Nails have popped in substrate under sheet membrane roofing

Causes

Substrate movement such as expansion/contraction 

Substrate deterioration

Substrate was nail-fixed rather than screw-fixed

Listed under: membranes, sheet membranes, Roof, cladding, moisture, fixings and hardware, fixings, roof cladding, sheet membrane roofing, leaks, weathertightness

Cause

Substrate movement such as expansion/contraction 

Repair

  • where the problem is extremely minor with no risk of leaks, watching to see whether it gets worse may be an appropriate first response

  • where it appears more serious, or the problem is getting worse, and there is a risk that the roof may leak, the membrane may need to be removed and the substrate nail fixings punched in or replaced with countersunk screws. If a new substrate is required it should be appropriate for the purpose, such as H3.2 CCA-treated, minimum 17 mm thick plywood. Ensure the recommendations and requirements of the membrane manufacturer are followed

  • if the membrane was installed in recent years, call the installer back. Roofs still under warranty should be repaired by the contractor who carried out the original membrane application or by another applicator approved by the membrane supplier

  • installation and/or repair of membrane roofs is typically not a DIY job. Membrane manufacturers and suppliers typically train and license applicators in the use of their membranes. A warranty may only apply where application or repair is carried out by someone licensed by the supplier

  • work on roofs is restricted building work under the Building Act and anyone engaged to carry out this work must be a licensed building practitioner or be supervised by an LBP

  • check the condition of membrane roofs at least once a year to ensure there is no debris on the roof, no damage and no breakdown of the membrane surface

Back to top

Cause

Substrate deterioration

Repair

  • as above. If a new substrate is required it should be appropriate for the purpose, such as H3.2 CCA-treated, minimum 17 mm thick plywood. Ensure the recommendations and requirements of the membrane manufacturer are followed

Back to top

Cause

Substrate was nail-fixed rather than screw-fixed

Repair

  • as for the first repair. Nails are not appropriate for fixing of substrates under roof membranes – countersunk screws are typically required by membrane manufacturers. Refer to manufacturer requirements and to Building Code Acceptable Solution E2/AS1 clause 8.5.5.1. E2/AS1 is accessible from the web page 

Back to top