Softwoods Blog

Building a deck from timber is one of the easier DIY projects that you can undertake that will have a lasting positive impact on both your lifestyle and your home’s value.

Once you’ve decided to undertake the project, the most critical part is the planning and calculation of the timber you require for your joists and bearers in order to properly support your decking structure.

The process involved in planning for your deck involves several steps, firstly, you need to calculate the floor load width of your bearers, then select your bearer size and post spacings based on this information, and lastly select the correct size of your joist based on their required span. The use of span tables and floor load width calculations will be explained in detail further in this article, and hopefully you will finish reading with a good idea of what’s required to build a great deck for your home.

Please keep in mind as you read this guide that if you would prefer to have all of the calculations and planning work done for you, the teams in our stores at Softwoods are more than happy to do it all for you at a moments notice. If you’d like a free quote on your decking project please get in touch at any time.

In order to create your own deck, familiarity with the parts is required. Bearers are the timbers that are attached to the stumps or posts that support the deck and Joists are the timbers that are attached across the bearers to which the decking boards are in turn attached.

In addition, the concept of single and continuous span must be explained. A bearer that is considered to be single span, is fixed to stumps at each end of it’s length with nothing in between to support it. A continuous span bearer is one that is supported at more than two points along it’s length. For example, a deck that is 1 metre long and 1 metre wide is likely to have only two bearers, one either side (running the length of the deck) and will be considered single span as each bearer will be supported only at each end. Alternatively, a deck that is 1m wide and 10m long will still have two bearers each running the length of the structure, but they will need support along the 10m length from several stumps, and as such will be considered to be continuous span.

The load that you put onto your deck can at times be very large indeed, so correct calculations of the stiffness and strength of the internal timbers of your deck are essential. The flexibility of timbers and their strength is taken into account in the Australian timber framing code that is used to create span tables for both Bearers and Joists. Selecting the correct timbers and the layout of your deck is relatively simple once you are able to interpret these tables which are based on engineering calculations that are far too complicated for most non engineering types.

To correctly calculate the minimum strength and placement of the timber that you should use on your deck, you need to first establish the floor load width of your bearers, and then the spacing of your posts. The image and text below is a simple guide to the concept of floor load width.

As you can see, there are three different possible variables in a floor load width calculation.

First is bearer A, which absorbs half of the load of distance Y, as well as the overhanging distance X

Bearer B is different in that it is internal and has a bearer on either side of it. Due to this, the floor load width of bearer B is half of both distances Y and Z

Bearer C is another different calculation in that it is only bearing a load in one direction. As such, the floor load width of bearer C is half of the distance Z

In order to calculate your own floor load width you will need an idea of the size of deck that you want to build.

As a practical exercise we will choose a deck that is 10 metres long and 6 metres wide. The deck will have four bearers of continuous span running the 10 metre length of the deck. Two are on the outside of the deck, and two internally, creating three gaps of approximately 2 metres

**(the best number of bearers, posts and joists is a highly variable proposition(both in terms of value, labour and structural integrity) and can be best determined by people with lots of experience in building and designing decks)

In order to establish the required size of your bearers and the post spacings for your deck you need to calculate the floor load width of your structure. We will use the diagram below for reference.

Both Bearers A and D are only bearing a load on one side. This load is equal to 1 metre each as they are bearing half of the distance between them and the nearest bearer.

Bearers B and C are however bearing a load on either side of themselves. In both instances the floor load width is equal to the sum of half of the total span on either side of the bearer (total span = 4m floor load width = 2m) for a visual representation of the floor load width, see the sketch below

Once you have determined the floor load width of your bearers you can proceed to selecting the size of your bearers and your post spacings using a span table. At Softwoods we use only F7 Kiln dried treated pine in our decking substructure. It is possible to use timber of a lower stress grade, but we feel that in order to guarantee the long life and performance of your deck it is worth using quality materials.

