Thursday, 24 May 2012

How To Build a Timber Carport

Ever wondered how the professionals can build a timber carport so easily?

Its starts with planning.
A good set of plans, or even an accurate hand drawn picture is always the first requirement.
Spend some time working out some of the crucial dimensions and angles prior to ordering materials, this will ensure an easy build and also a cost effective design.

The set out.
Setting out your structure is key to the success of the project, the structure must be level where required, posts must be plumb, and the roof must be the correct pitch.
Site positioning as per council requirements is also very important.
Spend some time going over your plans and make sure your have set your projects out as per the plans.
Usually your Carport will be positioned a specific distance from an existing structure ie. fence or house.
Measure this distance out from the fence or house and make a mark on the ground. this is your starting point. If your Carport is parallel with this fence or house, run a string line set out at equal distance from this structure.
Mark the centre of your first hole on the ground then measure your width or length in this case 3500mm and mark the centre of this hole.
Now measure the width 6000mm and mark these two.
You will then need to fine tune these hole positions. to do this, you can use the diagonal measurement. in this case it is 6946mm.
You will need a helping hand for this step.
Get your helper to hold the end of the tape measure in the centre of the first hole, while they do this measure the diagonal distance between holes. now get your helper to go to the other hole and measure this diagonal distance. what you want to achieve is the same diagonal distance over these four holes. If you get a different measurement you need to move the hole position left or right while still keeping your overall length and width correct. repeat this process until correct.
once these two hole positions are correct, you can then mark out your centre holes.

The easy bit.
Now it is just a matter of digging the holes. reference your council drawings for accurate widths and depths. On this project we would use 450mm wide holes 600mm deep. always ensure your holes are square all the way to the bottom and double check your depth, its easier to dig 50mm deeper than to be knocked back by your building inspector.
Another thing to remember is to have the bottom of the holes clean from rubble and debry, it is not well known but in fact a clean flat surface on the bottom of a post or stump hole ensures the concrete stays as one block and stops water infiltration. also try to remove any excess soil from site or at least the immediate area, the last thing you want is to be climbing over hills while trying to build.
Once the holes are dug, call your council and book your first inspection.

Post placement.
In this project, due to termite the problem in the area we are not placing our timber posts directly into the ground, instead we are using galvanised brackets concreted into the ground, our posts will then sit on top.
To ensure these brackets are positioned correctly and also perfectly level we have decided to use a set out Jig, this is essentially a timber box built at the same size as the carport which we can get level and square. once this is level and square, we simply screw out galvanised brackets to it and pour the concrete.

Pouring the concrete.
Before the concrete truck arrives, get your wheel barrow and shovel ready, wetting them down can also help the concrete slide off or out.
Once each hole is full, get a stick and poke around in the concrete, what you are trying to do is get the concrete into all the nooks and crannies while removing all the air pockets.
Make sure when you fill your holes that you don't move your posts or brackets too much, but don't worry too much if you do, you will have some time after the concrete goes in to correct any changes.
the concrete should be left to cure for 24hours.

The frame
Now that the concrete is cured you can remove the temporary timber framing and prepare for the framing stage.

You will need to decide or reference your plans for your posts length, we usually use the overall height to the top of the beams and cut all 6 posts the same length.
Check out your four corner posts and your two side posts to accept the side beams, in our case we used a 190mm high edge beam therefor a 190 checkout.
The good thing about using your jig to setup the supporting brackets is that you can prefabricate your posts knowing all heights are the same.
You can now temporarily screw your posts to the brackets in a roughly plumb position, ensuring you leave a 5 mm gap between the bottom of the post and the bracket to avoid long term rot.
You should now have 6 posts pointing directly into the sky.

Check measure from the outside of post to outside of post right down the bottom. these measurements will be used for your beam lengths (6000mm and 3500mm hopefully)
If they are different to your desired length and width by 10 or so millimetres don worry you will use these new measurements for your beam lengths.
So lets cut some beams.
Cut 2 x 6000mm and 2 x 3500mm beams with mitre cuts.
Lift the first 3500mm beam into place and nail into position ensuring that the end of the beam is flush with the outside of the post. Repeat the process with the remaining beams.
at this point you need to make sure the posts are all plumb, having set out the footings correctly and cutting your beams to the correct length all should be well, but it pays to check, Clamp a long piece of timber to the bottom of one post and to the top of the next post, as you get the structure level tighten the clamps, you should only need to do this on one side and one end, once these timbers are in place and the structure is straight you can install diagonal bracing as required and nail in place.
Make sure all beams are nailed correctly, drill holes and bolt into position.

Ridge Beam.
We know the structure is 6000mm long, so this is our ridge beam length. Cut the beam with square cuts on each end.
Getting the ridge beam into position does not need to be too hard, we use a timber ridge beam support at each end clamped at the correct height to support the ridge in the early stages of construction.
These supports allow for ridge beam height adjustment if required.

Marking out of rafters.
You will now need to mark out the position of your rafters on both side beams and the ridge beam.
Our spacings for this projects are 1200mm so simply mark 1200mm increments in the beams and ridge. Next to each mark place an X when you install your rafters they will cover this mark and ensure all rafters are placed correctly.
Now you need to determine the length and angle of the cuts on your rafters, the easiest way to do this is to measure from the face of the ridge to the inside face of the edge beam.
Measure this distance on both sides. If it is not the same on both sides, add it together then divide by two. This is your rafter length.
Calculating your angle is easy, if your roof pitch is 20 degrees then your angle is 20 degrees.
Remember that it is best to cut one rafter and unsure it fits prior to cutting the rest.
Ridge support
Once all your rafters are in place you will need to install a single piece of timber at each end to support the ridge beam. Leaving the ridge beam supports in place measure the distance from the top of your beam to the bottom of the ridge beam, cut two pieces this length and install and nail into place.

Now that all your rafters, beams, ridge and ridge support are in place you can install you roof battens.
The roof batten length will be the same as the structure length and the ridge length. It is best to always use full lengths of timber for roof battens as they add strength to the rafters and structure as a whole.
Your bottom roof batten needs to be place as close as possible to the edge beam while the top roof batten should be placed150mm from the centre of the ridge. it is also a good idea to check your ridge capping to ensure the batten is placed correctly. The centre roof batten is placed half way between the bottom and top batten. all battens should be nailed and batten screwed into position and be straight.

Frame completed.
Your new timber carport frame is now completed, you are right to move to the next step, roofing and guttering which I will cover in the next tutorial.

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