June 24, 2010
How to build a Pergola – Step Nine
Step Nine-Installing Gable Ends and Purlins
Install vertical struts
Now that you have installed all of the standard gable frames and the ridge you can move on to installing the gable ends. Once this is complete you have only purlins, guttering and roofing to go before your Pergola is complete!
The first step in installing your gable ends is the fastening of the vertical struts. Your vertical strut is positioned underneath the ridge (fitting into the notched section of the ridge) and it runs directly downwards to sit atop the bottom chord. Measure the distance between these two points and cut the vertical strut to length to ensure a neat fit between the bottom chord and the ridge. Fix the strut at the top first, by drilling and screwing into the notch in the ridge with a 100mm bugle screw. Then move on and fix the strut to the bottom chord with a 75mm nail in each face. Pre drill the strut to make it easier and avoid splitting.
Install end rafters
Once the vertical strut is installed it’s time to fix the end rafters. To start, take one of the gable end rafters and put it in place. Line the top end up with the top of the ridge and the bottom end with the start of the notch in the bottom chord (the rafter should fit snugly and the angle correspond exactly with the notch) Fix the rafter to the ridge with 2 x 100m bugle screws from a 45 degree angle into the top of the end rafter and through to fasten to the ridge.
Once the rafter is fixed to the ridge, temporarily fix the end of the rafter to the bottom chord with one 75mm bullet head nail into the bottom chord.
Repeat this process for all three remaining gable end rafters. Once all are in position and your pergola is all square and level you can fix the base of all of the gable end rafters to the bottom chords with 3 x 100mm bugle screws in each rafter.
Install starburst struts
The last part required for completion of the gable ends is the starburst struts. These struts are placed at the base of the vertical strut (in the middle of the bottom chord) and meet the inside edge of the gable end rafter about halfway up (on both sides, there are two per gable end) As they have been pre cut to fit your pergola, all that is required is that you fix the struts to both the bottom chord and the end rafters with 75 mm bullet head nails. Be sure to pre drill the holes in your struts to avoid splitting the timber.
If your roofing is polycarbonate it will save you a lot of time and fiddling around later if you fix purlin tape to the top face of each of the purlins prior to installing them. Do this first.
When installing purlins you will need to line the purlins up with the marks that you have previously placed on the rafters and also line up the rafters with the marks on the purlins. If they don’t line up try to pull the purlins as straight or as close to lining up as is possible.
Once you have a purlin in position, fix it to the rafters with a 100mm bugle screw (One per rafter) On the house side the bottom purlin needs to be fixed with a 120mm gap up the run of the rafter to allow for the internal gutter which you will install later (see the diagram below for guidance) The far side bottom purlin goes right up against the beam and will slot snugly into the notch in the bottom chord. The top purlins on both sides go right up against the edge of the ridge.
Once all purlins are installed the frame of your structure is complete. All that is now left for you to do is add the roofing and gutters.
How to build a Gable Roof Pergola – Step Ten – Install Gutters
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