Span tables are made up of variables based on the engineering within the timber framing code of Australia. There are many differing span tables available, the following link has a number of tables for your use (***note** all for use under 1m high**)

http://www.tabma.com.au/resources.php

Please be aware that there are also many variables with regards to the engineering of decks that are raised above ground. The use of double bearers, as required in AS 1684.2 is important to note and we recommended that if your deck is to be over the height of a metre that you should contact us for a quote and to help you with your plan to ensure your safety and compliance with your local council or shire.

For the purpose of our exercise we will use a span table for Decking bearers with a continuous span. In order to select the correct bearers we need to have established our floor load width, which in our case is 2 metres (always use the largest floor load width from within your structure)

In order to use the table, select the floor load width from among the top line of the table (in this case 1200mm, 1800mm etc) our example is 2m (2000mm) and use the corresponding column  (2400mm) below to select the appropriate size of bearer from the list on the left, and the post spacing measurement to match from within the column.

For example, our floor load width of 2m means that we need to use the 2400mm column to determine our bearer size and post spacing. We can select 190×45 bearers, which will require posts every 2.1 metres along our 10m long deck (resulting in a total of 6 posts per bearer) or we can use 190×70 bearers which will need a post every 2.6 metres (5 posts per bearer) As you can see it’s a case of determining what is the best and most economical, yet structurally effective combination. (**note** these calculations are based on the inclusion of a post at each end of the bearers, which is not always necessary) Please also note that the post spacing specified is a maximum of 2.1m. Although it’s not necessary to have your posts evenly spaced, you must not exceed 2.1m between any two posts. This allows you some flexibility in case there are any obstructions beneath your deck that you need to work around (the same concept of maximum spacing also applies to your joists)

Once we have our bearers and post spacings determined, we have to use another span table to decide on the correct joist size for our structure. The Joist span table below is for joists with a continuous span on a deck below 1metre in height.

To determine the correct joist required, we need to establish the spacing of our joists. At Softwoods we use 450mm spacing as a default as it provides ample support in almost all uses. We do use 400mm spacings with clear treated pine as it is slightly more flexible than our other decking materials. Please see an example of 450mm joist spacing below

With your joist spacing determined you can use the 450mm column to determine what size timber you will need for your joists. The numbers in the 450mm column refer to the distance that the joists are required to span between bearers. In our example we have a 2m span between bearers, so we need to scroll down until we find a number over 2000 and select the corresponding joist size from the list in the left hand column. As you can see on the table above, this will be a 140×35 joist. You can then determine the number of joists you will need by dividing 10 metres (10000mm) by 48.5 cm (485mm) which gives you 20.62 or 21 bearers. (**Note** 45mm thick Joists are usually preferred as it is much easier to affix decking boards that join over a joist when you have a little more space to work with)

The last thing that you need to do to calculate what you will need for your deck is to calculate the number of decking boards you will need. For our exercise we will use 90mm decking boards with a 5mm gap to allow for any movement. As our deck is 6m wide, we will need 6m (6000mm) divided by 95mm (each board and gap) which gives us 64 boards. Our deck also has to run the length of 10 metres, so we multiply 64 boards by 10 metres to give us 640 lineal metres of decking. When using random lengths of decking (as will usually be the case) an allowance of 15 to 20% of wastage is also recommended. You can also at this point calculate the number of nails you will need for your project by dividing the total lineal metres by .225. In this case we have 640 lineal metres, which divided by .225 gives us a total of 2844 nails.

Hopefully, this guide will have given you a good idea of what is required to accurately determine the amount and type of materials that you will need to build your deck. For further information or any inquiries you might have please get in contact with us at softwoods, we’d love to hear from you.

In what we at Softwoods see as a welcome and long overdue move, the Australian government will introduce new legislation this year to prevent the ongoing importation of illegally logged timber. As an environmentally concerned company, Softwoods make every effort to ensure that all imported timber that we buy has a verified chain of custody and is being logged from approved and sustainable areas. While chain of custody documentation is presently available on some imported timber, there is a concern that it’s authenticity is not always certain.

