Site Made Roof Trusses VS Prefabricated Roof Trusses

Site made Trusses vs Prefabricated Trusses

Not All Roof Trusses Are Created Equal

The Institute for Timber Construction (ITC-SA), South Africa’s professional body and regulator of the engineered timber structure industry, offers insight into the differences between prefabricated timber roof trusses and site made roof trusses.

Site-Made Timber Roof Trusses

Prefabricated Timber Roof Trusses

SITE MADE ROOF TRUSSES

VS

PRE-FABRICATED ROOF TRUSSES


DEFINITION

 


Handmade Timber Roof Trusses connected with bolts and nails OR Site application nail plates at the joints.  As the name implies, handmade roof trusses are made on-site, by hand.

Prefabricated Timber Roof Trusses are based on SANS 10160, 10163 & 10243 and connected with an accredited Engineering System's nail plates as per their design and supplied by an accredited ITC-SA Fabricator.

 


DESIGN

 


Has to comply with the tables in SANS 10400 or the details in the National Home Builders Registration Council's “Home Builders Manual”. These details limit the truss shape, roof slope and are for a maximum span of 8 meters. If these details are not complied with, in any way, then the roof structure is ILLEGAL and the design must be checked by a Professional Engineer. All structures with hips and valleys MUST be designed by an Engineer!

Designed using ITC-SA Accredited System Supplier. The metal connector plates used must be supplied by the specific engineering system that is being used. In addition, these plates must be the correct size and positioned in the right locations as per the standard methods and tolerances.

 


MANUFACTURING

 


Handmade and cut on site with manual carpentry tools. Assembled on site using nails and bolts. Timber member sizes, the number of bolts and bolt sizes as well as the number of nails and sizes are contained in SANS 10400 and the NHBRC's Home Builders Manual. NON COMPLIANCE WITH STATUTORY REQUIREMENTS IS VERY COMMON AND LEADS TO EXTENSIVE REMEDIAL WORK.

Cut to precision with Specialized Automated Machinery, Manufactured and assembled in a controlled environment with specialized equipment in jigs for a specific purpose using Engineered nail plates in accordance with SANS10163, 10243 and all relevant specifications and regulations. The ITC-SA accredited Fabricator will issue you with a Manufacturing Certificate to confirm that your structure was manufactured in accordance with all the relevant specications and regulations. Your structure is also covered by the accredited Fabricator's Product Liability Insurance.

 


ERECTION

 


Has to be done strictly in accordance with;

1. The Design Intent
2. NHBRC's Home Builders Manual and SANS 10243

The erection of site-made roof trusses is generally done by persons that are NOT accredited by the Institute for Timber Construction South Africa (ITC-SA) and may be incompetent! NO HIPS AND VALLEYS ALLOWED.

Has to be done strictly in accordance with;

1. The Design Intent
2. SANS 10243,

By a professionally competent company and / or person accredited by the Institute for Timber Construction South Africa (ITC-SA)

 


INSPECTION AND SIGNING-OFF OF TIMBER ROOF STRUCTURE,
AS PER NATIONAL BUILDING REGULATIONS TO OBTAIN AN
OCCUPATION CERTIFICATE FROM THE LOCAL MUNICIPALITY

 


Has to be inspected for compliance with Regulation A19 of the National Building Regulations, the Design intent and specific regulations and specifications related to Timber Roof Trusses, where a Registered  Professional Person (registered with the Engineering Council of South Africa) will take responsibility for the said structure. Once the roof is completed to the satisfaction of the Engineer, a Completion Certificate
will be issued that will allow the owner to obtain an Occupancy Certificate from the Local Municipality.

COMPLIANCE WITH THE REQUIREMENTS IS OFTEN PROBLEMATIC.

Has to be inspected for compliance with Regulation A19 of the National Building Regulations, the Design intent and specific regulations and specifications related to Timber Roof Trusses, where a Registered Professional Person (registered with ITC-SA and the Engineering Council of South Africa) will take responsibility for the said structure. Once the roof is completed to the satisfaction of the Engineer, a Completion Certificate will be issued that will allow the owner to obtain an Occupancy Certificate from the Local Municipality. By issuing an A19 Completion Certificate the Engineer takes responsibility for the structure and therefore the structure is covered by the Engineer's Professional Indemnity Insurance!

 


CONCLUSION

 


Statistics obtained by the Institute for Timber Construction South Africa show that 90% of these structures do not comply with relevant regulations and specifications as required by the National Building Regulations. They are found to be around ±20 - 40% more expensive than Prefabricated Timber Roof Trusses. Should there be any problems, you will generally have no recourse for remedy and will end up in tedious and costly Civil Litigation! Any savings that your builder may have wrongly advised you of will be negated many times over!

If these structures are erected by an accredited ITC-SA Roof Erector, you are guaranteed a Roof Structure that complies 100% and you have the peace of mind that, should you have any problems, there is recourse for remedy via the ITC-SA's Disciplinary Procedures for all its accredited members.

For more information, visit The Institute For Timber Construction

 
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