How to Build Pergola Roof?
Roughly mark out the area of where you want your pergola to go.
Next, build your profiles. Place these at least half a metre back from your outside corners.
Run stringlines from your profiles which will give you the outside area of your pergola. Where the stringlines meet will be the outside corner of your posts.
Measure the diagonals to ensure your pergola is square.
Dig your holes 400mm square by a minimum 500mm deep or until you hit solid ground.*
*Before you start digging contact your local utilities companies to make sure you don’t hit anything, you shouldn’t.
In the bottom of your holes place a concrete block for the posts to sit on so they are o the ground. This doesn’t need to be anything flash, just something to keep the post from taking on moisture. Scoria is also ideal.
Place the post in the hole up against the stringlines. Brace it, make sure it’s plumb and pour in the concrete.
Use a stick to vibrate the concrete to ensure there are no air bubbles.
24 hours later your concrete should be set so you can remove the braces, stringlines and profiles.
Now it’s time to mark the posts to length and then mark the rebates for the bearers to sit on.
For our pergola, it was 2m to the underside of the bearer.
Use an off cut of the bearer to mark the rebate in the post.
For a pergola any larger than this, you’ll need to increase the bearer size.
To transfer the rebate mark onto the other posts, knock in a nail on the rebate mark, place a straight piece of timber on the nail, use your spirit level to establish level, and transfer the mark to the next posts.
Trim the tops of the posts and cut out the rebates.
Cut The Bearers
This pergola is 3.5 meters long. We want the bearers to overhang by 300mm at each side so the bearers will be 4.1m long in total.
Stay Safe Hint
Use of power tools makes the completion of projects much easier, but appropriate safety equipment when using power tools is highly recommended.
Ear protection, eye wear and sturdy footwear should be considered the minimum requirement when using power tools and always use a residual current device when using electric power tools.
Shaping The Bearers
Come in 300mm from the end and down 35mm.
Before you put up the bearers, clamp them together then mark the positions of the 8 rafters that will sit on them. Use an offcut of a rafter to get the width right.
The pergola is 3 meters wide, so the rafters will be 3.6 metres long to include a 300mm overhang on each side. Shape the rafters the same way you shaped the bearers.
The battons sit on top of the rafters. The pergola is 3.5 meters long, so the battons will be 3.6 meters long. This includes a 50mm overhang on each side. A quick way to mark their positions is to line all the rafters up and mark them at the same time. These battons are being spaced 300mm apart but you can create any pattern you want.
Place the bearers in the rebates and clamp them while you drill the hole for the bolts. Put the bolts in.
Lay the rafters on the bearers in their pre marked positions. One skewed nail on each side is all that’s needed.
Lay the battons on top of the rafters in their marked positions, make sure you have the 50mm overhang and nail in place.
If you pre-drill the holes in each end you will stop the timber splitting.
In exposed areas or a structure any higher than this, it is advisable to attach braces from your bearer to your posts on a 45 degree angle. This should be a 100 x 50 H3.2, approximately 1m long.
Metal corrosion: Some environments in New Zealand are quite corrosive to metals. Metal fixings used in exterior building applications are therefore required to be protected against premature failure by either hot dipped galvanising (HDG) or in more aggressive environments the use of stainless steel. You should consult your local council for advice on the appropriate type to use.