To add to the complexity of this issue is the fact that the market in Australia for timber decking has for a long time dictated a strong preference for imported hardwoods. In order to buy these hardwoods ethically, the above mentioned chain of custody must be sought, however the knowledge that this is not at all times authentic creates a difficult bind for both the consumer and the buyer. This is why we are very pleased that the government is going to regulate these imports and provide a framework that ensures that the product that gets to market here in Australia is coming from the area that is specified by it’s chain of custody, and that it is legally sourced and not coming at the cost of another nations natural resources.

Below is the text of a December 2010 media release on the issue, and a link to the department’s site follows that.

9 December 2010
DAFF10/067L

Minister for Agriculture, Fisheries and Forestry, Senator Joe Ludwig, today announced the Gillard Government will introduce legislation restricting the importation and sale of illegally logged timber.

Minister Ludwig said the new laws will promote global trade in legally logged timber products and stop unfair competition in Australia between illegal and legal timber suppliers.

“Illegal logging is a major problem for many developing nations and directly threatens Australian timber jobs,” Minister Ludwig said.

“Internationally, illegal logging is estimated to cost more than $60 billion each year.

“After widespread industry consultation, the Australian Government will introduce legislation that carries penalties for importing illegally logged timber.”

Minister Ludwig said the legislation is one of many tough measures the Government is taking to combat illegal logging.

“Under the legislation, importers will now need to meet a due diligence test to ensure the timber they are sourcing has not been illegally logged,” Minister Ludwig said.

The new rules will apply to all timber products including sawn timber, wood panels, pulp, paper, wooden furniture and composite products. The legal origins of these products must be clearly verified according to requirements set out in the legislation.

“The legislation will encourage investment in the Australian timber industry and give consumers and businesses greater certainty about the timber products they buy,” Minister Ludwig said.

“This initiative will complement a global effort being championed by Australia, the United States and the European Union, to combat illegal logging and demand importers disclose the legal origins of their wood.”

The new legislation will be introduced into Parliament in 2011 after public consultation.

Department of Agriculture, Fisheries & Forestry

Being that this blog is here to provide information on Pergolas, Decks, Timber and outdoor entertaining using timber, it makes sense that we cover the types of timber that we sell at Softwoods and give you the reader as much information as possible about them, so that you can make an educated decision about what you are buying. This particular article covers CCA Treated Pine. My primary source in researching this article is the CSIRO, where you will find an exhaustive and likely more coherent outline than mine!

At Softwoods, most of the structural timber that we sell is plantation grown Radiata Pine. In order to prevent movement and rot and to deter pests such as termites and borers, the timber is put through a treatment process once it has been cut and before it is packed and distributed. This process, involves subjecting the cut timber to a solution of chemicals via a vacuum or pressure system which penetrates the timber with the solution and bonds chemically to the timber providing a defense against weathering, movement and pests. The timber is then kiln dried to lock in the treatment solution and remove any excess moisture (which if left wet will result in unpredictable movement)

There are several differing varieties of treatment available. The most common treatment that has been used reliably for decades is CCA or Copper, Chromium and Arsenic treatment. CCA is currently the most widely used timber preservative in Australia and is produced in approximately 120 plants across the country.

The use of CCA treatment will prolong the useful life of timber from a few years to over 40. It has been used as the primary type of timber treatment worldwide for a many years and is an amazingly reliable and low cost natural product.

The ingredients in the CCA solution are there to serve the following purposes:

Copper to prevent the growth of funghi

Arsenic to prevent termites and wood borers

Chromium to bond the copper and arsenic to the molecular structure of the timber.

The combination of these ingredients is dictated by Australian standards and is tightly regulated to ensure both the safety of the product and the appropriate mix for maximum effectiveness. The process of affixing the treatment formula to the timber ensures that all of the formula becomes chemically bonded to the timber and is unlikely to leech at any point. Since 2006 it has been necessary by law to ensure a high standard of fixation of treatment before any products can be dispatched from treatment.

The reason I’m talking about the importance of fixation of the treatment solution to the timber is that there is a recently arisen concern regarding the safety of using chemicals such as arsenic, and whether exposure to it is healthy for those building with the timber, as well as families, children, pets and soils that are near to the structure. This is a fair and justified concern, (and allaying this is the main purpose of writing this piece) as the safety of any product that becomes a part of your home should be examined as closely as possible.

