Thursday, February 9, 2012

Building a timber deck.

It is a nice change every now and then to shut the door on my workshop and go do a bit of carpentry instead of making furniture and joinery. Mind you, when it is around 40degreesC neither the workshop nor outside offer easy working conditions! Here in Perth we have had a run of days over 35 degrees and as high as 42. Humid as well, so the perspiration just pours off when swinging the hammer or doing anything physical!

So it was a pleasure to be building a timber deck for my customer Pam in Fremantle, with her friend Anna as a TA assisting me. I take my hat off to Anna for working so hard despite the heat and for being such a quick learner. Together we have been a good team and progress had motored along. Such an interesting old house. In a former life it was a bakery, now undergoing a serious renovation. It is always so interesting to me to work on old places. They just ooze with character.

In case deck building is something you're about to tackle and is not something you've done before, I hope this post may provide you with some ideas and tips for how to do it and make a really good job of it too...

Planning the job.
Once my customers had given me the dimensions and details of the position and height of the deck, my task was to first draw it up. The scale drawing process brings together the planing the construction, the dimensions and types of materials to be used, and the calculating of the quantities.  Within the Building Code of Australia we have "span tables" which provide guidance and minimum standards for the selection of materials and the specification of acceptable maximum spans for bearers and joists for decking. This deck was to be at floor level (about 450mm above the planned ground level) so there was no balustrading to consider. 
Doing a scale drawing enabled the specs and quantities to be calculated.
With the calculations and the scale drawing completed, I emailed off the drawing to my customers for approval. We met again to discuss the details further and a starting time and they ordered in the materials based on the quantities lists I had provided. After some discussion, CCA treated pine was chosen as the timber to use. All metal fixings (nails, screws, bolts, stirrups etc) would be hot dipped galvanised.
Setting out the job on site.
When I returned to commence the job, I found that the old concrete verandah had been removed, the soil level had been lowered, and Anna had used the drawing to pre-dig the holes for the metal stirrups which would be used in the place of timber stumps - to support the bearers. The timber was on site as with as most of the other materials that we would need. Everything was ready to go. Working backwards from the intended height of the decking surface, we determined the required level of the top of the bearers. We used my el-cheapo laser level to establish a reference line, and knew what height below that reference line the tops of the bearers had to be established. String lines helped to define the outer limits of the deck based on the required dimensions. The deck was to be in an L-shape, with the long leg being almost 10m ( 32.5 ft) by 2.1m (7 ft) wide. The short leg would be 7.5m long (24.5 ft) by 3.0m (10 ft) wide, meaning the 3.0m wide section extended a further 5.4m (17.5 ft) beyond the 2.1m section. This 10m long x 2.1m section was under an existing verandah. The edge of the deckline was to be directly below the verandah plate above it. This deck line was determined with the use of plumb lines from the top plate. The total area of decking would be about 37m2 (400 ft2).
Two views, one each of the legs of the "L shape" of the decking.

Laying out the bearers and stumps.
There are a number of ways to do this, but my preferred method is to make up the bearers full length, attach the metal stumps (stirrups), suspend the bearers levelled and in the correct positions, and pour the concrete around the stirrups. These days, it is common for bearers to be made up from two narrow sticks nailed and bolted together as a pair. In this way we made up the two bearers that were 10m long each, and the remaining 3 bearers which were 3m long each. The joints in the 10m bearers were staggered, mitred, and always over a stirrup. The bearers in this way were made from pairs of 120mm x 45mm CCA treated pine sticks.
The two 10m long bearers, propped up and in position, with concreting under way.   Temporary prop holding up the verandah until the new verandah posts go in.

The placement of frequent temporary supports, (made up of bricks, blocks, pieces of timber and fine-tuned with assorted packers) enabled the bearers with the stirrups already bolted on to be suspended over the holes ready for concreting. The laser level was used to ensure the bearers at each support and stirrup were leveled at the required height.  When the bearers were all set up ready, the concrete was mixed and poured around each of the 23 metal stirrups, and left for a couple of days to dry.
Detail showing the propped bearer with metal stirrup, suspended over the hole. The concrete would be poured half way up the 12 inch leg of the stirrup. Note also the staggered mitred joint in the bearer above the stirrup.  

