Building Our Back Deck

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The back of our house faces west. On a summer’s afternoon we would have our own little solar oven and unfortunately we were living in it! Quite a few years ago I built a deck on the back of the house across the kitchen and dining room area with translucent corrugated fibreglass sheeting as a roof and 70% shade cloth to cut the heat down on that end of the house. It worked well but there were problems –

  • It was only 1300mm deep (the width of our top step), not really wide enough to do anything on.
  • The flooring timbers were not full length and the joins looked like crap but also resulted in some unevenness of the surface (read trip hazard)
  • While the structure (supports, flooring and uprights) were hardwood, the roofing was repurposed pine and unpainted at that. Also the shade cloth tended to conduct rainwater down onto the ends of the pine rafters and they rotted away within a few years.

The result was a back deck which looked even more like crap and no longer provided any protection from the summer sun. Clearly it had to go and since Linda had been attempting to motivate me in that direction for some *mumble* years I decided that this year would be the year of the deck!

The old deck

In the interim I had put up a fabric cover to ameliorate the heat, the story of which is here, so that was the first thing to go, by unscrewing the timber holding it onto the fascia board. To facilitate the construction work on the supporting structure I decided to remove the timber from the existing deck after the uprights, rafters and roofing for the new deck had been put in place, thus having a stable surface to work from.

The New Deck

Due to the shortcomings of the old deck, the new design would be -

- Almost 2200 mm deep

- With treated pine, full length flooring and supporting structure

- Treated pine rafters which shouldn’t rot

- clear corrugated polycarbonate roofing which would keep out the UV but let the light and heat through in winter (with no northern windows either, it is a cold house in winter and we need all the solar heat gain we can get!). The roofing would also extend 200mm past the end of the rafters to prevent them getting wet.

With the new deck being 900mm deeper, the new design had the southern end being chamfered off at 45° starting from the end of the old deck, otherwise the end of the new deck would obstruct getting in and out of the rear door of the garage. This would especially be a problem if I was wheeling a wheelbarrow!


Construction

Footings

The edge of the new deck would be level with the end of the back steps, so the first task was to install stirrups to hold the uprights into concrete footings. I got hold of 5 hot dip galvanised 130mm leg stirrups to fit a 100mm post. They are designed to be bolted into a concrete slab, but I inserted 100mm galvanised bolts (with a nut on each side of the stirrup foot to secure the bolts prior to inserting them into the concrete. I then measured up and marked in the grass where the posts (and so the stirrups) were to be installed.

Using my 200mm post hole digger I dug down about 300 – 400mm into the dirt, in line with the end of the steps. It was pretty dry so I dug down a bit in each required hole, then ran some water from the hose into each hole until it was full and left them overnight to drain and soften. The next morning I was able to dig down to the full depth easily.

To make the footings I got hold of some high strength quick setting concrete bags, one per hole. I mixed them up one at a time in my wheelbarrow, only adding as much water as required, the less water the stronger the concrete. To make sure the footings were in the right place I ran a string line from the end of the steps to the garage, parallel to the house.

With the concrete footing in place I pushed the bolts (which extended from the bottom of the flange) into the wet concrete footing, making sure each one was lined up with the string line and held them there for a few minutes. The concrete went off pretty quickly and I left the footings to cure for a couple of days.

Uprights

The uprights are comprised of 5 off 90mm x 90mm x 3 metre long treated pine posts, and getting them put up was where I really needed the help of the others in our pod. With one or two people holding them vertical, checked by a spirit level, I used my drill/driver to install a couple of coach bolts through the stirrup sides and into the posts. We did put in some temporary braces through to stakes into the ground to improve the stability of each upright temporarily. When tied into the structure they would be plenty stable, but waving about in the breeze as they were was another matter!

The uprights were all the same length (3 metres) but the ground in the area is somewhat uneven, so that the tops of the uprights were not lined up and but needed to be all cut off so they were at the same height, they were long enough so that wouldn’t be a problem. To enable us to do this as well as tie them all together we used a 6 metre length of 45mm x 90mm treated pine, held up at the right height and squared off with a spirit level. It was then screwed into the two outside posts, and then (after checking they were vertical) screwed into the remaining posts. Once this was done we had to climb up some ladders and (for safety reasons) use hand saws to cut of the uprights which protruded above the horizontal timber, and yes, it was as much fun as it sounds!

This set the outer boundary of the deck.

Rafters

With the structure in place to support the outer end of the roof over the deck, it was time to put the rafters in place. I used 90mm x 35mm treated pine rafters, 4 metres long although I cut them half to give me twice and many 2 metre long rafters. To attach the rafters to the fascia board of the house below the guttering I used 110mm long x 40mm wide galvanised steel timber to timber joist hangers. They were screwed into the fascia 490mm centre to centre.

