*Roof Defects Flashcards
What are the common defects associated with poor design and construction of pitched roofs?
- Untreated timbers
- Inadequately sized timbers
- Omitted/removed roof members
- Eaves/verge overhang too small
- Sarking felt improperly installed
- Inadequate flashings/soakers at abutments
- Inadequate ventilation
- Inadequate pitch
- Nail sickness
- Delamination of tiles
- Bitumastic over-sealing
What is roof spread and how does it usually occur?
An outwards movement of the roof ususally caused by:
- Collars placed too high or removed completely to facilitate a habitable space within the roof
- Ceiling joists inadequately connected to rafters
Why is the roof’s pitch important?
- If coverings are laid at too low a pitch, rain and snow may penetrate
- Laying coverings on steeper pitches (up to the vertical) is not normally a problem, however all tiles must be nailed, as sole reliance on any nibs may be insufficient
What are the problems associated with roof covering laps?
- If the gauge is extended, thus reducing the lap, it will increase the likelihood of weather penetration
- If the gauge is reduced, thus increasing the lap, it will provide greater weather resistance but may result in an excessive load on the structure
What is nail sickness and why is it problematic?
Nail sickness is the term for when ferrous nails used to secure slates/tiles inevitably rust in the presence of the moisture present between the roof covering and sarking felt, causing slipped or missing slates/tiles that can lead to damp penetration
How can nail sickness be remediated?
- Slipped slates can be re-secured using ‘S’ shaped lead/copper clips (aka ‘tingles’), however this can be unsightly
- In replacement work, non-ferrous fixings (e.g. copper, aluminium) should always be used - AVOID galvanised steel
What are the common defects associated with slate roof coverings?
- Delamination
- Torching and bedding
- Split slates along the line of nail holes
- Nail sickness
- Broken head-nailed slates caused by wind uplift
- Wide joints between slates causing water penetration
- Well-laid slates lying close to each other causing water seepage due to capillary action
- Verge failure (half slates used at verges instead of slate-and-a-half, the former of which are difficult to secure properly against wind uplift)
- Inadequate overhang at verges (water cannot drip away from the face of the wall beneath)
- Bitumastic over-sealing (impedes ventilation)
What is torching and bedding and how may it be problematic?
- Traditional process of filling the gaps between slates and battens with mortar (commonly lime mortar and animal hair) to prevent rain or snow penetration where no boarding or felt was present
- Tends to shrink and fall out, leading to water penetration
- Also leads to inadequate ventilation to the underside of the slate
What factors would lead you to recommend re-covering a slate pitched roof rather than patch repairing it?
The extent of the problem and the condition of the battens beneath
What are the common defects associated with clay tile roof coverings?
- Delamination
- Cambered/non-cambered tiles - cambered tiles (i.e. concave profile across width) more liable to driving rain or snow penetration, non-cambered tiles increase the likelihood of capillary action
- Slipped tiles - insufficent nailing (should normally be every fourth or fifth course and around all verges, hips and ridges) or nail sickness
- Torching and bedding
- Efflorescence
- Verge failure (half slates used at verges instead of slate-and-a-half, the former of which are difficult to secure properly against wind uplift)
- Inadequate overhang at verges (water cannot drip away from the face of the wall beneath)
- Ridges and hips - lime mortar traditionally used to bed ridge and hip tiles loses its ability to bond with age, leading to loose or missing ridge/hip tiles
What defects can occur in a concrete tiled roof?
- Overloading - extra weight of concrete tiles may cause bowing/buckling of the roof structure where a previous slate/clay tile covering has been replaced
- Loss of surface/colour - originally, the finish of concrete tiles was only surface deep, so once weathered or damaged, the concrete beneath is revealed which is unsightly but does not impair performance
- Efflorescence
- Delamination
- Slipped tiles - insufficent nailing (should normally be every fourth or fifth course and around all verges, hips and ridges) or nail sickness
What problems are associated with replacing slated roof coverings with new concrete tiles?
Overloading - extra weight of concrete tiles may cause bowing/buckling of the roof structure where a previous slate/clay tile covering has been replaced
Regarding sagging of the roof, what defects would you look for in the roof space?
???
What are the common defects associated with metal roofs?
???
What are the potential problems with a roof structure incorporating trussed rafters?
- Roof trusses inappropriately stored or mishandled (physical damage, distortion, water saturation) leading to inadequate structural performance, water saturation and risk of rot
- Inadequate bracing of roof trusses - trussed roof likely to move or tilt sideways as a unit