![]() Part 2 has supplementary span tables on CD that requires more input to calculate timber sizes but delivers more choice. The simplified version is popular for its hard copy span tables and minimal information is required to determined spans. Part 2 is a lot more complex in relation to bracing calculation and requires the raking forces to be determined and the calculation of bracing expressed in kilo Newtons per metre designed to counter that force. To assess the amount of bracing a building requires under Part 4 only requires four steps, the bracing units are expressed as type A or type B and a simple table will indicate how many units are required. There is a limit placed on the maximum roof pitch in both documents of 30 degrees for Part 4 and 35 degrees for Part 2. The maximum width of a building designed under Part 4 is 12m where Part 2 can be used for building widths up to 16m and maximum external wall heights are 2.7m and 3m respectively. ![]() Part 4 can only be used in the two lower wind classifications of N1 and N2 where Part 2 covers wind classifications up to N4. ![]() The criteria in both versions are specifically for conventional timber-framed buildings of one or two storeys. But there are differences between the two Standards that users must be aware of that places limitations on the simplified version. Part 4 is referred to as the ‘Simplified’ version.Īs the name suggests, Part 4 being the ‘simplified’ version was developed as a more user-friendly document than Part 2. Part 2 and 4 are used in non-cyclonic areas and Part 3 is designed for the cyclonic areas of northern Australia. The other three parts provide building practices and procedures that assist in the correct specification and determination of timber members, bracing and connections.This is the document commonly used by engineers Part 1 relates to design criteria that can be used as a basis for the preparation of span tables and design data for the other parts.I appreciate everyone's help.AS 1684 Residential Timber Framed Construction has four parts: What makes this all confusing is I've found sites, such as which sell commercially made pergolas, some with 18 foot spans - simply using pairs of KNOTCHED 2x8 cedar members as the "entablature" (beam). While I'm asking for help - do I need the purlins/battens to tie everything together? Will they also help with the racking problem? Using 4x4 posts would be lighter and allow more room inside the decorative post end caps for longler galvanized brackets. That was because I assumed I needed that to allow for a sizable dowel. To prevent racking, can I use a large dowel (which is easiest for her non-timber framer husband) glued in place and 2 commercially available 7 guage angle brackets per post?Įarlier I had said I was planning to use 6圆 posts. To complicate things further, because my wife wants a "Roman" gazebo with round decorative columns covering each post, knee braces are difficult (impossible). Given that I live north of Seattle, can we assume it will spend much of its time closer to green than dry? Obviously fir is heavier, but also stronger. dry (12%)Īvg weight of douglas fir - 35 green 33 dry. To help with calculations, my internet search has come up with the following:Īvg weight of red cedar - 26 lb/cu. I thought the image you created was of the final structure AFTER doing the beam sizing calculations. ![]() Re: Size of fir or cedar beam to span 20'? Thanks in advance for any assistance anyone can offer. I know fir is stronger, but is the difference in strength enough to result in suitable beams being a 4x10 cedar vs. Can someone please tell me the minimum size to use? My miller "guesses" a rough sawn cedar 3x10 will do the job - but I'd like to know for sure. I've searched the internet and this forum (which seems to be my best bet to get an answer) end to end but can't find out what size beam I need. The local mill can offer me any size in fir or cedar. On top of the 3 beams will sit 11 22' 2圆s that will be 24" on center. For aesthetics, I'm looking to use three equal beams even if the front and back beams have a post centered under them and only the middle beam spans the 20'. Assuming the structure ends up at 20' on each side, even if I put posts around the perimeter that are 10' apart, I will still need at least one beam that spans 20', to avoid a centre post. ![]() My wife has asked me to build a flat-roofed 22'x22' pergola. I have a simple newbie question that (I hope) requires a simple answer. ![]()
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