Pre-Engineered Roof Truss or Built on Site Welded Steel - Can someone give me some advise.

[Longwood50]

I am building a bungalow home.  I have come across companies that do pre-engineered roof trusses.  They are slightly less expensive and supposedly go up much faster, and are stronger. 

However, I am a bit concerned since they obviously look at the architect plans and build to that spec.  If the home is actually slightly off, I worry the roof wont fit. 

Here is the checklist that the Truss company gave on the reason for all the advantages. 

Has anyone had experience with the pre-engineered truss roofs and can advise me as to whether they are a good or bad thing.  

I would save about 100,000 to 150,000 baht with the pre-enginnered but supposedly they go up in far less time, which is a huge advantage. 

[OneMoreFarang]

I have no direct experience with this. But in general, I would prefer pre-engineered roof trusses. 

I guess they are made somewhere is a factory where it's easy to work (not on a roof).

When the material arrives, you can inspect it and if necessary, complain before they install anything.

Compare that to work on the roof and you can only complain later if they did already bad work on your roof.

 

Just make sure you have clear conditions with that company like specification which allow i.e. x mm error and not more.

Maybe you know a welder who can judge the quality of the parts.

 

I would also insist that they measure themselves what they have to do for your roof.

Because if your measurement is wrong or maybe the roof is on one side 10mm longer than on the other side then that is not your problem if they do the measurement.

[McTavish]

Pre-engineered roof trusses are the way to go.  Old fashioned built-up heavy steel roof structures are ... old hat.  Pun intended.

 

SCG supplied our steel trusses, erected on site in a day.

[Longwood50]

3 hours ago, McTavish said:

SCG supplied our steel trusses, erected on site in a day

With SCG  were your trusses Galvanized Steel?  The quote we had was for galvanized and my understanding is that though it does not rust, it does not have the weight bearing.  

[McTavish]

13 hours ago, Longwood50 said:

With SCG  were your trusses Galvanized Steel?  The quote we had was for galvanized and my understanding is that though it does not rust, it does not have the weight bearing.  

Short answer, yes. 

It's not a hot-dipped galvanised steel product.  The steel is electroplated against rust and all cuts are treated with spray paint.

Trusses, by their design, carry the load which is evenly spread across the structure and are preferable to a built-up system IMO.  Built-up roofs employ 'king posts' to support a ridge beam to which everything is then welded.  One bad weld and the structure could fail under extreme weather loads (high wind) or an earthquake.

 

 

[brianthainess]

16 hours ago, Longwood50 said:

With SCG  were your trusses Galvanized Steel?  The quote we had was for galvanized and my understanding is that though it does not rust, it does not have the weight bearing.  

I strongly recommend painting them with silver oil based paint (it goes on like water) mine were welded on site, and the builder painted them at the time, curious I found out that it is the best for galv. as here in Thailand it is cold Galv. coated, starts to rust fairly quickly going by bits left over, after painting no rust came, that paint can also cover rust.

[McTavish]

9 minutes ago, brianthainess said:

I strongly recommend painting them with silver oil based paint (it goes on like water) mine were welded on site, and the builder painted them at the time, curious I found out that it is the best for galv. as here in Thailand it is cold Galv. coated, starts to rust fairly quickly going by bits left over, after painting no rust came, that paint can also cover rust.

You must be talking about a different system as SCG lightweight steel truss roofs do NOT require welding nor painting.

 

[freeworld]

21 hours ago, Longwood50 said:

I am building a bungalow home.  I have come across companies that do pre-engineered roof trusses.  They are slightly less expensive and supposedly go up much faster, and are stronger. 

However, I am a bit concerned since they obviously look at the architect plans and build to that spec.  If the home is actually slightly off, I worry the roof wont fit. 

Here is the checklist that the Truss company gave on the reason for all the advantages. 

Has anyone had experience with the pre-engineered truss roofs and can advise me as to whether they are a good or bad thing.  

I would save about 100,000 to 150,000 baht with the pre-enginnered but supposedly they go up in far less time, which is a huge advantage. 

Depends on how the trusses will be fixed and tied to the supporting structure.

[brianthainess]

13 minutes ago, McTavish said:

You must be talking about a different system as SCG lightweight steel truss roofs do NOT require welding nor painting.

 

I wasn't Talking about pre-made Trusts.

[Spamhead]

Yes. 

 

I think the word you're looking for is advice !

[DaLa]

Firstly , as a customer I would hazard a guess that the Roof Truss v Mild Steel ‘differences’ has been compiled by the Roof Truss company.

