Softwoods Blog

This post is further to an earlier post about how to build a DIY decking kit, where floor load width and components were discussed. If you are starting out, it’d be a good idea to read that first before you get to this post which covers building the substructure of your decking.

Once you have calculated the layout of your deck and have purchased the appropriate timber, you can start to build the substructure of your deck.

Although it may not seem like it, the substructure of your deck is the most important part of the deck and if installed correctly it will ensure that the finished decking  will be stable, structurally sound and most importantly, level.

You will need to start by marking your post locations. With any luck you won’t need to excavate the site, but if you do this is your first step. Before digging anything it’s also wise to check with relevant services and authorities to make sure that you’re not about to rupture a sewer or an electrical line.

If you are excavating, it makes sense to establish how far down you will have to go before you start to dig. It also makes sense to have a plan regarding the drainage of the site once you’ve built the deck, to ensure that you don’t have issues in future. To calculate how far you will need to dig, you need to establish your joist to bearer attachment method (covered in more detail later)  I’d recommend butting your joist into your bearers to remove  the need to excavate the additional height of each joist.

In getting your calculation exactly correct you need to leave allowances for your post shoes (we recommend that all posts be housed in shoes as this will ensure that your deck lasts for the longest possible time without being affected by pests or rotting of any sort) You will then need to add the height of your bearers and decking boards to establish the distance you need to dig (for decking that is at ground level)

If your deck is not at ground level, you can stake your site and run a string line at the level of the top of the decking boards.

When you have your site ready and you’ve marked your post locations according to the plans (using a string line and measuring tape) you can dig holes for each of the footings. The hole size required for your particular footings and area will vary, so please check with your council/shire as to what’s required.

Generally speaking for stirrup footings you need at least 200mm underground (and your hole needs to be another 100mm deeper than that)

tornado footings need to be 300mm underground, as well as another 100mm deep.

Please don’t take these measurements as gospel though as it’s important to ensure that your footings are adequate.

When digging holes for your posts, you should taper the hole so that it looks like the bottom of a champagne cork, this will add stability to the finished footing.

Once you have your footings in place, attach your posts to your post shoes. Prepare and pour concrete into holes, and sink post shoes into the wet concrete to the appropriate level. Clamp or prop each post at the correct angle so that it won’t move until the concrete dries completely. Allow the footing 24 hours to set before doing anything else.

Once the concrete has dried and your posts are set in position you will need to cut the tops of your posts to the correct height. Getting this correct is essential to a level deck. Use the string lines that you’ve set up at the desired level of the deck as a guide and cut the tops off of each post at the correct height.  The post tops can be a little lower than the tops of bearers so the cut doesn’t need to be perfect.  Use either a circular saw or a hand saw to do so. You will need to saw at 90 degrees to the ground, so you’ll need to be extremely careful and work safely at this point. Depending on your saw setup you’ll need to establish the safest way to complete this task without putting yourself or anyone else at risk. If you are using a handsaw, be sure to brace the post so that you don’t cause any unwanted sideways movement of the footing.

With your post tops all cut and level, you need to address how your bearers will attach to your posts. AS1684.2 1999 stipulates that decking construction requires the provision of double bearers. This means that each post requires two bearers to join it and the next post. There are a variety of acceptable options to achieve this. The first is to house a bearer on either side of the post (diagram below)

This requires that you cut a 20mm deep notch in the posts on either side to house the bearers, and bolt them both through the post. If you use this method to secure your bearers also use blocking pieces of timber at 900mm centres from each post, fixed with nails so that there is no movement of your bearers.

The second method you could use is to notch the post 45mm and attach two bearers together, bolting through the bearers and posts to attach (diagram below)

If you use this method, nail the bearers together at 300mm centres to prevent any movement.

The third method that you can connect with is to notch the post 20mm on each side at different levels so that one bearer is flush with the top of the post and the second has enough clearance over the post to butt into the joist and sit flush with the top of the joist. This method allows you to have a neat edge on the outside of the deck if it is visible. (diagram below)

If you are limited in clearance and excavating is difficult you can use just a post shoe to house your bearers and eliminate the posts.

Once you’ve selected your attachment method, mark your post tops and cut the appropriate notches into each post. Once complete, you can lift your bearers into position and clamp them into place, then drill and bolt them together using Cup head bolts. Once you’ve done this you can cut the ends of the bearers to size. You can reinforce the framework for your deck by using L brackets on the inside corners of the framework (or where the bearers meet the ledger (if this is the case))

The final step in building your decking substructure is to attach the joists to your bearers. Again there are a few variables at play here, which we will go through. The first step in attaching your joists should be to mark out where they will run as per your plans so that you have a clear idea of what you need to do.

If you are taking your deck all the way to the wall of your home, you will need to determine the manner in which you’d like to connect the deck to the wall and how this will affect the placement of your joists. You will need to install what is called a ledger (a piece of timber that is bolted into your wall) to which your joists will connect. Where the ledger is installed is determined by how your joists connect to your ledger. There are two generally accepted methods, firstly you can place the joist on top of the ledger and up against the wall, connecting the joist to the ledger with nails and a trip l grip bracket (image below)

(Trip L Grip Bracket)

Secondly, you can choose to butt the joist straight into the ledger and use a joist hanger bracket to fasten the joist in place with nails. (image below)

(Joist Hanger Bracket)

In connecting your joists to the bearers you can either run the joists directly over the top of the bearers or butt the joists into a bearer (if your bearers are laid out in the same manner as example 3 above) Depending on which approach you take you will either have to use trip l grip fasteners or joist hangers respectively. (images of each option displayed below)

Once you’ve connected your joists, trim the ends to size, and you are ready to install your decking boards.

