkshop.co.uk/forums/trus ... 52-15.html 3rd post from the end.

Another option might be to fake it - use bolts and stuff and then plug them?

It does get rather complicated when you want traditional joinery. One thing I would point out - I had a tame Structural Engineer run my designs thru this software to ensure they were up to the job.

HIH

Dibs

p.s. Google is good - an image search I mean. Visually seeing how others have put them together gives you a good understanding after you've seen a few hundred truss images.

 

[Halo Jones]

Thanks for the homework. I had seen your workshop epic (which looks amazing and means my "bothy" will never see light of day on this site!) but had missed the truss thread.

If done properly I really like the mix of wooden beams and steel but I just thought it would be nice to try something more traditional. Given all the different joints that can be used I think some people might get quite addicted to trying them all.

Assuming nothing collapses on top of me I'll let you know how I get on!

Halo