Ceiling joists sagging

Causes

Ceiling joist spans too great for the timber size 

Joists have been overloaded 

Poor quality timber

Cracked or broken timber

Light roof cladding has been replaced with a heavy roof cladding

Timber has rotted due to leaks or high roof space moisture

Build up of sand inside roof space in beachside properties with concrete or clay tile roofs

Internal wall has been removed

Listed under: Interior, insulation, timber and wood-based, health and safety, timber, Roof, cladding, roof space, moisture, durability, rot, roof cladding, concrete or clay tiles, leaks, mould, mould health and safety

Cause

Ceiling joist spans too great for the timber size 

Repair

  • existing framing of villas is likely to be undersized for the span and timber dimensions when compared to the current version of NZS 3604 Timber-framed buildings

  • one or more strongbacks could be installed (see drawing). These new beams are supported off load-bearing walls to provide support to ceilings (via hangers) and rafters. Jacks may be needed to lift the existing structure back into line before the strongbacks are installed

  • where walls are being removed or having significant repairs, timber, engineered steel beams or LVL (laminated veneer lumber) beams could be used in the ceiling space

  • flitching a new member alongside the existing (and fixing to it) may be possible in some cases

  • depending on the degree of sag in the joists, returning them to an absolutely level position may not be possible. The building owner may find a reduced sag acceptable, but if not, replacement of the timber joist(s) will be required

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Cause

Joists have been overloaded 

Repair

  • see the repair options above

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Cause

Poor quality timber

Repair

  • see the repair options above

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Cause

Cracked or broken timber

Repair

  • see the repair options above 

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Cause

Light roof cladding has been replaced with a heavy roof cladding

Repair

  • where a light roof cladding has been replaced with a heavy one, the roof structure will probably have needed strengthening to take the extra weight. This may not have been done, however, resulting in the sagging joists

  • one or more strongbacks could be installed (see drawing). These new beams are supported off load-bearing walls to provide support to ceilings and rafters. Jacks may be needed to lift the existing structure back into line before the strongbacks are installed

  • where walls are being removed or having significant repairs, timber, engineered steel beams or LVL (laminated veneer lumber) beams could be used in the roof space

  • flitching a new member alongside the existing and fixing to it may be possible in some cases

  • depending on the degree of sag in the joists, returning them to an absolutely level position may not be possible. The building owner may find a reduced sag acceptable, but if not, replacement of the timber joist(s) will be required

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Cause

Timber has rotted due to leaks or high roof space moisture

Repair

  • first, identify the cause of the leaks and/or high roof space moisture levels and remedy these

  • high roof space moisture may be the result of high levels of moisture passing into the roof space from the rooms below, for example through the gaps around recessed downlights. If this is the case, reduce moisture in the rooms:

    • install a rangehood over the kitchen stove and an exhaust vent near the shower in the bathroom, and vent both so that they take steam outside the house

    • dispose of unflued gas heaters

    • avoid drying laundry inside

    • open windows wide for at least 10 minutes each day

    • if there are many older-style downlights penetrating the ceiling, replace with more modern tighter-fitting lights (or ceiling-mounted lights)

  • replace damaged joists with new treated (H1.2) timber

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Cause

Build up of sand inside roof space in beachside properties with concrete or clay tile roofs

Repair

  • vacuum out the sand. If possible, consider installing a roof underlay to the underside of the rafters to reduce wind flow into the roof space 

  • install a strongback across the joists as above

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Cause

Internal wall has been removed

Repair

  • if a load-bearing internal wall has been removed, consult a registered structural engineer for potential solutions.

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