Fixing the joists.
Before the joists were fixed to the bearers, the aluminium flashing was rolled out along the tops of the bearers. This flashing prevents the ingress of moisture between the pairs of timber making up the composite bearers, and thus greatly improves the durability of the bearers.
The joist positions were set out over the bearers, at 365mm centres. This is a little closer than the original plan, but putting an extra joist in the span will improve the decking by marginally reducing the spring in the decking. I am happy to be accused of over-engineering. String lines were used to ensure the joists were nailed in straight lines, and each joist was skew nailed from each side into the bearer below at each junction. Lots of 4 inch galvanised nails, pounded in by hand  using my trusty old Cheney hammer.
While the concrete was curing, I was still able to cut the joists to length ready for fixing down the next day. The flashing has yet to be rolled out along the tops of the bearers.
The joints in the joists were always staggered, mitred and centred over the bearers. The bearers and joists were always left "over-long", to be cut to final length later.
The long run of the decking structure, with most of the joists now cut to length, determined via stringline.
The original verandah posts had to be removed in order to undertake this work, before the bearers could be positioned in place. Amazingly enough, the old verandah top plate was full length - 10m (over 32 feet) which is a long 8"x2" of jarrah! You can't get them like that any more...  Anyway, in order to do this and provide the support, I first had to pick up the plate half way along it's length. The picture above shows how I did this. Once the temporary support was in place, the original posts were removed. The bearer/stump positions had been planned so that the new verandah posts would each be over a stump. 
Pam pleased to see the joists all fixed down. Some cutting to length still to be done.
The nailing down of the joists is the part of the job I always find very satisfying. You can really see the progress unfolding as you go.

Tips for fixing down the decking.
The decking boards on a completed deck are what is seen the most, not the structure below it. It is therefore very important that the boards are nailed down straight, with regularly placed fixings, and with nothing that jarrs the eye. Here are a few tricks to doing it right:

1. Work from string lines. With a stingline taut between one end of the joist to the other, the line of nails should be beautifully in line. It will look really good.
Nailing down in progress. Sticks in the foreground under the stringlines and ready to be used.

2. Place the nails in a consistent staggered pattern. Putting the nails in a straight line weakens the joist below by helping it to split open over time. By alternating the nails either side of centre (ie. either side of the stringline) When hammering in the nails, move the stringline as you finish each nailing, or you will leave a dent from the string in the soft pine!

String line used with consistent nail placement pattern. Note the remaining spacer - the others have been removed. Note also the tidy butt joint under the stringline.
3. Use deformed shank nails and skew them. Deformed shank nails have spiral shanks. This gives them greater holding power. You can see them rotating as you drive them in! Skewing the nails give them additional holding power to resist the forces exerted by the decking boards over years as they respond to the constantly changing moisture content of the boards between winter and summer. Decking nails in extremes of the Australian climate are notorious for working their way up and out.The use of deformed shank nails and skewing them greatly helps increase the life of the decking and reduce the maintenance.
Deformed shank (spiral) galvanised decking nails, skewed. Doubly good holding power. 
4. Maintain a consistent gap between the boards. This is very important, and is easily achieved using spacers. For this deck, I used 5mm spacers. These were made by docking up a piece of melamine faced MDF which was kicking around my workshop.  A nail is driven half way through each spacer, which is docked to about 60mm x 30mm. This enables the spacers to hang on their nails in between the boards while the boards are pushed up and nailed in place.  I made up a pile of spacers, more than 20, to make the laying process easier.
A few spacers shown in place here. Short board in foreground yet to be cut to length
5. Use reference lines. A nice tight string line, laid the full length of the deck in the direction of the decking boards, helps to ensure the first boards go in a straight line. While the use of spacers helps to ensure nice even spacing, pushing bowed and sprung boards up to them will not always guarantee that the spacing will be perfect. You will also find that not all boards are necessarily machined to exactly the same width. Different machining runs can result in slightly different sizing. Possible errors growing and multiplying are brought back in check by the use of additional occasional reference lines exactly parallel to the original reference line. Subtle corrections can be made to bring things back into perfect visual alignment. 
Looking good. New verandah posts in place. Full length reference lines used to ensure lines remain straight.
6. Cut good joints and stagger them. If you have to join decking boards end-for-end, make sure you place the joins over the joists, and keep the joins as far away from other joins as possible (ie. stagger them and spread them over the deck). Good looking joints are obtained by a small chamfer on the top face at the end of each of the two boards at a joint. This V-joint is much more tidy visually than two ends butted up with their arises intact.

7. Finish the edge cleanly with a fascia.
Having a defined edge by the use of a fascia board makes a huge difference to the look and the finish of the deck. Daggy ends of a deck are not a good look. Housing them within a nice clean border makes for a much better product.
Fascia board made with use of a decking board. In this case the brick paving will be built up flush to the top of the decking. That's the retaining wall partly under construction.  
8. Use hand tools! Forget your drop saw and your nail gun. Seriously. For accuracy, speed and ease of operation, you just need a sharp tenon saw, a sharp block plane, a small try square and pencil, and a good quality hammer suitable for the task. When working under an array of nailing string lines, it does not make sense to walk each stick over to a drop saw, bring it back, and feed it under the stringlines again. While each board is laying on the joists, under the nailing stringlines, you can easily mark a square end over a joist, cut it to length beautifully square while laying on the joists with your tenon saw, and remove the arises on the ends with your black plane. Then insert the spacers and nail the stick down. I recommend pre-drilling the nail holes in the ends of the boards at the joins, to ensure the boards do not split at the ends. Skewed, of course.  Nail guns do not dress the joint like a hand driven nail will do. If you have a gap between the joist and the decking board, a nail gun will nail it down with the gap still there. A conventional hammer will close the gap as the nail is driven in, dressing it down. 