Having used CCA timber for over 29 years, we at Softwoods are completely confident in selling CCA timber products to you, however in certain instances of incorrect use CCA can be hazardous, and it’s with this in mind that we’d like to outline the following information.

CCA treatment in Australia is regulated by the Australian Pesticides and Veterinary Medicines Authority (APVMA) In March 2006 the APVMA implemented a series of precautionary restrictions on the use of CCA treated timber for structures where there is frequent and intimate contact with humans, such as playground equipment, picnic tables, handrails, decking boards, garden furniture and exterior seating. The use of CCA treated timber has not been banned for the overwhelming majority of it’s applications including industrial, commercial and agricultural uses, farm posts and marine applications.

In accordance with this ruling Softwoods have stopped selling CCA decking and handrails, and we use LOSP treated posts for our pergolas as well. We still use CCA treated pine for all internal members of our pergolas and decks, and this is perfectly safe and in compliance with the regulations.

Perhaps more importantly though, should be an explanation as to why this precautionary measure was put in place and what sort of risks are involved with intimate contact with treated pine?

The main concern with CCA treated timber is that it contains Arsenic. Arsenic itself is not a mutagen (an agent that changes genetic material often triggering the growth of cancer) but when it is ingested above tolerable limits it can act as a carcinogen (generally skin or liver cancers)

Luckily the amount of arsenic that humans can ingest is well known, as arsenic is a naturally occurring substance and has been found and monitored in the drinking water of several countries (Japan, Bangladesh, Argentina, Taiwan) As it is a naturally occurring substance (20th most common element on earth) it is to be expected that humans can withstand some level of arsenic ingestion before it has ill effects. Research has found that arsenic is safe to ingest at levels below 2ug/kg (there are 1,000,000,000ug per kg)

The Arsenic used in CCA is in a form (pentavalent arsenic(arsenate)) that is five to ten times less toxic than the most toxic form (trivalent arsenic(arsenite)) When affixed to the chemical structure of timber, the arsenate is modified into metal-metal complexes (info) or organometallic compounds (info) which pose no further risk.

Studies of the ingestion of the arsenic fixed to timber by treatment on animals have shown that the modification of the arsenate greatly reduces it’s toxicity. Though I personally don’t think that testing anything on animals is very nice, from my research into this subject it seems that some studies have been carried out, and they have overwhelmingly shown that ingestion of a small amount of treated pine has no effect on the health of the subjects. The aforementioned studies show that in beagle dogs, sheep and calves the feeding of treated timber to the animals resulted in no ill effects and the timber being excreted via the faeces and urine (even when fed as much as 113 grams per day for 25 days (how one manages to feed 113 gms of timber to a sheep for 25 days should be cause for another investigation perhaps?)

In order to get a proper understanding of the safety of using treated pine, this ingestion information must be taken in turn with the idea that the overwhelming majority of the treatment will be locked into the timber chemically for the extent of it’s life and will likely go nowhere. Having said this, it’s also prudent to point out that a very small amount of leaching can occur from the timber. This potentially poses a small danger to soil close to posts sunk inground. The leaching has been shown in studies to affect the 100mm surrounding each post. These studies showed that root crops grown next to CCA treated posts inground showed a small amount of arsenic content (which was determined to be in a safe organic form, and could be removed by peeling) If you are concerned, this leaching issue can be averted by either not growing anything within 100mm of a sunk post, lining your garden’s perimeter with a gardening plastic, or mounting all of your posts on post shoes which will lift them aboveground and prevent any leaching whatsoever. Softwoods mount all of our posts on post shoes (except occasionally with internal posts for decking)

Aside from leaching into soil, there are occasionally concerns about the potential for absorption of arsenic through the skin. This has been proven to be negligible, and no record of any negative effects is recorded. Regardless, it is recommended that gloves be worn when handling treated pine so that splinters and sawdust don’t get onto the hands where they can later be ingested. In addition to this, dust masks should be worn when sawing or sanding together with protective goggles. These are purely precautionary measures and make sense from a safety perspective regardless of any potential danger from the treatment of the timber. Painting of the treated pine will also assist with reducing any potential for dislodgeable arsenic, further protecting you from any potential hazard.

