How to plan deck layout?

Question

Hi All,

we are wanting to add a deck extension to our alfresco. I have drawn up a quick idea of what the measurements are. Could someone please help me figure out how many posts I need, bearers and also joists? Where do they go? I have watched countless videos and tutorials.

Under the alfresco is concrete, the deck would extend out from there across the back of the house. I’ve attached a photo of the drawing & a mock up from AI

We are wanting to do this on a budget as much as possible.

Total novice at this, but have always been quite the hobbyist.

JacobZ · Answer

Hi @Jessc995,

Considering you'll want to have as much airflow beneath the deck as possible, that really limits you in terms of what framing can be used. The only timber you can really use in this application is 90x45, which means the design will have to change considerably from above.

When acting as a bearer, a 90x45 can span 900mm between posts or pedestals and when acting as a joist it can span 1400mm between bearers.

So, to fit within the requirements of the joist span tables, you would need to add an additional bearer to the alfresco area and along the house.

To fit within the 900mm allowable span between posts or pedestals, the 6690mm bearer runs would need 8 supports each, with a slight overhang on each end, or 9 each without a slight overhang. The shorter bearer runs on the alfresco would need 5 supports each. Combined, you would need a total of 34-37 posts or pedestals depending on whether you are ok to have a slight overhang at the end of the long bearer runs.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

Jessc995 · Answer

Thankyou for your comment

The height to the top of the brick is 14.5cm I will attach a photo

JacobZ · Answer

Hi @Jessc995,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

The first thing we need to know is how high above the ground you would like your deck to finish. This height is often set by the bottom of the door to your home to get a flush transition from inside to outside.

This height will determine what calibre of timbers can be used. A larger timber like a 190x45 is able to span a longer distance, which reduces the number of posts and bearers required, but there is no point planning around using one if there is nowhere near enough height to use it.

So, when you can provide this height, we can start looking at the specific timbers and their orientation as well as post locations to ensure everything is in line with the relevant bearer and joist span tables.

I've mocked up a quick design primarily to show the direction of the frame and a potential layout; however, I should note that this design is not possible unless you are able to use 190x45 timbers. If the allowable height is lower than this, we would need to add additional bearers.

Once you let me know that height, we can start looking at a more concrete plan with post locations and specific materials.

Let me know what you think.

Jacob