10. Re-covering of Pitched Roofs

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planning@worthing.gov.uk

Technical Guidance Note 10: Re-covering of Roofs

Since the 6 April 2006 if you propose to re-cover the roof of your property a Building Regulations Application will be required. Usually a Building Notice application would be the most suitable for this type of work but should include the type of thermal insulation present and how this will be upgraded if required. Typical examples if using mineral fibre or cellulose fibre as quilt laid between and across the ceiling joists are:

• If no insulation or less than 50mm present then the existing will need to be increased to 250mm,
• If 50mm to 100mm present then the exisiting will need to be increased to 200mm.

For further information please contact Building Control or see Technical Guidance Note 33: Thernal Elements.

The following guidance points out the main items to be aware of when re-covering a roof:

Site Procedure

A thorough survey should be carried out, which should inclued observations of how the roof has performed to date, as well as checks of timber sizes. The appraisal should include checks for:

 
• Alignment; signs of decay; insect attack; corrosion of fasteners and fixings; evidence of movement around eaves and at all other connections.  Check supporting structure, bracing and impairment of end bearings.
     
     
• Check for under design of roof timbers, in particular purlins, and continuity of ceiling joists to prevent roof spread.
     
     
• Check for inadequate strutting.  Struts should bear on load bearing walls. Check for beams over landing areas.
     
     
• Check restraint at foot of rafters.  Raised tie roofs will need careful consideration.
     
     
• Compare weight of new roof covering with the existing; making allowances where appropriate for any additional loading which may be applicable due to water absorption (relevant when replacing slates with concrete tiles).

Action

After carrying out a survey, the Building Control Officer will be in able to decide what action is required; this may include:

 
• The roof structure is satisfactory, and no further action is necessary
     
     
• Some degree of strengthening is required.  This can be divided into two categories:
     
     
       
  1. A further survey of the roof is required by a suitably qualified chartered engineer or surveyor, and a report together with proposals and calculations submitted for consideration.
            
                
  2. The Building Control Officer is able to determine the degree of modification which is required in order to bring the roof up to a satisfactory standard.   
   

Typical Defects And Remedial Action

Purlins
 

Often found to be deflecting or undersized.  Solutions are normally:

 
• Reduce the spans by strutting, introduction of supporting beams, or as a last resort install roof trusses.
     
     
• Strengthen purlin by increasing the size of timbers, adding a steel section, designing a flitched beam or ply beam.

Rafters
 

Although the size is not generally a problem, they will need to be checked.  Deterioration is generally due to insect attack or decay, especially at the eaves, where timbers have been seated against solid walls and subjected to damp conditions.

Lateral Restraint

 
• Framing anchors should be specified where the rafters sit on the wall plate but the connections are inadequate.
     
     
• Ensure that additional restraining straps are provided to control vertical or lateral movement where required.
     
     
• Where rafters do not coincide with ceiling joists, ensure that an adequate method of lateral restraint is provided.
     
     
• Timber ties at eaves level connecting the base of the rafters may be required in some instances.  Where ties are only provided at intervals, and in the absence of calculations, the joints should be bolted.

If you have any further enquiries, please do not hesitate to contact:
 
  Building Control Group
  Planning Section
  Portland House
  Richmond Road
  Worthing
  West Sussex
  BN11 lLF
 
  Tel: 01903 221292

  
  E-mail: building.control@worthing.gov.uk 
  
    
  Fax: 01903 221152

  
  Answerphone: 01903 214034

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