I am installing a decking size 5.4m X 4.2m aprox. I plan to attach the decking to the side of the house by a joist attached to the house. The ground gently slopes away rom the house and so I plan to support the other side of the decking by posts. The decking planks will run parallel with the house so the support joists will run at rightangles to the house.
The problem I have is what size of joist I can use?
I am restricted by the hight above ground I can go as the house door is just 27cm above ground level and there are airbricks 14cm above fround level. I do not want to cover the airbricks and so plan to put a joist just below these but it only leaves me enough space for a 10cm hight. The joists will be 4.2m long. Can I use 10cm joists (2X4's) as the instructions I have read recomend (2X6's). If I can use 2X4's what spacing do I need along the length for support? If not what is my alternative?
Sorry this is so long but I really need help!!
Thanks