The World's Slowest Construction of a Merbau Deck/Pergola

[Blu_Rock]

I have been reading this forum for several years now and thought that I would share my deck/pergola building experience with anyone who is interesting in reading. This is my first posting on this forum so I hope it is of some use to those who are considering constructing their own deck. I stated building it in early December 2007 and am still going strong and am about 2/3 the way through. I have a slight (obsessive) tendency to over-engineer things but at least I know that it probably will not fall over in my lifetime.

I had been thinking about the design of a deck for the rear of my house for several years and I had a basic idea of what I wanted. As I wanted to have easy trailer access to the rear garden, the deck would need to have an angled side beside the drive to allow clearance for the trailer to fit between the existing garage and the deck. Seeing as I had one angled side, I tossed up a couple of design ideas that would make the overall structure more interesting (and difficult to construct, as I like a challenge) and settled on an octagonal protuberance as a feature. The deck was to be about 28 sq mtrs, have two sets of stairs and a pergola covering about half the deck. The rough plan below is not to scale.

Before construction began, I decided that a man can never have too many power tools and I shelled out for a 255mm Makita LS1040 compound mitre saw that I picked up on special for $330. Given the disturbing number of odd angles that my creation was to need, that was money well spent and I highly recommend this fine piece of equipment. It is built like all Makita stuff (made to last), consistently cuts the same angle and is a joy to use. A couple of months previously, I had bought a 14v Makita cordless drill and it too is a great piece of machinery and is a considerable improvement on the POS Ryobi 12v that I initially bought (will not maintain its charge over night and, even when fully charged, is gutless… what was I thinking when I wasted my money on that rubbish?).

I read up on deck construction on this forum and quickly discovered that I needed to get a hold of Alan Staines’ book Deck and Pergola Construction Manual “the Bible”. It is The definitive reference book and threw light on numerous finer points of deck construction that are essential for the uninitiated. After a fair bit of forum combing and deliberation, I opted for a treated pine structure with merbau decking and handrail.

Consulting Staines' span tables, I decided on using two by 90x45 for the bearers and 90x45 for the joists. I hired a posthole digger (the sort that uses a triangular frame rather than the widow-maker that requires two people to operate) and sunk the holes for the foundations. I planned on using F7 treated pine so there were about 20 odd footings to be dug. My block is on terrible reactive clay soil so I decided to go down 600mm and unfortunately I hit 4 pipes, 1 stormwater that I pierced in two places, 1 stormwater and 1 wastewater that I hit but did not break. Off to Bunnings (again) and got a PVC joiner, a mtr of PVC pipe and a rubber pipe joiner to fix the damage. From this experience, I would say only go down 600mm if the post footing sizes tables indicate that you absolutely need to go down that far, at 450mm I would had cleared the pipes.

I had got a hold of a cheap S/H cement mixer (almost new for $200) and began mixing the concrete for the foundations (it took a lot of concrete to fill those holes). I used stirrups to support the posts and held them in place while the concrete was setting by lightly screwing them to lengths of 90x90 treated pine that I had laid out. Not the usual way to do this but it worked. Concreting in the stirrups for the octagonal feature was a bit of a nightmare and I must have used every G-clamp at my disposal to get everything in the right place. After all the footings were in, I laid down weed mat and river pebbles to control weeds that may decide to grow under the deck.

Initially, before doing the research, I was going to use a ledger strip to attach the deck to my brick-veneer house but the code states that, generally, brick veneer walls are not to be used as load bearing structures for decks etc and therefore I would need another row of bloody footings.

Unfortunately, when I went to buy the 90x45 pine, the supply of F7 had all but dried up (at least in Canberra). Luckily, at the time of setting out the footings, I had over-engineered the number of footings and put them closer together than the span tables had indicated for a F7 structure. They were sufficiently close together to be suitable for the F5. Otherwise, I would have needed to up the bearer & joist specs. In the end, I did manage to get some F7 but about half of the bearers & joists are F5.

After using the water-in-a-clear-tube levelling method to mark off the stumps (90x90 treated pine for the central stumps and 90x90 merbau posts for the perimeter hand rail posts), I cut the stumps to length and circular sawed/chiselled out the numerous mortises for the bearer housings. I used 2x10mm coach bolts to secure the bearers to the stumps and posts and Pryda triplegrips to secure the joists to the bearers. The whole lot was braced in numerous places to ensure all was sound. I sealed all of the cut ands and joints with a couple of coats of Solarguard.

