Due to the current situation with coronavirus it is likely that roof trusses and Posi-Joists will be stored on site for a longer period of time than would normally be expected.
Guidance for the recommended storage of these products is summarised below.
SITE STORAGE OF TRUSSED RAFTERS
Trussed rafters can be safely stored vertically or horizontally at ground level, or on a properly designed storage platform above ground level in accordance with the points below:
- Whichever method is used, the units must not make direct contact with the ground or any vegetation.
- They must be arranged to avoid distortion, and securely restrained to prevent collapse.
- The delivery of trussed rafters should be arranged to minimise onsite storage time. However, if longer periods of time are necessary, the trusses should be protected with covers and fixed to allow proper ventilation.
- When stored vertically, bearers should be positioned to provide a firm and safe support with suitable props as illustrated in Figure 1.
- When stored horizontally, level bearers should be positioned between each truss node to prevent any distortion as shown in Figure 2.
No other method of storing trussed rafters is suitable, unless specific provision has been made in the design for an alternative temporary support load case.
SITE STORAGE OF POSI-JOISTS
Storage of joists on site should ideally be for a limited period of time prior to erection of the Posi-Joists. Posi-Joists should either be stored vertically or on the flat in accordance with the guidance below:
- If stored vertically there should be intermediate bearers at node points not within the bay of a joist, as shown in Figure 3.
- If stored in a flat position, sufficient bearings should be provided to prevent excessive lateral bending.
- It is recommend that completed Posi-Joists be strapped together and wrapped in a waterproof protective covering to protect them from short term exposure to inclement weather.
- Special precautions should be taken when stacking top chord supported floor cassettes to prevent the stack lozenging in storage.
- Additional bracing to the ends of the stack should be fixed to stop lateral movement. Care should be taken when handling the Posi-Joists to avoid bending, twisting or dropping.
PROLONGED SITE STORAGE
MiTek has an extremely experienced team of design and engineering staff, who have built up decades of knowledge around trussed rafter and Posi-Joist in relation to site conditions.
It is our experience that products stored in accordance with the above recommendations typically suffer no degradation that would negatively impact product their performance over a period of 3-6 months.
Trusses that have been erected but not covered with a roof covering benefit from air flow around them and typically do not suffer any degradation in performance over a period of up to 6 months.
Posi-Joists that have been erected but not decked should have a water proof membrane applied to prevent excessive exposure to moisture.
For joists that are installed and decked, advice should be sought from the manufacturer of the decking. Where non-waterproof deck materials have been used, there is a risk of problems resulting from prolonged exposure to damp materials
MiTek is well placed to offer support and advice to trussed rafter and Posi-Joist manufacturers. We can offer advice and relevant expertise on a case by case basis should there be concerns from sites regarding the condition of products after prolonged periods on site.
Enquiries on the above should initially be directed to our design office on 01384 451400 or firstname.lastname@example.org