Finally, the one thing you must be extremely careful to never do with treated pine is burn it. Burning CCA treated pine created toxic smoke that can be hazardous to health, so it is advised that CCA treated pine be disposed of through normal waste collection services, unless it is a large amount of timber (where you will have to make arrangements with your council for it’s safe disposal)

Hopefully in reading this article you will have developed an understanding of the idea that we have, which is that the correct use of CCA treated pine poses no risk whatsoever to you and your family. Whether through ingestion, contact through the skin or leaching into soil, treated pine has been regularly proven to be safe for human use. The preventative measures on certain usage should be viewed through the understanding that there are alternative treatments available that don’t contain arsenic, and that it makes sense to eliminate risk entirely, even if that risk is infinitesimally small.

Hipages recently made some videos for Softwoods, covering the services that we provide to our customers. One video covers our Pergola services and the other relates to Decking. Have a look for yourself.

Softwoods are committed to providing our customers with all of the care and advice that we can, and we are happy to present here our comprehensive instructions for building a pre cut Softwoods Pergola. This is an extremely long and comprehensive document that will help you through each and every aspect of the building of your structure. For ease of navigation and reading it has been broken into several posts that cover all of the elements required in your build.

This particular set of instructions is for a parallel attached gable roof pre cut pergola kit. Our pre cut pergola kits make the construction of a pergola considerably easier than previously because all of the angles and notches are cut to create a kit that will fit together simply, without the requirement of endless measuring and cutting.

Our assembly method also benefits from pre cutting, allowing a lot of the work to be done on the ground which makes for a safer build. In addition to these instructions there will be further posts on how to install Hip ends, freestanding pergolas and decks in future.

As a guide for you, most of our carpenters can finish a 6×4m parallel attached structure in approximately two days. We would advise that you should take your time and make sure that you are doing everything methodically and properly as it will save you time and money if you get everything right the first time. Following our instructions should mean that you are able to build your pergola as easily and quickly as possible.

Please click through to each article in the series for each step in the process.

Step One – What you need to consider before you build

Step Two – Identifying the elements of your Pergola

Step Three – Marking out

Step Four – Assemble Gable Frames

Step Five – Installing Fascia Brackets

Step Six – Installing Beams and Bottom Chords

Step Seven – Installing Posts

Step Eight – Installing the Rafters and Ridge

Step Nine – Installing Gable Ends and Purlins

Step Ten – Installing Gutters

Step Eleven – Installing Roofing

What You Need To Consider Before You Build

In building a Pergola, you can save yourself a lot of time and hassles down the line if you give some consideration to a few things before you start.

It is very important to check with your local council or shire before building any structure. It is your responsibility to ensure that all relevant approvals have been obtained and that the structure that you are attaching to (likely your home) is suitable to support the additional load imposed by your new pergola. In the absence of approval, a council or shire can reasonably demand that any structure you have built be pulled down. Obviously this is not a desirable outcome so we strongly recommend that you get your approval first!

Most local councils or shires require an application to be lodged detailing the proposed works and whether they meet engineering standards and local guidelines. Generally speaking a fee is required to lodge an application, and an approvals process is undertaken which usually takes a number of weeks (the timing can vary wildly from council to council) Plans and elevations are needed with the application, and if there are any issues your council or shire will usually contact you for clarification or further engineering.

If you are using Softwoods for your materials we will provide your plans and elevations free of charge for your application, and all of our pre cut structures are certified by our engineers. We also have a plan service, which charges a nominal fee for the preparation of plans for you should you require them.

Once you have approval, you will need to ensure that you have all of the necessary materials to make building your Pergola as safe and simple as possible.. Below is a list of these tools.

