Standing Seam

 

77% of failed roofs inspected have been standing seam

That's not to say every standing seam roof is bad. (Though it would be fairer to say aluminium rather than standing seam )

This poor track record is achieved by a vast number of installers that are not aware of the differences required in design and workmanship of aluminium rooflng and cladding compared to steel. Most installing both products exactly the same. The simple truth is that aluminium requires significant allowances for expansion.

Before placing an order with a roofing contractor, ensure that they have the ability and expertise to install aluminium.

 

Not allowing sufficient tolerance for expansion

Aluminium will expand up to 2mm per metre length ( subject to colour) , so a 3m length of flashing will be looking for 6mm of room to expand. In many instances flashings are incorrectly fixed to a butt strap creating a continuous flashing creating warping, failure of fixings and ultimately the possibility of components falling off the roof.

 

lap &nbs p 683

 

Incorrect fixings

Often carbon steel screws are used which are totally inappropriate for aluminium components, the fixings must be stainless steel ( or aluminium )

Carbon Fixings will react with the aluminium and fixing failure will result very quickly.

Oversized holes may be required to allow the flashing to expand - consult the fixing manufacturer, but under no circumstances should pop rivets be used in oversized holes.

 

Barrier tape

A barrier should always be placed between dissimilar materials - most commonly aluminium and steel to prevent galvanic corrosion. However, treated timber and other materials can also have a similar effect on aluminium and steel, therefore a barrier tape should be used in these circumstances.

There is a difference of opinion within the industry with regard to the plastic coating on steel sheets providing a barrier where it comes into contact with aluminium. We have some sympathy with those that state the outside face is good enough for this, but would always recommend a barrier tape be used. The wash coat ( reverse ) of steel sheets or paint ( PPC) on aluminium should not be accepted as suitable.

 

Walking on the standing seam

Each manufacturer specifies slight variations on how to walk on a standing seam roof - please ensure that their advice is sought. However, if you are designing such a roof then give the installer a chance. If it is required of him to walk on the seams only - provide him with a roof of suitable geometry to make this possible. steep slopes or severe curves are not appropriate unless you want a look like this. .

ladder

 

Further Reading

MCRMA Technical Paper No 11 ( section 6)

 

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