Quinn Building Supplies Ltd
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Roof Trusses in General Commonly asked questions
1. How are Roof Trusses Designed?
Roof Trusses are designed by an experienced Roof Truss Designer using a computer, programmed with a very specialist engineering / design package. Quinn Building Supplies Ltd is licensed by Gang-Nail to design and manufacture roof trusses using it' software in accordance with BS5268.
2. How are roof trusses made?
Pre-cut Timber components are inserted into a set-up (Type of Jig) Galvanised metal gang-nail plates are positioned at each joint intersection. They are then clamped at each joint under very high pressure using hydraulic "G" clamps. The Roof truss is then complete.
3. What Key factors determine the quality of a Roof Truss?
a. All Timber used in the manufacture of roof trusses should be Kiln Dried (to ensure minimal shrinkage when in position in the roof)
b. All Timber used should be Stress graded to C24 or TR26 (C24 and TR26 are high strength timber grades. Using these grades guarantees the strength of the roof truss.
c. Rafter size is important: On standard Fink Trusses the smallest rafter dimension of timber that we use is 4x1 1/2 (100 x 38)Some manufacturers will use lighter timber eg. 3 1/2 x 1 1/2 (87 x 38) in order to appear cheaper WE DO NOT DO THIS and we will not compromise on quality.
4. What is the manufacturing lead time?
Quinn Building Supplies Ltd operate a 2 to 3 week lead time from confirmation of order & measurements until the roof trusses arrive on your site.
5. Measurements - must be accurate.
This is Very Important as every set of Roof Trusses is designed and custom made specifically for one particular building. A final check of the block-work is essential as very often the block-work dimensions differ from the drawings/plans.
Measurements should be taken from the outside of the wall-plate to the outside of the wall-plate to get the actual span measurement.
**If the Measurements are wrong the Roof Trusses will be wrong**
6. How far should Roof Trusses spaced apart?
Most Roof trusses in N. Ireland are designed to be spaced at 16 inch (400mm) centres. We at Quinn Building Supplies Ltd design both Attic and standard Trusses to be spaced at 16 inch (400mm) centres.
In the South of Ireland the common practice is to space Roof Trusses at 2ft (600mm) centres. 400mm centres is our prefered option and we believe it makes a stronger/better roof.
7. When do you need extra Attic Trusses?
Generally it is necessary to double up (nailing two Roof trusses tight together) on either side of an opening. for example: when inserting Roof lights, Dormer windows, stairwells, chimneys etc.