Drop the right anchor!

Concrete screw-type anchors are increasingly used as a quick, simple and effective method for fixing bottom plates to concrete slabs

Initially designed as removable fasteners for fixing plant and machinery to concrete walls and floors, concrete screw-type anchors are a popular option for fixing timber bottom plates to concrete foundations in residential and commercial construction.

WHAT THEY OFFER

Screw-type concrete anchors offer some advantages:

• They are quick and easy to install – a hole is drilled in the concrete floor in the correct location, the timber framing lined up above and the screw-type anchor installed using either a power driver or manual socket or wrench.
• They can be removed easily if necessary – with no wedge, sleeve or adhesive holding them in place, they simply screw out.
• They put less stress on the concrete – as the screw-type concrete anchors do not have an expanding wedge or sleeve, they apply less expansion force than wedge or sleeve-type anchors.

“Screw-type concrete can be removed easily if necessary – with no wedge, sleeve or adhesive holding them in place, they simply screw out

Things to watch out for

However, there are some items to consider when using any type of post-installed anchor in concrete foundations:

• Does the fastener have the correct capacity strength to meet the requirements of NZS 3604:2011 Timber-framed buildings clauses 7.5.12.3 and 7.5.12.4?
• If the fastener is to be used as a hold-down at the end of a bracing panel, can it achieve the required characteristic tensile strength for this task?
• Can suitable cover to the fastener be achieved, especially in NZS 3604:2011 exposure zone D and where concrete and concrete masonry header block foundations are used? It may be necessary to specify stainless steel anchors in these locations. Figures 1 and 2 demonstrate how maximum covers can be achieved in two common situations.
• Is the drill bit the correct diameter – if worn, the bolt can be hard to install and may damage the concrete.

NOTE: Two BRANZ Appraisals cover a range of concrete hold-down fasteners, see www.branz.co.nz.