Mind your materials – framing

By - , Build 171

Proper on-site management of the delivery, storage, exposure and protection of building materials is critical to delivering quality buildings. In the second of this series of articles, we look at the correct care of framing materials.

Don't store framing on top of a curing slab.
Figure 1 The correct way to carry trusses.

LOOKING AFTER TIMBER or steel framing, particularly until the building is closed in, is essential to achieving a result for the client that is durable and serviceable. It encompasses:

  • planning the order of deliveries – ground-floor frames, first-floor frames, roof trusses or rafters in the right sequence
  • providing access for delivery vehicles
  • designating a clear level storage area for additional framing or a temporary holding area when frames and trusses cannot be lifted directly into their final location
  • protection of stored materials that need to be kept dry, such as manufactured floor joists
  • safe manual handling on site as frames and trusses are installed in their final location, particularly for first-floor frames and roof members
  • integration with the laying of the upper floors
  • managing weather and UV exposure where limits apply.

Plan deliveries to reduce handling

The ideal is for the frames and trusses to be delivered immediately before they are scheduled to be erected so they can be lifted into their final position and manual handling and storage time is minimised.

This involves:

  • truck access or at least being within safe reach of the truck’s hiab
  • ensuring frames and trusses are not racked during lifting
  • having temporary braces ready to install as the wall frames are erected
  • planning deliveries in the correct order to follow the installation of the ground-floor walls for a 2-storey building – first-floor framing, flooring, upper-floor walls, roof framing, roof underlay and cladding.

Tips for good timber framing storage

Provide correct storage for frames, trusses and packet or loose timber until they can be erected:

  • Fabricated items such as trusses, I-beams and prenailed frames should ideally be stored within a building or constructed shelter. Although material may be stored under covers, this should only be for a limited time, or the covers will need maintenance to ensure the timber stays dry.
  • Provide a dry, level, even base for storage. If outside, cover the ground with polythene immediately under the stack to avoid water condensing on the timber.
  • Support all stored timber clear of the underlying surface on evenly spaced dunnage.
  • Keep all kiln-dried framing covered. For packet timber, do not remove the protection until the timber is needed.
  • Do not store steel or timber frames or trusses over a newly poured slab or wet sheet floor.
  • If delivered as wet framing, fillet stacking will allow timber to dry before use.
Don't store framing on top of a curing slab.

Kiln-dried timbers

It is particularly important to keep kiln-dried timber dry. The advantages of using kiln-dried material – its stability and reduced likelihood of shrinkage – will be lost if the material gets wet. It is not uncommon to find materials poorly or carelessly stored on site.

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Things to avoid

Other examples of poor frame and truss care include:

  • tipping it from the delivery truck and leaving it where it lands
  • not storing it clear of the ground on dunnage
  • providing uneven or insufficient dunnage under the material so that it is not on an even or level base
  • leaving kiln-dried timber uncovered and exposed to the rain or not effectively protecting the timber from wetting
  • using it as a storage platform for other materials, causing deformation
  • allowing timber to sweat under covers
  • leaving steel or timber trusses lying uncovered on uneven ground among the grass or in the dirt, which can lead to distortion
  • misaligned bearers or dunnage.

Handling on site

Where frames and trusses have to be manually handled on site:

  • carry trusses and frames upright (see Figure 1)
  • have sufficient labour to spread the load and minimise the flexing of the frames and trusses.
Figure 1 The correct way to carry trusses.

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Erecting wall frames

When erecting frames:

  • do not distort or rack frames when standing them up
  • install initial holding-down fixings to locate frames
  • check frames for plumb and square
  • progressively install temporary braces.

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Erecting roof trusses

Where practicable, roof trusses should be placed by crane on the wall top plates at the time of delivery.

When erecting roof trusses:

  • a safe working platform such as a scaffold should be provided around the perimeter of the roof
  • erectors should be able to access the next required truss from the top of the truss stack
  • all members of the handling team should be protected from the risk of a fall
  • don’t distort or rack frames when standing them up
  • install locating fixings at each end of the truss
  • temporarily brace the trusses as installation proceeds.

Kiln-dried framing specifics

Kiln-dried framing has an ex-factory moisture content of 10–12%. The timber may swell due to the uptake of moisture when exposed during construction.

Take steps to keep kiln-dried timber framing as dry as is practicable:

  • Erect wall, floor and roof framing as quickly as possible.
  • Install roof cladding immediately after completing the roof framing to shelter the framing.
  • Install the wall underlay as soon as is practicable to provide initial weather protection to the framing – remember there are also exposure limits on flexible wall underlays. Although flexible wall underlay materials are not waterproof, they will help keep the erected framing drier but can be prone to damage from wind and other building activities. Where temporary weather protection is required, a BRANZ-Appraised temporary weather protection system or shrink wrapping the building should be specified.
  • H1.2 boron-treated framing timber should not be exposed to rain or kept in contact with wet ground or water ponded on a floor surface for extended periods as some boron can leach out of the timber. One manufacturer suggests 3 months is the maximum exposure allowed to ensure compliance with treatment requirements.
  • Rewrap remaining material after opening.

Steel framing specifics

While steel framing will not take up any moisture due to weather exposure, it is recommended that these steps are followed:

  • Wall frames and trusses that are stored on site before erection must be stored on a level platform clear of the ground on evenly spaced dunnage.
  • All swarf and steel fixings that are in channels should be cleaned out each day – if left exposed to moisture, rust spotting will occur.
  • Cement dust from drilling fixings should also be removed as it can create a corrosion cell if wetted.

Engineered timber care

Engineered timber members such as LVL and other engineered timber floor joists and rafters, should be treated on site as for kiln-dried framing.

Considerations include:

  • LVL has an ex-factory moisture content of 10–12% and may swell when exposed to moisture during construction
  • LVL should not be stored in contact with the ground
  • where appearance is critical, LVL and its fastenings must be protected from moisture both during construction and in service
  • where appearance is not critical, LVL can withstand some rain wetting during construction without significant structural degradation, but water staining and mould growth is possible.

Exposure limits for steel and timber

While there are no specific weather exposure limits set for both timber and steel framing, it is prudent to take these actions:

  • Minimise exposure by enclosing the framing as soon as is practicable. Where H1.2 boron treated timber framing has been left in the weather for more than 3 months – timber stored uncovered on site or as erected frames – verification that the treatment level is still adequate to satisfy the requirements of NZS 3640:2003 Chemical preservation of round and sawn timber may be required.
  • Keep floors the framing is installed over free of ponding water – remove bottom plates at doorways to allow water to drain.
  • Consider specifying a proprietary packer system, installed in accordance with the specific system instructions, that supports bottom plates clear of the floor.

Health and safety

Erecting first-floor and upper-floor structures, upper-floor wall frames and trusses is classified as working at height – over 3 m. That brings into play requirements to ensure that the work can be carried out safely, such as:

  • edge protection – scaffold
  • fall protection or restraint
  • barriers at upper-floor levels.

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Articles are correct at the time of publication but may have since become outdated.

Don't store framing on top of a curing slab.
Figure 1 The correct way to carry trusses.