Extreme How-To – September 2019

BEAM SPANS

RB 190 —This proposal makes

beam design for decks much more

flexible. The current table in the

IRC for sizing beams is based on

the span of the joist supported by

the beam, but it assumes those

joists are at their maximum allow-

able cantilever beyond the beam.

For decks with flush beams and

no cantilevered joists, the maxi-

mum beam span is incredibly

conservative. NADRA proposed

a footnote modification method

that will allow the table to be

more flexible and alter the values

based on the lesser amount of

cantilever. The example used in

the proposal showed how a beam

without cantilevered joists was

still being limited to a maximum

7 foot 4 inches, but with the new

footnote modification would actu-

ally be able to span 9 feet. The

committee agreed that this was

a much-needed flexibility to the

table and approved the proposal.

JOIST SPACING

RB 191 —This is a proposal

that deck builders may not be

thrilled about. The maximum

joist spacing of different thick-

nesses of wood decking assumes

each board is spanning at least

two joist bays, bearing on three

joists. The code change maintains

the maximum joists spacing for

decking supported on at least

three joists, but reduces the

maximum spacing for decking

supported by only two joists.

For these short lengths, the

maximum joist spacing will be

approximately half.

To learn more about deck code

updates and the evolving state of

the deck-building industry, visit

NADRA.org.

SPOT LIGHT

14 ExtremeHowTo.com

EHT

Whereas a beam without

cantilevered joists was being

limited to a maximum 7 ft. 4 in.

span, the new code modification

allows it to span 9 feet if the

joists terminate flush with the

beam.

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