 

Now as a Metallurgist:

The comparison suggests that the anti corrosive paint applied to the MS is somehow inferior;

If the ‘factory-made, anti corrosive screws’ are a dissimilar material to the roof truss sections then corrosion will occur regardless.

Why not manufacture the built on site roof out of HT steel, if it’s that critical (which in my opinion Tensile Strength is not the overriding attribute). How will it be ‘undersized’ if it’s designed correctly.

Design can be equally effective if calculated manually with pre-existing structural formula.

Speed of erection is correct, now factor in production times ( and delays)

Checking quality of mechanical fixings also requires physical inspection.

Installation of the final roof cover is a separate operation and has it’s own unique quality standards

 

I built a store (warehouse) 20M x 15M 5 years ago fabricated on site, no need for a warranty, I’m confident it will still be functional and sound in 20 years time.

[Bruce Aussie Chiang Mai]

Engineered prefab roof trusses definitely best if installed correctly.

I was involved with timber Gang nail roof trusses in Australia. Best thing since sliced bread.

Order once uprights in place measurementscan be taken.  We use to measure on site for some customers, maybe they would do that here.

[mikecha]

How is your roof prefab frame going to be fixed to the Wall/concrete structure?

 

 

here is normal have concrete leg where the truss sits on a side ledge then a bolt put through to anker off 

 

if you have a drawing  of what you are building i would be happy to e mail you advise  

we built our roof structure here and welded onsite but one word of advise is go  look at the structure before delivery,

 

take someone with you who knows about structure welding and if there is stress bends from to hot welding dont Yake let them make again 

as anti rust here is a spray can is better to use Nippon paint Primer then top coat 3 times we did that 4 years ago no rust as yet .

 

if u want send me your e mail  via this site 

 

[Longwood50]

2 hours ago, brianthainess said:

I strongly recommend painting them with silver oil based paint (it goes on like water) mine were welded on site, and the builder painted them at the time, curious I found out that it is the best for galv. as here in Thailand it is cold Galv. coated, starts to rust fairly quickly going by bits left over, after painting no rust came, that paint can also cover rust.

The SCG system I looked at was Galvanized Steel.  It was bolted together.  The only welding was there were something called a stud beam.  This as I understand it was a beam attached to each pillar and welded.  Then the roof assembly is bolted to the stud beam.  The remainder of the roof truss assembly would be lifted into place and bolted together.  

[brianthainess]

1 minute ago, Longwood50 said:

The SCG system I looked at was Galvanized Steel.  It was bolted together.  The only welding was there were something called a stud beam.  This as I understand it was a beam attached to each pillar and welded.  Then the roof assembly is bolted to the stud beam.  The remainder of the roof truss assembly would be lifted into place and bolted together.  

I'd still paint it with oil based silver gloss.

[Kinok Farang]

Ask them to send a rep out to do the measuring.

Meet him on-site with your builder and agree everything.

[Longwood50]

5 minutes ago, Kinok Farang said:

Ask them to send a rep out to do the measuring.

Meet him on-site with your builder and agree everything.

Yes the rep said they would send a person out to do the actual measuring.  I raised the same issue with them saying that though we had an architect plan there was no guarantee that the actual construction was perfect to the plan. 

 

 

[Kinok Farang]

21 minutes ago, Longwood50 said:

Yes the rep said they would send a person out to do the actual measuring.  I raised the same issue with them saying that though we had an architect plan there was no guarantee that the actual construction was perfect to the plan. 

 

 

Might be a good idea for your builder to fix the metal wallplate before the roofing lads turn up.Should be a doddle then.

[jojothai]

If the prefab is cheaper then its best IMHO to do it that way.

do not worry about tolerance, however TIT, what should be within 25 mm may not be. So get them out to measure, should not make it difficult.

i have seen enough crap welding here thai style for the bars sticking out of the column then then welded to the steel connector beam for the rafters in the standard thai build ad you want system. Its horrific.

Welding to bars is bad engineerng practice. I am a chartered civil eesngineer.

The prefab people should know the better system and even if using bars to the support, they are bolting the trusses which is then much safer as the trusses are a fixed length so any horizontal stress at the joint is not a problem.

When i built my own house i designed, and fitted custom brackets to provide easy welding. got them fabricated by a steel shop. but thats not normal.

However you also have the problem witj thai build what size rafters the builder uses and how well they can weld.