To be continued

[brynk]

welcome!

it is an interesting design & i look forward to seeing your structure and floor-board finish for the "turret". (hey it's not that bad - i'm feeling uninspired - but i know you know what i'm talkin about)

r's brynk

[Blu_Rock]

Brynk, thanks for the welcome

I was initially thinking of doing something fancy with the deck board layout for the turrent, but I have decided to go with a simple layout with its boards parallel with the the deck's other boards.

Half of the deck is going to be covered by a pergola that, in the long run, will be covered with laserlight. Staines provides a great deal of detail on how to go about attaching a pergola to a house’s fascia and as this was one area that I was uncertain about, I found this section of his book invaluable.

My house has metal fascias and the method that I selected to attach to this type of construction involved screwing 140x45mm noggings between the ends of the roof trusses using metal framing anchors. I then used 75mm, #14, type 17 roof batten screws to attach an external ledger to the noggings. The whole thing is pretty solid

From my searches of the Internet and this forum, it appears that the pergola’s roof requires a minimum of 5 degrees fall to have adequate drainage or whatever and as I suspected that head clearance between the finished deck height and the pergola’s beam (190x45mm F7 treated pine) may be a problem if too much fall was given, I went for the minimum amount of fall. As it turned out, at 180cm (about 6’ for you old timers) the top of my head has about 6” (150mm) clearance. The rafters are secured to the fascia ledger with hangers, and to the beam with non-obtrusive L-shaped gal brackets. I painted all the pergola timber, including the battens with a couple of coats of Solarguard (Manor Red) and screwed the rafters to the brackets with gal 8g 30mm button wafer screws and for the battens I used 120mm, #14, type 17 roof batten screws. There are a couple of oddly-cut rafters where the pergola’s roof tapers down in width and these took a while to shape to ensure a good joint

Regarding using treated pine for structural timber, I have never had to work with such dimensionally unstable timber in all my born days and it was a constant challenge to get everything more-or-less square and true. This stuff is really appalling and in my experience, unless you secure it down as soon as you get it, most of it will end up looking bloody banana shaped in short order. The first load of 90x45s that I got was initially all pretty straight as it was fresh out of the pack but that soon changed, even though I stored it on level ground and undercover. Some of it ended up so badly twisted and bent it was only good for bracing. The next load I got from Bunnings was all F7 that I used for the floor joists. I hand picked only straight lengths and had it all nailed down the following day. The joists have remained fairly straight even thought I have not laid the decking as yet.

[brynk]

Regarding using treated pine for structural timber, I have never had to work with such dimensionally unstable timber in all my born days and it was a constant challenge to get everything more-or-less square and true...

... and then thinking about my own experiences,

same with the mgp & finger-jointed battening .

[Chumley]

Hi Blu-Rock,

Great thread and good looking project. I've had similar problems with treated pine going artistic on me. I just finished a gazebo that I started in June last year (still have to post the last set of pics), so don't worry about the slow build - enjoy it.

Keep the thread going - it looks interesting.

Cheers,
Adam

[Blu_Rock]

Thanks Chumley.

I wanted to have a fairly chunky-looking handrail and I used 90x42 merbau for the job. For the rails that join the posts squarely, I used stop end housing joints. I used a router and a simple jig that I made to route out most of the material and then finished off the job with a sharp 35mm chisel. Joining the rails to the posts at the octagonal feature was a little more complicated and required a bit of planning to get a nice finish. These joints could be best described as angled dado joints. The housing tapers down from about 40mm deep to flush. I used a tenon saw and chisel to make these and they came up pretty well. As could be expected, the last one that I did was a much neater job than the first.

The cross section of the handrail is T-shaped and I routed out a shallow recess in the bottom of the top rail to ensure that the bottom rail would not bow over time (either inwards or outwards) and also the recess ensures that you will not be able to see a gap between the two pieces. Initially, the bottom piece was the full 90mm width, but that looked all together too chunky and so I ripped it down to 65mm.

I screwed the two pieces together with 3 x gal 75mm, #14, type 17 roof batten screws. Prior to making the deck, I had not previously used this type of screw (they are self counter sinking and have a hex drive to screw them in) and they are excellent. I used them in numerous other places when making the deck and even though they are probably a little expensive, they are just too convenient.

To secure the rails to the posts, I used gal screws that are screwed in from underneath the top rail. I countersunk them and it all turned out fairly neat and tidy. Prior to assembly, I routed the edges of the top rail with a rounding over bit. In the photo below you can see, on the LHS of the second rail along, where the router bit made a deeper than planned cut into rail when the bearing on the bottom of the bit fell to pieces. I thought I would tidy up the damage and install the rail regardless to serve as a reminder that cheap router bits (I think I paid about $25 for a set of 15 bits) are not made to last.