Easily the most important thing that you need to do in preparing to build your pergola is to create a safe work site. As you will no doubt understand, your well being is essential and it’s worth making sure that you feel safe at every stage of the building process.

Various stages of construction will require at least two people to complete so make sure that you have some helpers on hand for these. Also ensure that appropriately tall ladders are used when required and that your work site is clean and clearly flagged during construction to avoid children or other unauthorised people entering the potentially dangerous area. You will find handy safe work methods and tips on our website which we advise you to read carefully

It is also worth your time to make sure that if your timber is delivered in advance of your intended build date, that you ensure it is stored correctly. Timber will be subject to some movement if not stored correctly, so please ensure that it is tightly packed, off the ground and in a dry area (avoiding placing it on lawn is a good idea)

The last thing that you need to consider before you start to build is the painting of your timber. Not many people enjoy this part, but unfortunately it needs to be done, as a painted structure will withstand the weather infinitely better than one that’s unpainted. Again if you are buying your materials from Softwoods we can offer a painting service and deliver you your materials fully painted and only in need of a minor touch up upon completion of your build.

Use two painting trestles, and a roller or spraygun to paint all of the timber, and ensure that you use the paint to the manufacturers specifications. It’s important to get the painting right while the timber is on the ground as it is very difficult to repaint once your structure is built. Once you have painted your timber, store it with spacers so that the timber wont stick together as it dries. Once you are done with painting, it’s time to commence the build!

How to build a Gable Roof Pergola – Step Two – Identifying the elements of your Pergola

How to build a Gable Roof Pergola

Step Two- Identifying the elements of your Pergola

In order to successfully put together your pre cut pergola kit, you will need to be able to identify all of the elements of the structure. Furthermore we will be referring to all of the pieces by their names from here on in, so it makes sense to establish what is what at this point.

Your kit will be delivered with a bill of materials and a cutting list. The names of each timber on the list correspond to their names in the diagram below (click on the diagram to enlarge it) Before building anything, conduct a thorough check to ensure you have every piece of timber.

To help you identify and assemble the timber members they have been marked. The markings are on the cut ends so that they will be visible when the timber is painted and not visible once the structure is complete.  There are some members that you will need to mark, however we recommend that you should paint all members before marking anything.

Corner Posts are marked with a PC# on the notched out sections

Intermediate Posts are marked with a PM# on the notched out sections

Beams are marked with a BM# on the topside at one end

Bottom Chords are marked with a BM# on the topside at one end, the bottom chords have a notch in each end.

Standard Rafters are marked with a RS# on the topside at one end

Gable End Rafters are marked with a RG# on the topside at one end

Collar Ties are marked with a CT# on the topside at one end

The Ridge is marked with a RDG# on the topside at one end

Purlins are marked with a PR# on the topside at one end

Vertical Struts are marked with an ST# on the end cut

Starburst Struts are marked with a SB# on the end cut

Barge Boards are marked with a TB# on the internal face at one end

Once you have identified all of the timbers and painted them it’s time to start marking out

How to build a Gable Roof Pergola – Step Three – Marking Out

How to build a Gable Roof Pergola

Step Three – Marking out

Once steps one and two are completed it’s time to begin marking out your pergola. Marking out your pergola is not unlike a preparing food before you cook. Being well prepared allows you to put your pergola together quickly and easily, and means that you won’t have to stop or go back in the middle of building.

A major benefit of a Softwoods pre cut gable pergola is that a lot of the measuring and marking has been done for you. Other tasks that would have previously been done ‘in the air’ when the structure is partly constructed can now be done safely and accurately on the ground.

This makes the building process safer, quicker and easier for you. The key benefits of accurately marking at this point are that it will ensure that everything goes together accurately and quickly once you assemble the structure.

If you are marking and cutting your own pergola, this part of the process is EXTREMELY important, as it’s integral to your structure going together in an orderly manner. You will need to calculate all of the angles required to get the correct pitch for your structure, cut them accurately (as well as your posts and bottom chords) And you will need to measure the spacings for your rafters and purlins.

