Bridging, Blocking & Herringbone struts

Noggins, sometimes called bridging or blocking are timbers used all over the place during first fix/structural carpentry to strengthen and stiffen wall, floor and other timber structures. They are also used to provide a strong fixing for something that will be later fixed to the structure. For example, you may place them when building an interior Stud-work wall in such a position as to provide a solid fixing for the toilet cistern or a radiator that will be installed later on.

Another area where bridging would be used would be in between ceiling or floor joists to fix top or bottom wall plates to. Or, in between studs/ceiling joists in order to fix plasterboard to.

Cutting and fixing

Because lengths of timber are rarely perfectly straight, instead of taking a measurement from the exact position it will be situated between studs/joists, it's important to take the measurement at the end of those studs/joists instead.

For Example:

You are cutting blocking for a standard interior wall that will be fixed 1200mm up from the floor to strengthen the wall and provide a fixing for the edge of 1200mm wide sheets of plasterboard later on. You must take the measurements for the noggins in between the bottom of the studs where they are fixed to the plate, not at 1200mm high. You do this because it means when fixed in place the studs - no matter how bowed will then be forced straight and parallel.

Normal noggin

wall noggin bridging blocking

Normal bridging in a wall like above would be fixed straight across, with the centers being 1200mm above the floor. One end can be nailed straight through from the back of the stud. The other end has to be skew nailed at an angle because the previous block is in the way of nailing.

Staggered noggin

wall blocking

Staggered bridging can be used where the blocks don't have to carry the edges of a sheet material like plasterboard. Floor joists are one area where staggering the bridging would be OK. By staggering them you can install much quicker because you don't have to skew nail one end which is slightly more awkward and thus more time consuming. Both ends can be fixed straight through the back of the stud/joist.

Herringbone struts

herringbone strut supports

Herringbone struts are sometimes used instead of solid block bridging/noggin. They are better if there are lots of flexible pipes or cables that need to be passed between joists as they reduce the amount of drilling that needs to be done that weakens timbers and structures.

Setting out herringbone struts

herringbone strut supports

It's impossible to hold a piece of timber in place to mark the length of a herringbone strut. Instead, to set out and fix herringbone struts you need to set out the depth of the joists onto the top of the joists. First, mark a center line across the joists where the struts will be placed, mark this along the bottom of the joists if possible also, to help lining them up when fixing later. That line is marked on the picture above in red. Then, mark half the joist depth either side of that center line, marked in the picture in blue (joist depth shown by green line + arrows).

Once done, you can hold the timber being used from line to line as shown on the right hand side of the picture to mark the length and angle needed onto the strut.

Once cut, nail in place. This method of bracing also helps to straighten up twisted joists, as long as you don't adjust the lengths in any way. Fix the tight struts first (straightens joists) and leave the loose ones till last.

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