I am still tossing up whether or not to cough up the $500 or so to run 3 S/S balustrade wires between the posts. As the deck is only about 700mm off the ground there is no planning requirement to have balustrades but they look cool. I will decide about that later on. I have already checked with numerous suppliers (local, online, eBay and via recommendation from Loki's deck thread) and Loki is on the money as Miami Stainless in Burleigh Heads QLD came up the cheapest for what I am looking for (minimalist) and they appear to have a superior product (Streamline Threaded Insert/Swage Stud Method).

I found merbau to be a nice timber to work with (apart from the bleeding tannins) and it cuts/works easily and cleanly. The finish that I ended up applying to the handrail (and will also go on the deck) was Flood’s Spa-N-Deck cedar colour. This decision was not made lightly and I agonised over whether to use and oil-based stain or an alternative. The advice previously given by others on this forum convinced me that Spa-N-Deck was the way to go, mainly due to its longevity. This thread has a decent discussion on the pros and cons of different decking finishes but there are many other threads where the issue of deck finishes is discussed.

Bunnings sells Spa-N-Deck but I bought it considerably cheaper from Bristol.

[Blu_Rock]

Today, I finished off the first set of stairs that lead down to the garden. As you can see from the photos, they are fairly solidly built and they have taken more time to build than I had initially thought… but doesn’t everything. They are held up with four stirrups concreted into footings. They are also bolted onto the deck at the rear. The rise is 180mm, the going 350mm and they are about 1.4m wide. In the end, I decided to go with stainless steel decking screws, but more about that in another post.

There is a short handrail that bolts onto the side of the stairs and you can see one of the bolts hanging out in the second last photo. It matches the rest of the hand railing and its upper end attaches to one of the pergola’s posts via a joint that took me some time to figure out and cut. The compound saw has again proved invaluable for cutting difficult joints like this. I will paint the exposed timber in the joint before final assembly.

I have another set of stairs to build for the other side of the deck and they will lead to the drive. But for now, I have had enough and next weekend it will be back to laying the deck boards and hopefully, I will get them finished off.

[tim120977]

Hi Blu Rock,

I'm in the process of planning a deck at home and was looking at using 2 by 90mm by 45mm bearers like you did. I was just wondering if you could let me know what stump spacings, joist and bearer spans that you used? I was planning on using F7 TP but like yourself i'm having problems sourcing it so it will be F5 for me i think.

Cheers!

[Blu_Rock]

Tim

This post has a link to download a PDF that has joist span tables that cover F5 seasoned softwood. It shows 1300 for continuous spans and 1100 for single spans (I have 1300 joist spans at 450mm centres).

As far as the bearer spans are concerned, I used 1200 spans (continuous span) and the deck has no bounce, so I suppose all is well. In my case the load width is 1300.

This link has F5 bearer span tables (table 3) and for 2/90x45 with a 1200 load width it has a maximum 1700 continuous and single span. If you need more comprehensive F5 span tables, then I suggest that you start a new thread asking if anyone has the tables covering F5 timber.

Good luck with the build.

[tim120977]

Thanks Blu Rock,

That was exactly what i needed. I have already decided exactly what size my deck will be so i just have to work around that. At this stage i will have 2 90mm by 45mm F5 bearers will span 1300mm continous and the 90mm by 45mm F5 joist will span 1150mm continous @ 450mm centers. So hopefully it wont hve too much spring! The deck will be about 45m2 and It looks like i will have around 44 stumps which sounds like lot but i have a lot of long steps and mutible levels on this design. I will start a thread soon with some plans and progress pics.

Thanks again Blu Rock!

Tim.

[Blu_Rock]

Tim, you are welcome. With those spans, the deck will be solid and wont bounce. 44 stumps is a lot of bearer housings to notch out. I look forward to seeing your pics.

[Bloss]

Regarding using treated pine for structural timber, I have never had to work with such dimensionally unstable timber in all my born days and it was a constant challenge to get everything more-or-less square and true.

You must have got the stuff I leave after hand picking at the supplier! https://www.woodworkforums.com/images...py/biggrin.gif

After years of sorting at the site and then taking back timber to my suppliers that was simply too twisted and deformed to use I almost always now take the time to select my own at the suppliers premises. I reckon I choose maybe one in three sticks - sometime there is reasonable batch, but mostly it is pretty poor.

I assume those I reject are sold to someone else when in fact they should be sold as seconds or thirds. Radiata pine is always problematic and has become worse since they now harvest at 18-25 years when it used to be at 30-35years. The treatment doesn't help given it is a wet process, but you should demand dimensionally stable structural timber.