The steel c channels used for rafters on the standard thai rafters are coded wrongly. They have inferior grade that is coded higher than its strength. Its a stupid system.

I ordered what should have been ok, then found they supply 3 grades  two outside the design standards. I weighed and found the problem. Got the supplier to change them. Paid the extra for " full size". Its not a con by the supplier. They charge for the weight and i paid the extra.

You may note that the stupid system can result in problems with roofs bowing.

For painting, galvanized parts are good for Durability, however any cuts should be touched up with the appropriate galvanising spray. easy to get.

For any steel welding to get the connector points fitted for the trusses, use an epoxy paint for long term protection. Pay the extra. Its not difficult to find appropriate epoxy paint and worth paying a bit more.

The builders need to grind/ buff the weld areas clean, its most important before painting.

 

 

[MangoKorat]

A lot depends on the abilities of your contractor.  They will of course, prefer that they construct the roof trusses.

 

A) It gives them extra work

B) They can construct them is such a way that any 'run out' or other small discrepancies can be 'ironed out.

 

Being pedantic, I'd go for pre-fab trusses. However, the trusses in my house (built by the previous owner) were constructed on site and painted with what looks like zinc rich primer.  The house is about 13 years old now and there's no sign of any rust.

[MangoKorat]

On 11/29/2023 at 6:01 AM, McTavish said:

You must be talking about a different system as SCG lightweight steel truss roofs do NOT require welding nor painting.

 

The SCG system in your photo looks very complex - I presume that's how they spread the weight without using heavy members?  Does it take up most of the roof space?

 

I'm asking because I am considering and SCG or similar system for my next house but I very much want to utilise the roof space.

[McTavish]

13 hours ago, MangoKorat said:

The SCG system in your photo looks very complex - I presume that's how they spread the weight without using heavy members?  Does it take up most of the roof space?

 

I'm asking because I am considering and SCG or similar system for my next house but I very much want to utilise the roof space.

Trusses are spaced approx 1.5m or more apart and I find it easy to walk thru our ceiling, stepping from bottom chord to bottom chord.  I purposely left several long lengths of steel to use as walkways or work platforms.  It's far easier to move around than our other house with a heavy steel built-up roof. 

[MangoKorat]

6 hours ago, McTavish said:

Trusses are spaced approx 1.5m or more apart and I find it easy to walk thru our ceiling, stepping from bottom chord to bottom chord.  I purposely left several long lengths of steel to use as walkways or work platforms.  It's far easier to move around than our other house with a heavy steel built-up roof. 

What I was getting at is, can you still reasonably use the roof space for storage etc?  The only thing that interferes with that at my current house is the annoying hangers for the suspended ceiling, that will be designed out on my next build.

[McTavish]

1 minute ago, MangoKorat said:

What I was getting at is, can you still reasonably use the roof space for storage etc?  The only thing that interferes with that at my current house is the annoying hangers for the suspended ceiling, that will be designed out on my next build.

Yes you can but it depends on what u want to store. eg: I have a platform upon which I keep spare tiles for floors and walls.

[MangoKorat]

1 minute ago, McTavish said:

Yes you can but it depends on what u want to store. eg: I have a platform upon which I keep spare tiles for floors and walls.

Thanks, sounds like it would be too restrictive for what I want then.

[Thailand J]

On 11/29/2023 at 2:30 PM, Bruce Aussie Chiang Mai said:

I was involved with timber Gang nail roof trusses in Australia. Best thing since sliced bread.

 I held a senior position at Mitek in USA until 2007. Gang Nail was acquired by Mitek.

[BritManToo]

14 hours ago, MangoKorat said:

What I was getting at is, can you still reasonably use the roof space for storage etc?  The only thing that interferes with that at my current house is the annoying hangers for the suspended ceiling, that will be designed out on my next build.

Roof space in Thailand is hotter than hell, what could you possibly store there?

[MangoKorat]

11 hours ago, BritManToo said:

Roof space in Thailand is hotter than hell, what could you possibly store there?

I store quite a lot of stuff in there. I also seem to have spent a hell of a lot (too much) of time up there either fitting electrical gear, camera wiring etc. or fixing electrical faults - all the electrics and wiring are up there.

 

I'd probably store far more if it was fully boarded and had better access which would also mean I'm in and out quicke -  as you say, its hot as hell.

 

My next house (new build) will incorporate a fully boarded storage area with a hinged access hatch and a drop down loft ladder - if I can find one that accomodates Thai ceiling heights.