1. What is the purpose of spacing between exterior deck floorboards?
Answers:
To allow for expansion during the seasons.
Other answers:
To let water drain more easily?
To let water drain more easily?
Because when the wood gets wet it expands considerably.
Almost all pressure treated wood will arrive on the jobsite with quite a bit of water in it. If that is the case, you should butt the boards against each other, and a couple of days after installation, you will have space between your boards.
So in the heat of summer they have room to swell.
to let the rain run through so you do not have pooling water
what they said
the purpose is so that dirt and water have somewhere to drain off so that your deck doesnt become a huge nasty mud puddle
So there is room for the boards to move during different weather conditions and water will not sit on the top of the wood.
To let the water pass through so it doesn't soak into the boards and cause rot and mildew. You should also keep those spaces clear of debris as the deck ages.
Expansion. Wood expands and contracts with temperature changes and humidity even when sealed.
this not only gives the wood room to breathe ( prevents rot) , but also helps stop the boards from pulling the nails out as the weather changes.
To allow water to drain off so planks won't absorb and swell. If you are using treated 2x6's then they will shrink which eliminates the need for spacing during construction.
Supposedly it's for draining and swelling and all of that, but wood is porous, so even if you don't space them, water will pass through and small dirt, larger debris you would have to sweep off even if you spaced them. Wood is also porous and flexible enough that you don't necessarily have to allow for swelling.
You couldn't figure this out on your own? Where have you been?
Do your own homework.
To allow for drainage and expansion of boards.
The spacing allows debris (leaves, dirt, etc) to fall through so that moisture doesn't get trapped between the deck boards. The spacing also allows air to circulate around the deck boards so that they don't stay in a constantly wet state. For natural wood decking material (cedar, redwood, ipe and the like) it is essential that the material is able to dry out otherwise it will rot prematurely. For composite deck materials, the spacing allows debris to fall through so that the deck is easier to clean.
Expansion of the decking material has very little to do with the spacing in between deck boards. For a properly installed deck (with addequate airflow) the deck boards will contract over time as the moisture content in the wood decreases.