Fitting Joist Hangers to Beams

The beams (members marked with a BM#) have the positions of the rafters already located on them. About every 1200mm (exact measurement depends on your structure) there will be three holes punched into the face of the timber.  Holes 1 and 2 line up with corresponding holes in the joist hanger. Hole 3 forms a triangle with holes 1 and 2  to indicate the top side of the beam.

To fit, line up the joist hanger holes just above the single gang nail on flange with holes 1 and 2 on the beam. Drive a connector nail through the joist hanger into hole 1 leaving the head of nail just proud so that it can be pulled out if it clashes with the bolts of the fascia bracket fitted at a later stage.

Squeeze the joist hanger so the central hole on the opposite flange  is aligned with hole 2 on the face of the beam. Drive another connector nail through to complete the temporary attachment of the joist hanger to the beam again leaving the nail just proud. The remaining connector nails will be fitted after the rafter has been located in the joist hanger.

Repeat this process for all the joist hangers required in the structure. The result will be two beams with joist hangers positioned exactly to receive the gable frames.

Marking Rafter Positions on Purlins

The purlins (members marked with a PR#) are fitted to the top of the rafters after all gable frames have been installed. Pre marking on the purlins exactly where they should intersect with the rafters will allow the rafters to be easily pulled into square when the purlins are installed.

Arrange the purlins side by side on a level surface or on saw horses.  All of these members will be the same length. Position the beams with joist hangers attached so that they are on either side of the group of purlins and so that the ends of all members line up. The arrangement should look like the image below

Use an off cut or straight edge to mark a line across all of the purlins to correspond with the edge of the joist hangers. The result of the marking out is illustrated below

Repeat this process for the other joist hangers. The result will be two lines marked on each purlin that represent the position of each rafter.

Marking purlin locations on rafters

The last members you have to mark are the rafters.

Have a look at your plan you will be able to see how many spaces between the purlins there are on your structure. Measure the top edge (or run) of one of your internal rafters and subtract 70mm from this length.  Once you have that number, you will then need to divide it by the number of spaces.  This is the distance from the top (closest edge to the ridge) of one purlin to the top of the next purlin.  Mark this out on your rafters leaving out the bottom mark as that will be determined by the edge beam and the internal gutter.

For Example:

If x = 2400

Then 2400 – 70 = 2330

2330 divided by 3 spaces

2330/3 = 777 (round up)

Based on this calculation, you would place a mark 777mm from the top of the rafter then another mark 777mm down from that.  Please remember that you don’t need to mark the top or bottom purlin position.

Marking rafter locations on ridge

The top side of the ridge will have small scores along it to indicate where the centre of each rafter will go.   Similar to the number 3 holes marked on the beam.

Once this has been completed, it’s time to begin to assemble your gable frames in the next step.

How to build a Gable Roof Pergola – Step Four – Assemble Gable Frames

How to build a Gable Roof Pergola

Step Four-Assemble Gable Frames

The next step in building your Softwoods pre cut gable pergola is to assemble your gable frames. It’s at this point that you might finally start to get the feeling that you are actually building something! However as with the previous steps, this step is also preparation for the building to come.

Gable frames consist of the internal rafters and collar ties, which are made into an A shaped frame to be lifted into the structure once the beams have been installed. Your gable frames will provide the internal shape to your structure, so it’s important to make sure that they are all of a uniform shape and size. Your frames will be made on the ground then lifted into place later. You will need to do this on a flat surface for the most accuracy.

Layout rafters with bottom chord and ridge block

Lay the bottom chord on timber blocks (rafter stiffeners) on a flat surface and then place 2 rafters with their ends on the inside of the mitre (see the diagram below for a clear picture). The rafter edge will line up with the vertical face of the notch as well as the angle of the rafter.

Using a ridge spacer (supplied in the hardware box) as a makeshift ridge, move the rafters so they meet the ridge spacer at the top. Make sure the rafters are still in the correct position against the bottom chord. The rafters and ridge should look like the diagram above, and need to be elevated on rafter stiffeners as described previously so that it is easy to drill through the rafters in the coming steps.

