Construction question

I’m building a platform to support and solar heater for a pool. The dimenstions are roughly 5 x24 ft. I’m using posts that are cemented into the ground and they will be 8 feet part. My question is what size beam to I have to use? This structure will support a shingled roof of 1/2 inch plywood and two solar heaters and also snow in the winter. The joists will be 16" apart. I live in Canada by the way, just in case the codes are different in different countries.
While I’m at it I may as well ask how close I can place this structure to my neighbours property. Closed structures with footings require 3 feet of space. This is an open structure. I know bylaws vary and that I should phone my town but I wanted to get started tomorrow and Monday is holiday and … and…
Is there a general concensus that this is more like a fence than a building and that I can build it within a foot of my neighbour’s property? Sorry if this is vague but I just threw it in with the initial question.

The setback requirements are beyond the scope of this board, unless someone happens to know your local regulations. Help us out-what is the total weight of the items which this deck will support, excluding the shingled roof mentioned above? Give me that, and I can look at the span tables for Canadian and North American domestic wood species.

I was hoping that regulations would be pretty consistent from one town to another but I’m probably way off there.
The structure will support two solar heaters which I will estimate weigh a maximum of 300 pounds together when filled with water.

300 pounds over a 5 x 24 area = 2.5 pounds per square foot. If using two uprights, I’d use 6 x 6 and let in 2 x 6 mains, through bolted using hardware appropriate for the treatment of the wood-be very careful if using ACQ or QA-they behave differently with fasteners than does the old standby CCA. If four uprights, wrap a band joist of 2 x 6 and set cross joists on the span of your choice, set 16" OC with engineered joist hangers, again observing hardware and treatment issues. Either will deliver 10x load factor above the actual use.

As an occasional builder of decks, care to expand on this?

CMC fnord!

You will have to dumb this down for me. I’ve built a bunch of things but am not a builder and don’t know the language. Your answer seems to say that a 2x6 would be approriate if I have 4 posts for the the 24 ft span. I call this a beam but you call it a joist. I have already purchase a 2x8 for the job which is more than enough.
I did not plan on 6x6 posts. I will be using 4x4 posts because this platform is tied in to another deck and will not be standing alone.
I don’t know what a main is or a band joist.

Sure. Traditional pressure treated lumber was also referrred to as CCA, because the chemical product to make it rot resistant was chromated copper arsenate. Problem was that the arsenic was said to leach out into the soil surrounding a structure and could pose a health risk to kidlets.

ACQ or alkaline copper quat and a few others have replaced CCA treated woods for residential applications, beginning several years ago. What the building industry has since learned is that the newer chemicals react adversely with fasteners and engineered connectors, such that accelerated corrosion and shear strength failure was observed.

Teco, Simpson, and other engineered fastener manufacturers have stepped up the measure of corrosion protection on their products, and it is even more critical than it used to be to use proper fasteners, as the wrong nail/hanger combination can fail prematurely owing to electo-galvanic corrosion in the presence of the treatment juice.

I’m slowly using up my store of older engineered hangers and nails on interior-only products, and spec manufacturer endorsed hanger/nail combinations for all exterior or sill plate work.

Here’s a link to a .pdf from the Forest Products Lab on the topic.

A 2 x 6 isn’t rated for a free 24’ span, but based on how you arrange the posts, the span is broken up and although you’re using a smaller sawn dimension, stiffness increases. I’d arrange the four upright 4 x 4 to mark corners of a rectangle 5’ x 10’.

A piece of wood can be a joist if I’m putting a floor atop it, but that same piece becomes a rafter if I’m putting a roof atop it. Typically the term beam is reserved for dimensions greater than 2x, but may be made up of multiple 2x members glued and nailed or glued and bolted together. Think of the triple 2 x 12 which runs the long dimesion of a dwelling supported by lally columns in the basement-that’s a beam.

Back to your project. I’d take the 2 x 8’s you’ve bought and place one on either side of a pair of 4x posts and drill them along with the posts and install HDG 1/2" carriage bolts (two per upright) with hardware (big washers) to create a double member running 5/6* in width. Establish the elevation of this because when the 24’ members are set atop what you’ve just built at right angles thereto, the actual span(s) of the 2 x 8 will be 7/0, 10/0, and 7/0, the last being canteliever.

Use engineered hangers at the point of attachment to the existing structure, install full 2x dimension blocking between joists at 8/0 and 16/0. Finally, pull x and y diagonals and bump the whole thing square. Then you can either toe the joists down to the double post supports, or use engineered hold-down straps. Lastly, you’ll cut off the extra tails* of the 5/6 members (above).

You can avoid a lot of later problems if you just ask your neighbor.

Discuss it with him, show him where it will be, point out that the solar water heaters will be silent so as not to bother him, and so forth. Tell him you understand the ordinances would allow you to go to within 1 foot of his property, but you’re going to keep it 3 feet back so as not to crowd him. Get his approval & cooperation beforehand, and you’ll be much better off.