Let’s talk building a 10’ x10’ deck, either freestanding or attached. There are many codes that go into the building of a simple 10’ x10’ deck. Starting on the ground, how many posts does a 10’ by 10’ deck need?
An attached 10’x10’ deck needs 2 posts supporting a 2-ply non-incised 2×8 beam, upgrading the beam to 3-ply using incised wood. A freestanding 10’ x10’ deck needs 4 posts, supporting two pairs of 2-ply non-incised 2×8 beam, upgrading the beam to 3-ply using incised wood.
Before we delve in, a little warning codes differ between countries, states, provinces and even cities. For example, the IRC, which most American deck codes stem from allows a 2×8 SPF incised joist to span 11’1” with a 1’10”. The Canadian Wood Council, for us frozen deck builder in the north allow a span of 11’5” but limit the overhang to 1’4”. Do ask me why we can span longer but overhang less. It just what it is, but let’s design our 10’x10’ deck. I will try to design to both codes but at times I may fail, please refer to your local and country codes before you build. Wow! Let’s get that lawyer hat off and get our carpenter cap back on.
Footings for a 10×10 Deck
First, we will need footings for that deck. All jurisdictions require deck footings to be deeper than the frost level. Well, that’s anywhere from 6” in Florida to 100” in Minnesota. Check that frost level where you at, dig down below it.
Here in Calgary where I build decks, it’s only 48”. A little work but not to bad. Some places require soil bearing tests. In Calgary, we just make all our residential deck columns 10” in diameter. 4’ deep, 10” wide and extending 6” above grade with a saddle for the post to sit in. Don’t want that post sitting in the water and rotting.
In Canada, our maximum beam span, thus footings spacing is 8’ for a deck. The IRC limits a beam span to 7’4” between posts for a 3-ply 2×8 incised deck beams. We are going to have to massage these numbers a little to make this work. A deck beam is allowed to overhang the post-one-quarter of its span. If we take the smaller span of 7’4”, we can overhang 1’10”, which is great. We only need to hang over the beam 1’4” past the centre of the post on each side.
Posts for a 10×10 Deck
Speaking of deck post. Some places you are allowed to bury deck post. Resting the post on the concrete footing and then surround her with dirt. Not a chance in Calgary. All deck posts must sit in a galvanized saddle on top of the concrete pile. Wood rots faster when in contact with dirt and water. Got to keep them separated.
A 2-ply beam needs to be supported by a 4×4 post up too 6’5”, or at least in Canada. Tripling up that beam will require us to upgrade to a 6×6 post. Any post over 6’5” and up to 12’ will need to be a 6×6. Always end treat that 6×6 post for it won’t rot.
Beam for a 10×10 Deck
We have a few options with our deck beam. We can either do a 3-ply 2×8 incised SPF beam or a 2-ply 2×10 beam. If we use non-incised wood, like Yellow Pine, we can get away with a 2-ply beam. Incised wood has a higher level of fungi and rot treatment, which is a good idea for a beam to last longer.
“You’ve heard me talk about building code and you know I believe you should always build above code if possible.”Mike Holmes
The only drawback is with a higher deck with a patio under it. The incised wood won’t look as good. Let’s just go with a 3-ply 2×8 beam, incised on ground level deck. If its higher up the extra treatment won’t be needed but over building your deck, a little won’t be a bad idea. The extra ply will also allow us to shrink the beam’s depth by 2”, which is a good thing. Yeah, I know its only 1 ¾” but let’s not go there.
Joist for a 10’x10’ Deck
The Canadian Wood Council allow us to span 10’2” with a 2×8 incised SPF joist at 24” on centre. In Canada, we are required to reduce the on centre spacing to 16” to span our 10’ deck. The IRC 9’1” plus 1’10” overhang with incised joust at 24” on centre. With the joist overhanging the beam 1’0”, we have the option to space our joist 24”.
But I like to a sturdy deck, given the option I will always pick 16” on centre over 24”. There is just too much spring on decking spanning 24”. Besides, most 5/4 pressure-treated decking and composites require 16” joist spacing. It’s just better to go with 16” joist spacing. Again, better to overbuild then underbuild.
Decking for a 10’ x 10’ Deck
With our joist at 16” on centre, we are free to use 2x6s, 5/4”x5.5” or composite decking. I have work with them all and they all make great decking. If its economics your looking for, 5/4” decking is well priced. It will require more maintenance than composite but still is good decking.
If you’re ready to spend a little more money, go with capped composite decking or even PVC decking. It looks amazing, requires less maintenance and over the life of the deck will cost less. More money upfront but less over its lifetime. Check specs before joisting the deck as some thinner or scalloped decking will require closer joist spacing. With heat, composite decking becomes a little soft requiring more support but still a great choice. Under composite decking, I recommend joist flashing membrane; it will seal and protect the joist. Helping your joist to last as long as the decking. Some of that synthetic stuff can last 50 years!
Railing for a 10’ x10’ Deck
What do we know? Railing needs to be tall enough for someone can’t fall over it. Designed for it can’t be climbed over. With the baluster close enough to prevent little heads from squeezing in between.
In Calgary, a ground-level deck less than 2’ from the ground doesn’t require any railing. Many states let you get as high as 3’ before requiring railing. Back in Calgary, a deck up to 6’0” height needs 36” high railing. Anything higher than 6’ requires railing 42” high.
To prevent climbing, vertical baluster design works best. The bottom railed raised a few inches of the decking to allow water to run off is fine but anything else needs to be unclimbable. This does limit style a little. Recently I have seen some great looking horizontal railing and elaborate intertwining branch designs. Looks great but just aren’t safe, best to leave them on Pinterest.
Close enough to prevent squeezing in between is put at 4”. The space between baluster must not be bigger than 4”. Grab a softball; if you can throw it threw the railing, it’s too wide. Limiting yes, but safer.
Decks require guards requires a minimum of 2×8 rim and joists. Not a big deal as a 10’ x 10’ deck joist span requires 2×8, but the addition of railing reinforces their value. Also, 2x8s or greater allows for fascia mounted railing post.
Build a bigger Deck
Now that we worked through a 10 x 10 deck, I would like to suggest you think about building a bigger deck. A 100 square feet is a good start but will limit you to only a barbeque and a few chairs. If you want to add a table or a few friends, something a little bigger would be nice. Here are some more thoughts about deck sizing. But a bigger deck will require more post….
If you would like to get to know more about the deck post, joist or beams requirements, here are a couple of links to get you started. So many span charts to get you excited.