Place collar tie

Once rafters are in position, place the collar tie on top of the pair of rafters with the cut edge following the angle of the rafters. The rafters and collar tie should form an A shape.

To establish the exact position on the rafters that the collar tie should sit, measure from the edge of the rafter to the edge point of the collar tie on both sides and check if they are about the same. If you are unsure, have a look at the diagram below for the point that you should be measuring.

You may need to move the collar tie a few times until your measurements are the same or similar.

Drill and bolt collar ties

Drill 10mm holes for your bolts through the collar tie and rafter using the table and diagram below to determine their quantity and placement. You can clamp the collar tie to the rafters as you drill to make sure that there’s no movement of the frame as you drill.

Once the holes are drilled insert the bolts through the rafter and collar tie. You will need to knock the bolts in with a hammer. Because of the tight holes, the frame will be held firmly in place. There is no need to fix with washers and nuts at this stage.

Now your first gable frame is almost done. To continue with the next frame, place another set of rafters and a collar tie above the frame you’ve just made (see example below)

Line up the rafters and the collar ties so they are parallel with the first frames components. This should allow you to easily and accurately recreate the first frame, using the ridge block and the angle of the previous gable frame as a guide.

To make sure your collar ties all line up when the frames are installed, measure the distance between the two at both ends. If it is the same, the collar ties should all be straight.

Once you are confident that your new frame is in the correct shape, mark and drill the holes for your bolts through the collar tie and rafters as before, inserting the bolts once you are done. Repeat this process until all of your gable frames are assembled with bolts inserted on the ground, and then stand the frames up one by one and fit them with washers and nuts and tighten.

All of your gable frames should now be finished. Store them in a dry safe place until they are needed.

You can now move onto the next step, Installing Fascia Brackets.

How to build a Gable Roof Pergola – Step Five – Installing Fascia Brackets

How to build a Gable Roof Pergola

Step Five-Installing Fascia Brackets

The next step in installing your pergola is one of the most important. Fascia brackets are the method by which your pergola will be attached to your home. They form a strong bond between your house roof and your pergola, making sure that both your home and your pergola will not be affected by any weather or the weight of your structure.

Fascia brackets are designed to take the load of your pergola back into your home’s roof and make sure that this load is not borne by the house fascia.
It is very important to install your fascia brackets correctly to ensure sufficient structural support for both your pergola and your home. Fascia brackets and stiffeners are installed at 1200mm centres.

Install rafter stiffener

To install rafter stiffeners to your house rafters you will need to temporarily move your existing roofing so that you can have access to the rafters. Rafter stiffeners are lengths of timber that are used to provide additional support to the house rafters. Fascia brackets attach directly onto them.
Getting access to the house rafters can be achieved by unscrewing the metal sheeting or lifting up tiles. If you have a sheet roof, use an off cut or a couple of short props to make a cave like area to work in. However, be very careful not to crease your sheets in doing so.

Once you have access to the house rafters, use 75mm bullet head nails to fix the 70 x 35 rafter stiffener to the house rafter in a zig zag fashion with a maximum spacing of 100mm

Cut slot in fascia

Using a pencil, draw a line on the inside of house fascia lining up with the outside face of the 70 x 35 stiffener you have just installed. Use a straight edge to follow the outside edge of the stiffener around the house gutter and onto the outside of the fascia and mark this point. Cut a 60 x 7mm vertical hole through the house fascia starting just underneath the gutter. Before you cut anything double check that your first hole is located beneath the gutter’s lowest point.

Install end fascia brackets

Slide the bracket up through the slot you have just cut so that the outside face of the “T” section is flush with the outside of the gutter. Once the bracket is in position, drill holes and insert bolts through the rafter stiffener and rafter using 4 x M10 bolts.

Install the two end brackets first and use a string line to make sure the remaining intermediate brackets are all level. Once you have installed intermediate brackets, you can refix the house roof and proceed to the next step, installing the beams and bottom chords.

How to build a Gable Roof Pergola – Step Six – Installing Beams & Bottom Chords

How to build a Gable Roof Pergola