Laid much like lead, zinc roofs are laid in bays, typically with standing seam joints. Zinc should last for 50 years or more.
Zinc roofs can be laid to very low pitches, down to 3º depending on the type of jointing seam used.
Zinc can also be laid over insulation boards on top of an existing felt roof. A special vented plastic grid is laid below the zinc. Otherwise, zinc sheet can be laid over timber sarking. However, like lead, the space below the sarking should be vented and a building paper used to allow the zinc to slide a little.
The system of fixing zinc sheets is to form a ‘standing seam’. Zinc clips are then fixed back to the sarking and crimped over the standing seam. This allows each sheet to expand and contract. If the sheets are not fixed or vented correctly, atmospheric or thermal pumping can occur with changes in temperature. This is more of a problem on high roofs, where there can be very high wind pressure. Special vented joints can help to prevent this.
Metal tile roofs can be made to look like zinc, and are likely to be cheaper but not as long-lasting.
New zinc roof being laid. The new zinc will be shiny at first but will soon weather down to a grey, lead-like finish.
Professional help recommended?
If the flat roof is covering a large part of your building and needs major repair or replacement, get a professional survey before proceeding.
Who pays?
Roof repairs are normally a common responsibility.