9. Take pride in what you do, and be your own harshest critic.
It's never OK to say settle for second best and say "that'll do". With power tools it's easy to make a mess of cuts. Too much power and not enough control makes for a lack of accuracy. However with hand tools it's all up to you how much attention to detail that you maintain and how accurate your cuts and hammering will be. That's one of the great things about using hand tools. 

Worried that your skills are not up to it? Keep your tools sharp and your hand skills will improve quickly while you use them on the job. Don't settle for second best. If your cut isn't square, do it again.

Nice job, eh? And it is really so easy to do...

So there you go... the story of a deck. Thanks again to my ever reliable off-sider on this job, Anna, for being so quick to learn and for putting up with my demanding attention to detail.
Now Pam, it's time for you to enjoy that sherry on your new deck...


  1. Great job and good information I`m sure this will be a great benefit for any one looking to build a timber deck.

  2. Great article. Can threaded rod (16mm) be used instead of stirrups? Thanks

    1. You could use 16mm threaded rod, so long as the length between the concrete base and the underside of the bearer is not too great. I would ensure that these are no longer than 100mm max. I am not a structural engineer, but years of experience constructing stuff would lead me to consider this approach, wiht the following cautions: You would need to put a good bend in the rod which is encased in the concrete footings/post, so that you are not just trying to rely on the thread to key in and hold the rod vertically in the concrete, as well as removing the possiblity of any rotation. You would also need to have a washer and two nuts (so you can lock them) below the bearer, plus have a washer and nut above the bearer. The lower nuts would be handy for final levelling of the bearer top surfaces. The rods, washers and nuts would all need to be HDG (Hot Dipped Galvanised), not ordinary zinc plated, and then I would also coat them with lashings of cold galvanising painted on.
      Maybe you have a heap of such rod lying about which you'd like to use up, but I would stick with the HDG stirrups bolted on and bedded in concrete if I had a choice. I hope that helps! Good luck wiht your project.

  3. It's nice that you took pictures of the process of building your timber deck. It will give others an idea on how it was done. It's not an easy task, but with all the effort exerted by everyone, you've been able to finished it right away. Well, you're probably enjoying hanging out there at this moment. Hehe!

  4. Look very good. Thanks for the pictures too. I am starting on a deck and porch this weekend and you post will come in handy. Instead of decking nails do you think screws will be just as good to use?

  5. That depends on the screws you use and how you apply them. Ideally, marine grade stainless steel would be best if you use screws, so long as they are countersunk properly into the decking. The disadvantage with screws with pozi/philips/robertson drive heads is the fact that water pools in the recess in the heads, promoting corrosion of the head from the inside out! The screws need to have some straight shank below the head, as screws which are threaded all the day to the underside of the head are much weaker in both application and resisting against corrosion.
    With changes in moisture levels and heat, the timber decking boards will fluctuate throughout the year in their thickness. Even screwed boards in the outdoors can have their hold loosened by expansion and contraction, as the head is pulled further into the board by the power of the expanding wood. You can't always tighten slightly corroded screws - but you can punch down nails again. My choice?... Spiral shanked hot dipped galvanised nails. The domed heads shed water rather than hold it, they can be punched in again in later years if necessary, and they are quicker to apply. All the best with the decking!

  6. wow, that's exactiy perfect ....

    exterior remodel really renew the Home...

    nice suggestion of Building a timber deck.....

  7. Are those boards upside down? The reader side is for airflow between boards and joists?

    1. Gidday, Gary.
      Carpenters like to argue about about which way the reeding should be, up or down. If you read some of the manufacturers instructions, they will say "Reeding up" as an anti-slip measure. They will reed the best face of the board. Other manufacturers say "reeding down" to allow air flow between the joist and the underside of the board. I usually give customers a choice on this, but tend to prefer the non-slip argument.
      In truth, the boards should be laid with the HEART side of the stick DOWN, according to the CSIRO, for optimum durability in external application.
      So there's no simple answer to the question!

    2. So how do you keep it clean. Also if it was really wet wouldn't the grooves potentially fill up, the you could effectively aquaplane on the surface just like a flat board.Cleaning would be a more regular concern than slipping. Wouldn't it be prone to holding water in the grooves?

    3. Those are among the main arguments put forward by the "reeding down" proponents.
      It is an argument which still takes place all over the country!