Please remember that if you have any unanswered questions about DIY decking  we’d love to hear from you. We’d also love to be given the opportunity to quote on your decking project, regardless of where you are in Australia, we can ship a decking kit to you at great prices, designed to your exact specifications. We are also able to offer you a huge range of decking boards, Merbau, Kapur, a full range of Australian hardwoods and Clear Treated Pine.

Thanks for reading!

Step Seven-Installing Posts

The frame of your Softwoods pergola is almost complete and now it’s time to install posts to make the structure stand up. This step is once again very important to get right as once the posts are set it’s extremely difficult to fix any mistakes you have made to this point. Once you have the posts installed you will really be able to see some progress in your pergola and all of the preparing and marking out that you did earlier will start to pay off for you.

Marking the beam

From your plans you can work out where the posts are to be located. Measure and mark the centres of the post locations on the beam with a pencil line indicating where the centre of the post will be.

Measure and cut post to length

To determine the exact length the post needs to be, a few measurements are required. Firstly measure from the top of the beam at the position of each post, to the point on the ground where the posts will be fastened.

As the posts do not go to the very top of the beam, you will need to subtract from the measurement that you have a Post Set Down (PSD) amount, which is the depth of your beam minus the depth of the notch out on the post.

Finally, the amount the post will be above the ground is also required to be subtracted. This may vary depending on the style of post shoe you have or whether you plan to pave in the future. Use the diagram below to help you.

Just to be clear, the exact length of the post is the total height (from the top of the beam to the floor) minus the Post Set Down minus the ground clearance.

Once you are certain that you have this measurement correct carefully cut the post to this length with your power tools. After you have cut the post be sure to spray the cut ends with a timber preservative.

Fit the post shoe

Now that the posts have been cut to the correct length the post shoes need to be fitted for each post. Follow the appropriate instructions from the previous diagram to suit the post shoe type you have. Please pay particular attention to ensure that the base of the post is the distance you require above the seat of the post shoe.

Determine location of post hole and dig hole
Once you have all of your posts fitted with shoes you can move on to digging the holes to fit your posts and then concreting in the post shoes. Holes are located directly under the posts so that the posts can be easily plumbed.

A simple ‘plumb bob’ can be made by attaching a weight to the end of a piece of string. Attach the other end of the string to the beam at the position you have marked for the centre of each post. Let the weight hang just above ground level (you may need to adjust the length of string to achieve this) and (barring any howling winds!) it will be located directly above the centre of where you will need to dig the footing hole.

You will find the required footing size for your posts on your plans. Dig a hole to these dimensions at every point that a post is required. It is important that you make sure that your footings are the correct size as they are essential in anchoring your pergola in extreme weather conditions.

Fit the post and pour concrete

Now that you have your holes in place, you can fit the posts to the beam. The posts are to be fitted to the beam while the structure is still on props so that the beams don’t fall with the posts into the holes. Once the posts are fitted, the shoes should sit above the bottom of the holes that you have dug for them. This way you can fill the holes around the shoes and they can set in exactly the right place.

You should have already worked out where the centre of the posts are supposed to be on your beams, and marked this point. From this point, measure outward half of the width of the post in both directions from this mark. Eg an 88mm wide post measure and mark 44mm each side of the centre. This will locate where the edges of each post will be fixed.

Lightly project these marks down the face of the beam to provide a guide for lining the post up. To position the post place the post shoe in the hole first and lift the post up so that the beam rests nicely in the pre cut notch.

When the post aligns with the markings each side, clamp post and beam together. Final, small adjustments can be made by loosening and tightening your clamps.

Make sure that the post is level and when you’re satisfied that it is, drill through the post and the beam, using you spirit level to make sure that the post alignment is correct. Bolt the post to the beam using 2 or 3 M10 bolts. Make sure that you have the bolt heads on the outside of the beam.

Once you have fastened each post, mix your concrete according to the manufacturers instructions and pour it into the footing holes. Before you pour any concrete, do a last check to see that your beams and bottom chords are level as well as your posts.

Pouring the concrete, unless done very carefully may cause the post to be moved out of level – quickly check each post after pouring and return it to level if this occurs. Repeat this for all of the posts and also check the levels of previous posts as you go.

Once all of the concrete is poured, and all holes are filled, you should leave the structure propped until the concrete has set. It is best to leave it over night as working on the structure may result in your pergola being moved out of square as the concrete cures. Once the concrete has completely set, you can remove the props as it will now stand alone.

Now that you have completed this step, you can move onto the next phase, Installing the Rafters and Ridge.

How to build a Gable Roof Pergola – Step Eight – Installing the Rafters and Ridge

How to build a Gable Roof Pergola

For further information or any inquiries you might have please get in contact with us via the phone or the form below, we’d love to hear from you.