You should always take back to your supplier any pieces that were unusable and get a full refund - they often have to be a minimum of 1.8m and they often will refund only to the nearest 300mm, but you should not accept poor goods that are unfit for your intended use purpose.

BTW - Love your deck - great bit of work!

[Blu_Rock]

Bloss, I agree about hand selecting the timber. Since that first load, I have gone and hand select the timber. Depending on when you go, the good:bad ratio concerning relatively straight treated pine in the yard can vary from a good day 1:3 good:bad; to a bad day 1:6 or even worse.

I know that the yard will take back the lengths that are badly bowed/twisted but that is an inconvenience for me. That said, there are several lengths of the merbau decking (that came with the original load) that I will return for exchange as they are either badly bowed, twisted or wavy. As for the original load's deformed treated pine, I have been able to use that for bracing/shorter runs and therefore used it selectively.

In Canberra, there is a supplier that has a strict policy of ensuring the supply of straight treated pine but you pay a considerable preium for one of their employee's to go and hand select from the mill.

[Blu_Rock]

I have been plugging slowly away at laying the 90mmx19mm merbau decking timber and it was a very slow process to begin with. From the word go I had decided to go with screws to fasten down the decking because I have had experience with nails pulling out of the joists on a smaller deck that I put down about 10 years ago. It only took a couple of years before the nail heads started to pop up proud. With this current build, I started the job with countersunk galvanised square drive screws 10g x 50mm @ $60 per 1,000. I screwed in about 200 screws and sheared off about 10 where the thread joined the shank. Removing the stubs that were left in the joists was a major pain in the a#se. I came back to the forum and read up on what type of fasteners to use and how to go about screwing the boards down. This thread has an interesting discussion on the best type of fasteners to use and I was quickly convinced that I had to go with the stainless steel screw option. I know that most people recommend using 10g x 50mm type 17 non-trim head screws but my local specialty shop, Specialty Fasteners, recommended 9g x 53mm type 17 trim head screws @ $149 per 1,000, so I went with them.

I decided that I wanted a sleek look and therefore I wanted the “end capping” (i.e. the planks that close off the crawl space under the deck) to sit flush with the upper side of the deck. This required that all of the planks be cut to the exact length before they were laid. I could have done it easier and had the upper lengths hanging over the side of the deck, or the ends of the planks flush with the sides of the deck, but that was not the look I was going for.

I am more than a bit anally retentive when it comes to ensuring that everything is true and I really wanted all the screws to be lined up in perfectly straight rows. To get this result, I used a string line to set up two small wooden blocks at either end of the joists and then it was a matter of cutting 4 runs of decking to length, laying them temporarily down on the joists, pushing them together so that they were all straight, laying a straight length of 25mm x 25mm aluminium between the blocks to use as a straight edge and then marking out lines for the screw centres. I then used a template made from a scrap of 3 ply to mark in 15mm from either side of each plank. A time consuming process but the end result was worth the extra effort.

After reading this thread, I was going to buy a Carb-i-Tool to do the drilling and countersinking but ended up going with a much cheaper Snappy brand American-made 1/8" bit that Specialty Fasteners also sold for $15. I have put in about 2,000 screws with this baby and it is still going strong. I saw those so-called smart tool drill/countersink bits on eBay or somewhere but they look like a bit of a gimmick. That said, it is probably OK for beginners who have difficulty judging how far to countersink using a more conventional bit.

I then pre-drilled all the holes for those 4 boards, cleaned the swarf off the joists and then started to lay each plank using clouts as 3mm spacers between the planks. Some of the planks were either sitting up from the joists or were bowed so I used sliding G clamps to pull those boards down flush and parallel with the previous run. While laying the planks, I constantly checked that they were maintaining right angles to the wall that I was working off (by measuring to a line that I had marked off across the joists). This required a slight adjustment to the spacing between the planks every so often. I used a cordless drill to drive in the screws and had not problems with the stainless screws shearing off.

I did no want to end up ripping down last plank too skinny to fit the space left, so when it came to laying the last 10 or so planks, measured up the remaining space, made an allowance for the spaces between the planks and figured out how wide each would have to be. I ended up ripping down the last planks to 85mm wide and it all worked out nicely. Had I not done this, the last plank would have been about 40mm wide and looked out of place.

I am going to let the deck weather for a few months while I take care of the other set of stairs, enclose off the crawl space with dcking timber, make 2 sets of gates and a screen.

[Williamstown]

What is the purple/dark red paint, is it protection of some description?