With the rafters cut and ready to go and the joist hangers in place it was a simple matter to insert one end of the rafter into the hanger while supporting the other on the outer structure and then secure it with a screw in each side hanger into the rafter. With the free end of the rafter resting on the horizontal member running across the top of the upright posts, it was easy to attach them to the member using triple grips, screwed into the rafter and the member after ensuring the rafter was at right angles to the house with a try square.

To secure things first I installed a rafter at each end of the deck, then concentrated (thankfully with the help of a mate) on installing all of the other rafters. With the rafters in place the structure was a lot more solid, and didn’t move much at all if pressure was put on one of the uprights. Before I could attach the roofing sheets to the roof I needed to put battens onto the rafters. The battens were 40mm x 19mm treated pine and I used 4; one at the edge close to the house, one at the far end of the rafter and two 600mm in from each edge, screwed in to each rafter. This also contributed to the stability of the structure.

Roofing Material

While part of the reason for building the deck is to reduce the effect of the summer sun on the back of the house, I really didn’t want to shut out the light completely in the cooler parts of the year. So I chose clear corrugated polycarbonate roofing sheets, 2400mm x 850mm. They were a bit longer than I wanted but the polycarbonate sheets were not available in the 2100mm length which I was after, so I had to buy 2400mm and cut 300mm off the end. Which did using my hand held circular saw and a plastic cutting blade.

As mentioned previously, the old deck had the roofing sheets only going right to the end of the rafters with no overhang and when I put shade cloth over the top it allowed rainwater to soak into the ends of the rafters, eventually rotting them. I wanted to avoid this on the new deck, hence a 100mm overhang of the polycarbonate sheeting on the new deck.

With all of the sheets cut to size it was an easy matter to heave them up onto the top of the deck roof, end first and arrange them starting at one end so that each sheet  overlaps the next by 1.5 corrugations. Before I started fixing them to the rafters I made sure each sheet was pressed up hard to the fascia board up under the house guttering, to prevent rain leaking in.

Uprights, rafters and roof on

I used suntuff “Clearfix” screws to attach the roofing polycarbonate to the rafters, 15g x 50mm long, screwed into rafters and battens using my battery drill. It was a one-shot deal with no pilot hole being needed. In the roofing of the previous deck I did skimp on the screws holding the fibreglass roofing down and it had a tendency to flap up and down even in a moderate wind. I was determined to prevent this happening again I installed 4 screws the length of the sheet in the apex of every fourth corrugation and even in high winds the deck roofing has proven to be steady as a rock!

One other point, the polycarbonate roofing has a UV resistant coating on one side of the sheet and it is very important to make sure it goes uppermost during the roofing installation process. The previous fibreglass roofing had no such protection and the degradation by the sun was obvious after a few years.

The Decking

Now that the roofing was in I could work in inclement weather! But the weather stayed good anyway….. I left the decking timbers and supports on the old deck still in place so that it made navigation and ladder use easier when I was installing the roofing. While still being reasonably sound it didn’t look too crash hot so I removed it all, put a couple of pieces aside for another project but most of it was cut up and used to keep us warm that winter.

New and old flooring supports

I decided to leave the existing joists in place but install new full length ones as well. To provide a member for the joists to sit on I bolted a length of 90mm x 45mm treated pine onto the front of the uprights, carefully set up to be parallel to the front of the old deck and level, using our spirit level. Once checked and bolted in place I cut the joists out of 68mm x 40mm treated pine, long enough to go from the font of the deck back to the hardwood member screwed to the bricks of the house as part of the original deck.

Once they were cut and in place, I used 40mm screws in each side diagonally down into the supporting member to hold them in place. The original decking boards were fairly narrow hardwood, the new ones would be (you guessed it!) treated pine 90mm wide and 20mm thick and 5 metres long. They have a corrugated side and a flat side, I thought the corrugated side was to go uppermost for grip, but it appears it goes down, against the supporting members so that any rainwater doesn’t pool against the decking timbers and cause rot.

Decking done

I installed the timbers using screws which had a square driving hole which turned out to be quite decorative. With the decking secured I used my circular saw to cut the deck to the required length, the main part of the deck being 4.5 metres long, but also cutting back a 45° chamfer on the last third of the deck (as mentioned previously) so I could still get a wheelbarrow in and out the rear door of the garage, which faces the deck.

another view showing chamfer

My intention was to leave the light (almost white) colour of the decking timbers as is, but decided they would discolour over time anyway so I gave them a couple of coats of “natural” finish decking oil. I thought “natural” meant “clear” which would maintain the colour of the deck but it was in fact a coloured deck oil, but the colour has grown on me so that is OK. The rest of the deck got two coats of external grade white paint.

After deck oiling

The Covering

In summer, we have taken to covering the deck rooking with a light brown 90% shade cloth. This prevents the sun from hitting the back of the house (and the windows) directly. The Bricks in direct sun are regularly 10°C+ hotter than bricks under the shade of the shadecloth.

Completed, with shade cloth in place

 

 

 


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